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ORGANIC SPECTROSCOPY

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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 AFRICURE PHARMA, ROW2TECH, NIPER-G, Department of Pharmaceuticals, Ministry of Chemicals and Fertilizers, Govt. of India as ADVISOR, earlier assignment was with GLENMARK LIFE SCIENCES LTD, as CONSUlTANT, Retired from GLENMARK in Jan2022 Research Centre as Principal Scientist, Process Research (bulk actives) at Mahape, Navi Mumbai, India. Total Industry exp 32 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, 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 32 PLUS year tenure till date Feb 2023, 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 100 million plus hits on Google, 2.5 lakh plus connections on all networking sites, 100 Lakh plus views on dozen plus blogs, 227 countries, 7 continents, 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 38 lakh plus views on New Drug Approvals Blog in 227 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 He has total of 32 International and Indian awards

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WO 2016113415, Sandoz, Riociguat, New Patent


WO 2016113415, Sandoz, Riociguat, New Patent

STEFINOVIC, Marijan; (AT).
RICHTER, Frank; (AT).
GRIESSER, Ulrich; (AT).
LANGES, Christoph; (AT)

SANDOZ AG [CH/CH]; Lichtstrasse 35 4056 Basel (CH)

WO 2016113415

Novel method for purifying riociguat, useful for treating chronic thromboembolic pulmonary hypertension, pulmonary arterial hypertension, systemic sclerosis and Raynaud’s phenomenon. Also claims novel crystalline solvates of riociguat (eg ethyl acetate or butan-2-one solvate), useful as intermediates in the purification of riociguat. Bayer and licensee Merck have developed and launched riociguat.

The present filing appears to be the first filing from Sandoz on riociguat; however see WO2015095515, assigned to Novartis, parent company of Sandoz, claiming an ophthalmic composition comprising a soluble guanylate cyclase activator (eg riociguat).

Riociguat (BAY 63-2521 ), having the chemical name N-[4,6-Diamino-2-[1-(2-fluorobenzyl)-1 H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-5-yl]-N-methylcarbamic acid methyl ester, or sometimes also called or also sometimes called Methyl-(4,6-diamino-2-(1-(2-fluorobenzyl)-1 H-pyrazolo[3, 4-b]pyridin-3-yl)-5-pyrimidinyl)(methyl)carbamate is a stimulator of the soluble guanylate cyclase.

Riociguat has been approved for the treatment of inoperable, or persistent, recurrent chronic thromboembolic pulmonary hypertension (CTEPH) after surgery in adult patients and for the treatment of pulmonary arterial hypertension and is in development for the treatment of systemic sclerosis and Raynaud’s phenomenon.

(I)

The preparation of the compound of formula (I) and its purification are known. According to the experimental procedure of Example 8 of WO 03/095451 (comparable description in Chem. Med. Chem 2009, 4, 853-865), iodomethane is used as an alkylating agent in a late step and the purification of the crude riociguat either comprised preparatory HPLC steps or several steps of extracting, precipitating, suspending, washing, redissolving and reprecipitating riociguat, resulting in a long and tedious workup procedure with moderate yield.

In WO 201 1/064171 a potential genotoxic azo compound of formula III is used as a key intermediate, which under catalytic hydrogenation forms a compound of formula VIII.

The compound of formula VIII is further reacted with a methyl chloroformate or with a dimethyl carbonate derivative to form a compound of formula VI. The compound of formula VI is then methylated to form crude riociguat of formula (I).

Crude riociguat of formula (I) is then purified by a process comprising the intermediate isolation of a riociguat DMSO solvate of formula (II).

For the pharmaceutical use of riociguat, the solvent DMSO has to be removed. To that end, the compound of formula (II) is boiled in pharmaceutically acceptable solvents such as ketones, esters, ethers or alcohols. However, the riociguat obtained in this manner contains detectable amounts of DMSO.

These processes for the preparation of riociguat and their laborious purification protocols have a number of disadvantages which are unfavorable for industrial realization on a large scale.

On the one hand, the purification process according to WO 03/095451 require the repeated isolation of solid intermediates or preparatory HPLC, which ultimately results in a reduced yield of pure riociguat of formula (I) of pharmaceutical grade. Yet, traces of compound of formula (III) remain.

It is therefore one of the objects of the present invention to provide a process for the preparation of pure riociguat – compound of the formula (I) – which yields riociguat free from any genotoxic impurity and/or mutagenic impurity.

On the other hand, the process for the preparation of riociguat described in WO 201 1/064171 has a different serious drawback. It comprises the use of a DMSO solvate.

DMSO is an active pharmaceutical ingredient by itself. It is used as an active pharmaceutical ingredient in the treatment of interstitial cystitis. DMSO removal is difficult to achieve by the published processes. It is thus a further object of the invention to provide riociguat essentially free from DMSO and suitable for pharmaceutical use.

WO 2014/128109 discloses forms of riociguat, such as polymorphs and solvates, and describes a ¼ ethyl acetate solvate of riociguat in example 6. The X-ray powder

diffractogram in Tab.3 and figure 4 comprises reflexes at °2Theta positions of 9.1 and 25.6.

Thus, there is a need in the art for a process, which allows the preparation of pure riociguat free from any genotoxic impurity and/or mutagenic impurity which at the same time does not comprise residual DMSO.

Surprisingly, we have now identified a process for the purification of crude riociguat which yields riociguat which is essentially free from genotoxic impurities and DMSO. In particular, this novel process differs from the processes known to date in that the isolation of intermediates prior to the formation of riociguat is not required. This process allows to overcome the disadvantages of the processes known to date and to obtain riociguat in high yield and high purity and pharmaceutical acceptable quality essentially free of genotoxic impurities.

 

Examples

Preparative example

Preparation of crude riociguat

Riociguat was prepared as disclosed in example 7 of WO 201 1/064171 and had a chemical purity of 91.7% by the area of the riociguat peak in the HPLC-UV elution profile.

Comparative Example 1

Preparation of DMSO solvate

An amount of 4.505 g (0.0107 moles) of crude riociguat was dissolved in 8 ml DMSO at 100 °C. The obtained brownish, turbid solution was then cooled to 75 °C within 16 minutes. After that 55 ml of ethylacetate were added and the mixture was cooled to 25 °C (30 minutes). After 22 h the obtained precipiate was filtered off, washed with 14 ml EtOAc and dried for 4 hours at 50 °C at reduced pressure (50 mbar). The precipitate was analysed with XRPD, confirming that riociguat DMSO was obtained. The product was also analyzed by HPLC-UV-MS. Purity was calculated based on UV detection at 254nm. The so obtained riociguat DMSO solvate was 91 .92% pure.

Comparative Example 2

Preparation of riociguat form I from riociguat DMSO solvate

The entire product prepared in comparative example 1 (4.283 g = 0.009 moles) was reflux heated in 77 ml of ethylacetate at 78 °C for 1 h and then cooled to 25 °C. The white solid was filtered off with suction, washed with a total of 18 ml of ethyl acetate and dried at 50 °C under reduced pressure (50 mbar) for 5 hours. The dried product was then analyzed by XRPD, confirming identity of riociguat form I unequivocally.

Yield (dry): 3.224 g (0.0076 moles) = 75% for comparative example 2 and 72% overall (C.ex. 1 and 2). Total organic volatile impurity is higher than 1000 ppm and total DMSO content is higher than 100 ppm.

Example 1 ; Preparation of Riociguat ethylacetate solvate

Crude Riociguat (500 mg; Form I; 91 .7% percentage area purity) was dissolved in 2 ml DMF and heated to 100 °C to obtain a slightly turbid solution. After filtration through a 0.44 micron filter, 20 ml EtOAc were added to the hot solution (water bath 70°C) and allowed to stand. The temperature was slowly decreased to ambient temperature. Crystallization started after

10min. The yellowish, fine powder was filtered off and dried at ambient conditions. The PXRD indicated the formation of a new ethylacetate solvate. Yield 71 %, 97.8% purity.

Example 2; Preparation of the Methyl ethyl ketone (butan-2-one) solvate of Riociguat.

Crude Riociguat (500 mg; Form I; 91 .7% percentage area purity) was dissolved in 2 ml DMF at 100 °C to obtain a clear solution. After filtration through a 0.44 micron filter, 20 ml MEK were added. The hot solution (water bath 70 °C) was allowed stand. The temperature was then slowly decreased to ambient temperature. After 30 minutes yellowish, square-shaped crystals appeared, which were analyzed. Analysis confirmed that they were a new crystalline MEK-solvate. Yield 43%, 97.2% purity.

Example 3 ; Conversion of Solvated forms to Form I

Both the solvates from examples 1 and 2 can be converted to riociguat Form I by heating the material to 150°C under vacuum for an appropriate amount of time.

Example 4; Direct preparation of riociguat form I from crude riociguat using DMF-Acetone Crude Riociguat (200 mg; Form I; 91 .7% percentage area purity) was dissolved in 1.0 ml DMF at 100 °C to obtain a clear solution. After filtration through a 0.44 micron filter, 5 ml acetone was added. The hot solution (water bath 70 °C) was allowed to stand. Crystallisation occurred while the temperature was slowly decreased to ambient temperature. After 24 hours the precipitate was filtered off and dried at ambient conditions to obtain form I. Yield 78% ; 97.6% purity

///////////WO 2016113415, Sandoz, Riociguat, New Patent

The U.S. Food and Drug Administration approved Adempas (riociguat) to treat adults with two forms of pulmonary hypertension.


Skeletal formula of riociguat

October 8, 2013 — The U.S. Food and Drug Administration today approved Adempas (riociguat) to treat adults with two forms of pulmonary hypertension.

Pulmonary hypertension is caused by abnormally high blood pressure in the arteries of the lungs. It makes the right side of the heart work harder than normal. In its various forms, pulmonary hypertension is a chronic, progressive, debilitating disease, often leading to death or need for lung transplantation

read all at

http://www.drugs.com/newdrugs/fda-approves-adempas-pulmonary-hypertension-3927.html

In the area of pulmonary hypertension Adempas (Riociguat) is the first member of a novel class of compounds – so-called ‘soluble guanylate cyclase (sGC) stimulators’ – being investigated as a new and specific approach to treating different types of pulmonary hypertension (PH). Adempas has the potential to overcome a number of limitations of currently approved treatments for pulmonary arterial hypertension (PAH) and addresses the unmet medical need in patients with chronic thromboembolic pulmonary hypertension (CTEPH). It was approved for the treatment of CTEPH in Canada in September 2013, making it the world’s first drug approved in this deadly disease.
Riociguat has already shown promise as a potential treatment option beyond these two PH indications. An early clinical study was conducted in PH-ILD (interstitial lung disease), a disease characterized by lung tissue scarring (fibrosis) or lung inflammation which can lead to pulmonary hypertension, and, based on positive data, the decision was taken to initiate Phase IIb studies in PH-IIP (idiopathic pulmonary fibrosis), a subgroup of PH-ILD. Moreover, scientific evidence was demonstrated in preclinical models that the activity may even go beyond vascular relaxation. To prove the hypothesis Bayer is initiating clinical studies in the indication of systemic sclerosis (SSc), an orphan chronic autoimmune disease of the connective tissue affecting several organs and associated with high morbidity and mortality. If successful, Riociguat has the potential to become the first approved treatment for this devastating disease.

synthesis

Generic Name: Riociguat
Trade Name: Adempas
Synonym: BAY 63-2521
CAS number: 625115-55-1
Chemical Name: Methyl N-[4,6-Diamino-2-[1-[(2-fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-pyrimidinyl]-N-methyl-carbaminate
Mechanism of Action: soluble guanylyl cyclase (sGC) stimulator
Date of Approval: October 8, 2013(US)
Indication: Pulmonary Hypertension
Company: Bayer AG

Synthesis of bayer pulmonary hypertension drug Adempas-riociguat- from 2-fluorobenzylbromide

1)J. Mittendorf.; S. Weigand.; C. Alonso-Alija.; E. Bischoff.; A. Feurer.; M. Gerisch.; A. Kern.; A. Knorr.; D. Lang.; K. Muenter.; M. Radtke.; H. Schirok.; K.-H. Schlemmer.; E. Stahl.; A. Straub.; F. Wunder.; J.-P. Stasch. Discovery of Riociguat (BAY 63-2521): A Potent, Oral Stimulator of Soluble Guanylate Cyclase for the Treatment of Pulmonary Hypertension, ChemMedChem. 2009, 4, 853-865.
2)Cristina Alonso-Alija, Bayer Ag, Erwin Bischoff, Achim Feurer, Klaus Muenter, Elke Stahl, Johannes-Peter Stasch, Stefan Weigand, Carbamate-substituted pyrazolopyridinesWO2003095451 A1
3)Franz-Josef Mais, Joachim Rehse, Winfried Joentgen, Konrad SIEGEL, Process for preparing methyl methylcarbamate and its purification for use as pharmaceutically active compound,US20110130410
4)Claudia Hirth-Dietrich, Peter Sandner, Johannes-Peter Stasch, Andreas Knorr, Degenfeld Georges Von, Michael Hahn, Markus Follmann, The use of sGC stimulators, sGC activators, alone and combinations with PDE5 inhibitors for the treatment of systemic sclerosis (SSc)WO 2011147810A1
5)Li Liang, Li Xing-zhou, Liu Ya-dan, Zheng Zhi-bing, Li Song, Synthesis of riociguat in treatment of pulmonary hypertensionChinese Journal of Medicinal Chemistry(Zhongguo Yaowu Huaxue Zazhi), 21(2),120-125; 2011

Synthesis of bayer pulmonary hypertension drug Adempas-riociguat- from 2-chloronicotinaldehyde

Jens Ackerstaff, Lars BÄRFACKER, Markus Follmann, Nils Griebenow, Andreas Knorr, Volkhart Min-Jian Li, Gorden Redlich, Johannes-Peter Stasch, Stefan Weigand, Frank Wunder, Bicyclic aza heterocycles, and use thereofWO2012028647 A1
2)Claudia Hirth-Dietrich, Peter Sandner, Johannes-Peter Stasch, Andreas Knorr, Degenfeld Georges Von, Michael Hahn, Markus Follmann, The use of sGC stimulators, sGC activators, alone and combinations with PDE5 inhibitors for the treatment of systemic sclerosis (SSc)WO 2011147810A1

Synthesis of intermediate of bayer pulmonary artery hypertension drug Adempas-riociguat-WO2013086935

Jin Li, Xiaoyu Yang, Jingwei ZHU, Minmin Yang, Xihan Wu, Method for synthesizing 1-(2-fluorobenzyl)-1H -pyrazolo[3,4-b]pyridin -3-formamidine hydrochlorideWO2013086935 A1

Synthesis of intermediate of bayer pulmonary artery hypertension drug Adempas-riociguat -Pharma chemica 2013

veerareddy Arava, Surendrareddy Gogireddy, An expeditious synthesis of riociguat,  A pulmonary hypertension drugDer Pharma Chemica, 2013, 5(4):232-239

cut paste from my earlier post

Skeletal formula of riociguat

RIOCIQUAT

CAS NO 625115-55-1

Methyl N-[4,6-Diamino-2-[1-[(2-fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-pyrimidinyl]-N-methyl-carbaminate

9 APRIL2013

Bayer has been boosted by the news that regulators in the USA are fast-tracking the German group’s investigational pulmonary arterial hypertension riociguat.

The US Food and Drug Administration has granted priority review to the New Drug Application for riociguat, which Bayer filed in February on both sides of the Atlantic for PAH and a related condition, inoperable chronic thromboembolic pulmonary hypertension (CTEPH). The FDA bestows a priority review on medicines that offer major advances in care or that provide a treatment where no adequate therapy exists. The agency aims to complete its assessment within eight months from the submission of the NDA, rather than the standard 12 months.

Riociguat (BAY 63-2521) is a novel drug that is currently in clinical development by Bayer. It is a stimulator of soluble guanylate cyclase (sGC). At the moment Phase III clinical trialsinvestigate the use of riociguat as a new approach to treat two forms of pulmonary hypertension (PH): chronic thromboembolic pulmonary hypertension (CTEPH) andpulmonary arterial hypertension (PAH). Riociguat constitutes the first drug of a novel class of sGC stimulators

The submissions are based on two Phase III studies and riociguat, the first member of a novel class of compounds called stimulators of soluble guanylate cyclase (sGC), met its primary endpoint in both trials, a change in exercise capacity after 12- or 16 weeks respectively. The drug was generally well tolerated, with a good safety profile.

File:Riociguat-3D-balls.png

If approved, riociguat would be going up against Actelion’s Tracleer (bosentan) and Gilead Sciences/GlaxoSmithKline’s Letairis/Volibris (ambrisentan). Actelion, which has dominated the PAH market, has already filed its follow-up to Tracleer, Opsumit (macitentan).

Bayer PAH drug Riociguat gets priority review at FDA


 Skeletal formula of riociguat

RIOCIQUAT

CAS NO 625115-55-1

Methyl N-[4,6-Diamino-2-[1-[(2-fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-pyrimidinyl]-N-methyl-carbaminate

9 APRIL2013

Bayer has been boosted by the news that regulators in the USA are fast-tracking the German group’s investigational pulmonary arterial hypertension riociguat.

The US Food and Drug Administration has granted priority review to the New Drug Application for riociguat, which Bayer filed in February on both sides of the Atlantic for PAH and a related condition, inoperable chronic thromboembolic pulmonary hypertension (CTEPH). The FDA bestows a priority review on medicines that offer major advances in care or that provide a treatment where no adequate therapy exists. The agency aims to complete its assessment within eight months from the submission of the NDA, rather than the standard 12 months.

Riociguat (BAY 63-2521) is a novel drug that is currently in clinical development by Bayer. It is a stimulator of soluble guanylate cyclase (sGC). At the moment Phase III clinical trialsinvestigate the use of riociguat as a new approach to treat two forms of pulmonary hypertension (PH): chronic thromboembolic pulmonary hypertension (CTEPH) andpulmonary arterial hypertension (PAH). Riociguat constitutes the first drug of a novel class of sGC stimulators

The submissions are based on two Phase III studies and riociguat, the first member of a novel class of compounds called stimulators of soluble guanylate cyclase (sGC), met its primary endpoint in both trials, a change in exercise capacity after 12- or 16 weeks respectively. The drug was generally well tolerated, with a good safety profile.

File:Riociguat-3D-balls.png

If approved, riociguat would be going up against Actelion’s Tracleer (bosentan) and Gilead Sciences/GlaxoSmithKline’s Letairis/Volibris (ambrisentan). Actelion, which has dominated the PAH market, has already filed its follow-up to Tracleer, Opsumit (macitentan).

Bayer Submits Riociguat for EU and US regulatory approval to treat treat patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH)


File:Riociguat structure.svg

Methyl N-[4,6-Diamino-2-[1-[(2-fluorophenyl)methyl]-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-pyrimidinyl]-N-methyl-carbaminate

625115-55-1 CAS NO

Riociguat (BAY 63-2521) is a novel drug that is currently in clinical development by Bayer. It is a stimulator of soluble guanylate cyclase (sGC). At the moment Phase III clinical trialsinvestigate the use of riociguat as a new approach to treat two forms of pulmonary hypertension (PH): chronic thromboembolic pulmonary hypertension (CTEPH) andpulmonary arterial hypertension (PAH). Riociguat constitutes the first drug of a novel class of sGC stimulators.[1]

Sunday, February 10, 2013

Bayer HealthCare has submitted the oral investigational drug riociguat to treat patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH) for regulatory approval in the United States and in the European Union.

“These regulatory submissions for two distinct forms of pulmonary hypertension not only represent important progress in our cardiovascular pipeline but also fuel our hope to bring this much-needed new treatment option for these serious and potentially fatal diseases to patients and doctors soon,” said Kemal Malik, member of the Bayer HealthCare Executive Committee and Head of Global Development.Riociguat was discovered by Bayer and represents the first member of a novel class of compounds, the stimulators of soluble guanylate cyclase (sGC). Riociguat is the first drug to demonstrate clinical efficacy in a placebo controlled phase III trial in inoperable CTEPH patients.

In CHEST-1 patients treated with riociguat showed a statistically significant improvement from baseline in the six-minute walking test (6MWT) after 16 weeks, compared to those receiving placebo. The study included both patients with inoperable CTEPH and those with persistent or recurrent disease after a surgical procedure called pulmonary endarterectomy (PEA). The PATENT-1 study met its primary endpoint by demonstrating a statistically significant improvement  from baseline in the 6MWT, after 12 weeks compared with placebo. PATENT-1 included both treatment naïve symptomatic PAH patients and those pre-treated with ERAs or non-iv prostanoid monotherapy.

more info

File:Riociguat-3D-balls.png

Phase I clinical trials

One of the first studies was designed to test the safety profile, pharmacokinetics andpharmacodynamics of single oral doses of riociguat (0.25–5 mg). 58 healthy male subjects were given riociguat orally (oral solution or immediate-release tablet) in a randomised, placebo-controlled trial. Doses of riociguat were increased stepwise, and riociguat was well tolerated up to 2.5 mg.[7]

Phase II clinical trials

proof-of-concept study, reported by the University of Gießen Lung Center, was the first small study (in 4 PAH patients) to investigate safety, tolerability, pharmacokinetics and efficacy parameters.[8] The drug was well-tolerated and superior to NO in efficacy and duration.

An open-label, non-controlled phase II trial of riociguat in 75 adult patients (42 with CTEPH and 33 with PAH, all in World Health Organization (WHO) functional class II or III) evaluated the safety and tolerability, and the effects on hemodynamics, exercise capacity and functional class. Riociguat was given three times daily for 12 weeks. Doses were titrated at 2-week intervals from 1.0 mg three times daily to a maximum of 2.5 mg three times daily. Riociguat had a favourable safety profile, and also significantly improved exercise capacity and hemodynamic parameters such as pulmonary vascular resistance, cardiac output and pulmonary arterial pressure compared to baseline values.[9]

In addition, a phase II study of riociguat is underway in patients suffering from other forms of PH such as associated with interstitial lung disease (PH-ILD). First results from this study are expected in 2011.[10]

Phase III clinical trials

The phase III trials on riociguat are multi-center studies. The study program includes large randomized, double-blind, placebo-controlled pivotal trial phase (CHEST-1 and PATENT-1), and open-label extensions of these studies (CHEST-2 and PATENT-2). Details of these studies are reported on ClinicalTrials.gov, a register of studies maintained by the National Institutes of Health (NIH).[6]

  1.  “Background Riociguat”. Bayer HealthCare. Retrieved 15 December 2009.
  2. Yoshina S, Tanaka A, Kuo SC (March 1978). “Studies on heterocyclic compounds. XXXVI. Synthesis of furo[3,2-c]pyrazole derivatives. (4) Synthesis of 1,3-diphenylfuro[3,2-c]pyrazole-5-carboxaldehyde and its derivatives (author’s transl)” (in Japanese). Yakugaku Zasshi 98 (3): 272–9. PMID 650406.
  3. Stasch JP, Becker EM, Alonso-Alija C, et al. (March 2001). “NO-independent regulatory site on soluble guanylate cyclase”.Nature 410 (6825): 212–5. doi:10.1038/35065611.PMID 11242081.
  4. Evgenov OV, Pacher P, Schmidt PM, Haskó G, Schmidt HH, Stasch JP (September 2006). “NO-independent stimulators and activators of soluble guanylate cyclase: discovery and therapeutic potential”Nature Reviews. Drug Discovery 5 (9): 755–68. doi:10.1038/nrd2038PMC 2225477.PMID 16955067.
  5. Mittendorf J, Weigand S, Alonso-Alija C, et al. (May 2009). “Discovery of riociguat (BAY 63-2521): a potent, oral stimulator of soluble guanylate cyclase for the treatment of pulmonary hypertension”. Chemmedchem 4 (5): 853–65.doi:10.1002/cmdc.200900014PMID 19263460.
  6. ClinicalTrials.govRiociguat
  7. Frey R, Mück W, Unger S, Artmeier-Brandt U, Weimann G, Wensing G (December 2008). “Pharmacokinetics, pharmacodynamics, tolerability, and safety of the soluble guanylate cyclase activator cinaciguat (BAY 58-2667) in healthy male volunteers”. Journal of Clinical Pharmacology 48 (12): 1400–10. doi:10.1177/0091270008322906.PMID 18779378.
  8. Grimminger F, Weimann G, Frey R, et al. (April 2009). “First acute haemodynamic study of soluble guanylate cyclase stimulator riociguat in pulmonary hypertension”. The European Respiratory Journal 33 (4): 785–92.doi:10.1183/09031936.00039808PMID 19129292.
  9.  “ATS International conference”. American Thoracic Society. 2009.
  10. ClinicalTrials.gov NCT00694850 Impact of Multiple Doses of BAY 63-2521 on Safety, Tolerability, Pharmacokinetics and Pharmacodynamics in Patients With Interstitial Lung Disease (ILD) Associated Pulmonary Hypertension