Stereochemical basis for the anti-chlamydial activity of the phosphonate protease inhibitor JO146

Abstract

JO146, a mixture of two diastereomers of a peptidic phosphonate inhibitor for Chlamydial HtrA (CtHtrA), has reported activity against Chlamydia species in both human and koala. In this study we isolated the individual diastereomers JO146-D1 and JO146-D2 (in > 90% purity) and assessed their individual inhibitory activity against the serine protease human neutrophil elastase (HNE) which is structurally related to CtHtrA, as well as in Chlamydia trachomatis cell culture. JO146-D2 [S,S,R-Boc-Val-Pro-ValP(OPh)2], the isomer with the physiologically relevant valine at P1, had an approximate 2.5-fold in-crease in in vitro HNE inhibition potency over JO146-D1 [S,S,S-Boc-Val-Pro-ValP(OPh)2] and greater than 100-fold increase in cellular anti-chlamydial activity compared to JO146-D1 which possesses the unnatural valine at P1. JO146 and the individual diastereomers had excellent selectivity for the serine protease HNE over the potential off-target serine proteases trypsin and chymotrypsin. Docking studies supported the biological data with a geometrically unfavoured interaction observed between the P1 valine residue of JO146-D1 and the enzyme S1 sub-pocket.