Stereoselective Synthesis of Novel Bestatin Analogs

Abstract

Two new analogs of bestatin were prepared from D-leucine and D-valine in a stereoselective and efficient way. An aminopeptidase inhibitor bestatin shows significant biological effects on immunomodulation and is marketed for the treatment of acute myelocytic leukemia. The key intermediates, trans-oxazolidine methyl esters 2a and 2b, were obtained with more than 20 to 1 stereoselectivity in a one-pot procedure by the three cascade reactions between N-hydroxymethyl protected α-amino aldehydes (4a and 4b) and phenylsulfonylnitromethane (PhSO2CH2NO2) and the following in-situ ozonolysis. Basic hydrolysis of 2a and 2b, and then the peptide coupling with L-Leu-OMe produced the protected derivatives of two new bestatin analogs, 3a and 3b, respectively. The new isobutyl and isopropyl analogs of bestatin (1a and 1b) were produced in overall 51% and 38% yields, respectively, with high stereoselectivity from the corresponding protected α-amino aldehydes 4 in a six-step process.