Enzymatic semisynthesis of porcine despentapeptide (B26–30) insulin using unprotected desoctapeptide (B23–30) insulin as a substrate: Model studies

Unprotected porcine desoctapeptide(B23–30) insulin (DOPI) and the synthetic Gly‐Phe‐Phe were used as substrates for the trypsin‐catalyzed synthesis of despentapeptide(B26–30) insulin (DPPI). The DPPI synthesis was accompanied by a moderate oligomerization and by the formation of a side produce which was identified as a DOPI derivative having an extra peptide bond between the Gly(A1) and Arg(B22) and which was named des(23–63) proinsulin (1). Despite side reactions, the conditions were found where the overall DPPI yields were comparable to those obtained via di‐Boc DOPI, and these procedures were faster and simpler since the Boc protection and deprotection steps were omitted. The reaction progress was directly monitored by HPLC.