Industrial synthesis process of the compounds of formula (I) where R represents a linear or branched (C1-C6) alkyl group, characterized in that the alanine is condensed, of formula (III): with a compound of formula (IV): where R has the same meaning as in formula (I), under hydrogenation catalyzed by 5% carbon / palladium, in water, under a pressure between 1 and 30 bar, at a temperature between 10 and 60 ° C, in the presence of a amount of sodium hydroxide comprised between 0.5 and 0.5 moles per mole of derivative of formula (IV) used, to drive, after acidification of the reaction medium at a pH between 3 and 3.5, filtration and recrystallization of the precipitate obtained in acetonitrile, to the derivative of optically pure formula (I).
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