Abstract: The present invention relates to hitherto unknown intermediate of formula, in which R.sub.1 stands for hydrogen or a straight or branched aliphatic C.sub.1 -C.sub.20 carbon chain or an aryl or aralkyl group, aryl and "ar" meaning an aromatic or heterocyclic, 5- or 6-membered ring substituent containing 1 or 2 hetero atoms selected among O, S and N, R.sup.1 optionally being further substituted, and its chain being interrupted by hetero atoms like oxygen, or by carbonyl group(s); and R.sup.3 stands for hydrogen or C.sub.1 -C.sub.3 alkyl. The present intermediates can be used in a one step method for producing prodrugs of formula, where D-H =drug itself.