Template for stabilization of a peptide alpha-helix: Synthesis and evaluation of conformational effects by circular dichroism and NMR
Template for stabilization of a peptide alpha-helix: Synthesis and evaluation of conformational effects by circular dichroism and NMR
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DOI：
10.1021/ja964231a
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发表时间：
1997-07-16
影响因子：
15
通讯作者：
Bartlett, PA
中科院分区：
文献类型：
--
作者：
Austin, RE;Maplestone, RA;Bartlett, PA
双环二酸1被设计为用于肽α-螺旋的氢键模式的半刚性模板。受保护的前体7由3，5-二甲氧基苯甲酸叔丁酯分八步合成，并与L-丙氨酸和L-乳酸连接以提供适于偶联至肽的衍生物。以四种非对映异构体形式中的每一种获得酰胺8-N和酯12-O。通过X射线晶体学确定R，R-8-N的结构，这有助于非对映异构体的归属，并证实了季甲基的预期构象效应。双环酰胺和酯衍生物附加到肽EALAKA-NH 2，并在水溶液中使用圆二色性和NMR评价其对构象的影响。酰胺类似物对附加的肽仅有轻微的影响，而S，S-9-O中的酯连接模板在23 ℃诱导32-50%的螺旋特征，在0 ℃诱导49-77%的螺旋特征，这取决于测定方法;即使在70 ℃，显著的螺旋特征仍然存在。模板1诱导螺旋构象的能力与其与肽的N-末端的结构和电子互补性有关;当S，S-9-O中的羧酸酯质子化时，模板能力消失，并且在二甲基酰胺S，S-9-N-a中未观察到。用核磁共振研究了共轭物S，S-9-O的结构和动力学性质，并与乙酰化七肽13的结构和动力学性质进行了比较。酰胺氢化学位移的分散和温度依赖性以及观察到的残基内和残基间核Overhauser增强的模式都与共轭S，S-9-O的构象系综内的螺旋构象异构体的显著群体一致，与非结构化肽13相反。从N-15 T-1和T-2弛豫速率常数和测定的N-15标记的S，S-9-O衍生物的H-1-N-15杂原子NOE中推导出每个残基的广义序参数S-2;这些参数表明在4 ℃时沿着肽链具有高度构象刚性，C-末端残基的相对运动增加。这些数据与手性研究一致，并证明模板在诱导附加肽的螺旋行为方面特别有效。
The bicyclic diacid 1 was designed as a semi-rigid template for the hydrogen-bonding pattern of a peptide alpha-helix. The protected precursor 7 was synthesized in eight steps from tert-butyl 3,5-dimethoxybenzoate and linked to L-alanine and L-lactic acid to provide derivatives appropriate for coupling to a peptide. Both the amide 8-N and the ester 12-O were obtained in each of the four diastereomeric forms. The structure of R,R-8-N was determined by X-ray crystallography, which facilitated assignment of the diastereomers and confirmed the intended conformational effects of the quaternary methyl groups. The bicyclic amide and ester derivatives were appended to the peptide EALAKA-NH2, and their influence on the conformation was evaluated in aqueous solution using circular dichroism and NMR. The amide analogs have only a slight effect on the appended peptide, whereas the ester-linked template in S,S-9-O induces 32-50% helical character at 23 degrees C and 49-77% at 0 degrees C, depending on the method of determination; significant helical character persists even at 70 degrees C. The ability of the template 1 to induce the helical conformation is related to its structural and electronic complementarity to the N-terminus of the peptide; templating ability disappears when the carboxylate in S,S-9-O is protonated, and it is not observed in the dimethylamide S,S-9-N-a. The structural and dynamical properties of conjugate S,S-9-O were studied by NMR and compared with those of the acetylated heptapeptide 13. The dispersion and temperature dependence of amide hydrogen chemical shifts and the pattern observed for intra- and inter-residue nuclear Overhauser enhancements are all consistent with a significant population of helical conformers within the conformational ensemble of conjugate S,S-9-O, in contrast to the unstructured peptide 13. The generalized order parameter S-2 was derived for each residue from the N-15 T-1 and T-2 relaxation rate constants and H-1-N-15 heteronuclear NOEs determined for the N-15-labeled derivative of S,S-9-O; these parameters demonstrate a high degree of conformational rigidity along the peptide chain at 4 degrees C, with relative motion increasing for the C-terminal residues. These data are consistent with the chiroptical studies and demonstrate that the template is exceptionally effective in inducing helical behavior in an appended peptide.