SynopsisTo make a comparison of some of the various polymerization methods, p0ly-y-Dand L-glutamylglycine were synthesized through the mixed anhydride, carbodiimide, and pentachlorophenyl active ester methods. This last method proved to be best, on the basis of weight-average molecular weights (ww). A detailed study was also carried oiit to determine the optimum conditions for this method. The M , values of the polymers were determined by the sedimentation equilibrium method; it was found that the pentachlorophenyl active ester gave Mw values of up to 11,500 but the mixed anhydride and carbodiimide methods gaveTests with rabbit antianthrax immune serum showed that neither D-nor L-isomer precipitated with the antiserum, but that both were able to inhibit the precipitation of the antiserum by anthrax polypeptide. In addition, the D-polymer gave more inhibition than the L, which would indicate a specificity of the antibody for D-glutamic acid residues.values of only about 1000.In order to compare the different polymerization methods and to demonstrate the general usefulness of the pentachlorophenyl (PCPOH) active ester for y-polypeptide synthesis, poly-y-glutamylglycine was prepared by several methods. This polypeptide was also of interest because of its similarity to native polyglutamic acid (poly-y-D-glutamic acid),2-6 which gives a precipitation reaction with antianthrax immune serum7-12 (For the synthesis of this polymer, see Bruckner et ~1 .~~9~~) .Derivatives of the repeating unit of this polymer, y-glutamylglycine, are suitable model compounds for the study of polymerization for the following reasons. Racemization was not expected since the C-activated amino acid is the optically inactive glycine. Formation of diketopiperazine was im-* This is the eleventh in a series of papers concerned with the use of pentachlorophenvl active esters. For the previous paper in this series, see Kovacs, Kisfaludy, and Ceprini.1

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