Gupta A, Chauhan V S
International Centre for Genetic Engineering & Biotechnology, New Delhi, India.
Int J Pept Protein Res. 1993 May;41(5):421-6.
Six model dipeptide methylamides containing dehydroaminobutyric acid (delta Abu) of the type Boc-X-delta z Abu-NHCH3 and Box-X-delta E Abu-NHCH3, X = Ala, Val, Phe (Boc = tert-butoxycarbonyl), have been synthesized and their solution conformations explored using 300 MHz 1H NMR and IR spectroscopy. Studies based on delineation of intramolecularly hydrogen bonded NH groups in CDCl3 and (CD3)2SO revealed that none of the NH groups is appreciably solvent shielded. Difference NOE (Nuclear Overhauser Effect) studies have also failed to detect the presence of any discernible turn structure in these peptides. These studies indicate that the conformational preferences of peptides containing, alpha, beta-dehydroaminobutyric acid are different from those of delta ZPhe and delta ZLeu. It appears that steric interactions due to the beta-substituent in the dehydroamino acid moiety play an important role. Unlike delta ZPhe and delta ZLeu, which have relatively large beta-substituents, phenyl and isopropyl, respectively, and stabilize a beta-turn, the beta-methyl group of delta ZAbu or delta EAbu is readily accommodated in extended conformation. Clearly, the size of beta-substituent in dehydroamino acid crucially influences the conformational preferences. Thus, it may be possible to use different dehydroamino acids to introduce variable but definite constraints in synthetic peptides.
已合成了六种含有脱氢氨基丁酸（δAbu）的模型二肽甲基酰胺，其类型为Boc-X-δz Abu-NHCH3和Box-X-δE Abu-NHCH3，其中X = Ala、Val、Phe（Boc = 叔丁氧羰基），并使用300 MHz 1H NMR和红外光谱对它们的溶液构象进行了探索。基于在CDCl3和(CD3)2SO中对分子内氢键合NH基团的描绘所进行的研究表明，没有一个NH基团受到明显的溶剂屏蔽。差异核Overhauser效应（NOE）研究也未能检测到这些肽中存在任何可辨别的转角结构。这些研究表明，含有α,β-脱氢氨基丁酸的肽的构象偏好与δZPhe和δZLeu的不同。看来脱氢氨基酸部分中β-取代基引起的空间相互作用起着重要作用。与分别具有相对较大的β-取代基苯基和异丙基并稳定β-转角的δZPhe和δZLeu不同，δZAbu或δEAbu的β-甲基很容易以伸展构象容纳。显然，脱氢氨基酸中β-取代基的大小对构象偏好有至关重要的影响。因此，有可能使用不同的脱氢氨基酸在合成肽中引入可变但确定的限制。
