Enzymatic ester hydrolysis and coupling of various N-protected Δ2-dehydrotripeptide methyl esters (Boc–AA–ΔAA–AA–OMe) (4) by using protease papain in McIlvaine buffer are mainly described. The substrates (4) used were prepared by one-pot coupling of N-carboxy-α-dehydroamino acid anhydride (ΔAA·NCA) with N- and C-component l-α-amino acids (AA). Even in the enzymatic reaction of 4 containing an unusual ΔAA residue, the normal ester hydrolysis took place to give Boc–AA–ΔAA–AA–OH (6) and, in certain cases, the interesting unusual peptide bond cleavage at P2 of 6 occured further to give the unexpected N-(1,2-dioxoalkyl)–AA–OH. Besides examining in detail the differences between the enzymatic actions to the structures of 4, we also studied the mechanisms of the ester and peptide bond hydrolyses. As the results, the reverse enzymatic coupling of 4 with H–AA–ΔVal–OMe was first achieved to give dehydropentapeptide containing two ΔAA residues.
主要介绍使用
木瓜蛋白酶在McIlvaine
缓冲液中对各种N-保护的Δ2-
脱氢三肽甲
酯(Boc–
AA–Δ
AA–
AA–OMe)(4)进行酶促
酯水解和偶联反应。所用的底物(4)是通过一步法偶联N-羧基-α-
脱氢氨基酸酐(Δ
AA·NCA)与N-和C-端l-
α-氨基酸(
AA)制备的。即使在含有不寻常Δ
AA残基的4的酶反应中,正常的
酯水解也会发生,得到Boc–
AA–Δ
AA–
AA–OH(6),并且在某些情况下,进一步在6的P2位点发生有趣的非寻常肽键断裂,得到了意外的N-(1,2-二
氧烷基)–
AA–OH。除了详细研究酶对4结构作用的差异外,我们还探讨了
酯和肽键
水解的机制。结果表明,首次实现了4与H–
AA–ΔVal–OMe的反向酶偶联,得到了含有两个Δ
AA残基的
脱氢五肽。