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Conformational preference of bicyclic β-amino acid dipeptides.
Chirality ( IF 2 ) Pub Date : 2020-04-01 , DOI: 10.1002/chir.23220
Yuko Otani 1 , Seokhwi Park 1 , Tomohiko Ohwada 1
Affiliation  

Bridged bicyclic amino acids have high potential applicability as self‐organized, conformationally constrained synthetic building blocks that do not require assistance from hydrogen bond formation. We systematically investigated the intrinsic conformational propensities of dipeptides of bridged bicyclic β‐amino acids by means of accelerated molecular dynamics simulation and density functional theory (DFT) calculations in methanol, chloroform, and water. While the main‐chain conformation, represented by φ and θ values, is fixed by the nature of the bicyclic ring structure, rotation of the C‐terminal carbonyl group (ψ) is also restricted, converging to one or two minima. In endo‐type dipeptides, in which the two N‐ and C‐terminal amides are spatially close to each other, the C‐terminal amide plane is placed horizontally. In exo‐type dipeptides, in which the two amides are on opposite sides of the ring plane, the C‐terminal carbonyl group can take two types of positions: either parallel/antiparallel with the N‐terminal carbonyl or beneath the bicyclic ring, forcing the amide NHMe moiety to lie outside of the ring. We also examined the cis‐trans preference of model bicyclic amides. Although the parent amides exhibit cis‐trans equilibrium without any preference, addition of a methyl group on one of the bridgehead positions tips the equilibrium towards trans.

中文翻译:

双环β-氨基酸二肽的构象偏好。

桥联的双环氨基酸具有高度潜在的适用性,因为它们是自组织的,受构象约束的合成构件,不需要氢键形成的帮助。我们通过加速分子动力学模拟和密度泛函理论(DFT)在甲醇,氯仿和水中的计算,系统地研究了桥接双环β-氨基酸的二肽的固有构象倾向。虽然由φθ值表示的主链构象由双环结构的性质固定,但C末端羰基(ψ)的旋转也受到限制,收敛到一个或两个最小值。在远藤类型二肽,其中两个N和C末端酰胺在空间上彼此靠近,C末端酰胺平面水平放置。在两个酰胺位于环平面相对侧的exo型二肽中,C末端羰基可具有两种类型的位置:与N末端羰基平行/反平行或在双环下方,从而迫使酰胺NHMe部分位于环的外部。我们还研究了模型双环酰胺的顺反偏好。尽管母体酰胺毫无保留地表现出顺反平衡,但在桥头位置之一上添加甲基会使平衡趋向反式。
更新日期:2020-04-01
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