THE STRUCTURE AND RESONANCE RAMAN-SPECTRA - STRUCTURE CORRELATIONS FOR N-BENZOYL-DL-ALANINE ETHYL DITHIOESTER

An X-ray crystallographic analysis of N-benzoyl-DL-alanine ethyl dithioester demonstrates that it takes up a B-type conformation comparable to that found for N-acylglycine dithioesters in the crystalline state. B-conformations are characterized by small N.sbd.C.sbd.C.sbd.S(thiol) torsional angles resulting from an N.cntdot..cntdot..cntdot.S(thiol) interaction. In the present case the N.sbd.C.sbd.C.sbd.S.sbd. torsional angle is -23.degree. and the N.cntdot..cntdot..cntdot.S distance 2.830 .ANG.. A Raman spectroscopic study of a single crystal and a resonance Raman (RR) spectroscopic study of powdered N-benzoyl-DL-alanine ethyl dithioester establish the RR signature for the compound in its B-form. The RR spectra of the dithioester in CCl4 and H2O/CH3CN, aided by 13C.dbd.S substitution, provide information on the RR signatures of B, A, and C5 type conformers in solution. The A and C5 signatures for the N-acylalanine dithioester resemble closely those for an N-acylglycine dithioester but the B signature is perturbed markedly compared to that of a glycine analog.