No abstract

The hydrazones (I) react with the silane (II) to give the 6‐membered cyclic ylides (III) or the 5‐membered compounds (IV) depending on the configuration of (I).

Transpeptidation reactions catalyzed by chymotrypsin, pepsin, leucine aminopeptidase and thermolysin have been studied in heavy oxygen water (H218O). The 18O incorporation into the peptide bond of transpeptidation products and into the non‐hydrolyzed substrate has been measured. The rates of 18O exchange in the carboxylic groups of N‐acetylphenylalanine and leucine, catalyzed by pepsin and leucine aminopeptidase, respectively, have also been determined. These rates have been compared with that of the exchange in the presence of amino compounds which reversibly form amide bonds with the above carboxyl‐containing substances. The data obtained show that, in contrast to chymotrypsin, other enzymes studied do not form ‘acyl‐enzymes’ but function by the mechanism of general‐base catalysis. In other words, their catalytically active groups promote the abstraction of a proton from the mater molecule, which attacks the susceptible bond of the substrate. The structure of intermediate compounds in this type of catalysis and the mechanism of the transpeptidation reaction are discussed.

ChemInform Abstract Silylation of the hydrazides (I) with trimethylsilyl chloride (II) takes place exclusively at the oxygen atom, producing the hydrazonic acid esters (III).

Sorption properties with respect to noble metal compounds were examined for a new divinyl benzene cross-linked nitrogen-containing heterocyclic copolymer of 1-vinyl-1,2,4-triazole with acrylic acid. The sorption recovery of chloride complexes of Au(III), Pt(IV), Pd(II), and Ag(I), as well as of silver nitrate from acidic solutions was examined in relation to the nature and concentration of acids and the contact time between the phases.