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Synthesis of Aib‐ and Phe(2Me)‐Containing Cyclopentapeptides
Authors:Anthony Linden  Heinz Heimgartner
Institution:1. Institut für Chemie der Universit?t Zürich, Winterthurerstrasse 190, CH‐8057 Zürich, (phone: +41 44?635?4282;2. fax: +41 44?635?6812)
Abstract:Some recently described pentapeptides containing the α,α‐disubstituted α‐amino acids Aib and Phe(2Me) have been cyclized in DMF solution using diphenyl phosphorazidate (DPPA), O‐(1H‐benzotriazol‐1‐yl)‐N,N,N′,N′‐tetamethyluronium tetrafluoroborate/1‐hydroxybenzotriazole (TBTU/HOBt), and diethyl phosphorocyanidate (DEPC), respectively, to give the corresponding cyclopentapeptides in fair‐to‐good yields. In the case of peptides with L ‐amino acids, and (R)‐ and (S)‐Phe(2Me), the yields differed significantly in favor of the L /(R) combination. The conformations in the crystals of cyclo(Gly‐Aib‐(R,S)‐Phe(2Me)‐Aib‐Gly) and cyclo(Gly‐(R)‐Phe(2Me)‐Pro‐Aib‐Gly) have been determined by X‐ray crystallography, leading to quite different results. In the latter case, the conformation in solution has been elucidated by NMR studies.
Keywords:Peptides  Cyclopentapeptides  2‐Aminoisobutyric acid (Aib)  Phenylalanine  NMR Spectroscopy  X‐Ray crystallography  2‐Methylphenylalanine (Phe(2Me))
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