Water-Stable Helical Structure of Tertiary Amides of Bicyclic β-Amino Acid Bearing 7-Azabicyclo[2.2.1]heptane. Full Control of Amide Cis−Trans Equilibrium by Bridgehead Substitution
structures are generally susceptible to the environment; that is, helices may unfold in protic solvents such as water. For the generation of non-hydrogen-bonded ordered structures of amides (tertiaryamides in most cases), control of cis-trans isomerization is crucial, even though there is only a small sterical difference with respect to cis and trans orientations. We have established methods for synthesis
在许多情况下,非天然β-氨基酸低聚物的螺旋结构通过主链酰胺部分之间的分子内氢键显着稳定,但该结构通常易受环境影响;也就是说,螺旋可以在质子溶剂(如水)中展开。对于酰胺(大多数情况下为叔酰胺)的非氢键有序结构的产生,控制顺反异构化是至关重要的,即使顺反方向只有很小的空间差异。我们已经建立了合成受构象限制的 β-脯氨酸模拟物的方法,即桥头取代的 7-氮杂双环 [2.2.1] 庚烷-2-内-羧酸。我们的晶体学,一维和二维核磁共振,溶液中的 CD 光谱研究表明,桥头甲氧基甲基取代基使顺反平衡完全偏向沿着主链的顺酰胺结构,并且基于顺酰胺键的螺旋结构的产生与残基数量无关,从极简二聚体从四聚体、六聚体一直到八聚体,与溶剂(例如,水、醇、卤化溶剂和环己烷)无关。还检查了通过桥头取代控制酰胺平衡的一般性。并且不考虑溶剂(例如,水、醇、卤化溶剂和环己烷)。还检查了通过桥头取代控制酰胺平衡的一般性。并且与溶