Taxol isolation

Figure 2.2 Taxol, isolated from the bark of the Pacific yew...

Confirmation of taxol production by H10BA2 followed the protocol established in our investigation of taxol production by T. andreanae [1]. HPLC columns were calibrated with authentic taxol to determine retention times, and appropriate fungal eluants were examined by TLC, CIEIA and mass spectrometry [1]. Comparison of fast atom bombardment (FABMS) and electrospray mass spectrometry (ESMS) of yew-derived taxol (provided by Bristol Myers Squibb) with taxol isolated from P. raistrickii using CIEIA-guided fractionation showed that these metabolites are... 

Plants have also provided a key source of potential cancer treatments. A well-known example is paclitaxel (Taxol ), isolated from the bark of the Pacific yew tree, which has become a blockbuster drug and analogues have also been approved for use that demonstrate improved efficacy (Fig. 1.4) [6]. Taxol also provides an excellent example to illustrate the challenges that remain in total synthesis. Numerous examples of the total synthesis of Taxol have been reported [7-13]. However, the overall yield and the number of steps required means it is not economically viable to synthesise the quantities required for its medicinal application. It is therefore obtained industrially via a semi-synthetic route starting from 10-deacetylbaccatin HI, a biosynthetic precursor, which can be isolated, in much larger quantities than Taxol itself, from the leaves of a different species of yew tree. More recently however, a plant cell fermentation approach has been developed for the industrial production of Taxol. 

Taxol, isolated from Taxus brevefolia. Vincristine and Vinblastine isolated from Vinca rosea, and Taxotere, a semisynthetic form of Taxol, can induce Bcl-2 phosphorylation in tumor cell lines. The antiapoptotic potential of Bcl-2 has now been well established. But the biochemical mechanism of Bcl-2 action is still poorly understood (45). Haidar et al have shown that phosphorylated Bcl-2 can no longer prevent lipid peroxidation as required to protect cells from apoptosis (46). We have isolated and identified a novel polyphenol from Licorice that induces apoptosis, phosphorylating anti-apoptotic protein Bcl-2, causes G2/M cell cycle arrest in breast and prostate cancer cell lines (31). 

A new antitumor drug, taxol, has been isolated from the bark of Taxus brevifolia, the Pacific yew tree. Like vinblastine and colchicine, taxol inhibits cell replication by acting on microtubules. Unlike these other antimitotic drugs, however, taxol stimulates microtubule polymerization and stabilizes microtubules. 

Camptothecin was discovered as an active anticancer drug isolated from the bark of Camptotheca acuminata. The anticancer activity of camptothecin was discovered in the 1960s by the National Cancer Institute (NCI) as part of a systematic effort to screen for novel anticancer agents derived from natural products. Monroe Wall and Mansuhk Wani identified the chemical structure of camptothecin. They also identified the chemical structure of taxol, again under the auspices of the NCI. Susan Hoiwitz was contracted by the NCI to elucidate the anticancer mechanisms of camptothecin. She found in the early 1970s that camptothecin induced DNA breaks and attested DNA and RNA synthesis. However, it is approximately 12 years later, only after DNA topo-isomerase I (Topi) had been identified in human cells, that Leroy Liu and his coworkers found that Topi was the cellular target of camptothecin [reviewed in [1]. 

Wani MC, Taylor HL, Wall ME, Coggon P, McPhail AT. Plant antitumor agents. VI. The isolation and structure of taxol, a novel antileukemic and antitumor agent from Taxus brevifolia. J Am Chem Soc 1971 93 2325-7. 

The epothilones are natural products containing a 16-membered lactone ring that are isolated from mycobacteria. Epothilones A-D differ in the presence of the C(12)-C(13) epoxide and in the C(12) methyl group. Although structurally very different from Taxol, they have a similar mechanism of anticancer action and epothilone A and its analogs are of substantial current interest as chemotherapeutic agents.36 Schemes 13.59 to 13.66 summarize eight syntheses of epothilone A. Several syntheses of epothilone B have also been completed.37... 

Besides their essential roles in nature, isoprenoids are of commercial importance in industry. Some isoprenoids have been used as flavors, fragrances, spices, and food additives, while many are used as pharmaceuticals to treat an array of human diseases, such as cancer (Taxol), malaria (artemisinin), and HIV (coumarins). In contrast to the huge market demand, isoprenoids are present only in low abundance in their host organisms. Thus, isolation of the required isoprenoids consumes a large quantity of natural resources. Furthermore, owing to their structural complexity, total chemical synthesis is often not commercially feasible. For these reasons, metabolic engineering may provide an alternative to produce these valuable isoprenoids [88,89]. 

By using an elegant 13C-labeling study that involved incubation of Phoma sp. with 1-13C and 1,2-13C acetate, Oikawa et al. [9], were able to isolate the proposed biosynthetic intermediate phomactatriene (or Sch 49026), with 13C incorporation from singly labeled acetate units as indicated by in Fig. 8.3. Phomactatriene is strikingly reminiscent of taxadiene, a biosynthetic intermediate for Taxol . The net biosynthesis for both involves geranylgeranyl diphosphate (GGDP) cyclization [9]. It is noteworthy that prior to isolation of phomactins, the only known related structure is cleomeolide, a diterpene from the herb Cleome viscosa [10] that remarkably resembles phomactin H. 

There are natural targets whose syntheses have important practical applications. For example, paclitaxel (marketed as Taxol by Bristol-Myers Squibb) is an anticancer compound originally isolated from the bark of a species of yew tree, but for a long time it seemed that natural sources would not be sufficient to meet the need. Consequently, many chemists developed synthetic approaches to paclitaxel from readily available materials, although these are not yet fully practical for manufacturing. The quest continues, and a semisynthetic route has been developed starting with a compound isolated from yew needles that can be harvested without destroying the tree. An alternative approach has employed plantcell cultures in bioreactors to produce paclitaxel from yew needles (see Chapter 7 for discussion of related matters). 

Epothilones A, B and E (4,5 and 6) (Fig. 2) are representative members of a new class of bacterially derived natural products which exhibit potent biological activity. Isolated by Hofle and coworkers [6] from a soil sample collected near the Zambesi river, the compounds have provided a great deal of excitement in the scientific community due to their potent cytotoxicity against a number of multiple drug-resistant tumor cell lines and because of the mechanism by which they exert this effect. Like Taxol [7], the epothilones promote the combination of a- and 3-tubulin subunits and stabilize the resulting microtubule structures. This mode of action inhibits the cell division process and is, therefore, an attractive strategy for cancer chemotherapy [7,8]. 

Since the discovery of the anticancer potential of Taxol , a complex compound isolated from the bark extract of the Pacific yew tree, more than 20 years ago, there has been an increasing demand for the clinical application of this compound. First, the promising results of the 1991 clinical trials in breast cancer patients were announced, and soon after Bristol-Myers-Squibb trade-marked the name Taxol and used it as an anticancer drug. At that point, the only source of the drug was the bark of the endangered yew tree. Fortunately, it was soon discovered that a precursor of Taxol could be obtained from an extract of the tree needles instead of the bark. 

Since the discovery of the high anticancer activity of taxol, much attention has been drawn to its asymmetric synthesis. The total synthesis stood for more than 20 years as a challenge for organic chemists. The compound taxoids are diterpenoids isolated from Taxus species and have a highly oxidized tricyclic carbon framework consisting of a central eight-membered and two peripheral six-membered rings (see Fig. 7-2).21... 

A fine example of such a semi-synthesis is the preparation of the anti-cancer drug paclitaxel (Taxol ), a relatively scarce compound from Taxus brevifolia. Here, the natural and better accessible 10-deacetylbaccatin III, isolated from the leaves of Taxus baccata, provides the complicated ring system of paclitaxel, including all substituents with the right stereostructure (Scheme 5.1). In just four reaction steps [5] paclitaxel is obtained from 10-deacetylbaccatin III. 

Taxol i is a naturally occurring substance isolated from the Pacific yew tree Taxus brevifolia), which has been approved for clinical treatment of cancer patients. Taxol enhances polymerization of tubuhn and the consequent formation of stable microtubules, inhibiting cellular mitosis. 

These proteins can be isolated along with taxol-stabilized microtubules (Vallee, 1982), and they appear to be microtubule-assodated proteins which are specific to differentiated neuroblastoma cells (Olmsted and Lyon, 1981). Their role(s) remain to be established... 

Paclitaxel (21), formerly known as taxol , is a nitrogen-containing diterpenoid compound isolated from the bark of Taxus brevifolia Nutt. (Pacific yew). As an anticancer agent, paclitaxel acts as a tubulin stabilizer and leads to cell cycle arrest.Since paclitaxel was originally isolated from the bark of the slow-growing species, 77 brevifolia, sourcing was a major obstacle in the development of this drug and its introduction into the market.However, as described later in this chapter, this has now been overcome. 

Guo BH, Wang YC, Zhou XW, Hu K, Tan F, Miao ZQ, Tang KX, An endophytic Taxol-producing fungus BT2 isolated from Taxus chinensis var. mairei, African J Biotech 5 875-877, 2006. 

P-1534 leukemia, the Walker 256 carcinosarcoma, and the P388 leukemia. He also worked on isolation by extraction of 12 kg of Pacific yew bark with ethanol, followed by partition of the ethanol extract between chloroform and water. In his first publication in 1967, about 0.5 g of taxol was isolated from 12 kg of air-dried stem and bark from T. brevifolia, and the yield was about 0.004%, or 40 ppm. 

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