The synthesis of cyclic alpha-amino acids. 3. The synthesis of methyl (plus)- and (minus)-3-amino-3-C-carboxy-3-deoxypentopyranosides.

Abstract

Abstract Cyclization of D′-methoxy-diglycolaldehyde, prepared by periodate cleavage of methyl β-l-arabinopyranoside, with ethyl nitroacetate gave a mixture of stereoisomers of cyclic α-nitro ester, i.e. methyl (+)-3-deoxy-3-C-ethoxycarbonyl-3-nitropentopyranoside. Catalytic reduction of the cyclic α-nitro ester afforded an isomeric mixture of cyclic α-amino esters, from which, on column chromatography, there could be isolated four diastereoisomers of methyl (+)-3-amino-3-deoxy-3-C-ethoxycarbonylpentopyranoside. Hydrolysis of each diastereoisomer gave the corresponding cyclic (+)-α-amino acid having a skeleton of pentopyranoside. The stereochemistry of the isomeric amino acids was studied by NMR spectroscopy and chemical degradation. On the other hand, three enantiomeric cyclic (−)-α-amino acids were also obtained from methyl β-d-xylopyranoside by the analogous route as that from methyl β-l-arabinopyranoside.