Syntheses and characterization of tetra-gamma-benzyl-L-glutamates

Monodisperse tetra-gamma-benzyl-L-glutamates are prepared by coupling two kinds of dimers by means of dicyclohexylcarbodiimide and then converting a terminal group into the other. An o-nitrophenylthio group is used for blocking the amino terminal, and a p-nitrophenyl ester or an ethylamide substitutes the carboxyl end. The amino-terminal-deblocked tetramer, HCl,H-[Glu(OBzl)] 4-NHEt, is alos prepared. Infrared spectra in nujol mull indicate that all the tetramers are in the beta-structure of antiparallel chains in the solid state. Circular dichroism spectra show that the amino-terminal deblocked tetramer keeps the beta-conformation in ethylene dichloride, while it has the solvated sigma-conformation in trifluoroethanol and in dioxane.