Thermolysin as a catalyst in enzymatic synthesis of asparagine-containing peptides II

Thermolysin was used as a catalyst to obtain the following protected di‐ and tripeptide esters: Z‐Asn‐Leu‐OEt, Z‐Asn‐Phe‐OEt, Moz‐Asn‐Leu‐Gly‐OEt, Boc‐Asn‐Leu‐Gly‐OEt, Z‐Asn‐Leu‐Gly‐OEt, Moz‐Asn‐Leu‐Gly‐OBzl, Moz‐Asn‐Leu‐Gly‐OtBu, Moz‐Gln‐Leu‐Gly‐OEt, Moz‐Asn‐Ile‐Gly‐OEt, and Moz‐Asn‐Leu‐Ala‐OEt. These compounds were obtained in pure form and the yields exceeded 50 %, except for Moz‐Asn‐Leu‐Gly‐OtBu and Boc‐Asn‐Leu‐Gly‐OEt. H‐Cys(Bz1)‐OtBu and H‐Cys(Bz1)‐Pro‐Leu‐Gly‐NH2 were both inadequate as amino components for obtaining Moz‐Asn‐Cys(Bz1)‐OtBu, Z‐Asn‐Cys(Bz1)‐OtBu and Moz‐Asn‐Cys(Bzl)‐Pro‐Leu‐Gly‐NH2 in the thermolysin‐catalyzed reactions. In the attempted synthesis of the protected pentapeptide amide, this protease cleaved the Pro‐Leu bond of the amino component H‐Cys(Bz1)‐Pro‐Leu‐Gly‐NH2 and catalyzed the coupling between the resulting dipeptide amide and Moz‐Asn‐OH, thus yielding Moz‐Asn‐Leu‐Gly‐NH2 as the main product.