Process for the synthesis of alpha n alkylated amino acids and esters thereof, application to the synthesis of carboxyalkyl dipeptides

A process for the synthesis of compounds of formula (I):

• ##STR9## in which:
• R.sub.1 is linear or branched lower alkyl having 1 to 6 carbon atoms, inclusive,
• R.sub.2 is hydrogen or a linear or branched lower alkyl group having 1 to 4 carbon atoms, inclusive
• the two asymmetric carbn atoms both having the S configuration,
• wherein the starting material employed is a compound of formula (IV):
• ##STR10## in which:
• R.sub.1 has the same meaning as in formula (I), the asymmetric carbon having the S configuration, and in which process, when R.sub.2 in the product of formula (I) is other than the hydrogen atom, is first esterified, optionally in the presence of an acidic esterification catalyst, with a lower aliphatic alcohol of general formula R'.sub.2 OH in which R'.sub.2 denotes a linear or branched lower alkyl group having 1 to 4 carbon atoms, inclusive,
• to obtain a compound of formula (V):
• ##STR11## in which:
• R.sub.1 and R.sub.2 have the same meaning as in formula (I),
• the asymmetric carbon having the S configuration, and in which process the compound of formula V is then condensed with pyruvic acid by catalytic hydrogenation under pressure and with slight heating,
• the pressure being between 10 and 100 bars,
• the temperature being between 10.degree. and 60.degree. C.,
• in an aqueous or lower aliphatic alcohol medium, by itself or mixed with water,
• the catalyst being selected from nickel, platinum, palladium or rhodium, mixed with a support to produce a high proportion of the diastereoisomer of the compound of formula (I) in which the two asymmetric carbons have the S configuration.