A process for the preparation of an enantiomer of the formula (Ia) or (Ib) ##STR32## or the racemate thereof;
- in which R is H or a protective group, R.sub.1, and B is a radical of the formula V, Va, Vb, Vc, Vd or Ve ##STR33## in which R.sub.7 is H, Cl, Br, NH.sub.2 or OH, and R.sub.8, R.sub.9 and R.sub.10 independently of one another are H, OH, SH, NH.sub.2, NHNH.sub.2, NHOH, NHOalkyl having 1 to 12 C atoms, F, Cl, Br, alkyl or hydroxyalkyl or aminoalkyl or alkoxy or alkylthio having 1 to 12 C atoms, the hydroxyl and amino groups being unsubstituted or substituted by a protective group, phenyl, benzyl, secondary amino having 1 to 20 C atoms or tertiary amino having 2 to 30 C atoms, wherein the secondary amino and tertiary amino are radicals of the formula R.sub.14 R.sub.15 N, in which R.sub.14 is H or independently has the meaning of R.sub.15, and R.sub.15 is C.sub.1 -C.sub.20 alkyl, -aminoalkyl, -hydroxyalkyl;
- carboxyalkyl or carbalkoxyalkyl, the carbalkoxy group containing 2 to 8 C atoms and the alkyl group containing 1 to 6 C atoms;
- C.sub.2 -C.sub.20 alkenyl;
- phenyl, mono- or di(C.sub.1 -C.sub.4 alkyl- or C.sub.1 -C.sub.4 -alkoxy-)phenyl, benzyl, mono- or di(C.sub.1 -C.sub.4 alkyl- or C.sub.1 -C-alkoxy)benzyl;
- or R.sub.14 and R.sub.15 together are tetra- or pentamethylene, 3-oxa-1,5-pentylene, ---CH.sub.2 --NR.sub.16 --CH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 --NR.sub.16 --CH.sub.2 CH.sub.2 --, in which R.sub.16 is H or C.sub.1 -C.sub.4 alkyl, the amino group in aminoalkyl being unsubstituted or substituted by one or two C.sub.1 -C.sub.4 alkyl or -hydroxyalkyl groups, and the hydroxyl group in hydroxyalkyl is free or ethefified with C.sub.1 -C.sub.4 alkyl and R.sub.11 is H or C.sub.1 -C.sub.4 alkyl;
- or B is a radical of the formulae VI, VIa or VIb, or the dihydro derivative thereof;
- ##STR34## in which R.sub.11 is H or C.sub.1 -C.sub.4 alkyl and R.sub.12 and R.sub.13 independently of one another are as defined for R.sub.8 above and the hydrogen atoms of the NH.sub.2 group in formula VIb can be substituted by C.sub.1 -C.sub.6 alkyl or benzoyl;
- which comprises the steps of
- (a) reacting an enantiomer of the formula IIa or Hb, or the racemate thereof, ##STR35## in which R.sub.1 is a protective group, with a compound of the formulae X--CO--X, X--CS--X, X--SO--X, X--SO.sub.2 --X, X.sub.2 P--R.sub.6 or X.sub.2 P(O)--R.sub.6, in which X is a leaving group, R.sub.2 is linear or branched C.sub.1 -C.sub.18 alkyl, C.sub.5 -C.sub.8 cycloalkyl, phenyl, benzyl, or phenyl or benzyl which are substituted by C.sub.1 -C.sub.6 alkyl or C.sub.1 -C.sub.6 alkoxy, R.sub.3 and R.sub.4 independently of one another are H, linear or branched C.sub.1 -C.sub.18 alkyl, C.sub.5 -C.sub.8 cycloalkyl, phenyl, benzyl, or phenyl or benzyl which are substituted by C.sub.1 14 C.sub.6 alkyl or C.sub.1 -C.sub.6 alkoxy, or R.sub.3 and R.sub.4 together are tetramethylene, pentamethylene or 3-oxa-1,5-pentylene, R.sub.5 is H, linear or branched C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.8 cycloalkyl, phenyl, benzyl, or phenyl or benzyl which are substituted by C.sub.1 -C.sub.6 alkyl or C.sub.1 -C.sub.6 alkoxy, and R.sub.6 is linear or branched C.sub.1 -C.sub.2 alkyl or C.sub.1 -C.sub.12 alkoxy, C.sub.5 -C.sub.8 cycloalkyl or C.sub.5 -C.sub.8 cycloalkoxy, phenyl, or phenyloxy, benzyl or benzyloxy, or R.sub.6 is phenyl or phenyloxy or benzyl or benzyloxy which are substituted by C.sub.1 -C.sub.6 alkyl or C.sub.1 -C.sub.6 alkoxy, to give an enantiomer of the formula IIIa or IIIb, or the racemate thereof, ##STR36## in which Y is selected from the group consisting of --C(O)--, --C(S)--, --SO--, --SO.sub.2 --, R.sub.6 P.dbd. and R.sub.6 (O)P.dbd. in which R.sub.1 to R.sub.6 are as defined above,
- (b) reacting the product of step (a) with a nucleic base corresponding to a radical of formula V, Va, Vb, Vc, Vd or Ve, or the alkali metal salt thereof, or a nucleic base corresponding to a radical of formula VI, VIa or VIb, or the dihydro derivative or alkali metal salt thereof, in the presence or absence of a non-nucleophilic base, to give an enantiomer of the formula IVa or IVb, or the racemate thereof, ##STR37## in which M is H, an alkali metal or a non-nucleophilic base and Y is as defined above, and
- (c) converting the product of step (b) into the compound of the formula Ia or Ib, or the racemate thereof, by eliminating the group YOM, and, when R is H, the protective group, R.sub.1.