PURPOSE: To efficiently and economically obtain on an industrial scale an α- aminoglycol highly useful as an intermediate for HIV protease inhibitors, through reaction between an N-protected amino acid ester and a sulfoxide metal salt.

CONSTITUTION: (A) An N-protected amino acid ester of formula I (R1 and R2 are each an alkyl, aralkyl or aryl; P1 and P2 are each H, an amino-protecting group, or being combined into phthalyl group) is reacted with (B) a sulfoxide metal salt of formula II (M is a metal atom) (e.g. at -30 to 20°C for 1-10h) to produce an a aminoketosulfoxide of formula III, which is then reacted in the presence of an acid catalyst such as hydrochloric acid (e.g. in a solvent such as dimethylsulfoxide at 10-40°C for 3-10h) to produce an α- aminoketoaldehyde hemimercaptal of formula TV, which is then reduced (e.g. with sodium borohydride at-$10 to 10°C for 30-60min), thus obtaining the objective α-aminoglycol of formula V. The component A is pref. a L or D- phenylalanine ester protected with e.g. dibenzyl group.