Phosphodiesterase inhibitors. Part 1: Synthesis and structure–activity relationships of pyrazolopyridine–pyridazinone PDE inhibitors developed from ibudilast
作者:Robert W. Allcock、Haakon Blakli、Zhong Jiang、Karen A. Johnston、Keith M. Morgan、Georgina M. Rosair、Kazuhiko Iwase、Yasushi Kohno、David R. Adams
DOI:10.1016/j.bmcl.2011.04.021
日期:2011.6
Ibudilast [1-(2-isopropylpyrazolo[1,5-a]pyridin-3-yl)-2-methylpropan-1-one] is a nonselective phosphodiesterase inhibitor used clinically to treat asthma. Efforts to selectively develop the PDE3- and PDE4-inhibitory activity of ibudilast led to replacement of the isopropyl ketone by a pyridazinone heterocycle. Structure-activity relationship exploration in the resulting 6-(pyrazolo[1,5-a]pyridin-3-yl)pyridazin-3(2H)-ones revealed that the pyridazinone lactam functionality is a critical determinant for PDE3-inhibitory activity, with the nitrogen preferably unsubstituted. PDE4 inhibition is strongly promoted by introduction of a hydrophobic substituent at the pyridazinone N(2) centre and a methoxy group at C-70 in the pyrazolopyridine. Migration of the pyridazinone ring connection from the pyrazolopyridine 30-centre to C-40 strongly enhances PDE4 inhibition. These studies establish a basis for development of potent PDE4-selective and dual PDE3/4-selective inhibitors derived from ibudilast. (C) 2011 Elsevier Ltd. All rights reserved.