THE SOLUTION CONFORMATION OF CYCLIC BETA-CASOMORPHIN-5 ANALOGS

The solution conformation of two cyclic beta-casomorphin-5 analogues H -Tyr-c(-D-Orn-Phe-Pro-Gly-) 1 and H-Tyr-c(-Orn-Phe-Pro-Gly-) 2 in DMSO -d(6) was studied by NMR spectroscopy and accompanying force field cal culations. By especially employing H-1, C-13, and N-15 chemical shifts , respectively, the temperature coefficient of the amide proton chemic al shifts, (3)J(NH,C alpha H) and (3)J(C alpha H,C beta H) coupling co nstants, respectively, and nuclear Overhauser effects in the rotating frame (ROEs), in the case of 1, only one preferred conformer could be identified. In the case of 2, two or even more preferred conformers we re found, readily interconverting on the NMR time scale. Empirical for ce field calculations using the SYBYL 6.0 software (TRIPOS) corroborat e the experimental NMR results obtained. The conformational behavior o f the compounds studied is discussed with respect to the receptor spec ificity of the beta-casomorphins studied.