title: An efficient synthesis of 5-bromo-2-methoxy-6-methylaminopyridine-3carboxylic acid.
abstract: An efficient synthesis of 5-bromo-2-methoxy-6-methylaminopyridine-3-carboxylic acid (1), a carboxylic acid moiety of a potent dopamine D2 and D3 and serotonin-3 (5-HT3) receptors antagonist, (R)-5-bromo-N-(1-ethyl-4-methylhexahydro-1 ,4-diazepin-6-yl)-2-methoxy-6-methylaminopyridine-3-carboxamide, is described. Reaction of methyl 2,6-difluoropyridine-3-carboxylate (12) with methylamine in EtOH at -25 degrees C gave a mixture of methyl 2-fluoro-6-methylaminopyridine-3-carboxylate (13) and the regioisomer 14 in a ratio of 57 : 43. On the other hand, reaction of 12 and methyl 2,6-dichloropyridine-3-carboxylate (16) with sodium methoxide in tetrahydrofuran (THF) and CH2Cl2 provided the 2-methoxypyridine-3-carboxylic esters 20 and 23, respectively, as main products. Similar reaction of 16 in N,N-dimethylformamide (DMF) and MeOH proved to be highly regioselective for the 6-position. A much greater regioselectivity for substitution at the 6-position (>97%) was observed when 16 was treated with 4-methylbenzenethiolate anion in DMF (quantitative yield). After methoxylation of methyl 2-chloro-6-(4-methylbenzenethio)pyridine-3-carboxylate (25b) and successive oxidation of the 6-benzenethio moiety, nucleophilic substitution of the sulfoxide derivative 28 with methylamine gave the 6-methylamino derivative 8. Finally, bromination of 8 and alkaline hydrolysis produced the desired product 1 in an overall yield of 67%.
authors.affiliation: Discovery Research Laboratories, Dainippon Pharmaceutical Co, Ltd, Suita, Osak, Japan. yoshimi-hirokawa@dainippon-pharm.co.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Hirokawa
authors.forename: T
authors.initials: T
authors.lastname: Horikawa
authors.forename: S
authors.initials: S
authors.lastname: Kato
mesh_terms: D018492:Dopamine Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D009539:Nicotinic Acids / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D017448:Receptors, Dopamine D2 / Q000378:metabolism; D050637:Receptors, Dopamine D3; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
chemical_list: C423458:5-bromo-2-methoxy-6-methylaminopyridine-3-carboxylic acid; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D009539:Nicotinic Acids; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; C423459:methyl 2-methoxy-6-methylaminopyridine-3-carboxylate