LINEAR OLIGOPEPTIDES .147. CHEMICAL AND CRYSTALLOGRAPHIC STUDY OF THE REACTION BETWEEN BENZYLOXYCARBONYL CHLORIDE AND ALPHA-AMINOISOBUTYRIC-ACID

From the reaction mixture of benzyloxycarbonyl chloride and a-aminoisobutyric acid three crystalline compounds were isolated and characterized by chromatographic and spectroscopic techniques and Xray diffraction. Two of them are polymorphic forms of the N-protected amino acid, which differ in the orientation of the phenyl ring relative to the urethane moiety and in the packing modes of the molecules, including the intermolecular hydrogen- bonding arrangements. The third compound is the N-protected dipeptide, the formation of which is not unexpected in the synthesis of the N- benzyloxycarbonyl amino acid derivative. The crystal structure of the symmetric carboxylic anhydride from the N-protected amino acid, a reasonable reactive intermediate in the formation of the N-protected dipeptide, is also described.