Substituted isoxazoles as potent inhibitors of p38 MAP kinase

In a continuous effort to develop improved p38 MAP (mitogen-activated protein) kinase inhibitors, we focused our attention on the suitability of the isoxozole ring as a bioisosteric replacement for the imidazole ring of SB-203580. 3,4- and 4,5-disubstituted as well as 3,4,5-trisubstituted isoxazole derivatives were synthesized. These compounds were tested in an in vitro enzyme-linked immunosorbent assay of isolated p38 MAP kinase and for inhibitory potency against cytochrome P450. Compound 4a displays a highly promising profile for development as an anti-inflammatory agent owing to its enhanced suppression of cytokine release, decreased affinity for cytochrome P450 and a twofold decrease in IC50 toward isolated p38 MAP kinase.