Abstract: Polymeric form of a biologically active compound containing at least one -NH.sub.2 group in its molecule, adapted for the protracted release of said biologically active compound by enzymatic cleavage of the polymer in vivo in the organism. The active compound is bonded by its -NH.sub.2 group to the carboxylic group of an L-amino acid as for instance, .beta.-phenylalanine, tyrosine, tryptophane, lysine, arginine, glycine, alanine, leucine, citruline or ornithine, which latter is in twin bonded by its amino group to the terminal carboxylic group of the side chain of a substituted amide or ester of acrylic or methacrylic acid, said side chain constituting a linear moiety containing at least 3 carbon atoms.

Abstract: A new compound, 1,4-diacyloxy-2,3-butanediol, having the general formula ##EQU1## where R is hydrogen atom or methyl group. The compound can be used above all as a crosslinking agent in the preparation of crosslinked hydrophilic polymeric gels. This compound can be prepared by opening the epoxy ring in such a way, that 1 mole of 1,2-3,4-diepoxybutane is treated with 2 moles of unsaturated acid of the general formula ##EQU2## where R has the aforementioned meaning.