Chemistry and Biology of Taxol

One can view plants as a reference library of compounds waiting to be searched by a chemist who is looking for a particular property. Taxol, a complex polyoxygenated diterpene isolated from the Pacific Yew, Taxus brevifolia, was discovered during extensive screening of plant materials for antineoplastic agents during the late 1960s. Over the last two decades, interest in and research related to taxol has slowly grown to the point that the popular press now seems poised to scoop each new development. What was once an obscure compound, of interest only to the most masochistic of synthetic chemists and an equally small number of cellular biologists, has become one of the few organic compounds, which, like benzene and aspirin, is recognizable by name to the average citizen. In parallel, the scientific study of taxol has blossomed. Physicians are currently studying its effects on nearly every known neoplasm. Biologists are using taxol to study the mechanisms of cell function by observing the effects of its interactions with the cellular skeletal systems. Synthetic chemists, absorbed by the molecule's unique and sensitive structure and functionality, are exploring seemingly every available pathway for its synthesis. Indeed, the demand for taxol has risen so in the last five years that alternative sources to the extraction of T. brevifolia are being vigorously pursued. Because of the rapidly expanding scope of research in the multifaceted study of taxol, those who are interested in the field may find acquisition of a reasonable base of knowledge an arduous task. For this reason, this account attempts to bring together, for the first time, in a cogent overview the chemistry and biology of this unique molecule.     

The Conquest of Taxol

Much has been written about taxol, one of the newest weapons against cancer, and its producer, the Pacific Yew tree (Taxus brevifolia).

1 K. C. Nicolaou, W.-M. Dai, R. K. Guy, Angew. Chem. 1994, 106, 38–69; Angew. Chem. Int. Ed. Engl. 1994, 33, 15–44.

In this article, the authors give a frank and behind-the-scenes account of their encounter with this well-known molecule, which they and their collaborators faced as a synthetic target.

2 K. C. Nicolaou, Z. Yang, J.-J. Liu, H. Ueno, P. G. Nantermet, R. K. Guy, C. F. Claiborne, J. Renaud, E. A. Couladouros, K. Paulvannan, E. J. Sorensen, Nature (London) 1994, 367, 630–634.

3 K. C. Nicolaou, J.-J. Liu, Z. Yang, H. Ueno, R. K. Guy, E. A. Couladouros, E. J. Sorensen, J. Am. Chem. Soc. 1995, 117, 624–633.

4 K. C. Nicolaou, J.-J. Liu, Z. Yang, H. Ueno, E. J. Sorensen, C. F. Claiborne, R. K. Guy, C.-K. Hwang, M. Nakada, P. G. Nantermet, J. Am. Chem. Soc. 1995, 117, 634–644.

5 K. C. Nicolaou, Z. Yang, J.-J. Liu, P. G. Nantermet, C. F. Claiborne, J. Renaud, R. K. Guy, K. Shibayama, J. Am. Chem. Soc. 1995, 117, 645–652.

6 K. C. Nicolaou, H. Ueno, J.-J. Liu, P. G. Nantermet, Z. Yang, J. Renaud, K. Paulvannan, R. Chadha, J. Am. Chem. Soc. 1995, 117, 653–659.

Once again total synthesis is found to offer excellent opportunities for developing new synthetic strategies and novel reactions. The team of chemists who took up this challenge emerged with valuable experience and confidence in their skills.     

Total Synthesis of Taxol Enabled by Inter- and Intramolecular Radical Coupling Reactions

Taxol is a clinically used drug for the treatment of various types of cancers. Its 6/8/6/4-membered ring (ABCD-ring) system is substituted by eight oxygen functional groups and flanked by four acyl groups, including a β-amino acid side chain. Here we report a 34-step total synthesis of this unusually oxygenated and intricately fused structure. Inter- and intramolecular radical coupling reactions connected the A- and C-ring fragments and cyclized the B-ring, respectively. Functional groups of the A- and C-rings were then efficiently decorated by employing newly developed chemo-, regio-, and stereoselective reactions. Finally, construction of the D-ring and conjugation with the β-amino acid delivered taxol. The powerful coupling reactions and functional group manipulations implemented in the present synthesis provide new valuable information for designing multistep target-oriented syntheses of diverse bioactive natural products.     

Models for Taxol Biosynthesis: SeO2 Oxidation of Taxadiene

Together with the expected mono‐oxidized taxa‐4(20),11(12)‐diene‐5‐ol (1) and taxa‐4(5),11,20‐diene‐20‐ol (2), a new taxane skeleton, 3,12‐cyclotaxane (3), was obtained from chemical oxidation of taxadiene by selenium dioxide/t‐butylhydroperoxide.     

紫杉醇全合成

评论了紫杉醇合成了合成战略，合成路线，逆合成分析及展望，参考文献９篇。     

血清白蛋白对紫杉醇的化学修饰

采用两种方法由牛血清白蛋白和人血清白蛋白修饰紫杉醇,提高了水溶性.红外和紫外数据证实了修饰结果.     

Solid-state NMR studies of the molecular structure of Taxol

Solid-state 13C{1H} cross-polarization/magic angle spinning spectroscopy (CP/MAS) has been utilized to extract the molecular structure information of Taxol, which is an anti-tumor therapeutic medicine extracted from the yew bark. The 13C signals have chemical shift values quite consistent with those measured in solution phase, and the overall chemical shift range is over 200 ppm. Notably, most of the 13C resonances of the taxane ring have two clearly resolved spectral components except the resonance peaks of C-15, C-16 and C-17, which are located at the central part of the taxane ring. On the basis of our NMR data, we propose that these doublets originate from two slightly different molecular conformations of the taxane ring and still the central part of the ring remains structurally similar. Furthermore, it is demonstrated that the 13C chemical shift difference deduced from the doublet splittings can serve as a direct measure of the structural difference between the two conformations, which could possibly correlate with the anti-tumor activity of Taxol.     

薄层色谱法分离紫杉醇和三尖杉宁碱

建立了用薄层色谱分离紫杉醇和三尖杉宁碱的方法.方法中以正己烷-二氯甲烷-甲醇-三乙胺(体积比4.5∶3.5∶0.5∶1.0)四元体系为展开剂,在硅胶薄层板上成功地分离了紫杉醇和三尖杉宁碱,所得斑点清晰、无拖尾.同时以该体系为展开剂,使用薄层色谱法指导分离提取紫杉醇和三尖杉宁碱过程中反相色谱流分的合并,方法快速、简单、成本低,取得了满意的结果.     

紫杉醇构效关系研究新进展

综述了近年来在紫杉醇类似物构效研究中的最新进展,按照紫杉醇的A,B, C,D环修饰的顺序总结了新得到的40余种紫杉醇类似物结构与其生物活性之间的关系。     

Synthesis of novel thiol surrogate of Taxol: 2′-deoxy-2′-mercaptopaclitaxel

Paclitaxel analogues with a thiol group in place of the hydroxyl group on the C-13 side chain constitute an interesting avenue of research for the study of new taxoid compounds. A synthetic route for the preparation of the exact thiol surrogate product of Taxol^® by coupling (4S, 5S)-2,4-diphenyloxazoline-5-carboxylic acid with 7-triethylsilyl baccatin III, followed by ring-opening of the oxazoline intermediate with thiolacetic acid is described.     

微管蛋白聚合及其与紫杉醇作用的量热学研究

微管作为细胞骨架的主要成分之一，在细胞内执行许多功能.微管是一个动态的结构，既参与细胞运动和细胞内物质运输［‘个又感受、转导外界信号问的刺激产生相应灵敏的反应.尤其它是许多药物，如：紫杉醇（Taxol）、秋水仙素（Colchicine）、等作用的靶子问，因而，微管已成为筛     

A Tubulin‐Based Quantitative Assay for Taxol (Paclitaxel) with Enzyme Channeling Sensing

We report the development and characterization of a biosensor for sensitive and rapid determination of the anticancer agent Taxol (paclitaxel). The sensor is based on the interaction of Taxol with its receptor protein tubulin in conjunction with the separation‐free immunosensor technique of enzyme channeling. The sensor system consisted of a three electrode electrochemical cell containing a graphite carbon electrode modified with glucose oxidase and tubulin as working electrode poised at +40 mV (vs. Ag/AgCl). Addition of Taxol, horseradish peroxidase labeled Taxol, glucose and potassium iodide to the cell generated a cathodic current response that was proportional to the concentration of Taxol in the range of 10 to 1 000 pM.     

高效液相色谱法测定红豆杉培养细胞中紫杉醇的含量

采用Ｓｐｈｅｒｉｓｏｒｂ Ｃ_６Ｈ_５柱,以甲醇：乙腈：水（２：３：８．５）为流动相,在２２８ｎｍ波长下检测,对３种红豆杉即云南红豆杉（Ｔａｘｕｓ ｙｕｎｎａｎｅｎｓｉｓ）、红豆杉（Ｔ．ｃｈｉｎｅｎｓｉｓ）和欧洲红豆杉（Ｔ．ｂａｃｃａｔａ）培养细胞中紫杉醇（Ｔａｘｏｌ）的含量进行了测定。建立了一套简单、快速、准确的测定红豆杉培养细胞中紫杉醇的高效液相色谱方法,最低检出量可达０．５μｇ。     

正相色谱和反相色谱法分离提纯东北红豆杉中紫杉醇和三尖杉宁碱

以东北红豆杉树叶为原料,采用正相色谱和反相色谱法分离提纯了紫杉醇和三尖杉宁碱。反相色谱中使用了一种新颖的高分子填料。东北红豆杉枝叶经过一次正相色谱分离后,再经两次反相色谱分离,分离得到两种白色针状固体。经1H NMR和13C NMR测试表明,两种物质分别为紫杉醇和三尖杉宁碱,纯度达到98%以上,产率分别为树叶干重的0.0022%和0.0018%,回收率大于70%。     

微管蛋白的聚合和变性及紫杉醇的影响

微管系统在细胞中执行许多重要功能山．微管在细胞中呈现高度的时间和空间有序性,并与构成它的结构单元—一微管蛋白（土。l｝）lllil。）保持动态平衡,而且这种平衡是局域的和暂时的,Mit（Jlisou和Krscllner根据他们的微管体外实验及体内微管聚合特性称之为微管生长的动态不稳定性＊1．微管的生理功能正是与它的这种根本特性有关．另有研究发现微管是许多药物包括许多抗癌药物作用的靶子问．如紫杉醇（TaX01）＊等．因此国际上研究微管蛋白的聚合过程以及药物分子的作用是微管研究中的热点问题之一．生理状态下微管蛋白以。月异二聚体…     

反相HPLC法分析红豆杉树皮和树叶中紫杉醇及其类似物含量的研究

建立了红豆杉树皮和树叶中紫杉醇及四种类似物１０－脱乙酰浆果赤霉素Ⅲ（１０－ｄｅａｃｅｔｌｙ－ｂａｃｃａｔｉｎⅢ）浆果赤霉素（Ｂａｃｃａｔｉｎ（Ⅲ），脱乙酰－７－表－紫杉醇（１０ｄｅａｃｅｔｙｌ－７－ｅｐｉ－ｔａｘｏｌ）和Ｃｅｐｈａｌｏａｎｎｉｎｅ）的梯度和等梯度高效液相色谱分析方法。     

Formal synthesis of erythrodiene and spirojatamol via rhodium-catalysed Claisen rearrangement/hydroacylation

A novel procedure allows the synthesis of spiro[4.5]decane-1,6-dione 1, a key intermediate in the total synthesis of erythrodiene and spirojatamol. The key step is a combination of Claisen rearrangement of allyl vinyl ethers followed by an intramolecular hydroacylation catalysed by RhCl(cod)(dppe).     

Complete Biochemical Characterization of Pantaphos Biosynthesis Highlights an Unusual Role for a SAM-Dependent Methyltransferase

Pantaphos is small molecule virulence factor made by the plant pathogen Pantoea ananatis. An 11 gene operon, designated hvr for high virulence, is required for production of this phosphonic acid natural product, but the metabolic steps used in its production have yet to be established. Herein, we determine the complete biosynthetic pathway using a combination of bioinformatics, in vitro biochemistry and in vivo heterologous expression. Only 6 of the 11 hvr genes are needed to produce pantaphos, while a seventh is likely to be required for export. Surprisingly, the pathway involves a series of O-methylated intermediates, which are then hydrolyzed to produce the final product. The methylated intermediates are produced by an irreversible S-adenosylmethione (SAM)-dependent methyltransferase that is required to drive a thermodynamically unfavorable dehydration in the preceding step, a function not previously attributed to members of this enzyme class. Methylation of pantaphos by the same enzyme is also likely to limit its toxicity in the producing organism. The pathway also involves a novel flavin-dependent monooxygenase that differs from homologous proteins due to its endogenous flavin-reductase activity. Heterologous production of pantaphos by Escherichia coli strains expressing the minimal gene set strongly supports the in vitro biochemical data.