Selective O-acylation of unprotected N-benzylserine methyl ester and O,N-acyl transfer in the formation of cyclo[Asp-Ser] diketopiperazines
作者:Mattia Marchini、Michele Mingozzi、Raffaele Colombo、Cesare Gennari、Marco Durini、Umberto Piarulli
DOI:10.1016/j.tet.2010.10.007
日期:2010.12
The synthesis of two diastereomeric cyclo[Asp-N-Bn-Ser] diketopiperazines (2a and 2b) was investigated Initial formation of the Boc-aspartyl-N-benzyl serine isopeptide methyl esters (4a and 4b) was observed which derive from the selective O-acylation of unprotected (S)- or (R)-N-benzylserine This unexpected O-acylation is preferred over the formation of the tertiary amide and the resulting ester bond is stable in solution to O N-acyl transfer The O N-acyl migration is then triggered by cleavage of the Boc protecting group and treatment with base which also promotes immediate cyclization to the diketopiperazines (C) 2010 Elsevier Ltd All rights reserved