Conformation and Chiral Effects in 伪,尾,伪-Tripeptides

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• 作者：Carlos J. Saavedra ; Alicia Boto ; Rosendo Hern谩ndez ; Jos茅 Ignacio Miranda ; Jesus M. Aizpurua
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：July 20, 2012
• 年：2012
• 卷：77
• 期：14
• 页码：5907-5913
• 全文大小：478K
• 年卷期：v.77,no.14(July 20, 2012)
• ISSN：1520-6904

文摘

Short 伪,尾,伪-tripeptides comprising a central chiral trisubstituted 尾^2,2,3*-amino acid residue form unusual 纬-turns and 未-turns in CDCl₃ and DMSO-d₆ solutions but do not form 尾-turns. Thermal coefficients of backbone amide protons, 2D-NMR spectra, and molecular modeling revealed that these motifs were strongly dependent on the configuration (chiral effect) of the central 尾-amino acid residue within the triad. Accordingly, SSS tripeptides adopted an intraresidual 纬-turn like (C6) arrangement in the central 尾-amino acid, whereas SRS diastereomers preferred an extended 未-turn (C9) conformation. A different SRS-stabilizing bias was observed in the crystal structures of the same compounds, which shared the extended 未-turn (C9) found in solution, but incorporated an additional extended 尾-turn (C11) to form an overlapped double turn motif.