Polydepsipeptides. 5. Experimental conformational analysis of poly(L-alanyl-L-lactic acid) and related model compounds.
Polydepsipeptides. 5. Experimental conformational analysis of poly(L-alanyl-L-lactic acid) and related model compounds.
复制标题
聚缩酚肽。
作者：
R. Ingwall;C. Gilon;M. Goodman
本文报道了沉积肽模型化合物乙酰-l -丙氨酸甲酯、乙酰-l -乳酸n -甲酰胺和乙酰-l -丙酰-l -乳酸n -甲酰胺的实验构象分析以及顺序聚沉积肽聚（l-丙酰-l -乳酸）的构象分析。用红外光谱和核磁共振波谱法在稀有机溶液中检测模型沉积肽。乙酰-l -丙氨酸甲酯和乙酰-l -乳酸n-甲基酰胺都不具有分子内氢键构象。另一方面，在稀氯仿或稀四氯化碳溶液中，乙酰-l -丙酰-l -乳酸n -甲酰胺强烈倾向于在其n -甲酰胺基团的N-H氢原子和其乙酰基的羰基氧原子之间形成分子内氢键的构象。理论和实验的圆二色性比较表明，聚l-丙烯酰-l -乳酸在氯仿溶液中部分有序，其重复单元约有50%在R10螺旋上，我们之前的理论分析发现这种有序构象具有较低的分子内构象能。
In this paper we report an experimental conformational analysis of the depsipeptide model compounds acetyl-L-alanine methyl ester, acetyl-L-lactic acid N-methylamide, and acetyl-L-alanyl-L-lactic acid N-methylamide and of the sequential polydepsipeptide poly(L-alanyl-L-lactic acid). The model depsipeptides were examined in dilute organic solutions by infrared and nuclear magnetic resonance spectroscopy. Neither acetyl-L-alanine methyl ester nor acetyl-L-lactic acid N-methylamide assumes an intramolecularly hydrogen-bonded conformation. Acetyl-L-alanyl-L-lactic acid N-methylamide, on the other hand, in dilute chloroform or dilute carbon tetrachloride solutions, strongly favors a conformation with an intramolecular hydrogen bond between the N-H hydrogen atom of its N-methylamide group and the carbonyl oxygen atom of its acetyl group. Comparison of theoretical and experimental circular dichroism suggests that poly(L-alanyl-L-lactic acid) is partially ordered in chloroform solution with approximately 50% of its repeat units in the R10 helix, an ordered conformation found by our previous theoretical analysis to have a low intramolecular conformational energy.