Biocatalytic and chemical routes to all the stereoisomers of methionine and ethionine sulfoxides

Biotransformations of the N-phthaloyl derivatives of D- and L-methionine and of D- and L-ethionine by Beauveria bassiana ATCC 7159 or Beauveria caledonica ATCC 64970 produce the corresponding (S-S) sulfoxides in good yield and diastereomeric excess. Pure (SSSC) diastereomers can be obtained from L-series substrates by crystallisation of the biotransformation extract, and the corresponding (SSRC) products obtained from D-series substrates by chromatography of the biotransformation extract. Hydrogen peroxide-catalysed oxidation of the N-phthaloyl derivatives of D- and L-methionine and of D- and L-ethionine gives diastereomeric mixtures from which the (SSSC) and (RSRC) diastereomers can be obtained by crystallisation, and the (SSRC) and (RSSC) diastereomers obtained by chromatography. N-Cbz- and N-t-Boc methionines are also converted to sulfoxides with predominant (S-S) configuration by both B, bassiana and B. caledonica, but the isolated yields and d.e. of products were generally lower than those obtained from the N-phthaloyl substrates. Removal of the N-phthaloyl group from diastereomerically pure methionine and ethionine sulfoxides gave the corresponding amino acid sulfoxides in high yield; removal of N-Cbz and N-t-Boc groups from protected methionine sulfoxides was also achieved without loss of configuration at sulfur. (C) 1994 Elsevier Science Ltd. All rights reserved.