| Popis: |
Nα-(Phenethylphosphono)-l-alanyl-l-proline 1, a potent inhibitor of angiotensin converting enzyme, exhibits two 31P n.m.r. resonances (intensity ratio one to one), which exchange with a constant (k1) of about 1 s−1 and a free energy of activation ΔG*=∼ 20kcal/mol at 23° in deuterated dimethylsulfoxide. Two resonances in exchange are also observed in deuterium oxide at pH 7.5. Thus the exchanging 31P resonances report the s-cis, s-trans conformational equilibrium about the alanyl-proline peptide bond. Similar results were observed with Nα-[(O-phenyl)-phenethylphosphono]-l-alanyl-l-proline 2. Nα -(O-phenylphospho)-l-alanyl-l-proline, 3 Nα-(O, O′-diphenylphospho)-l-alanyl-l-proline 4, and Nα-[2-(2-oxo-1, 3, 2-dioxaphosphiranyl)]-l-alanyl-l-proline 5 in deuterated dimethyl sulfoxide, deuterium oxide, and deuterochloroform. A 13C n.m.r. spectrum of 5 confirmed the presence of s-cis and s-trans resonances for the proline carbons in the same intensity ratio observed by 31P n.m.r. |
