Synthesis of homochiral amino acid pyrazine and pyrrole analogues of glutamate antagonists
作者:Andrew Dinsmore、Paul M. Doyle、Matthias Steger、Douglas W. Young
DOI:10.1039/b110979k
日期:2002.2.22
Use of the acid 7 and the aldehydes 23a and 23b in “ring switching” reactions with hydrazines has given β-(1-aminopyrrole)amino acids as kinetic products. The products from the reaction of the aldehyde have been converted into β-(pyrazine)amino acids by an equilibration–dehydration sequence. A variety of homochiral reduced heterocyclic amino acids containing two chiral centres has been prepared in this way. Some of the product amino acids undergo “reverse ring switching” to the corresponding pyroglutamic acid derivatives.
The lithiumenolates of N-Boc protected pyroglutamic ethyl or tert-butyl esters react with electrophiles in good yield without epimerization of the chiral centre. With benzyl bromides the process is stereospecific, yielding exclusively the trans isomer. However, with other reactive electrophiles a 2:1 trans/cis diastereomeric mixture was obtained, regardless of the steric bulk of the ester group.