An efficient enzymatic preparation of rhinovirus protease inhibitor intermediates

The development of an efficient route for the preparation of (2S)-2-3-{(5-methylisoxazol-3-yl)carbonyl]amino}-2-oxopyridin-1(2H)-yl]pent-4-ynoic acid (4), a key intermediate in the synthesis of a human rhinovirus (HRV) protease inhibitor, is presented. In the presence of 40% acetonitrile, the alkaline protease from Bacillus lentus can catalyze the kinetic resolution of racemic ester 7 to afford (S)-acid 4 in 49% chemical yield/per cycle with 98% ee and >98% HPLC purity. The (R)-ester can then be readily recycled via a DBU catalyzed epimerization. The enzymatic preparation described here is superior to the existing chemical resolution route, exhibiting lower costs as well as higher yields, enantioselectivity, and substrate loads. In addition, this protease displays broad substrate specificity toward this class of compounds and can be easily extended to the preparation of other tripeptide mimetics of rhinovirus protease inhibitors.