DEHYDROOLIGOPEPTIDES .20. UNUSUAL PEPTIDE-BOND CLEAVAGE OF DEHYDROTRIPEPTIDE ESTERS CONTAINING ALPHA-DEHYDROAMINO ACID RESIDUE AT P-2 BY USING PAPAIN

Enzymatic ester hydrolysis and coupling of various N-protected Delta(2 )-dehydrotripeptide methyl esters (Boc-AA-Delta AA-AA-OMe) (4) by usin g protease papain in McIlvaine buffer are mainly described. The substr ates (4) used were prepared by one-pot coupling of N-carboxy-alpha-deh ydroamino acid anhydride (Delta AA.NCA) with N- and C-component L-alph a-amino acids (AA). Even in the enzymatic reaction of 4 containing an unusual Delta AA residue, the normal ester hydrolysis took place to gi ve Boc-AA-Delta AA-AA-OH (6) and, in certain cases, the interesting un usual peptide bond cleavage at P-2 of 6 occured further to give the un expected N-(1,2-dioxoalkyl)-AA-OH. Besides examining in detail the dif ferences between the enzymatic actions to the structures of 4, we also studied the mechanisms of the eater and peptide bond hydrolyses. As t he results, the reverse enzymatic coupling of 4 with H-AA-Delta Val-OM e was first achieved to give dehydropentapeptide containing two Delta AA residues.