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Pirodavir, R-77975
4 – [2 – [1 – (6-Methyl-3-pyridazinyl)-4-piperidinyl] ethoxy] benzoic acid ethyl ester
 ethyl 4-{2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]ethoxy}benzoate
ethyl 4-[2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]-ethoxy]benzoate
Janssen (Originator)
Phase II
Pirodavir (R 77975) is the prototype of a novel class of broad-spectrum antipicornavirus compounds. Although its predecessor, R 61837, a substituted phenyl-pyridazinamine, was effective in inhibiting 80% of 100 serotypes tested (EC80) at concentrations above 32 micrograms/ml, pirodavir inhibits the same percentage of viruses at 0.064 micrograms/ml. Whereas R 61837 was active almost exclusively against rhinovirus serotypes of antiviral group B, pirodavir is broad spectrum in that it is highly active against both group A and group B rhinovirus serotypes.
Pirodavir is also effective in inhibiting 16 enteroviruses, with an EC80 of 1.3 micrograms/ml. Susceptible rhinovirus serotypes were rendered noninfectious by direct contact with the antiviral compound. Their infectivity was not restored by dilution of virus-drug complexes, but was regained by organic solvent extraction of the compound for most serotypes.
Neutralized viruses became stabilized to acid and heat, strongly suggesting a direct interaction of the compounds with viral capsid proteins. Mutants resistant to R 61837 (up to 85 times the MIC) were shown to bear some cross-resistance (up to 23 times the MIC) to the new compound, indicating that pirodavir also binds into the hydrophobic pocket beneath the canyon floor of rhinoviruses.
Pirodavir acts at an early stage of the viral replication cycle (up to 40 min after infection) and reduces the yield of selected rhinoviruses 1,000- to 100,000-fold in a single round of replication.
The mode of action appears to be serotype specific, since pirodavir was able to inhibit the adsorption of human rhinovirus 9 but not that of human rhinovirus 1A. Pirodavir is a novel capsid-binding antipicornavirus agent with potent in vitro activity against both group A and group B rhinovirus serotypes.
US 4992433
The condensation of 2-(1-benzylpiperidin-4-yl)ethanol (I) with 4-hydroxybenzoic acid ethyl ester (II) by means of triphenylphosphine and diazenedicarboxylic acid diethyl ester in THF gives 4-[2-(1-benzylpiperidin-4-yl)ethoxy]benzoic acid ethyl ester (III) as fumarate salt. This compound is debenzylated by hydrogenation with H2 over Pd/C in ethanol, yielding the free product (IV), which is finally condensed with 3-chloro-6-methylpyridazine (V) by means of K2CO3 in DMF.
B. Preparation of the Final Compounds EXAMPLE 25

A mixture of 10.4 parts of 3-chloro-6-methylpyridazine, 22.4 parts of ethyl 4-[2-(4-piperidinyl)ethoxy]benzoate butanedioate (1:1), 8.6 parts of sodium carbonate and 0.9 parts of N,N-dimethylformamide was stirred for 3 hours in an oil bath at C. After cooling, water and dichloromethane were added and the layers were separated. The organic layer was dried, filtered and evaporated. The residue was purified by column chromatography over silica gel using a mixture of trichloromethane and ethanol (99:1 by volume) as eluent. The pure fractions were collected and the eluent was evaporated. The residue was crystallized from a mixture of 2,2′-oxybispropane and 2-propanone (75:25 by volume). The precipitated product was filtered off and dried, yielding 17 parts (56.8%) of ethyl 4-[2-[1-(6-methyl-3-pyridazinyl)-4-piperidinyl]-ethoxy]benzoate; mp. C. (comp. 1).

Journal of Medicinal Chemistry, 2003 ,  vol. 46,   15  p. 3181 – 3184

Scheme 1.  Synthesis of Pirodavir (3) and Related Compounds

see mp and nmr data in supp file
US2985657 * Oct 12, 1959 May 23, 1961 Paul A J Janssen 1-(aroylalkyl)-4-heterocyclylpiperazines
US4068383 * Sep 30, 1976 Jan 17, 1978 Hoechstmass Balzer Gmbh & Co. Tape measure reel
US4451476 * Oct 17, 1983 May 29, 1984 Sterling Drug Inc. Isoxazoles as antiviral agents
US4604127 * May 15, 1985 Aug 5, 1986 Eli Lilly And Company Herbicidal pyridazinylimidazolidinone compounds
EP0137242A2 * Aug 20, 1984 Apr 17, 1985 Sterling Winthrop Inc. (Substituted) Phenyl-aliphatic-isoxazoles useful as antiviral agents and preparation thereof
EP0156433A2 * Mar 15, 1985 Oct 2, 1985 Janssen Pharmaceutica N.V. Anti-virally active pyridazinamines
EP0211457A2 * Jul 9, 1986 Feb 25, 1987 Janssen Pharmaceutica N.V. Novel (4-substituted-piperazinyl)pyridazines
JPS5877866A *       Title not available
read also
Antimicrobial Agents and Chemotherapy, 1995 ,  vol. 39,  2  p. 290 – 294

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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 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, 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...... , 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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