Convergent Chemical Synthesis of Proteins by Ligation of Peptide Hydrazides
Convergent Chemical Synthesis of Proteins by Ligation of Peptide Hydrazides
复制标题
通过肽酰肼连接聚合化学合成蛋白质
DOI：
10.1002/anie.201203843
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Liu, Lei
中科院分区：
文献类型：
--
作者：
Fang, Ge-Min;Wang, Jia-Xing;Liu, Lei
Total chemical synthesis of proteins can exert atomically precise control on protein composition, and thereby offer the potential of solving a multitude of problems in biomedicine.[1] A common strategy for protein chemical synthesis involves the preparation of peptide segments on solid phase and subsequent condensation of these segments in solution. At present, the most successful approach for the condensation of peptide segments is native chemical ligation, which was invented by Kent et al.[2] In this method, a C-terminal peptide thioester reacts chemoselectively with an N-terminal Cys–peptide under mild reaction conditions in aqueous solution to generate a new peptide bond. The use of native chemical ligation for the preparation of proteins from just two peptide segments is straightforward.[3] For syntheses involving multiple peptide segments, the intrinsic dual reactivity of a bifunctional Cys–peptide–thioester must be controlled to prevent side reactions from occurring at the wrong sites.[4] As an N-terminal Cys can be reversibly protected, the C-to-N sequential ligation of peptide segments can be readily accomplished by using the PG–Cys–peptide–thioester (Scheme 1 a).[5] In contrast, the N-to-C sequential assembly of peptide segments is more challenging because of the difficulty in protecting a thioester. To overcome this problem, Kent et al. developed a kinetically controlled ligation which makes ingenious use of the reactivity difference between aryl and alkyl thioesters (Scheme 1b).[6] The efficacy of this strategy has been shown by the convergent syntheses of several proteins consisting of up to six peptide segments.[7] Furthermore, several groups,[8, 9] including ours,[10] developed ester or amide functionalities which can be converted into thioesters through an intramolecular acyl transfer (Scheme1c). In particular, the very recently developed approaches of the acyl transfer of secondary amides allow the synthesis of proteins by N-to-C assembly of multiple segments.[9] By using this strategy, Brik et al. recently accomplished the convergent synthesis of tetraubiquitin using a thioester equivalent equipped with protected N-methylcysteine.[11]New methods in the arsenal of sequential peptide ligation may further enhance the efficiency and flexibility of convergent protein synthesis. In this regard, we seek to achieve convergent protein synthesis which solely relies on the ligation of peptide hydrazides (Scheme1d). As shown previously,[12] an unprotected peptide hydrazide can be readily converted into a thioester by NaNO2 and an external thiol. This thioester can undergo native chemical ligation with a Cys–peptide in good yield. An important advantage of this ligation approach is that peptide hydrazides can be readily prepared at low cost by using either Boc (tert-butoxycarbonyl) or Fmoc (9-fluorenylmethoxycarbonyl) solid-phase peptide synthesis. The possibility of conducting both N-to-C and C-to-N sequential ligation with peptide hydrazides also promises flexibility in the synthetic design. Nonetheless, during the development of a hydrazide-based method for convergent protein synthesis we encountered several interesting problems. The solutions to these problems, as reported herein, constitute the basis for a new and general method for convergent protein synthesis.
