Vincristine from catharanthine

Scheme 4.7 Biosynthesis of vinblastine and vincristine from catharanthine and vindoline...

Extensive biotransformation studies have been conducted with the As-pidosperma alkaloid vindoline, but much less work has been done with monomeric Iboga and dimeric alkaloids from this plant. The long-standing interest in this group of compounds stems from the clinical importance of the dimeric alkaloids vincristine and vinblastine, both of which have been used for more than 2 decades in the treatment of cancer. Few mammalian metabolites of dimeric Catharanthus alkaloids have been characterized. Thus the potential role of alkaloid metabolism in mechanism of action or dose-limiting toxicities remains unknown. The fact that little information existed about the metabolic fate of representative Aspidosperma and Iboga alkaloids and Vinca dimers prompted detailed microbial, mammalian enzymatic, and chemical studies with such compounds as vindoline, cleavamine, catharanthine, and their derivatives. Patterns of metabolism observed with the monomeric alkaloids would be expected to occur with the dimeric compounds. 

Goodbody and co-workers (7/9) have examined the production of alkaloids in root and shoot cultures induced from seedlings of C. roseus. The pattern of alkaloids in the root cultures was similar to that of the roots from intact plants. Thus ajmalicine (39) and catharanthine (4) were produced, but no vindoline (3), a major leaf alkaloid, and no bisindole alkaloids. Similarly, the pattern of the alkaloid content of the shoot cultures was like that of the leaves of the intact plant, showing the presence of vindoline (3), catharanthine (4), and ajmalicine (39), with 3 predominating. A search for the bisindole alkaloids in the cultures indicated the presence of anhydrovinblastine (8) and leurosine (11) in the shoot cultures (2.6 and 0.3 xg/g fresh weight, respectively), but no vinblastine (1) or vincristine (2). 

The enzyme-catalyzed formation of anhydrovinblastine (8) from catharanthine (4) and vindoline (3) was first examined by Kutney and co-workers (170,219) using a cell-free preparation. [ao f- H]Catharanthine (4) and [acety/- C]vindoline (3) were incubated for 3-8 hr, both separately and jointly with a preparation from C. roseus, which led to the isolation of labeled anhydrovinblastine (8) and leurosine (11) incorporations were of the order of 0.54 and 0.36%, respectively. On this basis, anhydrovinblastine (8) was proposed as the key biosynthetic intermediate en route to vinblastine (1) and vincristine (2). 

The extremely low yield of vincristine (2) from intact plants has made pursuit of its biosynthesis a very challenging problem, which at this point in time remains unsolved. Kutney et al. have used both anhydrovinblastine (8) (227) and catharanthine N-oxide (107) (233) as precursors to vincristine (2) in a cell-free preparation, but incorporation levels were extremely low. Therefore, the question of whether vinblastine (1) is an in vivo, as well as an in vitro, precursor remains to be answered. Several possibilities exist for the overall oxidation of vinblastine (1) to vincristine (2), including a direct oxidation of the A-methyl group or oxidative loss of the N-methyl group followed by N-formylation. 

Within the natural products field, the investigation of complete biosynthetic pathways at the enzyme level has been especially successful for plant alkaloids of the monoterpenoid indole alkaloid family generated from the monoterpene gluco-side secologanin and decarboxylation product of tryptophan, tryptamine [3-5]. The most comprehensive enzymatic data are now available for the alkaloids ajmalicine (raubasine) from Catharanthus roseus, and for ajmaline from Indian Rauvolfia serpentina [6] the latter alkaloid with a six-membered ring system bearing nine chiral carbon atoms. Entymatic data exsist also for vindoline, the vincaleucoblastin (VLB) precursor for which some studies on enzymatic coupling of vindoline and catharanthine exist in order to get the so-called dimeric Catharanthus indole-alkaloids VLB or vincristine [7-9] with pronounced anti-cancer activity [10, 11]. 

If the C-15, C-16 bond is oxidatively cleaved, the secodine skeleton results (the proposed progenitor of the Aspidosperma and the iboga systems) through alternative Diels-Alder type cyclizations to afford tabersonine and catharanthine. The bisindole alkaloids of Catharanthus roseus reflect the union of vindoline and catharanthine to afford anhydrovinblastine modification affords the clinically significant alkaloids, vinblastine (VLB) and vincristine (VCR Fig. 39). The alkaloids, particularly VCR, are important as anticancer agents and have led to the development of the semisynthetic derivatives vindesine and vinorelbine (Fig. 40). Synthetic approaches are available to join the monomeric precursors. The enzymatically controlled sequence of reactions from tabersonine to vindoline has been elucidated. 

This reaction has been extensively studied in the case of the chlopromazine radical (R -mediated aminopyrine (S) oxidation [41], a typical reaction for xenobiotics, as well as in the case of the vindoline radical (R -mediated catharanthine (S) oxidation [42], a key reaction in the biosynthesis of the anticancer drugs, vinblastine and vincristine, which are obtained from Catharanthus roseus. 

Catharanthine (LIV) and vindoline (Lin) are regarded as the monomeric precursors of the dimeric alkaloids vinblastine and vincristine, via a-3 ,4 -anhydrovinblastine. C. roseus peroxidase catalyzes the coupling reaction of catharanthine and vindoline (Scheme XXVI) to lead to a-3 ,4 -anhydrovinblastine (XLVH) or, more properly, to an iminium intermediate (LVI) from which a-3 ,4 -anhydrovinblastine is directly derivated [52,74,166]. a-3 ,4 -Anhydrovinblastine is then converted to vinblastine (XLIX, R = CH3) and vincristine (XLIX, R = CHO) in C. roseus plants [167-169], a-3 ,4 -Anhydrovinblastine (XLVn), or the unstable iminium intermediate (LVI) formed during the coupling reaction, is then assumed to be the precursor of all dimeric alkaloids in C. roseus. 

The chemical coupling of catharanthine and vindoline to yield anhydrovinblastine led to the obvious hypothesis that this compound might also be the first product of dimerization in the plant, and the dimeric precursor of vinblastine and vincristine. For three years it was not possible to find anhydrovinblastine in the plant, until Scott et al. in 1978 [115], by modifying the established methods for extraction and purification of alkaloids, isolated anhydrovinblastine from C. roseus plants, with incorporation of radiolabelled catharanthine and vindoline, thus proving that anhydrovinblastine was actually a natural product. 

In literature very little is published on the extraction of alkaloids on an industrial scale. The few papers available were published between 1950 and 1970 and concern the isolation of alkaloids from whole plants or plant parts 168,169). The extraction of catharanthine and vinblastine from C. roseus leaves on a pilot plant scale is described by Atta-ur-Rahman et al. (170). Svoboda developed a method for the extraction of ajmalicine, vinblastine, and vincristine which has been used by Eli Lilly Co. (169,171-173). Supercritical fluid extraction is a method which is used for the extraction of caffeine from coffee beans. This method also seems of interest for further studies of other alkaloids. 

C43H50N4O6, Mr 718.89, dark red cryst., mp. 179 C (decomp.), [a]o -550° (C2H5OH). Cytotoxic alkaloid from the European periwinkle, Vmca minor (Apocy-naceae). Like the Vinca alkaloids, vinblastine and vincristine, V. consists of a catharanthine and a vin-doline part, but being connected in the 10-position. IM. Planta Med. 54, 214 (1988). - (CAS 107290-03-9]... 

Vinblastine (117) and vincristine, well-known antitumor bisindole alkaloids, are biogeneticaUy derived from the coupling of vindoHne (123, Aspi-dospema type) and catharanthine (124, Iboga type). Recent progress (since a comprehensive review by Kam and Choo ) on the chemistry of these alkaloids is described in this section. 

Both vindoline (9) and catharanthine (10) are of great importance, as coupling of these two compounds (possibly via an iminium intermediate) leads to 3, 4 -anhydrovinblas-tine (57), a direct precursor to both vinblastine (57) and vincristine (56) (Fig. 34.15) (Blasko and Cordell, 1990 Stuart et al., 1978). Enzymes from cell-free systems of Catharanthus roseus have been demonstrated to carry out this coupling (Endo et al., 1988). The reaction also can be catalyzed by horseradish peroxidase (Goodbody et al, 1988) or... 

A key intermediate in the biosynthesis of all iridoid indole alkaloids is the glu-coside strictosidine (isovincoside. Fig. 260). Strictosidine is transformed to aj-malicine, which is a precursor of stemmadenine, tabersonine, vindoline and catharanthine (Fig. 261). The dimeric alkaloids, like vinblastine (vincaleuco-blastine) and vincristine (Fig. 259) are derived from monomeric precursors, e.g. catharanthine and vindoline. 

Two vinca alkaloid anticancer drugs (vincristine and vinblastine) and two precursors (catharanthine and vindoline) were extracted fixm periwinkle leaves and separated on a Cjg column k = 2S4 nm). Good resolution and complete elution were achieved in 15 min using a 62/38/0.3 water (0.1M phosphate buffer at pH 4.14)/acetonitrile/acetic acid mobile phase [1395a]. Linear response was reported over the range from 0.25-25 pg injected. 

L-Tryptophan is an indole ring containing aromatic amino acid derived via the shikimate pathway. The tryptophan-derived alkaloids are found in eight families, of which, Apocynaceae, Loganiaceae, Rubiaceae, and Nyssaceae are the best sources. The alkaloids under discussion are the Catharanthus alkaloids, namely, ajmalicine, tabersonine, catharanthine, vindoline, vinblastine, vincristine and vincamine as well as terpenoid alkaloids derived from other families, namely, yohimbine, reserpine, strychnine, brucine, and ellipticine. The above-mentioned alkaloids are pharmacologically very important and hence extremely valuable. This chapter describes various aspects of the tryptophan-derived alkaloids like occurrence, biological activity, phytochemistry, and commercial and biotechnological aspects. 

Vinblastine and vincristine are synthesized from monomers catharanthine and vindoline. Vinblastine and vincristine differ in the nature of the substituent group on the dihydroindole moiety, which is either a methyl group (vinblastine) or a formyl group (vincristine) [20]. 

Catharanthine is reported to stimulate the release of amylase from pancreatic fragments by causing an increase in cytoplasmic and cause extensive degran-ulatirm of pancreatic acinar cells with accumulation of membrane material in the Golgi region. Catharanthine is also reported to be the indole part of vinblastine and vincristine required for interaction to tubulin [35, 36],... 

Initially, vincristine and vinblastine were isolated from leaves of the Madagaskar periwinkle, however, the yield was very low. The plant tissue contains only 0.0002% vinblastine (Noble, 1990), and the vincristine content is even lower. Therefore, a partial synthesis for the dimeric indole alkaloids was developed starting from the monomers vindoline and catharanthine (Dewick, 2002). 

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