This invention relates to compounds of general formula I, in which S is a carbohydrate core matrix; a is a pharmaceutically active moiety; L is a linker a covalent bond; n is an integer of 2 to 19; and R' is hydrogen, thioalkyl or X-Z in which Z is a lipophilic anchor and X is a linker or covalent bond. Formulae Va, Vb and Vc where R4-R9 are as defined in the specification; and delivery systems for pharmaceutically active agents.