泛素化蛋白的化学合成及半合成

蛋白质翻译后修饰（post-translational modifications,PTMs）在调节蛋白质的结构和功能上发挥着重要作用,异常的蛋白质翻译后修饰会导致某些疾病的发生.泛素化（ubiquitination）作为一类重要的蛋白质翻译后修饰,已经被证明与细胞的稳态以及细胞内部的多条信号通路有关,主要参与细胞内蛋白的定位、调节和降解以及细胞周期、基因表达、信号传递、损伤修复、炎症免疫等多种生命过程.然而,对于泛素蛋白的相关研究虽然进行了多年,但是许多重要的科学问题尚未研究清楚,其中如何高效地获得大量、均一的泛素化蛋白是最重要的挑战之一.近年来,蛋白质化学合成及半合成手段的发展,很大程度上解决了这一难题.本文主要针对目前常用的泛素化蛋白的化学合成和半合成方法进行综述.     

Isolation and structure elucidation of ovalicin

The structure of ovalicin, a metabolite of the fungus Pseudeurotium ovalis with immunosuppressive activity, has been determined to be 11 .     

Chemical modification and anticancer effect of prenylated flavanones from Taiwanese propolis

Our previous studies demonstrated that eight prenylated flavanones (1-8), isolated from Taiwanese propolis, were capable of a broad spectrum of biological activities. Among them, nymphaeol A (3), nymphaeol B (4) and nymphaeol C (7), abundant in Taiwanese propolis, exhibited cytotoxicity against cancer cell lines. It therefore seemed interesting to improve their activity via a semi-synthetic strategy. In this study, 12 novel prenylated flavanones were synthesised in our laboratory and their activities were assessed for two human prostate cancer cell lines, PC-3 and DU-145, and a human hepatoma cell line, Hep-3B. Of these compounds, 10c, 11 and 12 showed more potent cytotoxicity against the PC-3 cell line than 5-Fu. Using cytometric analysis followed by double staining with annexin V-FITC and propidium iodide, it was observed that these compounds induced apoptosis as well. This suggests that prenylated flavanones 10c, 11 and 12 may have anticancer potential for further development.     

Isolation and structure elucidation of 11-desacetoxywortmannin

The structure of 11-desacetoxy-wortmannin ( 3 ), a new antiinflammatory metabolite of the fungus Penicillium funiculosum THOM, has been elucidated by physico-chemical methods and chemical correlation with wortmannin ( 1 ).     

Optimisation of chemical protein cleavage for erythropoietin semi-synthesis using native chemical ligation

Selective protein cleavage at methionine residues is a useful method for the production of bacterially derived protein fragments containing an N-terminal cysteine residue required for native chemical ligation. Here we describe an optimised procedure for cyanogen bromide-mediated protein cleavage, and ligation of the resulting fragments to afford biologically active proteins.     

Isolation and structure elucidation of ishwarol B

Ishwarol B was isolated from the bark oil of Cedrelopsis grevei and its structure elucidated by 1D and 2D NMR spectroscopy.     

Chemical biology of salinomycin

Cancer stem cells (CSC) have been shown to be refractory to conventional therapeutic agents, can promote metastasis, and have been linked to cancer relapse. The natural product Salinomycin has been identified by means of high throughput phenotypic screening as a selective killer of CSC in vitro and in vivo. In this article we comprehensively review the chemistry of Salinomycin, documenting early total syntheses, along with strategies that have been developed over the years to effectively modify this natural product at key positions with the view to establish a robust structure-activity-relationship and to delineate the complex mechanism of action of this fascinating molecule in the context of cancer research. Then, we document the biology of Salinomycin, putting forward phenotypic alterations that have been observed in the relevant biological models and highlighting how chemistry has been instrumental in discovering unprecedented physiological features of cancer stem cells that can be exploited for therapeutic benefits.     

Artificial chemokines: combining chemistry and molecular biology for the elucidation of interleukin-8 functionality

How can we understand the contribution of individual parts or segments to complex structures? A typical strategy to answer this question is simulation of a segmental replacement followed by realization and investigation of the resulting effect in structure-activity studies. For proteins, this problem is commonly addressed by site-directed mutagenesis. A more general approach represents the exchange of whole secondary structure elements by rationally designed segments. For a demonstration of this possibility we identified the alpha-helix at the C-terminus of human interleukin-8 (hIL-8). Since this chemokine possesses four conserved cysteine residues, it can easily be altered by ligation strategies. A set of different segments, which are able to form amphiphilic helices, was synthesized to mimic the C-terminal alpha-helix. Beside sequences of alpha-amino acids, oligomers of non-natural beta(3)-amino acids with the side chains of canonical amino acids were introduced. Such beta-peptides form helices, which differ from the alpha-helix in handedness and dipole orientation. Variants of the semisynthetic hIL-8 proteins demonstrated clearly that the exact side chain orientation is of more importance than helix handedness and dipole orientation. The activity of a chimeric protein with a beta-peptide helix that mimics the side chain orientation of the native alpha-helix most perfectly is comparable to that of the native hIL-8. Concepts like this could be a first step toward the synthesis of proteins consisting of large artificial secondary structure elements.     

Isolation and elucidation of the structure of homocryptolepinone

The structure of a new indolobenzazepine alkaloid, homocryptolepinone, isolated from extracts of the roots of the indigenous Ghanaian medicinal plant Cryptolepis sanguinolenta, is reported. The structure was determined using mass spectrometric, one-dimensional nOe difference nmr, and inverse-detected two-dimensional nmr experiments which included HMQC, IDR-(Inverted Direct Response)-HMQC-TOCSY, and HMBC experiments. The structure of homocryptolepinone is significant in that it may provide insight into the biogenesis of the benzpyrrolizinobenzazepine portion of the structure of the complex spiro nona-cyclic alkaloid cryptospirolepine previously isolated in these laboratories from C. sanguinolenta, and which has no precedent in alkaloid chemistry.     

Synthesis and structure elucidation of new cytotoxic azathioxanthones

A series of new cytotoxic azathioxanthones 7a-h was synthesized and characterized by their spectral data.     

Quindolinocryptotackieine: the elucidation of a novel indoloquinoline alkaloid structure through the use of computer‐assisted structure elucidation and 2D NMR

Numerous indoloquinoline alkaloid structures have been identified from extracts of the West African plant Cryptolepis sanguinolenta. Recently, through the use of 2D NMR methods and cryogenic NMR probe technology in conjunction with computer‐assisted structure elucidation (CASE) methods, the structures of some chemical degradation products of this family of alkaloids have also been reported. We now report the characterization of a novel indoloquinoline dimeric alkaloid, quindolinocryptotackieine, through the extensive utilization of CASE methods. The NMR data presented here were collected over a decade earlier before the elucidation of the structure was possible, since manual analysis did not present a conclusive structure, whereas CASE produced a series of structures from which the structure could be verified. The original mass spectrometric (MS) data collected for the sample were problematic. Contemporary MS data were instead recollected from remaining small quantities of this alkaloid using modern instrumentation. The re‐collected data gave a usable molecular ion and several key fragment ions that were diagnostically useful. Copyright © 2003 John Wiley & Sons, Ltd.     

New pyrazole-annulated azathioxanthenes as potential intercalators: Synthesis and structure elucidation

As part of our program aiming at developing efficacious intercalating agents, a new series of pyrazole-annulated azathioxanthenes 15a-e has been synthesized. Structure elucidation of 15a-e was based on their spectral data and especially the NOESY nmr spectrum of analog 15a .     

Chemical constituents of Prangos tschiniganica; structure elucidation and absolute configuration of coumarin and furanocoumarin derivatives with anti-HIV activity.

The methanol extract of the dried aerial parts of Prangos tschimganica gave three new coumarin derivatives and 30 known coumarin derivatives. Their structures were established on the basis of chemical and spectroscopic evidence. Absolute configuration of the isolated compounds were determined by using a modified Mosher's method. Some of the isolated compounds showed anti-HIV activity.     

NMR solvent shifts and structure elucidation in coumarins

The use of the solvent shift techniques enables the position of methyl, methoxyl and aromatic protons in coumarins to be determined and should prove a valuable aid to structural elucidation in this class of compounds.     

Applications of a HOUDINI-based structure elucidation system

SESAMI, a comprehensive program for the elucidation of the structure of complex compounds of carbon, incorporates a structure reduction-based structure genearator (COCOA). Observed limitations with this program in the solution of higher molecular weight unknowns prompted the development of a structure generator (HOUDINI) which embodies a new concept, convergent structure generation. A comparison of the performance of COCOA-based and HOUDINI-based SESAMI using a set of complex, naturally occurring compounds as a test set of unknowns revealed faster execution times and more efficient processing of ambiguous structural information for the latter.     

Triterpenoids from Eugenia grandis: structure elucidation by NMR spectroscopy

A new pentacyclic triterpenoid, 2alpha,3beta-dihydroxylup-12-en-28-oic acid (1) and a rarely encountered pentacyclic triterpenoid, 3beta-hydroxylup-12-en-28-oic acid (2), together with five known compounds, friedelin (3), 3beta-friedelinol (4), betulinic acid (5), oleanolic acid (6) and beta-sitosterol (7) were isolated from the chloroform extract of stem bark of Eugenia grandis (Syn: Syzygium grande). The structure and stereochemistry of the new compound (1) and the rarely encountered compound (2) were established by 1D and 2D NMR spectroscopic techniques. All the above isolated compounds from this plant are reported for the first time.     

Crystal structure and spectroscopic elucidation of 3-phenylpyridinium hydrogensquarate

The novel 3-phenylpyridinium hydrogensquarate (1) has been synthesized and its structure and properties are elucidated spectroscopically, thermally and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-spectroscopy, TGA, DSC, DTA and ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectrum. 3-Phenylpyridinium hydrogensquarate, crystallizes in the space group P?1 and the ions in the unit cell are joined into layers by intermolecular NH?OC_(Sq) bonds with bond lengths of 2.625 and 2.626 Å, respectively. Hydrogentartarates form dimers by strong OCOH?OCO interactions (2.499 Å).