Synthesis of enantiopure (aMe)Dip and other a-methylated ß-branched amino acid derivatives

This report describes the synthesis of the two enantiomerically pure -methylated -branched phenylalanine derivatives, (S)- and (R)--methyl-,-diphenylalanine - (Me)Dip - starting from the chiral building blocks (R)- and (S)-N-Boc-N,O-isopropylidene--methylserine methyl esters, respectively. The key step involves a double alkylation with a Grignard reagent on an ester group. The use of the same protocol for the preparation of other -methylated -branched serine derivatives is also described. © 2003 Elsevier Science Ltd. All rights reserved