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寡肽类化合物一般具有较强的生物活性,多数可作为药物或药物前体,因此成为人们的研究热点之一.目前寡肽的合成方法主要有液相法、固相法及酶促合成法,这些合成方法往往需要对氨基酸的活性基团进行选择性保护,步骤繁琐.近期研究发现,在水-醇体系中α-氨基酸被磷酰化为N-磷酰-α-氨基酸后,可发生自组装聚合肽反应;在无水条件下,N,O-二(三甲基硅基)-α-氨基酸可与磷酰化试剂如O,O-亚苯基磷酰氯反应生成N-磷酰-α-氨基酸,后者也可通过自组装反应得到二~八肽,但这些N-磷酰-α-氨基酸的制备均需使用有机磷试剂.我们发现,在无机磷试剂如PCl5等辅助下,α-氨基酸同样可以发生自组装反应,得到一系列寡聚肽,这既可为寡聚肽的合成提供一种新的方法,同时,因无机磷试剂在原始地球条件下更可能存在,因而对于揭示多肽及蛋白质的起源具有重要意义.氨基酸的自组装反应具有链锁反应的特点,因此必须控制反应条件实现对反应的控制。 相似文献
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磷酰化丝氨酸形成六配位磷中间体的理论研究 总被引:2,自引:2,他引:0
用MNDO方法对磷酰化丝氨酸仿生化反应机理中六配位磷中间体的形成过程进行了研究.磷酰化丝氨酸(1)形成分子内磷酸-羧酸分子内混酐的五配位磷中间体(2)后,其酸性质子解离,分子经过具有氢桥键结构的过渡态,使氨基酸侧链羟基上的氢通过氢键作用向磷上的O1进行转移,然后再经过构型由三角双锥向八面体的转变,形成六配位磷中间体(3).氢桥键的存在使反应过渡态能量降低,其相对能量为148.5kJ/mol.理论计算较成功的解释了六配位磷中间体的形成机理以及磷酰化丝氨酸仿生化反应中羧基和侧链羟基共同参与的实验结果. 相似文献
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用MNDO方法对磷酰化丝氨酸仿生化反应机理中所形成的六配位磷中间体(3)可能的3个异构体的结构及其反应活性进行了研究.在六配位磷中间体3的6根键中,丝氨酸的羧基氧O3与磷之间的键最弱,最易断裂生成新的五配位磷中间体4,4的P_N键断裂得到磷酰基的N→O转位反应产物5.对于六配位磷中间体3中的两个异丙氧基,位于丝氨酸侧链羟基O6对面的异丙氧基较另一个易于离去(约低37kJ/mol)并得到中间体6,接着甲醇从O6对面新产生的空隙进攻中间体6中的磷,生成磷上酯交换产物9.六配位磷中间体机理比较好地解释了实验中所发现的磷酰化丝、苏氨酸仿生化反应的多样性和复杂性. 相似文献
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咪唑催化磷酰化丝,苏氨酸及其酯的活化反应 总被引:1,自引:2,他引:1
咪唑对磷酰化氨基酸的活化反应具有较强的催化作用,磷酰化丝、苏氨酸在咪唑催化下不仅能发生溶剂解反应,如磷酯交换,羧基活化成酯、成肽及磷酰基的N-O迁移等,而且还会发生分子内环化反应,对于化学性质非常稳定的磷酰化丝、苏氨酸酯在咪唑催化下也会发生上述反应,反应机理推测为丝、苏氨酸的侧链基团羟基在咪唑的存在下亲核进攻磷原子形成五配位中间体。 相似文献
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It was discovered that polypeptides were formed by self-assembly of N,O-bis(trimethylsilyl)amino acids with the assistance of O-phenylene phosphorochloridate.[1] There were three steps involved in the self organization reactions, the activation of amino acid, the elongation of peptide chain and the termination of the chain reaction,among which the activation of amino acid -the formation of imino (alkyl)acetoxyphosphoranes was the key step. The formation process of the penta-coordinated phosphorus intermediates was showed in scheme 1.[2,3,4] Through further studies of the mechanism of self-assembly reaction, it was found that carbonyl groups of the intermediates attacked by the neuclophilic groups were direct reson of the formation of peptides. However, the peptides in the solution were very difficult to be separated and analyzed. 相似文献
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Conformational Analysis of Tripeptide Models: The Influence of α,α-disubstituted α-Amino Acids on the Secondary Structure. NMR and CD Investigations The conformational properties of α,α-disubstituted α-amino acids are discussed on the basis of NMR, CD, X-ray, and molecular-mechanics studies on tripeptide models 1 . It is shown that different disubstituted amino acids do not exert the same influence on secondary-structure formation. Thus, the choice of substituents allows the construction and stabilisation of different conformations of oligopeptide chains. 相似文献
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A New Synthetic Route to β,α-Unsaturated α-Amino Acids A versatile new synthetic pathway for the preparation of βγ-unsaturated α-amino acids ( 1 ) is presented. Cu(I)-catalyzed addition of ethyl isocyanoacetate ( 2 ) to α-chloro carbonyl compounds ( 3 ) gives 5-chloroalkyl-2-oxazolin-4-carboxylates ( 4 ) in high yields. A reductive elimination on 4 by means of zinc yields the N-formyl derivatives of βγ-unsaturated α-amino carboxylates ( 5 ), which on acid hydrolysis lead to the free amino acids 1 . The five different βγ-dehydro-α-amono acids 1b-1f have been prepared by this method. 相似文献
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α-Amino acids react with aldehydes in the presence of a cyanide source to form α-amino nitriles in what can be considered a decarboxylative variant of the classical Strecker reaction. This unprecedented transformation does not require the use of a metal catalyst and provides facile access to valuable α-amino nitriles that are inaccessible by traditional Strecker chemistry. 相似文献
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A method for the synthesis of β3-amino acids starting from α-amino acids is described. This conversion can be effected by an eight-step procedure which involves the transformation of the carboxylic group into an alkyne followed by a selenium-mediated conversion of the carbon-carbon triple bond to a Se-phenyl selenocarboxylate intermediate. The reactive Se-phenyl selenocarboxylate intermediates can be trapped with water, alcohols or the amine of an amino acid derivative to give β3-amino acids, β3-amino esters or mixed peptides, respectively. The whole transformations of the carboxylic group into an alkyne and of the alkyne group into β3-amino acids may not require purification of the intermediate products but a work-up and isolation procedure of crude materials. 相似文献
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α-Amino acids are easily accessible through abiotic processes and were likely present before the emergence of life. However, the role they could have played in the process remains uncertain. Chemical pathways that could have brought about features of self-organization in a peptide world are considered in this review and discussed in relation with their possible contribution to the origin of life. An overall scheme is proposed with an emphasis on possibilities that may have led to dynamically stable far from equilibrium states. This analysis defines new lines of investigation towards a better understanding of the contribution of the systems chemistry of amino acids and peptides to the emergence of life. 相似文献
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Masayasu Akiyama Masayoshi Hasegawa Haruyuki Takeuchi Kazuyuki Shimizu 《Tetrahedron letters》1979,20(28):2599-2600
N-Benzyloxy-DL-α-amino acids are transformed with phosgen to N-benzyloxy-DL-α-amino acid anhydrides which react smoothly with the amino component of peptides to give the corresponding N-benzyloxypeptides. 相似文献
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Ghorai A Gayen A Kulsi G Padmanaban E Laskar A Achari B Mukhopadhyay C Chattopadhyay P 《Organic letters》2011,13(20):5512-5515
A 1,4-linked triazole/amide based peptidomimetic macrocycle, synthesized from a triazole amide oligomer of cis-furanoid sugar triazole amino acids, possesses a conformation resembling the D-,L-α-amino acid based cyclic peptides despite having uniform backbone chirality. It undergoes a unique mode of self-assembly through an antiparallel backbone to backbone intermolecular H-bonding involving amide NH and triazole N2/N3 as well as parallel stacking via amide NH and carbonyl oxygen H-bonding, leading to the formation of a tubular nanostructure. 相似文献