A process for the preparation of an acid of formula (I), as the individual (R) enantiomer or (S), or a salt thereof wherein R is a protected amino group; and the asterisk * denotes the stereogenic carbon atom, comprising contacting an ester of formula (II), as mixture of (R,S) enantiomers, or a salt thereof, wherein R1 is straight or branched C1-C6 alkyl, optionally substituted with phenyl; (the asterisk * and R defined above), with a lipase from Candida antarctica, under conditions effective to obtain a mixture comprising an acid of formula (I), as the individual (R) enantiomer, and an ester of formula (II), as the individual (S) enantiomer; the subsequent hydrolysis of the latter to obtain an acid of formula (I), as the individual (S) enantiomer; and, if desired, the conversion of an acid of formula (I), either as the (R) or (S) enantiomer, to a salt thereof.