Synthesis of Peptidyl Methylcoumarin Esters as Substrates and Active-Site Titrants for the Prohormone Processing Proteases Kex2 and PC2

Peptidyl methylcoumarin amides are well established as model substrates for understanding protease specificity, but the corresponding methylcoumarin esters have attracted scant attention despite their potential utility in active-site titration and mechanistic characterization. We have devised techniques for the synthesis and deprotection of extended peptidyl methylcoumarin esters in good to moderate yields, and we have demonstrated their suitability for steady-state characterization and active-site titration of the Saccharomyces cerevisiae processing protease Kex2. Additionally, we have used one of these compounds to active-site titrate the homologous enzyme PC2, which had not previously been feasible using other types of substrates. These compounds should thus prove widely suitable for use as substrates and active-site titrants not only for proteases of the prohormone processing family but also for a wide range of other serine proteases.