Abstract: The invention relates to a process for the preparation of 5-(1-hydroxy-2-urethanethylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione derivatives, which are precursors of chiral tetramic acid derivatives.According to this process, an N-urethane-protected .alpha.-amino acid N-carboxy-anhydride is reacted with Meldrum's acid in an inert organic solvent medium in the presence of a tertiary amine.This process makes it possible to conserve the chirality of the starting material and in particular to simplify the synthesis of 4-amino-3-hydroxy acids and the derivatives thereof via the tetramic acid route.

Abstract: An enzymatic process for the determination of beta-lactam antibiotics in a biological liquid, comprising the steps of: (1) incubating the liquid with soluble D-alanyl-D-alanine-carboxypeptidase produced by Actinomadura R 39, said enzyme being immobilized on a water-insoluble support, the beta-lactam antibiotic reacting with the immobilized enzyme to form an inactive and equimolecular enzyme-antibiotic complex; (2) separating the immobilized enzyme from the liquid and washing it; (3) incubating the immobilized enzyme with a substrate solution to hydrolyze it and form an amount of D-alanine corresponding to the residual enzymatic activity; (4) determining the amount of D-alanine formed; and (5) comparing the determination of step (4) with a standard to obtain the concentration of the antibiotic in the biological liquid; as well as a test set for carrying out this process and comprising the necessary reagents.

Abstract: L-pyroglutamyl-L-prolinamide is useful for correcting metabolic or endocrinal disorders connected with senescence. It can be prepared by reacting L-pyroglutamic acid with L-prolinamide.