A readily synthesized cyclic pyrrolysine analogue for site-specific protein "click" labeling

A concise route was developed for the facile synthesis of a cyclic pyrrolysine analogue bearing an azide handle. Directed evolution enabled the encoding of this non-natural amino acid in both prokaryotic and eukaryotic cells, which offers a highly efficient approach for the site-specific protein labeling using click chemistry.     

Sweetening cyclic peptide libraries

Enzymatic macrolactamization of linear glycosidated peptides provides access to an important class of drug-like molecules. The work presented in this issue [1] shows that it may be possible to make complex libraries of glycosidated cyclic peptides by incorporating glycosidated amino acids into linear peptides via solid-phase peptide synthesis followed by thioesterase-mediated peptide cyclization.     

On-resin native chemical ligation for cyclic peptide synthesis

A novel cysteine derivative, N(alpha)-trityl-S-(9H-xanthen-9-yl)-l-cysteine [Trt-Cys(Xan)-OH] has been introduced for peptide synthesis, specifically for application to a new strategy for the preparation of cyclic peptides. The following steps were carried out to synthesize the cyclic model peptide cyclo(Cys-Thr-Abu-Gly-Gly-Ala-Arg-Pro-Asp-Phe): (i). side-chain anchoring of Fmoc-Asp-OAl via its free beta-carboxyl as a p-alkoxybenzyl ester to a solid support; (ii). stepwise chain elongation of the peptide by standard Fmoc/tBu solid-phase chemistry; (iii). removal of the N-terminal Fmoc group; (iv). coupling of Trt-Cys(Xan)-OH; (v). selective Pd(0)-promoted cleavage of the C-terminal allyl ester; (vi). coupling of the C-terminal residue, i.e., H-Phe-SBzl, preactivated as a thioester; (vii). selective removal of the N(alpha)-Trt and S-Xan protecting groups under very mild acid conditions; (viii). on-resin cyclization by native chemical ligation in an aqueous milieu; and (ix). final acidolytic cleavage of the cyclic peptide from the resin. The strategy was evaluated for three supports: poly[N,N-dimethacrylamide-co-poly(ethylene glycol)] (PEGA), cross-linked ethoxylate acrylate resin (CLEAR), and poly(ethylene glycol)-polystyrene (PEG-PS) graft resin supports. For PEGA and CLEAR, the desired cyclic product was obtained in 76-86% overall yield with initial purities of approximately 70%, whereas for PEG-PS (which does not swell nearly as well in water), results were inferior. Solid-phase native chemical ligation/cyclization methodology appears to have advantages of convenience and specificity, which make it promising for further generalization.     

A systematic nomenclature for cascade polymers

Cascade (dendritic) polymers are discrete, highly branched, monodisperse polymers that possess branching patterns described by a mathematical progression. A systematic nomenclature that accurately represents these molecules is described. © 1993 John Wiley & Sons, Inc.     

化学标记与蛋白质/多肽的识别检测

化学标记技术可以实现选择性地标记蛋白质/多肽分子,从而极大地提高了对蛋白质/多肽的识别效率和检测灵敏度,是突破蛋白质/多肽化学组成局限和仪器分析检测能力瓶颈的有效途径.本文对目前这一领域的研究现状扼要地进行了综述,主要包括针对蛋白质/多肽分子中内源氨基酸残基的标记策略、蛋白质/多肽分子中翻译后修饰基团的标记策略、基因编码表达肽段的标记策略以及配体/抗体亲和标记策略.透过这些研究所取得的成果,可以断定化学标记技术将会不断发展并将在蛋白质及蛋白质组学研究中发挥重要作用.     

A cyclic RGD-coated peptide nanoribbon as a selective intracellular nanocarrier

We have synthesized a peptide-based supramolecular building block consisting of a cyclic Arg-Gly-Asp (cRGD) peptide segment and a beta-sheet-forming peptide segment. The block peptide was shown to self-assemble into a cRGD-coated nanoribbon structure, as revealed by circular dichroism (CD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) studies. We have shown that this cRGD-coated nanoribbon can encapsulate hydrophobic guest molecules and deliver them into cells. Colocalization of the nanoribbon with LysoTracker and the selective intracellular delivery results suggests that the cRGD-coated nanoribbon is likely to be internalized into the cells through integrin receptors.     

Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes for labeling human cancer cells

Strain-promoted cycloadditions of cyclic nitrones with cyclooctynes proceed with rate constants up to 3.38 ± 0.31 M(-1) s(-1) in CD(3)CN, or 59 times faster than the analogous reaction of azides. This highly specific modular labeling strategy can be applied for direct labeling of proteins and for live cell imaging of cancer cells.     

A new strategy for synthesis of branched cyclic peptide by Asn side-chain hydrazide ligation

Here, we report a new strategy for rapid synthesis of branched peptide by side-chain hydrazide ligation at Asn. The hydrazide was converted to thioester at Asn side chain by NaNO₂ and thiol reagent, and sequential ligation with an N-terminus Cys-peptide efficiently afforded the branched peptide. A branched cyclic peptide was successfully synthesized by side-chain ligation with a two-Cys-peptide and formation of a disulfide bond. This approach provides a new way for expeditious synthesis of branched peptides and facilitates the design of neopeptides as functional bio-mimics.     

Dimethyl isotope labeling assisted de novo peptide sequencing

Here, we explore a de novo sequencing strategy in which we combine Lys-N protein digestion with differential isotopic dimethyl labeling to facilitate the (de novo) identification of multiply charged peptides in ESI-MS, both under CID and ETD conditions. For a large fraction of the Lys-N generated peptides, all primary amines are present at the N-terminal lysine, enabling specific labeling of the N-terminus. Differential derivatization of only the peptide N-terminus in combination with the simultaneous fragmentation of the corresponding isotopologues allows the straightforward distinction of N-terminal fragments from C-terminal and internal fragments. Furthermore, also singly and multiply charged N-terminal fragments can easily be distinguished due to the mass differences of the isotope labeled fragment pairs. As a proof of concept, we applied this approach to proteins isolated from an avocado fruit, and were able to partially de novo sequence and correctly align, with green plant homologues, a previously uncharacterized avocado ascorbate peroxidase.     

Synthesis of the chlorofusin cyclic peptide

An efficient and convergent solution-phase synthesis of the cyclic peptide of the natural product chlorofusin, a reported inhibitor of the MDM2-p53 interaction, is detailed.     

Synthesis of water-soluble scaffolds for peptide cyclization, labeling, and ligation

The synthesis and applications of water-soluble scaffolds that conformationally constrain side chain unprotected linear peptides containing two cysteines are described. These scaffolds contain a functionality with orthogonal reactivity to be used for labeling and ligation. This is illustrated by the chemical ligation of two dissimilar constrained peptides via oxime ligation or strain-promoted azide-alkyne cycloaddition in aqueous media.     

Prepatellamide A, a new cyclic peptide from the ascidianLissoclinum patella

A new cyclic peptide, prepatellamide A (1), along with three known cyclic peptides (2)— (4), was isolated from the ascidianLissoclinum patella. The structure of prepatellamide A was determined from one- and two-dimensional¹H and¹³C NMR spectra. The known cyclic peptides were identified as patellamides A (2), B (3) and C (4).     

A synthesis of RGD model cyclic peptide by palladium-catalyzed carbonylative macrolactamization

Cyclic peptidic RGD models were efficiently synthesized by Pd(P(t-Bu)3)2-catalyzed carbonylative macrolactamization in the presence of 4 A molecular sieves under 10 atm of carbon monoxide.     

Structural requirements for the biosynthesis of backbone cyclic peptide libraries

BACKGROUND: Combinatorial methods for the production of molecular libraries are an important source of ligand diversity for chemical biology. Synthetic methods focus on the production of small molecules that must traverse the cell membrane to elicit a response. Genetic methods enable intracellular ligand production, but products must typically be large molecules in order to withstand cellular catabolism. Here we describe an intein-based approach to biosynthesis of backbone cyclic peptide libraries that combines the strengths of synthetic and genetic methods. RESULTS: Through site-directed mutagenesis we show that the DnaE intein from Synechocystis sp. PCC6803 is very promiscuous with respect to peptide substrate composition, and can generate cyclic products ranging from four to nine amino acids. Libraries with five variable amino acids and either one or four fixed residues were prepared, yielding between 10(7) and 10(8) transformants. The majority of randomly selected clones from each library gave cyclic products. CONCLUSIONS: We have developed a versatile method for producing intracellular libraries of small, stable cyclic peptides. Genetic encoding enables facile manipulation of vast numbers of compounds, while low molecular weight ensures ready pharmacophore identification. The demonstrated flexibility of the method towards both peptide length and composition makes it a valuable addition to existing methods for generating ligand diversity.     

A synthetic strategy for the preparation of cyclic peptide mimetics based on SET-promoted photocyclization processes

A novel method for the synthesis of cyclic peptide analogues has been developed. The general approach relies on the use of SET-promoted photocyclization reactions of peptides that contain N-terminal phthalimides as light absorbing electron acceptor moieties and C-terminal alpha-amidosilane or alpha-amidocarboxylate centers. Prototypical substrates are prepared by coupling preformed peptides with the acid chloride of N-phthalimidoglycine. Irradiation of these substrates results in the generation of cyclic peptide analogues in modest to good yields. The chemical efficiencies of these processes are not significantly affected by (1) the lengths of the peptide chains separating the phthalimide and alpha-amidosilane or alpha-amidocarboxylate centers and (2) the nature of the penultimate cation radical alpha-heterolytic fragmentation process (i.e., desilylation vs decarboxylation). An evaluation of the effects of N-alkyl substitution on the amide residues in the peptide chain showed that N-alkyl substitution does not have a major impact on the efficiencies of the photocyclization reactions but that it profoundly increases the stability of the cyclic peptide.