Imidazo[l,2-a]pyridines: I: Synthesis and Inotropic Activity of New 5-Imidazo[l,2-a]pyridinyl-2(l//)-pyridinone Derivatives1)

Abstract

A series of l,2-dihydro-5-imidazo[l,2-a]pyridinyl-2(l//)-pyridonones was synthesized and evaluated for positive inotropic activity. l,2-Dihydro-5-imidazo[l,2-a]pyridin-6-yl-6-methyI-2-oxo-3-pyridinecarbonitrile (11a) hydrochloride monohydrate (E-1020) was found to be a potent and selective inhibitor of phosphodiesterase III and a long-acting, potent, orally active positive inotropic agent. Additional imidazo[l,2-a]pyridin-2-yl (3a), -3-yl (16), -7-yl (20) and -8-yl (24a) compounds were also prepared. Altering the pyridine substitution from the 2-position to the 6-position produced a 2-fold increase in the i.v. cardiotonic potency (EDS0) from 52 to 23/ig/kg, while substitution at the 3-, 7- or 8-position reduced potency. In the 2-positional isomers, introduction of halogen groups enhanced the activity and 3-chloro-l,2-dihydro-5-(6-fluoroimidazo[l,2-a]pyridin-2-yl)-6-methyl-2(l//)-pyridinone (3u) was the most potent (i.v. ED,n 11 lig/kg) in this series. E-1020 is presently under development for the treatment of congestive heart failure. © 1991, The Pharmaceutical Society of Japan. All rights reserved.