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Penciclovir2DCSD.svgChemSpider 2D Image | Penciclovir | C10H15N5O3

Penciclovir

  • Molecular FormulaC10H15N5O3
  • Average mass253.258 Da

Cas 39809-25-1
97845-62-0 (Na salt)

Launched – 1996 PERRIGO, Herpes labialis

2-Amino-1,9-dihydro-9-[4-hydroxy-3-(hydroxymethyl)butyl]-6H-purin-6-one
2-Amino-9-[4-hydroxy-3-(hydroxymethyl)butyl]-1,9-dihydro-6H-purin-6-one
2-Amino-9-[4-hydroxy-3-(hydroxyméthyl)butyl]-1,9-dihydro-6H-purin-6-one
359HUE8FJC

BRL-39123; penciclovir; BRL 39123A; penciclovir sodium; Denavir; Vectavir; Euraxvir; Fenivir

Penciclovir [USAN:INN:BAN]

  • BRL 39123
  • BRL-39123
  • CCRIS 9213
  • Denavir
  • HSDB 8123
  • Penciclovir
  • Penciclovirum
  • Penciclovirum [INN-Latin]
  • UNII-359HUE8FJC
Title: Penciclovir
CAS Registry Number: 39809-25-1
CAS Name: 2-Amino-1,9-dihydro-9-[4-hydroxy-3-(hydroxymethyl)butyl]-6H-purin-6-one
Additional Names: 9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]guanine; PCV
Manufacturers’ Codes: BRL-39123
Trademarks: Denavir (SKB); Vectavir (SKB)
Molecular Formula: C10H15N5O3
Molecular Weight: 253.26
Percent Composition: C 47.42%, H 5.97%, N 27.65%, O 18.95%
Literature References: Carba analog of ganciclovir, q.v., active against several herpes viruses. Prepn: U. K. Pandit et al., Synth. Commun. 2, 345 (1972); R. L. Jarvest, M. R. Harnden, US 5075445 (1991 to Beecham). Synthesis: M. R. Harnden et al., J. Med. Chem. 30, 1636 (1987); J. Hannah et al., J. Heterocycl. Chem. 26, 1261 (1989). Crystal and molecular structures: M. R. Harnden et al., Nucleosides Nucleotides 9, 499 (1990). In vitro activity of enantiomers in comparison with acyclovir, q.v.: G. Abele et al.,Antiviral Chem. Chemother. 2, 163 (1991); against herpes simplex viruses: A. Weinberg et al., Antimicrob. Agents Chemother. 36,2037 (1992). Clinical pharmacokinetics: S. E. Fowles et al., Eur. J. Clin. Pharmacol. 43, 513 (1992). HPLC determn in plasma and urine: J. R. McMeekin et al., Anal. Proc. 29, 178 (1992). Review of development and antiviral activity: M. R. Harnden, Drugs Future14, 347-358 (1989).
Properties: White crystalline solid from water, (monohydrate), mp 275-277°; also reported as colorless matted needles, mp 272-275°. uv max (in water): 253 nm (e 11500). uv max (aq 0.01N NaOH): 215, 268 nm (e 18140, 10710). Sol in water (20°): 1.7 mg/ml, pH 7.
Melting point: mp 275-277°; mp 272-275°
Absorption maximum: uv max (in water): 253 nm (e 11500); uv max (aq 0.01N NaOH): 215, 268 nm (e 18140, 10710)
Derivative Type: Sodium salt
Manufacturers’ Codes: BRL-39123A
Properties: Occurs as monohydrate, stable crystalline solid. Sol in water (20°): >200 mg/ml. 30 mg/ml soln has pH 11.
Therap-Cat: Antiviral.
Keywords: Antiviral; Purines/Pyrimidinones.
Penciclovir is a guanosine analogue antiviral drug used for the treatment of various herpesvirus infections. It is a nucleoside analoguewhich exhibits low toxicity and good selectivity. Because penciclovir is absorbed poorly when given orally (by mouth) it is more often used as a topical treatment. It is the active ingredient in the cold sore medications Denavir (NDC 0135-0315-52), Vectavir and Fenivir. Famciclovir is a prodrug of penciclovir with improved oral bioavailability.

Penciclovir was approved for medical use in 1996.[2]

Developed and launched by SmithKline Beecham (SB; now GlaxoSmithKline) and now marketed in the US by Prestium Pharma and ex-US by Novartis, penciclovir (Vectavir; Fenivir; Denavir; Euraxvir) is a 1% topical cream indicated for the treatment of recurrent herpes labialis (cold sores) in adults and children 12 years of age and older

APPROVALS

THE US

In September 1996, the compound was approved by the US FDA for cold sore treatment , and was launched in the US in 1997.

EUROPE

In December 1995, SB filed for European approvals of the drug . In  1997, the drug was approved in Belgium  Iceland Denmark  Norway  Ireland . In January 2003, the drug was launched in Sweden . In May 2007, the drug was launched in Portugal .

JAPAN

In December 1995, SB filed for Japanese approval of the drug .

CHINA

In September 1999, the compound was approved in China

FDA

https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/020629s016lbl.pdf

Chemically, penciclovir is known as 9-[4-hydroxy-3-(hydroxymethyl)butyl] guanine. Its molecular formula is C10H15N5O3; its molecular weight is 253.26. It is a synthetic acyclic guanine derivative

Penciclovir is a white to pale yellow solid. At 20°C it has a solubility of 0.2 mg/mL in methanol, 1.3 mg/mL in propylene glycol, and 1.7 mg/mL in water. In aqueous buffer (pH 2) the solubility is 10.0 mg/mL. Penciclovir is not hygroscopic. Its partition coefficient in n-octanol/water at pH 7.5 is 0.024 (logP = -1.62).

Medical use

In herpes labialis, the duration of healing, pain and detectable virus is reduced by up to one day,[3] compared with the total duration of 2–3 weeks of disease presentation.

Mechanism of action

Penciclovir is inactive in its initial form. Within a virally infected cell a viral thymidine kinase adds a phosphate group to the penciclovir molecule; this is the rate-limiting step in the activation of penciclovir. Cellular (human) kinases then add two more phosphate groups, producing the active penciclovir triphosphate. This activated form inhibits viral DNA polymerase, thus impairing the ability of the virus to replicate within the cell.

The selectivity of penciclovir may be attributed to two factors. First, cellular thymidine kinases phosphorylate the parent form significantly less rapidly than does the viral thymidine kinase, so the active triphosphate is present at much higher concentrations in virally infected cells than in uninfected cells. Second, the activated drug binds to viral DNA polymerase with a much higher affinity than to human DNA polymerases. As a result, penciclovir exhibits negligible cytotoxicity to healthy cells.

The structure and mode of action of penciclovir are very similar to that of other nucleoside analogues, such as the more widely used aciclovir. A difference between aciclovir and penciclovir is that the active triphosphate form of penciclovir persists within the cell for a much longer time than the activated form of aciclovir, so the concentration within the cell of penciclovir will be higher given equivalent cellular doses.

SYN

Choudary, B.M.; Geen, G.R.; Grinter, T.J.; MacBeath, F.S.; Parratt, M.J.
Influence of remote structure upon regioselectivity in the N-alkylation of 2-amino-6-chloropurine: Application to the synthesis of penciclovir
Nucleosides Nucleotides 1994, 13(4): 979

PATENT

US 6573378

PATENT

CN 102070636

PAPER

https://www.tandfonline.com/doi/abs/10.1081/SCC-120026312?journalCode=lsyc20Selective and Practical Synthesis of Penciclovir

Pages 3897-3905 | Received 01 May 2003, Published online: 19 Aug 2006

9-[4-Hydroxy-3-(hydroxymethyl)butyl]guanine
(Penciclovir)[3a,b] (1)
………………………as a colorless crystalline solid: m.p. 268.4–269.2C [Lit.[3a,b]
275–277C]. UV (H2O) max 252 and 273 (sh) nm [Lit[3a,b] 253 and 270
(sh) nm].

1HNMR (DMSO-d6) 1.42 (pseudo septet, 1H, J¼7 Hz, H-30),
1.69 (pseudo q, 2H, J¼7 Hz, H-20), 3.37 (ddd, 2H, J¼11, 7 and 7 Hz)
and 3.41 (ddd, 2H, J¼11, 7 and 7 Hz) (CH2OH), 3.98 (t, 2H, J¼7 Hz,
H-10), 4.42 (t, 2H, J¼7 Hz, OH), 6.42 (br s, 2H, NH2), 7.67 (s, 1H, H-8),
10.50 (br s, 1H, H-1).

The 1HNMR spectrum is in good agreement with
the literature data.[3a,b]

3 (a) Harnden, M.R.; Jarvest, R.L.Tetrahedron Lett. 1985, 26, 4265–4268;

(b) Harnden, M.R.;Jarvest, R.L.; Bacon, T.H.; Boyd, M.R. J. Med. Chem. 1987, 30,1636–1642;

PAPER

Improved industrial syntheses of penciclovir and famciclovir using N2-acetyl-7-benzylguanine and a cyclic side chain precursor.

The synthesis of penciclovir by two related ways has been reported: 1) The reaction of 2-(hydroxymethyl)butane-1,4-diol (I) with formaldehyde (or an aldehyde such as trimethylacetaldehyde) (II) by means of H2SO4 (or p-toluenesulfonic acid, TsOH) gives the dioxane (III), which by reaction first with methanesulfonyl chloride and triethylamine and then with NaI in acetone affords the corresponding 5-(2-iodoethyl)-1,3-dioxane (IV). The reaction of (IV) with 2-amino-6-chloropurine (V) by means of K2CO3 in DMF gives the corresponding condensation product (VI), which is finally hydrolyzed and deprotected with refluxing 2M aqueous HCl. 2) The reaction of triol (I) with 2,2-dimethoxypropane (VII) by means of TsOH gives the corresponding 1,3-dioxane (VIII), which by reaction with triphenylphosphine and CBr4 is converted to the 5-(2-bromoethyl) derivative (IX). The reaction of (IX) with the purine (V) by means of K2CO3 as before affords the corresponding condensation product (X), which is hydrolyzed and deprotected with 2M HCl as before.
AND
This compound has been obtained by two similar ways: 1) The reaction of 6-chloropurine-2-amine (I) with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (II) by means of K2CO3 in DMF gives the expected condensation product (III), which is methanolized with HCl/methanol yielding 2-[2-(2-amino-6-methoxypurin-9-yl)ethyl]malonic acid dimethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol affords the corresponding diol (V), which is finally converted into pecnciclovir by hydrolysis with 2N NaOH. 2) The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (VI) by means ofK2CO3 in DMF gives the expected condensation product (VII), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (VIII). The reduction of (VIII) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (IX), which is finally converted into penciclovir by hydrlysis with 2N HCl.
AND
A synthesis of famciclovir that corresponds to that previously published and studies on its oral bioavailability in rats and mice, identifying famciclovir as the preferred prodrug of BRL-39123 (penciclovir), have been published.
AND
The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (II) by means ofK2CO3 in DMF gives the expected condensation product (III), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (V), which is finally converted into famciclovir by reductive dechlorination with H2 over Pd/C in ethyl acetate/triethylamine.
PAPER
Synth Commun 1972,2345-351
This compound has been obtained by two similar ways: 1) The reaction of 6-chloropurine-2-amine (I) with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (II) by means of K2CO3 in DMF gives the expected condensation product (III), which is methanolized with HCl/methanol yielding 2-[2-(2-amino-6-methoxypurin-9-yl)ethyl]malonic acid dimethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol affords the corresponding diol (V), which is finally converted into pecnciclovir by hydrolysis with 2N NaOH. 2) The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (VI) by means ofK2CO3 in DMF gives the expected condensation product (VII), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (VIII). The reduction of (VIII) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (IX), which is finally converted into penciclovir by hydrlysis with 2N HCl.
PAPER
Tetrahedron Lett 1985,264265-68
This compound has been obtained by two similar ways: 1) The reaction of 6-chloropurine-2-amine (I) with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (II) by means of K2CO3 in DMF gives the expected condensation product (III), which is methanolized with HCl/methanol yielding 2-[2-(2-amino-6-methoxypurin-9-yl)ethyl]malonic acid dimethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol affords the corresponding diol (V), which is finally converted into pecnciclovir by hydrolysis with 2N NaOH. 2) The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (VI) by means ofK2CO3 in DMF gives the expected condensation product (VII), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (VIII). The reduction of (VIII) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (IX), which is finally converted into penciclovir by hydrlysis with 2N HCl.
PAPER
J Med Chem 1987,301636-42
PAPER
Journal of Zhejiang University SCIENCE A 2013 Vol.14 No.10 P.760-766

10.1631/jzus.A1300238

Accelerated effect on Mitsunobu reaction via bis-N-tert-butoxycarbonylation protection of 2-amino-6-chloropurine and its application in a novel synthesis of penciclovir

Author(s):  Li-yan Dai, Qiu-long Shi, Jing Zhang, Xiao-zhong Wang, Ying-qi Chen
Affiliation(s):  . Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China
Corresponding email(s):   dailiyan@zju.edu.cn
Key Words:  2-amino-6-chloropurine, Mitsunobu reaction, bis-Boc protection, Penciclovir (PCV)
1.  Introduction
 Numerous nucleoside analogues in which the sugar residues have been replaced by acylic side-chains have been found to exhibit high antiviral activity (De Clercq, 1991). Purine derivatives (Fig. 1), in the majority N9 position, represent a plurality of important active substances endowed with antiviral activity. This group of compounds includes acyclovir (ACV) 1 (Schaeffer et al., 1978), ganciclovir (GCV) 2 (Ogilvie et al., 1982; Martin et al., 1983), penciclovir (PCV) 3 (Harnden et al., 19851987; Harnden and Jarvest, 1987), and famciclovir (FCV) 4 (Geen et al., 1992), and so on. Since Schaeffer et al. (1978) discovered that acyclovir is a promising anti-herpes virus agent, several groups have undertaken intensive studies to develop still more potent and effective acylic nucleoside analogues (Ashton et al., 1982; Smith et al., 1982; Martin et al., 1983). As a result, penciclovir (PCV) 3 and its pro-drug famciclovir (FCV) 4 were found to be potent and highly selective antiviral agents against both the herpes simplex virus (HSV) and the vari-cella-zoster virus (VZV) (Tippie et al., 1984). It was also reported that 3 exhibits anti hepatitis B virus (HBV) and duck hepatitis B virus (DHBV) activity (Korba and Boyd, 1996; Shaw et al., 1994).
Fig.1
Purine derivatives

To synthesize 3 and 4, 2-amino-6-chloropurine (ACP) is commonly used as a starting material, coupling with alkyl halide side chains (Geen et al., 1990; Geen et al., 1992; Kim et al., 1998; Brand et al., 1999; Toyokuni et al., 2003). However, considering its isomerization at N7 and N9 positions under acidic or alkaline conditions, the most challengeable issue is the selectivity of a N-alkylation at the N7 or N9 position of ACP. Normally, alkylation takes place at the N9 position as well as at the N7 position of the purine moiety, and the N9/N7 ratio is usually less than 6:1 (Kim et al., 1998). Accordingly, to improve this ratio, several approaches have been reported, mainly involving changing the structure of the side chains (Geen et al., 1992) and modification of the ACP (Brand et al., 1999). For example, as reported by Zheng et al. (2004) (Fig. 2), a side chain 6 was synthesized and separated readily at 0 °C. After coupling 6 with 2-amino-6-chloropurine 7, the ratio of the product 9-isomer purine (8a) and the 7-isomer purine (8b) could reach about 10:1. However, the reaction temperature must be strictly controlled as 6 decomposes easily even at room temperature and then an extra careful column chromatography separation procedure would be required to obtain pure 8a. Thus, finding a more practical and efficient method, which could avoid the formation of N7-alkylated compound and shorten the synthetic steps to obtain ACP, becomes attractive.

Fig.2
Synthesis of penciclovir (PCV) with conventional method

The Mitsunobu reaction might be an alternative (potential) approach (Mitsunobu, 1981; Swamy et al., 2009). This reaction has become a very popular chemical transformation due to its mildness, occurring under essentially neutral conditions, and its stereospecificity, proceeding with complete Walden inversion of stereochemistry (Mitsunobu, 1981). Moreover, it permits C-O, C-S, C-N, or C-C bonds formed by the condensation of an acidic component with a primary or a secondary alcohol. Actually, some literature has already reported successful Mitsunobu coupling of ACP and adenine with allylic and benzylic alcohol, showing a good N9 selectivity (Yang et al., 2005; Kitade et al., 2006; Yin et al., 2006). However, a poor to modest yield (20%–50%) and a limited substrate scope were observed. In order to improve these yields, Lu et al. (2007) developed a modified Mitsunobu method to couple purine with alcohols in a higher temperature (70 °C), along with two rounds of the Mitsunobu reaction; yet its long reaction procedure and poor atom economy weaken its potential. The poor solubility of ACP or its derivatives in THF, the preferred solvent for Mitsunobu reactions, is likely the primary reason for these defects being observed.

A possible process to improve the solubility of ACP is to make use of the tert-butoxycarbonyl group (Boc), which can serve as the protection of the exocylic amino groups functionality and increase the lipophilicity of the base portion of the purine. Another advantage of the Boc protection group is that its acidolytic removal is less sensitive to steric factors and can also be removed under neutral conditions (Hwu et al., 1996; Siro et al., 1998). In contrast, a few studies have recently been reported that apply the Boc group in the protection of nucleobase (Sikchi and Hultin, 2006; Porcheddu et al., 2008). As described by Porcheddu et al. (2008), solubility of nucleobases, including guanine, was increased in some organic solvents after protected by Boc groups. In addition, some results in our previous study (Yang et al., 2011) demonstrated a very good improvement in coupling purine derivatives under Mitsunobu conditions. Thus, it could be safer to presume that protecting amino groups of ACP with Boc would be an ideal way for its application in the synthesis of PCV 3 and offer similar results as shown under Mitsunobu conditions.

In this study, we firstly synthesized a bis-Boc protected ACP, namely, bis-Boc-2-amino-6-chloropurine 9 (Fig. 3) and investigated its solubility in several different Mitsunobu solvents, then coupling bis-Boc-2-amino-6-chloropurine 9 with a large scope of alcohols confirmed its good reactivity for a Mitsunobu reaction and successfully developed a new and efficient method for the preparation of PCV using Mitsunobu coupling reaction as the key step.

Fig.3
Synthesis of bis-Boc-6-chloropurine 9
a: 2-amino-6-chloropurine, 4,4-dimethylaminopyridine (DMAP), THF and Boc2O, 25 °C, N2; b: MeOH, NaHCO3, 55 °C

2.  Experimental
2.1.  General
 Acetic ether and hexane, used for extraction and chromatography, were distilled. Absolute anhydrous THF used in the Mitsunobu reactions were prepared by distillation over a drying agent (Na/benzophenone). All other reagents were purchased and used without further purification. Thin-layer chromatography (TLC) analyses were conducted on the Merck Kieselgel 60 F254 plates. Flash chromatography was performed using a silica gel Merck 60 (particle size 0.040–0.063 mm). All 1H NMR and 13C NMR spectra were recorded on the BRUKER AVANCE DX500 (BRUKER AVANCE, Germany), using CDCl3 or d6-DMSO as solvent at room temperature. Chemical shifts are given in 10−6 relative to tetramethylsilane (TMS) and the coupling constants J are given in Hz. TMS served as an internal standard (δ=0) for 1H NMR, and CDCl3 was used as an internal standard (δ=77.0×10−6) for 13C NMR. Melting points (mp) were obtained on a Melting Point WRR (Shanghai Precision & Scientific Instrument Co., Ltd., China).
2.2.  Bis-Boc-2-amino-6-chloropurine (9)
 1. t-Butyl-2-[bis(t-butoxycarbonyl)amino]-6-chloro-9H-purine-9-carboxylate (9a)

To a 250 ml N2-flushed flask with dry THF (100 ml), equipped with a magnetic stir bar, 2-amino-6-chloropurine (2.0 g, 11.8 mmol) and DMAP (0.14 g, 1.18 mmol) were added. Boc2O (10.3 g, 47.2 mmol) was added to the stirred suspension under an N2atmosphere, then the reaction mixture was stirred for 6 h at room temperature (TLC analysis indicated the disappearance of 2-mino-6-chloropurine). The excess amount of THF was removed, and the crude product was dissolved in AcOEt (400 ml), washed with HCl aqueous (2 mol/L, 1×30 ml) and brine (2×50 ml), dried with Na2SO4 and concentrated in vacuo to give a white solid (5.2 g, 94.5%). mp 51–52 °C; 1H NMR (500 MHz, CDCl3): δ=1.47 (s, 18H, C(CH3)3), 1.69 (s, 9H, C(CH3)3), 8.58 (s, 1H, CH); 13C NMR (125 MHz, CDCl3δ=153.8, 152.0, 151.8, 150.6, 145.5, 144.7, 130.8, 88.0, 83.9, 28.0.

2. Bis-Boc-2-amino-6-chloropurine (9)

A solution of the white solid obtained above (14 g, 30 mmol) in MeOH (400 ml) was added to saturated NaHCO3 aqueous (200 ml), then the turbid solution was stirred at 55 °C for 2 h, at which point clean conversion to bis-Boc protected adenine was observed by TLC. After evaporation of MeOH, the residue mixture was cooled, added 5 mol/L hydrochloric acid to get pH=7 (approximate). A large amount of white solid formed, the reaction mixture was filtrated and then dried under a vacuum to give a white solid 9 (10.5 g, 95.5%). mp 101.3–103.3 °C; 1H NMR (500 MHz, CDCl3): δ=1.50 (s, 18H, C(CH3)3), 8.41 (s, 1H, CH); 13C NMR (125 MHz, CDCl3δ=153.5, 151.9, 151.6, 151.3, 145.6, 128.5, 82.7, 28.5.

2.3.  5-(2-hydroxyethyl)-2,2-dimethyl-1,3-dioxane (5)

2-hydroxymethyl-1,4-butanediol 11 (8.10 g, 67.4 mmol) and 2,2-dimethoxypropane (13 ml, 105.7 mmol) were dissolved in dry THF (20 ml). The mixture was stirred and p-toluenesulfonic acid monohydrate (0.64 g, 3.4 mmol) was added, the clear solution was stirred at room temperature for 12 h, triethylamine (10 ml) was added to quench the reaction, and the solution was stirred for 30 min. Then solvents were removed to leave a colorless liquid, the residue was subject to column chromatography on silica gel eluted with 2:1 EtOAc/hexane to give a colorless liquid 5 (6.2 g, 61.5%), R f=0.46 (2:1 EtOAc/hexane). 1H NMR (500 MHz, CDCl3): δ=3.99 (dd, 2H, Heq. J 1=11.80 Hz, J 2=4.45 Hz, CH2); 3.80 (t, 2H, J=6.71 Hz, CH2), 3.34 (dd, 2H, Hax. J 1=11.80 Hz, J 2=8.11 Hz, CH2), 1.90–1.98 (m, 2H, CH and OH), 1.62 (q, 2H, J=6.85 Hz, CH2 ); 13C NMR (125 MHz, CDCl3): δ=100.5, 69.8, 60.4, 31.9, 30.3, 21.2.

2.4.  Bis-Boc-2-amino-6-chloro-9-[2-(2,2-dimethyl-1,3-dioxan-5-yl)ethyl] purine (12)

Bis-Boc-2-amino-6-chloropurine 9 (1.0 equivalent) was added to a solution of the side chain 5 (1.1 equivalent) and phosphine reagent (1.1 equivalent) in anhydrous THF under N2 atmosphere at 0 °C, the resulting solution was treated with di-p-nitrobenzyl azocarboxylate (DNAD) (1.1 equivalent) dropwise and the reaction mixture was continued at room temperature for 8 h, then the solvent was evaporated and the residue dissolved in cyclohexane. The triphenylphosphane oxide precipitated and was filtered off and then the filtrate evaporated under reduced pressure. The product was purified by a column chromatography on silica gel to obtain the pure products as a white solid. mp>280 °C (dec); 1H NMR (500 MHz, CDCl3): δ=8.36 (s, 1H, CH), 4.02 (t, 2H, J=7.23 Hz, CH2), 3.79 (dd, 2H, Heq. J 1=11.57 Hz, J 2=4.46 Hz, CH2), 3.56 (dd, 2H, Hax. J 1=11.57 Hz, J 2=8.77 Hz, CH2), 1.67 (q, 2H, J=7.22 Hz, CH2), 1.53–1.61 (m, 1H, CH), 1.47 (s, 18H, C(CH3)3), 1.39 (s, 3H, CH3), 1.36 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3): δ=154.3, 151.7, 151.5, 151.1, 128.0, 104.8, 81.7, 71.5, 50.8, 33.7, 28.6, 26.2, 25.7.

2.5.  2-amino-6-chloro-9-[2-(2,2-dimethyl-1,3-dioxan-5-yl) ethyl]purine (8a)

A mixture of compound 12 (2.56 g, 5.0 mmol), 2,6-dimethyl pyridine (1.18 ml, 10 mmol) and dry DCM (20 ml) was stirred at 0 °C, then TBTMS-OTf was added dropwise; after the addition, the reaction mixture was stirred at room temperature until TLC showed that compound 12 had completely disappeared. Then 30 ml saturated ammonium chloride solution was added, separated the organic layer, extracted with DCM (2×20 ml), combined and washed by saturated NaCl (2×40 ml), dried with anhydrous sodium sulfate and evaporated to give a white solid (1.21 g, 78%). mp 125–126 °C; 1H NMR (500 MHz, CDCl3): δ=8.07 (s, 1H, CH) , 6.99 (s, 2H, NH2), 4.12 (t, 2H, J=7.31 Hz, CH2), 3.82 (dd, 2H, 4′-Heq, J 1=11.79 Hz, J 2=4.50 Hz, CH2), 3.53 (dd, 2H, 4′-Hax, J 1=11.79 Hz, J 2=8.80 Hz, CH2), 1.74 (q, 2H, J=7.30 Hz, CH2), 1.53–1.65 (m, 1H, CH), 1.36 (s, 3H, CH3), 1.31 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3): δ=159.94, 150.31, 150.26, 141.84, 132.11, 100.52, 68.14, 52.90, 31.32, 26.84, 26.05.

2.6.  9-[4-hydroxy-3-(hydroxymethyl)butyl] guanine (PCV 3)

Compound 12 (5.12 g, 10 mmol) was dissolved in THF (20 ml) hydrochloric acid (2 mol/L, 20 ml). The mixture was stirred for 2 h at 70 °C, and then slowly warmed to reflux for 2 h. After evaporation of the THF under reduced vacuum, 10% aqueous NaOH solution was added to neutralize the residual liquid, and a large amount of off-white solid formed, filtered, washed with acetone and then water, and dried under vacuum to give an off-white solid 3 (2.07 g, 82%). mp 274.6–276.9 °C.

3.  Results and discussion
 To begin with, bis-Boc-2-amino-6-chloropurine 9 was synthesized from 2-amino-6-chloropurine 7 in high yield followed by Subhakar’s procedure (Dey and Garner, 2000). The solubility of bis-Boc-2-amino-6-chloropurine 9 was investigated and the results are shown in Table 1. Unlike 2-amino-6-chloropurine 7, known for its notorious insolubility in most common solvents, the solubility of 9 in DCM, methylbenzene, acetonitrile, and especially in THF was increased dramatically.

Table 1

Mole fraction solubility x of bis-Boc-2-amino-6-chloropurine 9 in different Mitsunobu solvents

T (K) (±0.05 K) Solubility x a (%)


THFb DCMb Methylbenzeneb Acetonitrileb
273.15 0.1141 0.0493 0.0213 0.0150
278.15 0.1191 0.0552 0.0253 0.0178
283.15 0.1251 0.0613 0.0303 0.0210
288.15 0.1299 0.0664 0.0349 0.0244
293.15 0.1352 0.0734 0.0405 0.0288
298.15 0.1399 0.0809 0.0470 0.0347
303.15 0.1463 0.0894 0.0544 0.0417
308.15 0.1523 0.0983 0.0634 0.0501
313.15 0.1581 0.1081 0.0734 0.0617
  • a: the solubility of bis-Boc-2-amino-6-chloropurine 9 was measured by our previous method with temperature ranging from 273.15 K to 313.15 K (Wang et al., 2008) at atmospheric pressure. The laser monitoring observation technique was used to determine the disappearance of the solid phase in a solid and liquid mixture

b: all the solvents were further purified by distillation in dry agent (Na/benzophenone) and the sample bis-boc-2-amino-6-chloropurine 9 was dried in vacuum for over 2 d

As shown in Table 1, THF, which is the most common solvent in Mitsunobu reaction, has great solubility for bis-Boc-2-amino-6-chloropurine 9. Afterwards, the best solvent THF was taken for coupling 9 with a number of alcohols under normal Mitsunobu conditions to investigate its reactivity. The results were illustrated in Table 2. We clearly learned that bis-Boc-2-amino-6-chloropurine 9, as an excellent nucleophilic precursor, was able to react with a large number of alcohols, including primary alcohol, secondary alcohol, allyl alcohol, benzyl alcohol, etc., with high N9 selectivity and yields. Moreover, tert-Butyl alcohol still could not react with a protected purine as in the previous study (Yang et al., 2011), owing to its steric hindrance in tertiary carbon.

Table 2

Investigation of the reactivity of bis-Boc-2-amino-6-chloropurine 9 with different alcohols

Entry Alcohol Product Isolated yield (%)
1 10a 90.2
2 10b 86.6
3 10c 83.3
4 10d 84.8
5 10e 86.4
6 10f 81.2
7 10g 81.5
8 10h 80.7
9 10i 0
  • a): a mixture of 9 (1.0 equivalent), alcohol (1.1 equivalent) and phosphine reagent (1.1 equivalent) in anhydrous THF stirring under N2 atmosphere at 0 °C, then treated with azo-reagent DNAD (1.1 equivalent) warmed to room temperature; b): the mixture of the products from procedure a, THF (20 ml) and aqueous hydrochloric acid (2 mol/L, 20 ml) was refluxed for 2 h at 70 °C
  • According to the research results above, it is more reasonable and assuring to prepare PCV via a Mitsunobu reaction. This novel method for the preparation of PCV is indicated in Fig. 4. First, the side chain of 5-(2-hydroxyethyl)-2,2-dimethyl-1,3 -dioxane 5 was achieved through the commercially available starting material 2-hydroxymethyl-1,4-butanediol 11 reacting with 2,2-dimethoxypropane catalyzed by p-toluenesulfonic acid. The free –OH group of compound 5 is not necessary to be converted to the other leaving group such as chlorine, tosylate or methanesulphonate, which is always taken as a necessary step in the previous method or many other previous studies for the preparation of PVC till now (Harnden and Jarvest, 1985; Harnden et al., 1987; Zheng et al., 2004), making the synthesis of the side chain part of our method much more convenient and practical.
Fig.4
Synthesis of penciclovir (PCV) with new method
a: 2,2-dimethoxypropane, p-toluenesulfonic acid, THF; b: 1.1 equivalent of the side chain 5, 1.1 equivalent of PPh3, and 1.1 equivalent of azodicarboxylate reagent at rt. in THF; c: TBDMS-OTf, DCM; d: aqueous hydrochloric acid (2 mol/L), THF; e: aqueous hydrochloric acid (2 mol/L)

Our next objective was the synthesis of PCV. As was expected, bis-Boc-2-amino-6-chloropurine 9 combined with the side chain 5(1.1 equivalent) under normal Mitsunobu conditions successfully obtained the desired N9-alkylated compound 12 in 92% yield without the undesired N7 alkylation by-product being formed. Importantly, the reaction conditions were significantly milder than those reported in recent studies (Geen et al., 19901992; Kim et al., 1998; Brand et al., 1999; Toyokuni et al., 2003), requiring only 1.1 equivalent of each of the alcohol, PPh3 and DNAD, and proceeding to completion within 60 min at room temperature. This is mainly due to the enhanced solubility of the compound 9 as mentioned above. By process c in Fig. 4, compound 8a was obtained under neutral conditions. It is 1H and 13C NMR spectra further indicated that no 7-isomer purine (8b) was formed. Subsequently, we could obtain PCV 3 in an acid condition as procedure e; or directly starting from 12, where hydrolytic dechlorination and deprotection step(s) were accomplished in one pot under mild acid conditions (2mol/L, hydrochloric acid in THF at room temperature) to afford the target PCV 3 in 80%–85% yield (process d). The overall yield of PCV from 11 was 44.5% higher than that in previous study (16%) (Zheng et al., 2004).

4.  Conclusions
 In this study, ACP was protected with a bis-Boc carbamate group and showed a significant increase of solubility in the favorite Mitsunobu solvents. Coupling bis-Boc-2-amino-6-chloropurine 9 with different alcohols indicated a higher N9 selectivity and good reactivity in a Mitsunobu reaction. The results provided a convenient and practical protocol to prepare PCV from ACP, avoiding the presence of undesired N7 by-product and requiring only a few synthetic steps with higher yields.

References

[1] Ashton, W.T., Karkas, J.D., Field, A.K., Tolman, R.L., 1982. Activation by thymidine kinase and potent antiherpetic activity of 2’-nor-2’-deoxyguanosine (2’NDG). Biochemical and Biophysical Research Communications, 108(4):1716-1721.
[2] Brand, B., Reese, C.B., Song, Q., Visintin, C., 1999. Convenient syntheses of 9-[4-hydroxy-3-(hydroxymethyl)butyl] guanine (penciclovir) and 9-[4-acetoxy-3-(acetoxymethyl) butyl]-2-amino-9H-purine (famciclovir). Tetrahedron, 55(16):5239-5252.
[3] De Clercq, E., 1991. Broad-spectrum anti-DNA virus and anti-retrovirus activity of phosphonylmethoxyalkylpurines and pyrimidines. Biochemical Pharmacology, 42(5):963-972.
[4] Dey, S., Garner, P., 2000. Synthesis of tert-butoxycarbonyl (Boc)-protected purines. The Journal of Organic Chemistry, 65(22):7697-7699.
[5] Geen, G.R., Grinter, T.J., Kincey, P.M., Jarvest, R.L., 1990. The effect of the C-6 substituent on the regioselectivity of N-alkylation of 2-aminopurines. Tetrahedron, 46(19):6903-6914.
[6] Geen, G.R., Kincey, P.M., Choudary, B.M., 1992. Regiospecific Michael additions with 2-aminopurines. Tetrahedron Letters, 33(32):4609-4612.
[7] Harnden, M.R., Jarvest, R.L., 1985. An improved synthesis of the antiviral acyclonucleoside 9-(4-hydroxy-3-hydroxymethylbut-1-yl) guanine. Tetrahedron Letters, 26(35):4265-4268.
[8] Harnden, M.R., Jarvest, R.L., Bacon, T.H., Boyd, M.R., 1987. Synthesis and antiviral activity of 9-[4-hydroxy-3-(hydroxymethyl) but-1-yl] purines. Journal of Medicinal Chemistry, 30(9):1636-1642.
[9] Hwu, J.R., Jain, M.L., Tsay, S.C., Hakimelahi, G.H., 1996. Ceric ammonium nitrate in the deprotection of tert-butoxycarbonyl group. Tetrahedron Letters, 37(12):2035-2038.
[10] Kim, D.K., Lee, N., Kim, Y.W., Chang, K.Y., Kim, J.S., Im, G.J., Choi, W.S., Jung, I.H., Kim, T.S., Hwang, Y.Y., 1998. Synthesis and evaluation of 2-amino-9-(3-hydroxymethyl-4-alkoxycarbonylo-xybut-1-yl) purines as potential prodrugs of penciclovir. Journal of Medicinal Chemistry, 41(18):3435-3441.
[11] Kitade, Y., Ando, T., Yamaguchi, T., Hori, A., Nakanishi, M., Ueno, Y., 2006. 4’-fluorinated carbocyclic nucleosides: synthesis and inhibitory activity against S-adenosyl-l-homocysteine hydrolase. Bioorganic & Medicinal Chemistry, 14(16):5578-5583.
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[13] Lu, W., Sengupta, S., Petersen, J.L., Akhmedov, N.G., Shi, X., 2007. Mitsunobu coupling of nucleobases and alcohols: an efficient, practical synthesis for novel nonsugar carbon nucleosides. Journal of Organic Chemistry, 72(13):5012-5015.
[14] Martin, J.C., Dvorak, C.A., Smee, D.F., Matthews, T.R., Verheyden, J.P.H., 1983. 9-(1,3-dihydroxy-2-propoxymethyl) guanine: a new potent and selective antiherpes agent. Journal of Medicinal Chemistry, 26(5):759-761.
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[16] Ogilvie, K.K., Cheriyan, U.O., Radatus, B.K., Smith, K.O., Galloway, K.S., Kennell, W.L., 1982. Biologically active acyclonucleoside analogues. II. The synthesis of 9-[[2-hydroxy-1-(hydroxymethyl)ethoxy]methyl] guanine (BIOLF-62). Canadian Journal of Chemistry, 60(24):3005-3010.
[17] Porcheddu, A., Giacomelli, G., Piredda, I., Carta, M., Nieddu, G., 2008. A Practical and efficient approach to PNA monomers compatible with Fmoc-mediated solid-phase synthesis protocols. European Journal of Organic Chemistry, 2008(34):5786-5797.
[18] Schaeffer, H.J., Beauchamp, L., Miranda, P.D., Elion, G.B., Bauer, D.J., Collins, P., 1978. 9-(2-hydroxyethoxymethyl) guanine activity against viruses of the herpes group. Nature, 272(5654):583-585.
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[22] Toyokuni, T., Walsh, J.C., Namavari, M., Shinde, S.S., Moore, J.R., Barrio, J.R., Satyamurthy, N., 2003. Selective and practical synthesis of penciclovir. Synthetic Communications, 33(22):3897-3905.
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PAPER
Image result for penciclovir synthesis

SYN

EP 0141927; ES 8602791; ES 8603887; ES 8603888; JP 1994293764; US 5075445

This compound has been obtained by two similar ways: 1) The reaction of 6-chloropurine-2-amine (I) with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (II) by means of K2CO3 in DMF gives the expected condensation product (III), which is methanolized with HCl/methanol yielding 2-[2-(2-amino-6-methoxypurin-9-yl)ethyl]malonic acid dimethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol affords the corresponding diol (V), which is finally converted into pecnciclovir by hydrolysis with 2N NaOH. 2) The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (VI) by means ofK2CO3 in DMF gives the expected condensation product (VII), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (VIII). The reduction of (VIII) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (IX), which is finally converted into penciclovir by hydrlysis with 2N HCl.

References

  1. Jump up^ “Penciclovir”Merriam-Webster Dictionary. Retrieved 2016-01-22.
  2. Jump up^ Long, Sarah S.; Pickering, Larry K.; Prober, Charles G. (2012). Principles and Practice of Pediatric Infectious Disease. Elsevier Health Sciences. p. 1502. ISBN 1437727026.
  3. Jump up^ Farmaceutiska Specialiteter i Sverige – the Swedish official drug catalog. [http://www.fass.se Fass.se –> Vectavir. Retrieved on August 12, 2009. Translated from “Tiden för läkning, smärta och påvisbart virus förkortas med upp till ett dygn.”
Penciclovir
Penciclovir2DCSD.svg
Clinical data
Pronunciation /ˌpɛnˈsklˌvɪər/[1]
Trade names Denavir
AHFS/Drugs.com Monograph
MedlinePlus a697027
Pregnancy
category
  • AU: B1
  • US: B (No risk in non-human studies)
Routes of
administration
Topical
ATC code
Legal status
Legal status
Pharmacokinetic data
Bioavailability 1.5% (oral), negligible (topical)
Protein binding <20%
Metabolism Viral thymidine kinase
Elimination half-life 2.2–2.3 hours
Excretion Renal
Identifiers
CAS Number
PubChem CID
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
ECHA InfoCard 100.189.687 Edit this at Wikidata
Chemical and physical data
Formula C10H15N5O3
Molar mass 253.258 g/mol
3D model (JSmol)

/////////////Penciclovir, BRL-39123,  BRL 39123A, penciclovir sodium, Denavir, Vectavir, Euraxvir, Fenivir,

C1=NC2=C(N1CCC(CO)CO)NC(=NC2=O)N

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DR ANTHONY CRASTO

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DR ANTHONY MELVIN CRASTO Ph.D

DR ANTHONY MELVIN CRASTO Ph.D

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 PHARMACEUTICALS 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 year tenure till date Dec 2017, 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, 50 Lakh plus views on dozen plus blogs, He makes himself available to all, contact him on +91 9323115463, email amcrasto@gmail.com, Twitter, @amcrasto , He lives and will die for his family, 90% paralysis cannot kill his soul., Notably he has 19 lakh plus views on New Drug Approvals Blog in 216 countries......https://newdrugapprovals.wordpress.com/ , 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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