β-ケトアミノ酸の還元

抄録

A new approach has been established for the stereoselective synthesis of β-hydroxyamino acid (7). α-C-acylamino acid esters (3) were prepared by the acid hydrolysis of oxazole-4-carboxylate derivatives (2), which were easily obtained by the reaction of methyl 2-isocyanoacetate (1) with acyl halides or acid anhydrides in the presence of organic bases. The reduction of (2) to β-hydroxy-α-amino acid esters (6) was examined by the following two methods (A and B). Method A: Hydrogenation of (3) over PtO₂ or reduction with NaBH₄. Method B: Hydrogenation of (4) over PtO₂ or reduction with NaBH₄, LiBH₄ and Ca (BH₄)2. By the method A, erythro-(6) was obtained predominantly. The relative stereochemistry of the reaction products erythro-(6) and threo-(6) was also discussed. Ester hydrolysis of (6) afforded β-hydroxyamino acids (7).