OPTIMIZATION OF THE RETRORACEMISATION PROCEDURE FOR ALPHA-AMINO-ACIDSUSING (S)-2-[(N-ALKYLPROLYL)AMINO]BENZOPHENONES, RECYCLABLE CHIRAL AUXILIARIES

The retroracemisation procedure developed by Belokon and coworkers has been re-examined using a variety of new (S)-2-[(N-alkylprolyl)amino]b enzophenone chiral auxiliaries. It has been found that (S)-2-[(N-benzy lprolyl)amino] and (S)-2-[(N-1-(naphthalenyl-1-methyl)prolyl)amino] be nzophenones ((S)-BPB and (S)-NPB) when used in conjunction with Ni(NO3 )(2) . 6H(2)O and a racemic alpha-amino acid preferentially form a sin gle diastereoisomer in the presence of a mild base such as sodium meth oxide. Decomposition of this complex under acidic conditions leads to the isolation of the (S)amino acid in good yield, and in 55 to 99% e.e . The retroracemisation abilities of a polymer supported form of the ( S)-BPB ligand have also been investigated and preliminary results for this are presented here. (C) 1997 Elsevier Science Ltd.