Ma S, Richardson J F, Spatola A F
Department of Chemistry, University of Louisville, Kentucky 40292.
Biopolymers. 1993 Jul;33(7):1101-10. doi: 10.1002/bip.360330712.
The solid state conformations of cyclo [Gly-Pro psi[CH2S] Gly-D-Phe-Pro] and cyclo [Gly-Pro psi[CH2-(S)-SO]Gly-D-Phe-Pro] have been characterized by X-ray diffraction analysis. Crystals of the sulfide trihydrate are orthorhombic, P2(1)2(1)2(1), with a = 10.156(3) A, b = 11.704(3) A, c = 21.913(4) A, and Z = 4. Crystals of the sulfoxide are monoclinic, P2(1) with a = 10.662(1) A, b = 8.552(3) A, c = 12.947(2) A, beta = 94.28(2), and Z = 2. Unlike their all-amide parent, which adopts an all-trans backbone conformation and a type II beta-turn encompassing Gly-Pro-Gly-D-Phe, both of these peptides contain a cis Gly1-Pro2 bond and form a novel turn structure, i.e., a type II' beta-turn consisting of Gly-D-Phe-Pro-Gly. The turn structure in each of these peptides is stabilized by an intramolecular H bond between the carbonyl oxygen of Gly1 and the amide proton of D-Phe4. In the cyclic sulfoxide, the sulfinyl group is not involved in H bonding despite its strong potential as a hydrogen-bond acceptor. The crystal structure made it possible to establish the absolute configuration of the sulfinyl group in this peptide. The two crystal structures also helped identify a type II' beta-turn in the DMSO-d6 solution conformers of these peptides.
通过X射线衍射分析对环[甘氨酸-脯氨酸ψ[CH₂S]甘氨酸-D-苯丙氨酸-脯氨酸]和环[甘氨酸-脯氨酸ψ[CH₂-(S)-SO]甘氨酸-D-苯丙氨酸-脯氨酸]的固态构象进行了表征。硫化物三水合物的晶体为正交晶系，空间群P2(1)2(1)2(1)，a = 10.156(3) Å，b = 11.704(3) Å，c = 21.913(4) Å，Z = 4。亚砜的晶体为单斜晶系，空间群P2(1)，a = 10.662(1) Å，b = 8.552(3) Å，c = 12.947(2) Å，β = 94.28(2)，Z = 2。与采用全反式主链构象和包含甘氨酸-脯氨酸-甘氨酸-D-苯丙氨酸的II型β-转角的全酰胺母体不同，这两种肽均含有顺式Gly1-Pro2键，并形成一种新型转角结构，即由甘氨酸-D-苯丙氨酸-脯氨酸-甘氨酸组成的II'型β-转角。这些肽中的每一种的转角结构都通过Gly1的羰基氧与D-Phe4的酰胺质子之间的分子内氢键得以稳定。在环状亚砜中，亚磺酰基尽管具有很强的作为氢键受体的潜力，但并未参与氢键形成。晶体结构使得确定该肽中亚磺酰基的绝对构型成为可能。这两种晶体结构还有助于在这些肽的DMSO-d6溶液构象体中识别出II'型β-转角。
