Stereoselection in the synthesis of threo- and erythro-3-amino-2-hydroxy-4-phenyl-butanoic acid using chiral acetal templates

Boron trifluoride-diethyl ether mediated addition of trimethylsilylcyanide (TMSCN) to the chiral acetals derived from Z-L- and Z-D-phenyl alaninal, (Z=N-benzyloxycarbonyl), and (+)-(2S,4S)- and (–)-(2R,4R)-2,4-pentanediol stereoselectively gave the four stereoisomers of the 3-amino-2-hydroxy-4-phenylbutanoic acid, key intermediates for bestatin and bestatin analogues.