| Summary: | Abstract
A convenient and efficient method for the synthesis of (–)-bestatin, epibestatin, phebestin, and (3S,4R)-4-amino-3-hydroxy-5-phenylpentanoic acid is reported. The key step is a proline-catalyzed α-hydroxylation of an aldehyde derived from d-phenylalanine, which leads to incorporation of a hydroxyl group at the α-position of that aldehyde with good yield and very high diastereoselectivity. Bestatin and its diastereomer epibestatin are synthesized from the same starting material using the same sequence of reactions, except for proline as the catalyst. An O-MOM and Boc-protected amino acid, a common intermediate for bestatin, was coupled with a dipeptide, H-Val-Phe-OMe followed by global deprotection to yield phebestin. (3S,4R)-4-Amino-3-hydroxy-5-phenylpentanoic acid was also synthesized in eight steps from the same starting material. The reported synthetic route offers a general method for the synthesis of such types of compounds and their analogues by changing the proline catalyst and/or the starting material from d- to l-phenylalanine.
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