Participation of either the Nâ or Nα of l-methyl lysinate (2) in peptide bond formation could be selectively achieved by the use of either isobutyl chloroformate (method A) or N,N-bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOP-Cl) (method B), respectively. The amidation performed according to method A gives high yields of the dipeptides 3a-e, irrespective of the amino acids used. In method B, Nα amidation is highly preferred especially with bulky amino acids, yielding 4a, 4c and 4e. The less bulky 4b and 4d gave 4.5 and 20 regioselection Nα/Nâ amidation ratios. A mechanistical rationalization for these selectivities is discussed.
可以使用异丁基
氯甲酸酯(方法A)或N,N-双(2-氧代-3-
噁唑啉基)
磷酰
氯(BOP-Cl)(方法B)分别选择性地实现赖
氨酸(2)的Nα或Nε参与的肽键形成。按照方法A进行的酰胺化反应能够高产率地得到二肽3a-e,不受所用
氨基酸的影响。在方法B中,Nα酰胺化反应特别倾向于与体积较大的
氨基酸反应,生成4a、4c和4e。体积较小的4b和4d则分别得到4.5和20的Nα/Nε酰胺化选择比。本文讨论了这些选择性的机制解释。