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DR ANTHONY MELVIN CRASTO, Born in Mumbai in 1964 and graduated from Mumbai University, Completed his Ph.D from ICT, 1991,Matunga, Mumbai, India, in Organic Chemistry, The thesis topic was Synthesis of Novel Pyrethroid Analogues, Currently he is working with GLENMARK LIFE SCIENCES LTD, Research Centre as Principal Scientist, Process Research (bulk actives) at Mahape, Navi Mumbai, India. Total Industry exp 30 plus yrs, Prior to joining Glenmark, he has worked with major multinationals like Hoechst Marion Roussel, now Sanofi, Searle India Ltd, now RPG lifesciences, etc. He has worked with notable scientists like Dr K Nagarajan, Dr Ralph Stapel, Prof S Seshadri, Dr T.V. Radhakrishnan and Dr B. K. Kulkarni, etc, He did custom synthesis for major multinationals in his career like BASF, Novartis, Sanofi, etc., He has worked in Discovery, Natural products, Bulk drugs, Generics, Intermediates, Fine chemicals, Neutraceuticals, GMP, Scaleups, etc, he is now helping millions, has 9 million plus hits on Google on all Organic chemistry websites. His friends call him Open superstar worlddrugtracker. His New Drug Approvals, Green Chemistry International, All about drugs, Eurekamoments, Organic spectroscopy international, etc in organic chemistry are some most read blogs He has hands on experience in initiation and developing novel routes for drug molecules and implementation them on commercial scale over a 30 PLUS year tenure till date June 2021, Around 35 plus products in his career. He has good knowledge of IPM, GMP, Regulatory aspects, he has several International patents published worldwide . He has good proficiency in Technology transfer, Spectroscopy, Stereochemistry, Synthesis, Polymorphism etc., He suffered a paralytic stroke/ Acute Transverse mylitis in Dec 2007 and is 90 %Paralysed, He is bound to a wheelchair, this seems to have injected feul in him to help chemists all around the world, he is more active than before and is pushing boundaries, He has 9 million plus hits on Google, 2.5 lakh plus connections on all networking sites, 90 Lakh plus views on dozen plus blogs, 233 countries, 7 continents, He makes himself available to all, contact him on +91 9323115463, email, Twitter, @amcrasto , He lives and will die for his family, 90% paralysis cannot kill his soul., Notably he has 33 lakh plus views on New Drug Approvals Blog in 233 countries...... , He appreciates the help he gets from one and all, Friends, Family, Glenmark, Readers, Wellwishers, Doctors, Drug authorities, His Contacts, Physiotherapist, etc

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Divalproex sodium

Divalproex sodium.png
Divalproex Sodium | ≥99%(HPLC) | Selleck | HDAC inhibitor


  • 44089

WeightAverage: 144.2114
Chemical FormulaC8H16O2

UNII614OI1Z5WI, CAS number99-66-1, 76584-70-8

2-propylpentanoic acid, DIVALPROEX SODIUM76584-70-8Valproate semisodiumEpivalDepakoteSodium divalproateSemisodium ValproateAbbott 50711ValdisovalValproic Acid 
CAS Registry Number: 99-66-1 
CAS Name: 2-Propylpentanoic acid 
Additional Names: 2-propylvaleric acid; di-n-propylacetic acid 
Trademarks: Convulex (Pharmacia); Depakene (Abbott) 
Molecular Formula: C8H16O2 
Molecular Weight: 144.21 
Percent Composition: C 66.63%, H 11.18%, O 22.19% 
Literature References: Antiepileptic; increases levels of g-aminobutyric acid (GABA) in the brain. Prepn: B. S. Burton, Am. Chem. J.3, 385 (1882); E. Oberreit, Ber.29, 1998 (1896); M. Tiffeneau, Y. Deux, Compte Rend.212, 105 (1941). Anticonvulsant activity: H. Meunier et al.,Therapie18, 435 (1963). Toxicity data: Jenner et al.,Food Cosmet. Toxicol.2, 327 (1964). Comprehensive description: Z. L. Chang, Anal. Profiles Drug Subs.8, 529-556 (1979). Review of teratogenicity studies: H. Nau et al.,Pharmacol. Toxicol.69, 310-321 (1991); R. Alsdorf, D. F. Wyszynski, Expert Opin. Drug Safety4, 345-353 (2005). Review of pharmacology and clinical experience in epilepsy: E. M. Rimmer, A. Richens, Pharmacotherapy5, 171-184 (1985); in psychiatric disease: D. R. P. Guay, ibid.15, 631-647 (1995); in migraine prophylaxis: C. E. Shelton, J. F. Connelly, Ann. Pharmacother.30, 865-866 (1996). Review of pharmacodynamics and mechanisms of action: W. Löscher, Prog. Neurobiol.58, 31-59 (1999). 
Properties: Colorless liquid with characteristic odor. bp 219.5°. nD24.5 1.425. d40 0.9215. pKa 4.6. Very sol in organic solvents. Soly in water: 1.3 mg/ml. LD50 orally in rats: 670 mg/kg (Jenner). 
Boiling point: bp 219.5° 
pKa: pKa 4.6 
Index of refraction:nD24.5 1.425 
Density: d40 0.9215 
Toxicity data: LD50 orally in rats: 670 mg/kg (Jenner) 
Derivative Type: Sodium salt (1:1) 
CAS Registry Number: 1069-66-5 
Additional Names: Sodium valproate 
Trademarks: Depacon (Abbott); Depakin (Sanofi-Synthelabo); Dépakine (Sanofi-Aventis); Epilim (Sanofi-Aventis); Ergenyl (Sanofi-Synthelabo); Leptilan (Dolorgiet); Orfiril (Desitin) 
Molecular Formula: C8H15NaO2 
Molecular Weight: 166.19 
Percent Composition: C 57.82%, H 9.10%, Na 13.83%, O 19.25% 
Properties: White, odorless, crystalline, deliquescent powder. pKa 4.8. Hygroscopic. One gram is sol in 0.4 ml water; 1.5 ml ethanol; 5 ml methanol. Practically insol in common organic solvents. LD50 orally in mice: 1700 mg/kg (Meunier). 
pKa: pKa 4.8 
Toxicity data: LD50 orally in mice: 1700 mg/kg (Meunier) 
Derivative Type: Sodium salt (2:1) 
CAS Registry Number: 76584-70-8 
Additional Names: Sodium hydrogen bis(2-propylpentanoate); divalproex sodium; valproate semisodium 
Manufacturers’ Codes: Abbott 50711 
Trademarks: Depakote (Abbott); Valcote (Abbott) 
Molecular Formula: C16H31NaO4 
Molecular Weight: 310.40 
Percent Composition: C 61.91%, H 10.07%, Na 7.41%, O 20.62% 
Derivative Type: Magnesium salt 
Trademarks: Depamag (Sigma-Tau) 
Molecular Formula: C16H30MgO4 
Molecular Weight: 310.71 
Percent Composition: C 61.85%, H 9.73%, Mg 7.82%, O 20.60% 
Therap-Cat: Anticonvulsant; antimanic; antimigraine.Keywords: Anticonvulsant; Antimigraine; Antimanic.

Synthesis Reference

Daniel Aubert, Francis Blanc, Henri Desmolin, Michel Morre, Lucette Sindely, “Valproic acid preparations.” U.S. Patent US5017613, issued January, 1965.


Patent sodium is one of the most widely used epileptic agents presently available in the market. Both the constituents, valproic acid and sodium valproate themselves have also been used for the treatment of epileptic seizures and convulsions. But their utility has remained restricted since valproic acid is a liquid and is difficult to formulate for an oral dosage form whereas sodium valproate is a hygroscopic solid with poor stability characteristics. Divalproex sodium is an oligomer having 1:1 molar ratio of valproic acid and sodium valproate containing 4 to 6 units. The relevant prior art includes US 4,988,731 (’73I) relates to a non-hygroscopic stable sodium hydrogen divalproate oligomer. Its probable structure is shown in Fig 1

Figure imgf000002_0001

Fig 1 – Divalproex sodiumWhere M is a about 2.As can be seen from the displayed structure, one mole each of the valproic acid forms coordinate bonds with the sodium of the sodium valproate molecule, and the valproate ion is ionically bonded to the sodium atom. The structure is thus consistent with the unique characteristic of the compound. However the preferred mode of representing Divalproex sodium is by reference to single compound of the formula{(CH3CH2CH2)2CHCO2} {(CH3CH2CH2)2CHCO2}Na, HThe said patent also describes two alternative processes for the preparation of the oligomer. According to one aspect, the oligomer is produced by dissolving sodium valproate and valproic acid in equimolar amount in acetone and crystallizing from chilled acetone at around O0C. Alternatively Divalproex sodium can be isolated from a two component liquid medium, which includes acetone where in half equivalent of NaOH to the valproic acid present, preferable as a solution in an acetone miscible solvent eg. water. The new compound can be recovered from the liquid phase by evaporating the solvent(s) and, if desired, the new compound can be recrystallized, for instance from acetonitrile or others or the material may be spay-dried, lyophilized or purified by chromatography.US ‘731 claims yield of 90% of theory.Drawbacks of the above mentioned reported methods for the preparation of Divalproex sodium described in US 4988731 are difficult to reproduce on a large scale and provides inconsistent yields and the material obtained is not always free flowing in nature. The process involves the crystallization of a 1:1 mixture of valproic acid and sodium valproate from a chilled solution of acetone, followed by washing with chilled acetone. Divalproex sodium is as such fairly soluble in acetone at temperatures above 1O0C and extreme care has to be. taken while performing washing with chilled acetone as any rise in temperature would lead to the loss of yield. This problem actually comes to the fore while scaling up the process during commercialization since during centrifugation of the large volume the temperature of the mixture rises and acetone has to be cooled below O0C, which require large amount of liquid nitrogen or dry ice. Moreover it was also observed that due to the cooled nature of the solvent, the isolated Divalproex sodium absorbs considerable amount of moisture and therefore requires longer time to dry eventually leading to longer time cycle for the otherwise simple single step process. Also the high moisture content in the recovered acetone makes it unsuitable for reuse. Alternatively, to avoid absorption of water, the centrifugation had to be carried out under a blanket of dry nitrogen gas. These additional infrastructural loads add to input costs eventually making the otherwise single step low cost process becoming uncompetitive and economically unviable.Similarly the other process involves the addition of half molar equivalent of sodium hydroxide dissolved in water to valproic acid and the solvent has to be evaporated to obtain crude product, which has to be recrystallized to get Divalprox of the desired specification. The process is operationally tedious and requires the reduction in the level of water in the reaction mass via evaporation of the solvent followed by re- crystallization from acetonitrile making the process lengthy and economically unviable. There is therefore a need for operationally making this single step process more efficient and high yieldingExample I:To lOOg of Valproic acid with stirring at 20-300C, powdered NaOH ( 13g; half molar) is added & the resulting reaction mixture is stirred at 40-500C for 1 hr. Then acetonitrile(600ml) is added to obtain clear solution at 40-500C and the solution is charcoalized at 40-500C followed by filtration at 40-500C through hyflo-bed. The resultant reaction mixture was stirred at 10-200C for 2-3 hr. The solid , thus obtained, was filtered and product was dried at 40-450C for 10-12 hr. (102.25g, 95%)Example II;To lOOg of Valproic acid with stirring at 20-300C, powdered NaOH (13g; half molar) is added & the resulting reaction mixture is stirred at 30-400C for 1 hr. Then acetone (600ml) is added to obtain clear solution at 30-400C and the material is charcoalized at 30-400C followed by filtration through hyflo-bed. The resultant reaction solution was stirred at -5°C to -1O0C for 2-3 hr. The solid , thus obtained, was filtered and product was dried at 40-450C for 10-12 hr. ( 55g, 51.11%) Example III:To a solution of Valproic acid (10Og) in dichloromethane (200ml) at 20-300C, powdered caustic (13g ; half molar) is added & the reaction mixture is stirred at 30- 400C for 1 hr to get clear solution. Then acetonitrile (600ml) is added to it inorder to crystallize the product. The solid, thus obtained, is further stirred at 0-50C for 2-3 hr followed by filtration. The product was dried at 40-450C for 10-12 hr. (10Og; 93%)Example IV:To a solution of Valproic acid (10Og) in diisopropyl ether(200ml) at 20-300C, powdered caustic (13g ; half molar) is added & the reaction mixture is stirred at 40-500C for 1 hr to get clear solution. Then acetonitrile (800ml) is added to it inorder to crystallize the product. The solid, thus obtained, is further stirred at 0-50C for 2-3 hr followed by filtration. The product was dried at 40-450C for 10-12 hr. (104g; 96.65%)Example V:To a solution of Valproic acid (10Og) in methyl tertiary butyl ether(200ml) at 20- 300C, powdered caustic (13g ; half molar) is added & the reaction mixture is stirred at 40-500C for 1 hr to get clear solution. Then acetonitrile (800ml) is added to it inorder to crystallize the product. The solid, thus obtained, is further stirred at 0-50C for 2-3 hr followed by filtration. The product was dried at 40-450C for 10-12 hr. (102g;94.79%)Example VI:To a solution of Valproic acid (10Og) in toluene (200ml) at 20-300C, powdered caustic (13g ; half molar) is added & the reaction mixture is stirred at 40-500C for 1 hr to get clear solution. Then acetonitrile (800ml) is added to it inorder to crystallize the product. The solid, thus obtained, is further stirred at 0-50C for 2-3 hr followed by filtration. The product was dried at 40-450C for 10-12 hr. (101g; 93.87%)Example VII: A mixture of sodium valproate (6Og) and valproic acid (52.04g) was taken in acetonitrile (800ml) and heated at reflux to obtain a clear solution, which was filtered through hyflo-bed to remove suspended particles. Then the solution was stirred at 10- 200C for 2-3 hr. The solid, thus obtained, was filtered and washed with acetonitrile (100ml). The product was dried at 40-450C for 10-12 hr. (105g ; 93.75%)Example VIII;To a solution of valproic acid (10Og) in methanol (200ml) at 20-300C5 caustic (13g; half molar) is added & the reaction mixture is stirred at 20-300C for 1 hr. Then the methanol was recovered at reduced pressure and acetonitrile (600ml) is added to it with stirring. The reaction mixture was further stirred at 0-50C for 2-3 hr. The solid, thus obtained, is filtered, washed with acetonitrile (100ml) and product was dried at 40-45°C for 10-12 hr.(102g; ~ 95%) Example IX:To a solution of valproic acid (10Og) in methanol (200ml) at 20-300C, caustic (13g; half molar) is added & the reaction mixture is stirred at 20-300C for 1 hr. Then the methanol was recovered at reduced pressure and acetone (600ml) is added to it with stirring. The reaction mixture was further stirred at -5°C to -1O0C for 2-3 hr. The solid, thus obtained, is filtered, washed with chilled acetone (100ml) and product was dried at 40-450C for 10-12 hr.(54g; ~ 50.11%)Example X:To a solution of valproic acid (10Og) in ethanol (200ml) at 20-300C, caustic (13g; half molar) is added & the reaction mixture is stirred at 20-300C for 1 hr. Then the ethanol was recovered at reduced pressure and acetonitrile (600ml) is added to it with stirring.The reaction mixture was further stirred at 0-50C for 2-3 hr. The solid, thus obtained, is filtered, washed with acetonitrile (100ml) and product was dried at 40-450C for 10-12 hr.(101g; ~ 93.87%)Example XI: To a solution of valproic acid (10Og) in ethanol (200ml) at 20-30°C, caustic (13g; half molar) is added & the reaction mixture is stirred at 20-300C for 1 hr. Then the ethanol was recovered at reduced pressure and acetone (600ml) is added to it with stirring. The reaction mixture was further stirred at -5°C to -100C for 2-3 hr. The solid, thus obtained, is filtered, washed with chilled acetone (100ml) and product was dried at 40-450C for 10-12 hr.(55g; ~ 51%)ADVANTAGES:> The process is high yielding. > The process produces Divalproex sodium with improved flowability.> The process produces Divalproex sodium that is non-hygroscopic and more stable.> The process is industrially feasible, precise, reproducible and does not require sophisticated infrastructure.

Divalproex Sodium is a stable coordination compound comprised of sodium valproate and valproic acid with anticonvulsant and antiepileptic activities. Divalproex dissociates to the valproate ion in the gastrointestinal tract. This agent binds to and inhibits gamma-aminobutyric acid (GABA) transaminase and its anticonvulsant activity may be exerted by increasing brain concentration of GABA and by inhibiting enzymes that catabolize GABA or block the reuptake of GABA into glia and nerve endings. Divalproex may also work by suppressing repetitive neuronal firing through inhibition of voltage-sensitive sodium channels.

Valproate semisodium is a mixture of valproic acid and its sodium salt in a 1:1 molar ratio. It is used for the management and treatment of seizure disorders, mania, and prophylactic treatment of migraine headache. It has a role as an antimanic drug, an anticonvulsant and a GABA agent. It contains a valproic acid and a sodium valproate.

Divalproex sodium, valproate sodium, and valproic acid, are all similar medications that are used by the body as valproic acid. Therefore, the term valproic acid will be used to represent all of these medications in this discussion.

Valproate (VPA) and its valproic acidsodium valproate, and valproate semisodium forms are medications primarily used to treat epilepsy and bipolar disorder and prevent migraine headaches.[2] They are useful for the prevention of seizures in those with absence seizurespartial seizures, and generalized seizures.[2] They can be given intravenously or by mouth, and the tablet forms exist in both long- and short-acting formulations.[2]

Common side effects of valproate include nausea, vomiting, sleepiness, and dry mouth.[2] Serious side effects can include liver failure, and regular monitoring of liver function tests is therefore recommended.[2] Other serious risks include pancreatitis and an increased suicide risk.[2] Valproate is known to cause serious abnormalities in babies if taken during pregnancy,[2][3] and as such it is not typically recommended for women of childbearing age who have migraines.[2]

Valproate’s precise mechanism of action is unclear.[2][4] Proposed mechanisms include affecting GABA levels, blocking voltage-gated sodium channels, and inhibiting histone deacetylases.[5][6] Valproic acid is a branched short-chain fatty acid (SCFA) made from valeric acid.[5]

Valproate was first made in 1881 and came into medical use in 1962.[7] It is on the World Health Organization’s List of Essential Medicines[8] and is available as a generic medication.[2] It is marketed under the brand names Depakote, among others.[2] In 2018, it was the 131st most commonly prescribed medication in the United States, with more than 5 million prescriptions.[9][10]


Valproic acid (VPA) is an organic weak acid. The conjugate base is valproate. The sodium salt of the acid is sodium valproate and a coordination complex of the two is known as valproate semisodium.[11]

Medical uses

It is used primarily to treat epilepsy and bipolar disorder. It is also used to prevent migraine headaches.[12]


Valproate has a broad spectrum of anticonvulsant activity, although it is primarily used as a first-line treatment for tonic–clonic seizuresabsence seizures and myoclonic seizures and as a second-line treatment for partial seizures and infantile spasms.[12][13] It has also been successfully given intravenously to treat status epilepticus.[14][15]

Mental illness

Bipolar disorder

Valproate products are also used to treat manic or mixed episodes of bipolar disorder.[16][17]


A 2016 systematic review compared the efficacy of valproate as an add-on for people with schizophrenia:[18]

There is limited evidence that adding valproate to antipsychotics may be effective for overall response and also for specific symptoms, especially in terms of excitement and aggression. Valproate was associated with a number of adverse events among which sedation and dizziness appeared more frequently than in the control groups.[18]
showOutcomeFindings in wordsFindings in numbersQuality of evidence

Dopamine dysregulation syndrome

Based upon five case reports, valproic acid may have efficacy in controlling the symptoms of the dopamine dysregulation syndrome that arise from the treatment of Parkinson’s disease with levodopa.[19][20][21]


Valproate is also used to prevent migraine headaches. Because this medication can be potentially harmful to the fetus, valproate should be considered for those able to become pregnant only after the risks have been discussed.[22]


The medication has been tested in the treatment of AIDS and cancer, owing to its histone-deacetylase-inhibiting effects.[23]


Contraindications include:

Adverse effects

See also: List of adverse effects of valproic acid and List of adverse effects of valproate semisodium

Most common adverse effects include:[22]

Serious adverse effects include:[22]

Valproic acid has a black box warning for hepatotoxicitypancreatitis, and fetal abnormalities.[22]

There is evidence that valproic acid may cause premature growth plate ossification in children and adolescents, resulting in decreased height.[26][27][28][29] Valproic acid can also cause mydriasis, a dilation of the pupils.[30] There is evidence that shows valproic acid may increase the chance of polycystic ovary syndrome (PCOS) in women with epilepsy or bipolar disorder. Studies have shown this risk of PCOS is higher in women with epilepsy compared to those with bipolar disorder.[31] Weight gain is also possible.[32]


Valproate causes birth defects;[33] exposure during pregnancy is associated with about three times as many major abnormalities as usual, mainly spina bifida with the risks being related to the strength of medication used and use of more than one drug.[34][35] More rarely, with several other defects, including a “valproate syndrome”.[36] Characteristics of this valproate syndrome include facial features that tend to evolve with age, including a triangle-shaped forehead, tall forehead with bifrontal narrowing, epicanthic folds, medial deficiency of eyebrows, flat nasal bridge, broad nasal root, anteverted nares, shallow philtrum, long upper lip and thin vermillion borders, thick lower lip and small downturned mouth.[37] While developmental delay is usually associated with altered physical characteristics (dysmorphic features), this is not always the case.[38]

Children of mothers taking valproate during pregnancy are at risk for lower IQs.[39][40][41] Maternal valproate use during pregnancy increased the probability of autism in the offspring compared to mothers not taking valproate from 1.5% to 4.4%.[42] A 2005 study found rates of autism among children exposed to sodium valproate before birth in the cohort studied were 8.9%.[43] The normal incidence for autism in the general population is estimated at less than one percent.[44] A 2009 study found that the 3-year-old children of pregnant women taking valproate had an IQ nine points lower than that of a well-matched control group. However, further research in older children and adults is needed.[45][46][47]

Sodium valproate has been associated with paroxysmal tonic upgaze of childhood, also known as Ouvrier–Billson syndrome, from childhood or fetal exposure. This condition resolved after discontinuing valproate therapy.[48][49]

Women who intend to become pregnant should switch to a different medication if possible or decrease their dose of valproate.[50] Women who become pregnant while taking valproate should be warned that it causes birth defects and cognitive impairment in the newborn, especially at high doses (although valproate is sometimes the only drug that can control seizures, and seizures in pregnancy could have worse outcomes for the fetus than exposure to valproate). Studies have shown that taking folic acid supplements can reduce the risk of congenital neural tube defects.[22] The use of valproate for migraine or bipolar disorder during pregnancy is contraindicated in the European Union, and the medicines are not recommended for epilepsy during pregnancy unless there is no other effective treatment available.[51]


Valproate in elderly people with dementia caused increased sleepiness. More people stopped the medication for this reason. Additional side effects of weight loss and decreased food intake were also associated with one-half of people who become sleepy.[22]

Overdose and toxicity

FormLower limitUpper limitUnit
Total (including
protein bound)
50[52]125[52]µg/mL or mg/l
Free6[52]22[52]µg/mL or mg/l

Excessive amounts of valproic acid can result in sleepiness, tremorstuporrespiratory depressioncomametabolic acidosis, and death.[54] In general, serum or plasma valproic acid concentrations are in a range of 20–100 mg/l during controlled therapy, but may reach 150–1500 mg/l following acute poisoning. Monitoring of the serum level is often accomplished using commercial immunoassay techniques, although some laboratories employ gas or liquid chromatography.[55] In contrast to other antiepileptic drugs, at present there is little favorable evidence for salivary therapeutic drug monitoring. Salivary levels of valproic acid correlate poorly with serum levels, partly due to valproate’s weak acid property (pKa of 4.9).[56]

In severe intoxication, hemoperfusion or hemofiltration can be an effective means of hastening elimination of the drug from the body.[57][58] Supportive therapy should be given to all patients experiencing an overdose and urine output should be monitored.[22] Supplemental L-carnitine is indicated in patients having an acute overdose[59][60] and also prophylactically[59] in high risk patients. Acetyl-L-carnitine lowers hyperammonemia less markedly[61] than L-carnitine.


Valproate inhibits CYP2C9glucuronyl transferase, and epoxide hydrolase and is highly protein bound and hence may interact with drugs that are substrates for any of these enzymes or are highly protein bound themselves.[24] It may also potentiate the CNS depressant effects of alcohol.[24] It should not be given in conjunction with other antiepileptics due to the potential for reduced clearance of other antiepileptics (including carbamazepinelamotriginephenytoin and phenobarbitone) and itself.[24] It may also interact with:[22][24][62]

  • Aspirin: may increase valproate concentrations. May also interfere with valproate’s metabolism.
  • Benzodiazepines: may cause CNS depression and there are possible pharmacokinetic interactions.
  • Carbapenem antibiotics: reduce valproate levels, potentially leading to seizures.
  • Cimetidine: inhibits valproate’s metabolism in the liver, leading to increased valproate concentrations.
  • Erythromycin: inhibits valproate’s metabolism in the liver, leading to increased valproate concentrations.
  • Ethosuximide: valproate may increase ethosuximide concentrations and lead to toxicity.
  • Felbamate: may increase plasma concentrations of valproate.
  • Mefloquine: may increase valproate metabolism combined with the direct epileptogenic effects of mefloquine.
  • Oral contraceptives: may reduce plasma concentrations of valproate.
  • Primidone: may accelerate metabolism of valproate, leading to a decline of serum levels and potential breakthrough seizure.
  • Rifampicin: increases the clearance of valproate, leading to decreased valproate concentrations
  • Warfarin: valproate may increase free warfarin concentration and prolong bleeding time.
  • Zidovudine: valproate may increase zidovudine serum concentration and lead to toxicity.



Although the mechanism of action of valproate is not fully understood,[24] traditionally, its anticonvulsant effect has been attributed to the blockade of voltage-gated sodium channels and increased brain levels of gamma-aminobutyric acid (GABA).[24] The GABAergic effect is also believed to contribute towards the anti-manic properties of valproate.[24] In animals, sodium valproate raises cerebral and cerebellar levels of the inhibitory synaptic neurotransmitter, GABA, possibly by inhibiting GABA degradative enzymes, such as GABA transaminasesuccinate-semialdehyde dehydrogenase and by inhibiting the re-uptake of GABA by neuronal cells.[24]

Prevention of neurotransmitter-induced hyperexcitability of nerve cells, via Kv7.2 channel and AKAP5, may also contribute to its mechanism.[63] Also, it has been shown to protect against a seizure-induced reduction in phosphatidylinositol (3,4,5)-trisphosphate (PIP3) as a potential therapeutic mechanism.[64]

It also has histone-deacetylase-inhibiting effects. The inhibition of histone deacetylase, by promoting more transcriptionally active chromatin structures, likely presents the epigenetic mechanism for regulation of many of the neuroprotective effects attributed to valproic acid. Intermediate molecules mediating these effects include VEGFBDNF, and GDNF.[65][66]

Endocrine actions

Valproic acid has been found to be an antagonist of the androgen and progesterone receptors, and hence as a nonsteroidal antiandrogen and antiprogestogen, at concentrations much lower than therapeutic serum levels.[67] In addition, the drug has been identified as a potent aromatase inhibitor, and suppresses estrogen concentrations.[68] These actions are likely to be involved in the reproductive endocrine disturbances seen with valproic acid treatment.[67][68]

Valproic acid has been found to directly stimulate androgen biosynthesis in the gonads via inhibition of histone deacetylases and has been associated with hyperandrogenism in women and increased 4-androstenedione levels in men.[69][70] High rates of polycystic ovary syndrome and menstrual disorders have also been observed in women treated with valproic acid.[70]


Some metabolites of valproic acid. Glucuronidation and β-oxidation are the main metabolic pathways; ω-oxidation metabolites are considered hepatotoxic.[71][72] Details see text.

Taken by mouth, valproate is rapidly and virtually completely absorbed from the gut.[71] When in the bloodstream, 80–90% of the substance are bound to plasma proteins, mainly albumin. Protein binding is saturable: it decreases with increasing valproate concentration, low albumin concentrations, the patient’s age, additional use of other drugs such as aspirin, as well as liver and kidney impairment.[73][74] Concentrations in the cerebrospinal fluid and in breast milk are 1 to 10% of blood plasma concentrations.[71]

The vast majority of valproate metabolism occurs in the liver.[75] Valproate is known to be metabolized by the cytochrome P450 enzymes CYP2A6CYP2B6CYP2C9, and CYP3A5.[75] It is also known to be metabolized by the UDP-glucuronosyltransferase enzymes UGT1A3UGT1A4UGT1A6UGT1A8UGT1A9UGT1A10UGT2B7, and UGT2B15.[75] Some of the known metabolites of valproate by these enzymes and uncharacterized enzymes include (see image):[75]

  • via glucuronidation (30–50%): valproic acid β-O-glucuronide
  • via beta oxidation (>40%): 2E-ene-valproic acid, 2Z-ene-valproic acid, 3-hydroxyvalproic acid, 3-oxovalproic acid
  • via omega oxidation: 5-hydroxyvalproic acid, 2-propyl-glutaric acid
  • some others: 3E-ene-valproic acid, 3Z-ene-valproic acid, 4-ene-valproic acid, 4-hydroxyvalproic acid

All in all, over 20 metabolites are known.[71]

In adult patients taking valproate alone, 30–50% of an administered dose is excreted in urine as the glucuronide conjugate.[75] The other major pathway in the metabolism of valproate is mitochondrial beta oxidation, which typically accounts for over 40% of an administered dose.[75] Typically, less than 20% of an administered dose is eliminated by other oxidative mechanisms.[75] Less than 3% of an administered dose of valproate is excreted unchanged (i.e., as valproate) in urine.[75] Only a small amount is excreted via the faeces.[71] Elimination half-life is 16±3 hours and can decrease to 4–9 hours when combined with enzyme inducers.[71][74]


Valproic acid is a branched short-chain fatty acid and the 2-npropyl derivative of valeric acid.[5]


Valproic acid was first synthesized in 1882 by Beverly S. Burton as an analogue of valeric acid, found naturally in valerian.[76] Valproic acid is a carboxylic acid, a clear liquid at room temperature. For many decades, its only use was in laboratories as a “metabolically inert” solvent for organic compounds. In 1962, the French researcher Pierre Eymard serendipitously discovered the anticonvulsant properties of valproic acid while using it as a vehicle for a number of other compounds that were being screened for antiseizure activity. He found it prevented pentylenetetrazol-induced convulsions in laboratory rats.[77] It was approved as an antiepileptic drug in 1967 in France and has become the most widely prescribed antiepileptic drug worldwide.[78] Valproic acid has also been used for migraine prophylaxis and bipolar disorder.[79]

Society and culture

Valproate is available as a generic medication.[2]

Approval status

FDA-labelled indication?[1]

TGA-labelled indication?[12]

MHRA-labelled indication?[80]
Literature support
EpilepsyYesYesYesLimited (depends on the seizure type; it can help with certain kinds of seizures: drug-resistant epilepsy, partial and absence seizures, can be used against glioblastoma and other tumors both to improve survival and treat seizures, and against tonic–clonic seizures and status epilepticus).[81][82][83][84]
Bipolar maniaYesYesYesLimited.[85]
Bipolar depressionNoNoNoModerate.[86]
Bipolar maintenanceNoNoNoLimited.[87]
Migraine prophylaxisYesYes (accepted)NoLimited.
Acute migraine managementNoNoNoOnly negative results.[88]
SchizophreniaNoNoNoWeak evidence.[89]
Agitation in dementiaNoNoNoWeak evidence. Not recommended for agitation in people with dementia.[90] Increased rate of adverse effects, including a risk of serious adverse effects.[90]
Fragile X syndromeYes (orphan)NoNoLimited.[66]
Familial adenomatous polyposisYes (orphan)NoNoLimited.
Chronic pain & fibromyalgiaNoNoNoLimited.[91]
Alcohol hallucinosisNoNoNoOne randomised double-blind placebo-controlled trial.[92]
Intractable hiccupsNoNoNoLimited, five case reports support its efficacy, however.[93]
Non-epileptic myoclonusNoNoNoLimited, three case reports support its efficacy, however.[94]
Cluster headachesNoNoNoLimited, two case reports support its efficacy.[95]
West syndromeNoNoNoA prospective clinical trial supported its efficacy in treating infantile spasms.[96]
HIV infection eradicationNoNoNoDouble-blind placebo-controlled trials have been negative.[97][98][99]
Myelodysplastic syndromeNoNoNoSeveral clinical trials have confirmed its efficacy as a monotherapy,[100] as an adjunct to tretinoin[100] and as an adjunct to hydralazine.[101]
Acute myeloid leukaemiaNoNoNoTwo clinical trials have confirmed its efficacy in this indication as both a monotherapy and as an adjunct to tretinoin.[102][103][104]
Cervical cancerNoNoNoOne clinical trial supports its use here.[105]
Malignant melanomaNoNoNoOne phase II study has seemed to discount its efficacy.[106]
Breast cancerNoNoNoA phase II study has supported its efficacy.[107]
Impulse control disorderNoNoNoLimited.[108][109]

Off-label uses

In 2012, pharmaceutical company Abbott paid $1.6 billion in fines to US federal and state governments for illegal promotion of off-label uses for Depakote, including the sedation of elderly nursing home residents.[110][111]

Some studies have suggested that valproate may reopen the critical period for learning absolute pitch and possibly other skills such as language.[112][113]


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Clinical data
Other namesvalproate sodium (USAN US)
License dataUS DailyMedValproate_sodium
showIUPAC name
CAS Number1069-66-5 
PubChem CID16760703
CompTox Dashboard (EPA)DTXSID6023733 
ECHA InfoCard100.002.525 
Chemical and physical data
Molar mass166.196 g·mol−1
3D model (JSmol)Interactive image
Clinical data
Trade namesDepakote, others
Other namessemisodium valproate, divalproex sodium (USAN US)
License dataUS DailyMedDivalproex_sodium
showIUPAC name
CAS Number76584-70-8 
PubChem CID23663956
CompTox Dashboard (EPA)DTXSID6023733 
ECHA InfoCard100.002.525 
Chemical and physical data
Molar mass310.410 g·mol−1
3D model (JSmol)Interactive image

Valproate exists in two main molecular variants: sodium valproate and valproic acid without sodium (often implied by simply valproate). A mixture between these two is termed semisodium valproate. It is unclear whether there is any difference in efficacy between these variants, except from the fact that about 10% more mass of sodium valproate is needed than valproic acid without sodium to compensate for the sodium itself.[114]

Brand names of valproic acid

Branded products include:

Brand names of sodium valproate

  • Tablets – Diplexil-R by Bial.
United States
  • Intravenous injection – Depacon by Abbott Laboratories.
  • Syrup – Depakene by Abbott Laboratories. (Note Depakene capsules are valproic acid).
  • Depakote tablets are a mixture of sodium valproate and valproic acid.
  • Tablets – Eliaxim by Bial.
  • Epilim Crushable Tablets Sanofi[116]
  • Epilim Sugar Free Liquid Sanofi[116]
  • Epilim Syrup Sanofi[116]
  • Epilim Tablets Sanofi[116]
  • Sodium Valproate Sandoz Tablets Sanofi
  • Valpro Tablets Alphapharm
  • Valproate Winthrop Tablets Sanofi
  • Valprease tablets Sigma
New Zealand
  • Epilim by Sanofi-Aventis

All the above formulations are Pharmac-subsidised.[117]

  • Depakote Tablets (as in USA)
  • Tablets – Orlept by Wockhardt and Epilim by Sanofi
  • Oral solution – Orlept Sugar Free by Wockhardt and Epilim by Sanofi
  • Syrup – Epilim by Sanofi-Aventis
  • Intravenous injection – Epilim Intravenous by Sanofi
  • Extended release tablets – Epilim Chrono by Sanofi is a combination of sodium valproate and valproic acid in a 2.3:1 ratio.
  • Enteric-coated tablets – Epilim EC200 by Sanofi is a 200-mg sodium valproate enteric-coated tablet.
UK only
  • Capsules – Episenta prolonged release by Beacon
  • Sachets – Episenta prolonged release by Beacon
  • Intravenous solution for injection – Episenta solution for injection by Beacon
Germany, Switzerland, Norway, Finland, Sweden
  • Tablets – Orfiril by Desitin Pharmaceuticals
  • Intravenous injection – Orfiril IV by Desitin Pharmaceuticals
South Africa
  • Syrup – Convulex by Byk Madaus[118]
  • Tablets – Epilim by Sanofi-synthelabo
  • Tablets – Epilim by Sanofi-Aventis
  • Types are Syrup, Extended release mini tablets, Gastric resistant coated tablets, Gastric resistant soft capsules, Extended release capsules, Extended release tablets and Extended release coated tablets
  • Tablets – Depakene by Kyowa Hakko Kirin
  • Extended release tablets – Depakene-R by Kyowa Hakko Kogyo and Selenica-R by Kowa
  • Syrup – Depakene by Kyowa Hakko Kogyo

In much of Europe, Dépakine and Depakine Chrono (tablets) are equivalent to Epilim and Epilim Chrono above.

  • Tablets – Epival 200 (enteric coated tablet) and Epival 500 (extended release tablet) by Iran Najo
  • Slow release tablets – Depakine Chrono by Sanofi Winthrop Industrie (France)

Depalept and Depalept Chrono (extended release tablets) are equivalent to Epilim and Epilim Chrono above. Manufactured and distributed by Sanofi-Aventis.

India, Russia and CIS countries
  • Valparin Chrono by Torrent Pharmaceuticals India
  • Valprol CR by Intas Pharmaceutical (India)
  • Encorate Chrono by Sun Pharmaceutical (India)
  • Serven Chrono by Leeven APL Biotech (India)

Brand names of valproate semisodium

  • Brazil – Depakote by Abbott Laboratories and Torval CR by Torrent do Brasil
  • Canada – Epival by Abbott Laboratories
  • Mexico – Epival and Epival ER (extended release) by Abbott Laboratories
  • United Kingdom – Depakote (for psychiatric conditions) and Epilim (for epilepsy) by Sanofi-Aventis and generics
  • United States – Depakote and Depakote ER (extended release) by Abbott Laboratories and generics[22]
  • India – Valance and Valance OD by Abbott Healthcare Pvt Ltd, Divalid ER by Linux laboratories Pvt Ltd, Valex ER by Sigmund Promedica, Dicorate by Sun Pharma
  • Germany – Ergenyl Chrono by Sanofi-Aventis and generics
  • Chile – Valcote and Valcote ER by Abbott Laboratories
  • France and other European countries — Depakote
  • Peru – Divalprax by AC Farma Laboratories
  • China – Diprate OD


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External links

Clinical data
Trade namesDepakote, Epilim, Convulex, others
Other namesValproic acid; Sodium valproate (sodium); Valproate semisodium (semisodium); 2-Propylvaleric acid
License dataUS DailyMedValproic_acidUS FDAValproic%20acid
Routes of
By mouthintravenous
ATC codeN03AG01 (WHO)
Legal status
Legal statusAU: S4 (Prescription only)CA℞-onlyUK: POM (Prescription only)US: ℞-only
Pharmacokinetic data
BioavailabilityRapid absorption
Protein binding80–90%[1]
MetabolismLiverglucuronide conjugation 30–50%, mitochondrial β-oxidation over 40%
Elimination half-life9–16 hours[1]
ExcretionUrine (30–50%)[1]
showIUPAC name
CAS Number99-66-1 
PubChem CID3121
NIAID ChemDB057177
CompTox Dashboard (EPA)DTXSID6023733 
ECHA InfoCard100.002.525 
Chemical and physical data
Molar mass144.214 g·mol−1
3D model (JSmol)Interactive image


Publication numberPriority datePublication dateAssigneeTitleCA1144558A *1979-10-221983-04-12Francis E. FischerProcess for making sodium hydrogen divalproateUS4988731A *1979-08-201991-01-29Abbott LaboratoriesSodium hydrogen divalproate oligomerUS5212326A *1979-08-201993-05-18Abbott LaboratoriesSodium hydrogen divalproate oligomerWO2001032595A1 *1999-11-022001-05-10Cilag AgMethod for producing compounds of the valproinic acidUS20030018215A1 *2001-06-292003-01-23Procos S.P.A.Process for the preparation of sodium divalproatePublication numberPriority datePublication dateAssigneeTitleUS20110040122A1 *2009-08-112011-02-17Sci Pharmtech, Inc.Method for preparing metal salt of valproic acidCN102942467A *2012-10-172013-02-27山东方明药业集团股份有限公司Preparation method of divalproex sodiumCN103183600A *2011-12-302013-07-03北大方正集团有限公司Method for preparing divalproex sodium

////// divalproex, Anticonvulsant,  Antimigraine, Antimanic, valproic acid, sodium valproate








59467-70-8 CAS NO OF FREE BASE

59467-94-6 MALEATE, Launched – 1982, Roche (Originator)

59467-96-8 (HCl)

CAS Registry Number: 59467-70-8
CAS Name: 8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine
Molecular Formula: C18H13ClFN3
Molecular Weight: 325.77
Percent Composition: C 66.36%, H 4.02%, Cl 10.88%, F 5.83%, N 12.90%
Literature References: Short-acting deriv of diazepam, q.v. Prepn: R. I. Fryer, A. Walser, DE 2540522eidem, US 4280957 (1976, 1981 both to Hoffmann-La Roche); A. Walser et al., J. Org. Chem. 43, 936 (1978). HPLC determn in plasma: S. L. Eeckhoudt et al., J. Chromatogr. B 710, 165 (1998). Toxicity data: L. Pieri et al., Arzneim.-Forsch. 31, 2180 (1981). Series of articles on pharmacology, metabolism, pharmacokinetics, clinical experience: ibid. 2177-2288; Br. J. Clin. Pharmacol. 16, Suppl. 1, 1S-199S (1983). Review of pharmacology and therapeutic use: J. W. Dundee et al., Drugs 28, 519-543 (1984); in treatment of status epilepticus: D. F. Hanley, J. F. Kross, Clin. Ther. 20, 1093-1105 (1998). Clinical evaluation for intranasal treatment of febrile seizures in children: E. Lahat et al., Br. Med. J. 321, 83 (2000).
Properties: Colorless crystals from ether/methylene chloride/hexane, mp 158-160°. uv max (2-propanol): 220 nm (e 30000).
Melting point: mp 158-160°
Absorption maximum: uv max (2-propanol): 220 nm (e 30000)
Derivative Type: Maleate
CAS Registry Number: 59467-94-6
Manufacturers’ Codes: Ro-21-3981/001
Trademarks: Dormicum (Roche)
Molecular Formula: C18H13ClFN3.C4H4O4
Molecular Weight: 441.84
Percent Composition: C 59.80%, H 3.88%, Cl 8.02%, F 4.30%, N 9.51%, O 14.48%
Properties: Crystals from ethanol/ether, mp 114-117° (solvated). LD50 in male mice (mg/kg): 760 orally; 86 i.v. (Pieri).
Melting point: mp 114-117° (solvated)
Toxicity data: LD50 in male mice (mg/kg): 760 orally; 86 i.v. (Pieri)
Derivative Type: Hydrochloride
CAS Registry Number: 59467-96-8
Manufacturers’ Codes: Ro-21-3981/003
Trademarks: Hypnovel (Roche); Versed (Roche)
Molecular Formula: C18H13ClFN3.HCl
Molecular Weight: 362.23
Percent Composition: C 59.68%, H 3.90%, Cl 19.57%, F 5.24%, N 11.60%
Properties: Sol in aqueous solns.
NOTE: This is a controlled substance (depressant): 21 CFR, 1308.14.
Therap-Cat: Anesthetic (intravenous); anticonvulsant; sedative, hypnotic.
Keywords: Anesthetic (Intravenous); Anticonvulsant; Sedative/Hypnotic; Benzodiazepine Derivatives.

A short-acting hypnotic-sedative drug with anxiolytic and amnestic properties. It is used in dentistry, cardiac surgery, endoscopic procedures, as preanesthetic medication, and as an adjunct to local anesthesia. The short duration and cardiorespiratory stability makes it useful in poor-risk, elderly, and cardiac patients. It is water-soluble at pH less than 4 and lipid-soluble at physiological pH.

Midazolam (/mɪˈdæzəlæm/, marketed in English-speaking countries and Mexico under the trade names DormicumHypnovel, andVersed,) is a short-acting drug in the benzodiazepine class developed by Hoffmann-La Roche in the 1970s. The drug is used for treatment of acute seizures, moderate to severe insomnia, and for inducing sedation and amnesia before medical procedures. It possesses profoundly potentanxiolyticamnestichypnoticanticonvulsantskeletal muscle relaxant, and sedative properties.[6][7][8] Midazolam has a fast recovery time and is the most commonly used benzodiazepine as a premedication for sedation; less commonly it is used for induction and maintenance of anesthesia.Flumazenil, a benzodiazepine antagonist drug, can be used to treat an overdose of midazolam, as well as to reverse sedation.[7] However, flumazenil can trigger seizures in mixed overdoses and in benzodiazepine-dependent individuals, so is not used in most cases.[9][10]


Administration of midazolam by the intranasal or the buccal route (absorption via the gums and cheek) as an alternative to rectally administereddiazepam is becoming increasingly popular for the emergency treatment of seizures in children. Midazolam is also used for endoscopyprocedural sedation and sedation in intensive care. The anterograde amnesia property of midazolam is useful for premedication before surgery to inhibit unpleasant memories. Midazolam, like many other benzodiazepines, has a rapid onset of action, high effectiveness and low toxicity level. Drawbacks of midazolam include drug interactions, tolerance, and withdrawal syndrome, as well as adverse events including cognitive impairment and sedation. Paradoxical effects occasionally occur, most commonly in children and the elderly, particularly after intravenous administration. The drug has also recently been hastily introduced for use in executions in the USA in combination with other drugs.

Midazolam is a short-acting benzodiazepine in adults with an elimination half-life of one to four hours; however, in the elderly, as well as young children and adolescents, the elimination half-life is longer. Midazolam is metabolised into an active metabolite alpha1-hydroxymidazolam. Age related deficits, renal and liver status affect the pharmacokinetic factors of midazolam as well as its active metabolite. However, the active metabolite of midazolam is minor and contributes to only 10 percent of biological activity of midazolam. Midazolam is poorly absorbed orally with only 50 percent of the drug reaching the bloodstream. Midazolam is metabolised by cytochrome P450 (CYP) enzymes and by glucuronide conjugation. The therapeutic as well as adverse effects of midazolam are due to its effects on the GABAA receptors; midazolam does not activate GABAA receptors directly but, as with other benzodiazepines, it enhances the effect of the neurotransmitter GABA on the GABAA receptors (↑ frequency of Cl− channel opening) resulting in neural inhibition. Almost all of the properties can be explained by the actions of benzodiazepines on GABAA receptors. This results in the following pharmacological properties being produced: sedation, hypnotic, anxiolytic, anterograde amnesia, muscle relaxation and anti-convulsant.Midazolam maleate is a benzodiazepine that is commercialized by Astellas Pharma and Roche as an intravenous or intramuscular injection for the long-term sedation of mechanically ventilated patients under intensive care. The drug is also available in a tablet formulation, and is currently distributed in various markets, including Germany, Japan, Switzerland and the U.K. In March 2002, two lots of a syrup formulation were recalled in the U.S. due to the potential presence of a crystalline precipitate of an insoluble complex of midazolam and saccharin. Subsequently, the injection and syrup formulations of the product were both withdrawn from the U.S. market. In 2010, a Pediatric Use Marketing Authorization (PUMA) was filed for approval in the E.U. by ViroPharma for the treatment of prolonged, acute, convulsive seizures in infants, toddlers, children and adolescents, from 3 months to less than 18 years. In 2011, a positive opinion was assigned to the PUMA and final approval was assigned in June 2011. The product was launched in the U.S. in November 2011. This product was filed for approval in Japan in 2013 by Astellas Pharma for the conscious sedation in dentistry and dental surgery. In the same year the product was approved for this indication.

In terms of clinical development, a nasal formulation of the drug is in phase III clinical trials at Upsher-Smith for rescue treatment of seizures in patients on stable anti-epileptic drug regimens who require control of intermittent bouts of increased seizure activity (seizure clusters). The Hopitaux de Paris had been developing a sublingual tablet formulation of midazolam to be used in combination with morphine for the treatment of pain in children following bone fractures; however, no recent development has been reported for this indication. NovaDel Pharma had been developing the compound preclinically for the treatment of generalized anxiety, however no recent developments have been reported.

Midazolam achieves its therapeutic effect through interaction with the gamma-aminobutyric acid benzodiazepine (GABA-BZ) receptor complex. Subunit modulation of the GABA-BZ receptor chloride channel macromolecular complex is hypothesized to be responsible for some of the pharmacological properties of benzodiazepines, which include sedative, anxiolytic, muscle relaxant, and anticonvulsive effects in animal models. GABA acts at inhibitory synapses in the brain by binding to specific transmembrane receptors in the plasma membrane of both pre- and post-synaptic neurons, opening ion channels and bringing about a hyperpolarization via either chloride or potassium ion flow.

In 2008, fast track designation was assigned to midazolam maleate in the U.S. for the treatment of seizure disorders.

In 2009, Orphan Drug Designation was received in the U.S. by for the treatment of seizure disorders in patients who require control of intermittent bouts of increased seizure activity (e.g. acute repetitive seizures, seizure clusters). This designation was assigned in the U.S. for the treatment of nerve agent-induced seizures.

In 2010, midazolam maleate was licensed to Upsher-Smith by Ikano Therapeutics for the treatment of acute repetitive seizure in patients with epilepsy. However, in 2010, Ikano closed and dissolved its business. Previously, Ikano had transferred to Upsher-Smith ownership of it nasal midazolam maleate program.


Midazolam is among about 35 benzodiazepines which are currently used medically, and was synthesised in 1975 by Walser and Fryer at Hoffmann-LaRoche, Inc in the United States.Owing to its water solubility, it was found to be less likely to cause thrombophlebitis than similar drugs.The anticonvulsant properties of midazolam were studied in the late 1970s, but not until the 1990s did it emerge as an effective treatment for convulsive status epilepticus. As of 2010, it is the most commonly used benzodiazepine in anesthetic medicine. In acute medicine, midazolam has become more popular than other benzodiazepines, such as lorazepam and diazepam, because it is shorter lasting, is more potent, and causes less pain at the injection site.Midazolam is also becoming increasingly popular in veterinary medicine due to its water solubility.

Midazolam is a water-soluble benzodiazepine available as a sterile, nonpyrogenic parenteral dosage form for intravenous or intramuscular injection. Each mL contains midazolam hydrochloride equivalent to 1 mg or 5 mg midazolam compounded with 0.8% sodium chloride and 0.01% edetate disodium with 1% benzyl alcohol as preservative, and sodium hydroxide and/or hydrochloric acid for pH adjustment. pH 2.9-3.7.

Midazolam is a white to light yellow crystalline compound, insoluble in water. The hydrochloride salt of midazolam, which is formed in situ, is soluble in aqueous solutions. Chemically, midazolam HCl is 8-chloro-6-(2-fluorophenyl)-1-methyl-4H– imidazo[1,5-a] [1,4] benzodiazepine hydrochloride. Midazolam hydrochloride has the molecular formula C18H13ClFN3•HCl, a calculated molecular weight of 362.25 and the following structural formula:

Midazolam HCl structural formula illustration

In the Netherlands, midazolam is a List II drug of the Opium Law. Midazolam is a Schedule IV drug under the Convention on Psychotropic Substances. In the United Kingdom, midazolam is a Class C controlled drug. In the United States, midazolam (DEA number 2884) is on the Schedule IV list of the Controlled Substances Act as a non-narcotic agent with low potential for abuse.

midaolam hydrochloride NDA 018654, 075154


U.S. Pat. No. 4,280,957

U.S. Pat. No. 5,693,795

U.S. Pat. No. 6,512,114

Midazolam Maleate
Drugs Fut 1978, 3(11): 822

Bioorganic and Medicinal Chemistry, 2012 ,  vol. 20,  18  pg. 5658 – 5667

Journal of Heterocyclic Chemistry, 1983 ,  vol. 20,  3  pg. 551 – 558.. 32 maleate

WO 2001070744

WO 2001002402

WO 2012075286

US2011/275799 A1… no 5

Journal of Organic Chemistry, 1978 ,  vol. 43, p. 936,942, mp free base, nmr

US4280957 May 15, 1978 Jul 28, 1981 Hoffmann-La Roche Inc. Imidazodiazepines and processes therefor
US6262260 * Mar 23, 2000 Jul 17, 2001 Abbott Laboratories Process for the preparation of midazolam
US6512114 Jun 30, 1999 Jan 28, 2003 Abbott Laboratories Process for the preparation of Midazolam



4H-imidazo[1,5-a][1,4]benzodiazepines or, more simply, imidazobenzodiazepines, are a class of benzodiazepines having the general formula (I),

wherein the 1,4-diazepine ring is fused with a 1,3-imidazole ring. The main compounds part of the 4H-imidazo[1,5-a][1,4]benzodiazepines are Midazolam of formula (IV):

an active ingredient currently commercially available as a hydrochloride salt under the name of Versed or Hypnovel for anaesthetic and sedative use and the maleate salt currently commercially available under the name Dormicum or Flormidal.
Other important compounds are Climazolam of formula (VII):

Imidazenil of formula (VIII):

1-Hydroxymidazolam of formula (IX):

and Desmethyl midazolam of formula (X):

all these being biologically active substances and having psychotropic and sedative action.
The synthesis of the Midazolam as described in U.S. Pat. No. 4,280,957 of Hoffmann-La Roche provides for the decarboxylation reaction of the 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid of formula (VI) according to the following scheme:

The process for preparing the intermediate (VI) via basic hydrolysis of the corresponding ester is described in such patent publication and it is well known in the art.
The thermal decarboxylation reaction in high boiling solvent such as mineral oil at 230° C. for 5 min results in a mixture of products of Midazolam of formula (IV) and of Isomidazolam of formula (IV-bis), a non-pharmacologically active isomer, at a 80:20 ratio. The two products are separated by chromatography.
At industrial level, the formation of the Isomidazolam isomer impurity requires a further isomerisation reaction performed on the mixture of the two compounds to convert the isomer into the active product. The reaction mixture obtained from the thermal decarboxylation is thus subjected to basic treatment under the action of KOH in EtOH followed by an acid treatment which thus provides a mixture of Midazolam-Isomidazolam at a 95:5 ratio. The final removal of the Isomidazolam impurity from the product occurs through crystallisation of the product from AcOEt and EtOH. In order to limit this isomerisation treatment, in the subsequent U.S. Pat. No. 5,693,795 of Hoffmann-La Roche dated 1999, there is described a process for performing the decarboxylation of the compound of formula (VI) in n-butanol in a continuous tubular reactor with a 4 minutes permanence period with a yield between 47-77%. However, the reaction, performed at high temperature and pressure (280° C., 100 bars) results in the formation of a considerable percentage of Isomidazolam (85:15 Midazolam/Isomidazolam ratio) which still requires the basic isomerisation step.
Lastly, in U.S. Pat. No. 6,512,114 of Abbott Laboratories there is described the decarboxylation of the compound of formula (VI) in mineral oil or in N,N-Dimethylacetamide (DMA) at 160-230° C. for at least 3 hours obtaining a 3/1 to 6/1 Midazolam/Isomidazolam ratio with a yield of isolated product equal to just 54%.
Though performed using dedicated apparatus and in extreme conditions, the prior art processes do not allow selectively performing the decarboxylation reaction of the intermediate (VI) to Midazolam thus requiring a further synthetic passage followed by crystallisation with ensuing reduction of the overall yield.

Midazolam (8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine) is represented by the following structural formula (I):

Figure US07776852-20100817-C00001

Midazolam is a central nervous system (CNS) depressant, used for short term treatment of insomnia. Like other benzodiazepines, midazolam binds to benzodiazepine receptors in the brain and spinal cord and is thus used as a short-acting hypnotic-sedative drug with anxiolytic and amnestic properties. It is currently used in dentistry, cardiac surgery, endoscopic procedures, as a preanesthetic medication, as an adjunct to local anesthesia and as a skeletal muscle relaxant. Depending on the pH value, midazolam can exist in solution as a closed ring form (I) as well as an open ring form (IA), which are in equilibrium, as shown in Scheme 1:

Figure US07776852-20100817-C00002

The amount of the open ring form (IA) is dependent upon the pH value of the solution. At a pH value of about 3, the content of the open ring form (IA) can be 40%, while at pH value of 7.5, the closed ring form (I) can be more than 90%.

Clinical studies have demonstrated that there are no significant differences in the clinical activity between midazolam hydrochloride and midazolam maleate, however the use of intravenous midazolam hydrochloride has been associated, in some cases, with respiratory depression and arrest.

U.S Pat. No. 4,280,957 (hereinafter the ‘957 patent) describes a synthetic process for preparing midazolam, which is depicted in Scheme 2 below. This process includes reacting 2-aminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-bezodiazepine (II) with acetic anhydride in dichloromethane to produce 2-acetamido-methyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-bezodiazepine (III). The latter is heated with polyphosphoric acid at 150° C. to produce 8-chloro-6-(2-fluorophenyl)-3a,4-dihydro-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine of formula (IV), which is purified by column chromatography. Compound IV is then mixed with toluene and manganese dioxide and heated to reflux to afford midazolam base, which is crystallized from ether to yield a product with mp of 152-154° C.

Figure US07776852-20100817-C00003

The ‘957 patent further describes an alternative process which includes reacting 2-aminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-bezodiazepine (II) (optionally as a dimaleate salt) with triethylorthoacetate in ethanol and in the presence of p-toluenesulfonic acid to afford 8-chloro-6-(2-fluorophenyl)-3a,4-dihydro-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine (IV). This product is dissolved in xylene and treated with activated manganese dioxide to afford the crude base, which is reacted in situ with maleic acid in ethanol and crystallized by addition of ether to produce the midazolam maleate having melting point of 148-151° C. The process is depicted in Scheme 3 below.

Figure US07776852-20100817-C00004

The preparation of midazolam maleate from the isolated midazolam base is also described in a further example of the ‘957 Patent, wherein a warm solution of midazolam base in ethanol is combined with a warm solution of maleic acid in ethanol. The mixture is diluted with ether and at least part of the solvents is evaporated using a steam bath to obtain crystalline midazolam maleate having melting point of 148-151° C. The yield and the purity of the obtained midazolam maleate are not disclosed.

U.S. Pat. No. 6,512,114 (hereinafter the ‘114 patent) describes another synthetic process for preparing midazolam, which is depicted in Scheme 4 below. According to this Process, the starting material 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylic acid (V) is heated in mineral oil for 3 hours at 230° C. until it is decarboxylated, followed by treatment with potassium tert-butoxide, to afford midazolm (I), isomidazolam (VI) and a midazolam dimmer (VII). Midazolam base is obtained in 54.5% yield after two re-crystallizations from ethyl acetate and heptane; however, the purity of the product is not disclosed.

Figure US07776852-20100817-C00005

The preparation of midazolam by conventional routes is liable to produce impurities such as isomidazolam (VI) and a midazolam dimmer (VII), and possibly other impurities. There is, therefore, a need in the art for a midazolam purification process that will provide highly pure midazolam containing minimal amounts of impurities produced. The present invention provides such a process.

This example describes the preparation of midazolam base as taught in the ‘957 patent.

16 g (0.03 mol) of 2-aminomethyl-7-chloro-5-(2-fluorophenyl)-2,3-dihydro-1H-1,4-bezodiazepine dimaleate was dissolved in 200 ml of toluene and 10 ml of 25% ammonium hydroxide solution was added and mixing was maintained for an hour. Then, the phases were separated and the toluene phase was dried by azeotropic distillation using a Dean Stark apparatus. 7 ml (0.038 mol) of triethylorthoacetate was added and the solution was heated to reflux for 4 hours, after which time the solution was left to cool to ambient temperature. 25 ml of methyl tert-butyl ether was added and the mixture was cooled overnight to produce 8-chloro-6-(2-fluorophenyl)-3a,4-dihydro-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine, which was isolated by filtration. The product was mixed with 200 ml of toluene and dried by azeotropic distillation using a Dean Stark apparatus. Then, 30 g of manganese dioxide was added and the mixture was heated to reflux for two hours. The excess manganese dioxide was filtered off to afford a solution of midazolam base in toluene, which was evaporated to obtain a product having 97.9% purity and containing 0.44% of impurity VIII and 1.14% of impurity IX (according to HPLC).




2-Aminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-benzodiazepine dimaleate

A suspension of 17 g (0.05 m) of 7-chloro-1,3-dihydro-5-(2-fluorophenyl)-2-nitromethylene-2H-1,4-benzodiazepine-4-oxide in 200 ml of tetrahydrofuran and 100 ml of methanol was hydrogenated in presence of 17 g of Raney nickel at an initial pressure of 155 psi for 24 hrs. The catalyst was removed by filtration and the filtrate was evaporated. The residue was dissolved in 50 ml of 2-propanol and warmed on the steambath. A warm solution of 17 g of maleic acid in 60 ml of ethanol was added and the salt was allowed to crystallize by cooling in the ice bath. The final product consisted of yellow crystals with mp 196



Acetic anhydride, 7 ml., was added to a solution of 6.16 g. of crude 2-aminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-benzodiazepine in 200 ml. of methylene chloride. The solution was layered with 200 ml. of saturated aqueous sodium bicarbonate and the mixture was stirred for 20 minutes. The organic layer was separated, washed with sodium bicarbonate, dried over sodium sulfate and evaporated to leave 6.2 g. resinous 2-acetaminomethyl-7-chloro-2,3-dihydro-5-(2-fluorophenyl)-1H-1,4-benzodiazepine. This material was heated with 40 g. of polyphosphoric acid at 150 water, made alkaline with ammonia and ice and extracted with methylene chloride. The extracts were dried and evaporated and the residue (5.7 g.) was chromatographed over 120 g. of silica gel using 20% methanol in methylene chloride. The clean fractions were combined and evaporated to yield resinous 8-chloro-3a,4-dihydro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[ 1,5-a][1,4]benzodiazepine. A mixture of this material with 500 ml. of toluene and 30 g. of manganese dioxide was heated to reflux for 11/2 hours. The manganese dioxide was separated by filtration over celite. The filtrate was evaporated and the residue was crystallized from ether to yield a product with m.p. 152 was recrystallized from methylene chloride/hexane



Potassium t-butoxide, 0.625 g. (5.5 mmol), was added to a solution of 1.625 g. (5 mmol) of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine in 20 ml. of dimethylformamide cooled to -30 nitrogen for 10 min. at -30 ml. of glacial acetic acid and was then partitioned between aqueous bicarbonate and toluene/methylene chloride (3:1 v/v). The organic layer was separated, dried and evaporated. The residue was chromatographed over 60 g. of silica gel using 25% (v/v) methylene chloride in ethyl acetate. The less polar product was eluted first and was crystallized from ethylacetate/hexane to yield product with m.p. 180



Potassium t-butoxide, 0.125 g. (1.1 mmol) was added to a solution of 0.325 g. (1 mmol) of 8-chloro-6-(2-fluorophenyl)-1-methyl-6H-imidazo[1,5-a][1,4]benzodiazepine in 20 ml. of dimethylformamide cooled to -30 -30 by addition of 0.2 ml. of glacial acetic acid and was partitioned between aqueous sodium bicarbonate and methylene chloridetoluene (1:3). The organic phase was washed with water, dried and evaporated. The residue was chromatographed over 20 g. of silica gel using ethyl acetate for elution. After elution of starting material, product was collected and crystallized from ether/hexane, m.p. 156

hyd and dihydrochloride


8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine dihydrochloride

A solution of 0.32 g (1 mmol) of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine in 5 ml of ethanol was treated with excess ethanolic hydrogen chloride. The salt was crystallized by addition of 2-propanol and ether. The colorless crystals were collected, washed with ether and dried to leave a final product with mp 290

EXAMPLE 258-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine hydrochloride

A solution of 0.325 g (1 mmol) of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine in 3 ml of ethanol was combined with a suspension of 0.4 g (1 mmol) of the dihydrochloride of this compound in 5 ml of ethanol. After filtration, the solution was treated with ether and heated on the steambath for 5 min to crystallize. The crystals were collected, washed with ether and dried to leave the monohydrochloride with mp 295



8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine maleate

A warm solution of 6.5 g (0.02 m) of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine in 30 ml of ethanol was combined with a warm solution of 2.6 g (0.022 m) of maleic acid in 20 ml of ethanol. The mixture was diluted with 150 ml of ether and heated on the steam bath for 3 min. After cooling, the crystals were collected, washed with ether and dried in vacuo to yield a final product with mp 148



Midazolam, can be described according to scheme 4 indicated below:

Materials and Methods
8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepin-3-carboxylic acid of formula (VI)Figure US20110275799A1-20111110-C00029was prepared according to processes known in the art (e.g. U.S. Pat. No. 4,280,957) which comprise the basic hydrolysis of the corresponding ester.
For the reactions performed in the microreactor, the solutions containing the substrates to be decarboxylated were loaded into 5 and 10 mL gastight glass syringes (Hamilton, item n. 81527, 81627) mounted on syringe pumps (KD Scientifics, model KDS100). A pipe made of PTFE® (OD=1.58 mm, ID=0.8 mm, Supelco, item n. 58696-U) was used for making the reaction channel.A counterpressure valve sold by Swagelok (item n. SS-SS1-VH) was used for regulating the flow within the channel.Example 1Synthesis of the Compound of Formula (V)—Example of the Invention


50 g (0.135 mol) of 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepin-3-carboxylic acid of formula (VI) and 250 mL of ethanol were loaded into a two-neck 500 mL flask, equipped with a magnetic stirrer. 40 mL of an aqueous solution of 1 M HCl are dripped in about 10 minutes. The open di-hydrochloride intermediate of formula (V) starts precipitating into the reaction environment already after 3 minutes from the beginning of the addition of the acid solution. The mixture is maintained stirred at RT for 3 hrs and then it is filtered on buckner washing the solid with ethanol. The moist product is dried in an oven under vacuum at 60° C. up to reaching a constant weight. A light yellow crystalline product is obtained (51.5 g, 83% yield). The crude product was used for the decarboxylation without further purifications.

ESI-MS [MeCN+0.1% HCOOH]: m/z 388 (V); 370 (VI).

1H-NMR (250 MHz, CD3OD): 2.52 (s, 3H); 4.27-4.41 (m, 2H); 7.22-8.1 (m, 7H). M.p.: 217° C.

Example 2

Synthesis of Midazolam of Formula (IV)—Performed in Batch—Example of the Invention

30 g (0.065 mol) of 5-(aminomethyl)-1-{(4-chloro-2-[(2-fluorophenyl)carbonyl]phenyl}-2-methyl-1H-imidazole-4-carboxylic acid dihydrochloride of formula (V) and 90 mL of NMP are loaded into a three-neck 250 mL flask, equipped with a magnetic stirrer and coolant. The mass is heated using an oil bath at T=195-203° C. for one hour. Thus, 1 mL of solution is collected for performing HPLC analysis. The reaction product is Midazolam having 82% titre (w/w) (determined via HPLC titre correcting it using the solvent) and it contains 1% of Isomidazolam. The product is extracted using Isopropyl acetate after raising the pH to 10 by adding aqueous Na2CO3.

Example 3

Synthesis of Midazolam of Formula (IV)—Performed in a Micro-Reactor—Example of the Invention

3.22 g (7 mmol) of 5-(aminomethyl)-1-{4-chloro-2-[(2-fluorophenyl)carbonyl]phenyl}-2-methyl-1H-imidazole-4-carboxylic acid dihydrochloride of formula (V) and 10 mL of NMP are loaded into a 10 mL flask equipped with a magnetic stirrer. In order to facilitate the complete solubilisation of the substrate, it is necessary to slightly heat the reaction mixture (about 40° C.) for a few minutes. The solution thus obtained is transferred into a 10 mL gastight glass syringe mounted on a KDS100 syringe pump (FIG. 1) and the flow is regulated at 1.0 mL/h so as to set a residence period of 30 minutes at 200° C. The reaction product is Midazolam having an 89% titre (w/w) (determined via HPLC titre correcting it using the solvent) and containing 3% (w/w) of Isomidazolam.

Example 4Synthesis of Midazolam of formula (IV)—Comparison of the InventionA table is reported which summarises the results of the decarboxylation of the compound of formula (V) and (V-bis) (for the latter see Examples 6 and 7) obtained according to some embodiments of the invention and those obtained by way of experiment through the decarboxylation of the intermediate of formula (VI) (process of the prior art) both performed in 3 volumes of NMP at 200° C., both in batch method (Example 4) and in continuous method with the microreactor (MR) made of PTFE of FIG. 1. (Examples 4-1, 4-2, 4-3).

Example substrate Mode Solv. T° C. t min. Midazolam (p/p) Isomidaz. (P/P)
2 (V) Batch NMP 200 60 82 1
3 (V) MR NMP 200 30 89 3
7 (V-bis) Batch NMP 200 60 68 3
4 (VI) Batch NMP 200 60 78 18
4-1 (VI) MR NMP 200 38 81 17
4-2 (VI) MR NMP 200 20 77 18
4-3 (VI) MR NMP 200 15 58 22
U.S. Pat. No. (VI) Tubular n-BuOH 290 4 85 * 15 *
5,693,795   reactor          
U.S. Pat. No. (VI) Batch Olio 230 180 75 * 25 *
6,512,114     min.     87.5 * 12.5 *
      or DMA        
* = Midazolam/Isomidazolam ratio only (other impurities not considered).

The product of the comparative experiments 4, 4-1, 4-2, 4-3 and of the two USA patents should be subjected to a further isomerisation process to reduce the high amount of Isomidazolam so as to be able to obtain Midazolam free of Isomidazolam after further crystallization, which would not be required for the product obtained according to the invention (examples 2 and 3).

Midazolam maleate, dihydrochloride  and monohydrochloride
Example 8
Preparation of 8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine maleate (Midazolam Maleate)


A 4-neck RBF was charged under nitrogen flow with: 10 g of Midazolam (IV) (prepared according to example 2) and 40 mL of Ethanol. The slurry was stirred until complete dissolution at 25/30° C. In an other flask was prepared the following solution: 3.72 g of maleic acid are dissolved in 15 mL of Ethanol. The slurry was stirred until complete dissolution at 25/30° C. The maleic acid solution is dropped in 30/40 minutes and keeping T=25/30° C. into the solution containing Midazolam. The slurry was cooled down at −15° C. in one hour and kept at that temperature for at least 2 hours. The slurry was then filtered and the cake was washed with 40 mL of cool Ethanol. The filter was discharged and the product was dried at 40° C. under vacuum for 2 hours and then at 60° C. for 8 hours. 12.8 g of Midazolam Maleate as white solid were collected (Molar yield=94.5%). m.p.=149-152° C. (by DSC).

Example 9
Preparation of 8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine dihydrochloride (Midazolam dihydrochloride)


A 4-neck RBF was charged under nitrogen flow with: 1 g of Midazolam (IV) (prepared according to example 2) and 15 mL of Ethanol. The slurry was stirred until complete dissolution at 25/30° C. 5 mL of a ethanolic solution of Hydrochloric acid 2N were slowly added. 20 mL of Isopropanol were added over 30 minutes at RT. The slurry was cooled down at −15° C. in one hour and kept at that temperature for at least 2 hours. The slurry was then filtered and the cake was washed with 10 mL of cool isopropanol. The filter was discharged and the product was dried at 40° C. under vacuum for 2 hours and then at 60° C. for 8 hours. Midazolam dihydrochloride as white solid was collected.


Example 10

Preparation of 8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1,5-a][1,4]benzodiazepine hydrochloride (Midazolam hydrochloride)

A 4-neck RBF was charged under nitrogen flow with: 1 g of Midazolam (IV) (prepared according to example 2) and 10 mL of Ethanol. The slurry was stirred until complete dissolution at 25/30° C. In an other flask was prepared the following suspension: 1.22 g of Midazolam dihydrochloride (prepared according to example 9) and 15 mL of Ethanol. The Midazolam ethanolic solution was added to the Midazolam dihydrochloride suspension. After filtration, the solution was treated with MTBE and heated at 60° C. until crystallization. After cooling to RT, the slurry was filtered, the cake washed with MTBE and the product was dried to provide Midazolam (mono)hydrochloride as a white solid.


Midazolam is prepared from 2-amino-5-chloro-2’-fluoro benzophenone, which undergoes cyclization with ethyl ester of glycine in presence of pyridine to form benzodiazepinone. Amide is converted to thioamide (which is much reactive) by treatment with phosphorouspentasulphide. Reaction of the thioamide with methylamine proceeds to give the amidine; this compound is transformed into a good leaving group by conversion to the N-nitroso derivative by treatment with nitrous acid. Condensation of this intermediate with the carbanion from nitro methane leads to displacement of N-nitroso group by methyl nitro derivative; the double bond shifts into conjugation with the nitro group to afford nitro vinyl derivative. Reduction with Raney nickel followed by reaction with methyl orthoacetate leads to fused imidazoline ring. Dehydrogenation with manganese dioxide converts it into an imidazole to give midazolam.
Uses: Midazolam has been used adjunctively with gaseous anaesthetics. The onset of its CNS effects is slower than that of thiopental, and it has a longer duration of action. Cases of severe post-operative respiratory depression have occurred.






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