RESUMO
The nucleoside antibiotic, 3'-azido-3'-deoxythymidine, or simply, azidothymidine has shown great promise in inhibiting the human immuno deficiency virus and in reducing mortality among AIDS patients. Conformational properties of azidothymidine have been investigated by quantum-mechanical PCILO method and compared with those of the parent nucleoside, thymidine. The results indicate great similarity between them and this similarity is remarkably striking in the situations that prevail in aqueous solution. This result has important biological significance in explaining the drug action of azidothymidine.
RESUMO
The conformational proclivity of leucine and methionine enkephalinamides in deuterated dimethyl sulphoxide has been investigated using proton magnetic resonance at 500 MHz. The resonances from the spin system of the various amino acid residues have been assigned from the 2-dimensional correlated spectroscopy spectra. The temperature variation of the amide proton shifts indicates that none of the amide proton is intramolecularly hydrogen-bonded or solvent-shielded. The analysis of vicinal coupling constants, 3JHN.C 2 H,along with temperature coefficients and the absence of characteristic nuclear Overhauser effect cross peaks between the NH protons reveal that there is no evidence of the chain folding in these molecules. However, the observation of nuclear Overhauser effect cross peaks between the NH and the CαH of the preceding residue indicates preference for extended backbone conformation with preferred side chain orientations particularly of Tyr and Phe in both [Leu5] - and [Met5]-enkephalinamides.