Alkaloids roseus

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

Vinca alkaloids are derived from the Madagascar periwinkle plant, Catharanthus roseus. The main alkaloids are vincristine, vinblastine and vindesine. Vinca alkaloids are cell-cycle-specific agents and block cells in mitosis. This cellular activity is due to their ability to bind specifically to tubulin and to block the ability of the protein to polymerize into microtubules. This prevents spindle formation in mitosing cells and causes arrest at metaphase. Vinca alkaloids also inhibit other cellular activities that involve microtubules, such as leukocyte phagocytosis and chemotaxis as well as axonal transport in neurons. Side effects of the vinca alkaloids such as their neurotoxicity may be due to disruption of these functions. 

Iridoids and their related alkaloids are widely spread in angiosperms and are found in 13 orders and 70 families including Rutales, Buxales, Hamamelidales, Comales, Loasales, Gentianales, etc. Important iridoids are loganin, found in high amounts in Strychnos nux-vomica and in Catharanthus roseus, and secologanin found especially in Caprifoliaceae. 

The two alkaloids vinblastine and vincristine found in Catharanthus roseus have been recent targets of total synthesis because of their potency in cancer chemotherapy. The reduced tree diagram for the Fukuyama plan to vincristine is shown in Figure 4.66. There are three points of convergence, four branches leading to the target product and four tiers of reaction yields. 

Two deoxygenations of naturally occurring compounds have been reported. Anhydrovinblastine, an important intermediate for the anticancer drug navelbine, was prepared by Doris and coworkers from leurosine, an abundant alkaloid from the Madagascan periwinkle Catharantus roseus, in 70% yield by using Cp2TiCl (Scheme 5) [46]. 

Salutaridinol 7-0-acetyltransferase catalyzes the conversion of the phenanthrene alkaloid salutaridinol to salutaridinol-7-Oacetate, the immediate precursor of thebaine along the morphine biosynthetic pathway in P. somniferum (Fig. 10.7).26 Acetyl CoA-dependent acetyltransferases have an important role in plant alkaloid metabolism. They are involved in the synthesis of monoterpenoid indole alkaloids in medicinal plant species such as Rauwolfia serpentina. In this plant, the enzyme vinorine synthase transfers an acetyl group from acetyl CoA to 16-epi-vellosimine to form vinorine. This acetyl transfer is accompanied by a concomitant skeletal rearrangement from the sarpagan- to the ajmalan-type (reviewed in2). An acetyl CoA-dependent acetyltransferase also participates in vindoline biosynthesis in Catharanthus roseus, the source of the chemotherapeutic dimeric indole alkaloid vinblastine (reviewed in2). Acetyl CoA deacetylvindoline 4-O-acetyltransferase catalyzes the last step in vindoline biosynthesis. A cDNA encoding acetyl CoA deacetylvindoline 4-0-acetyltransferase was recently successfully isolated.27... 

Recently, Cordell and collaborators (51) reported the discovery of (—)-16-epi-(Z)-isositsirikine (48) from the leaves of Catharanthus roseus (L.) G.Don and Rhazya stricta Decaisne, the first isositsirikine-type alkaloid with Z geometry in the C-20 ethylidene side chain. Moreover, they gave reliable structure assignments for (-)-( )-isositsirikine (46) and (—)-16-epi-( )-isositsirkine (47). 

Leurosine (75) (Scheme 20) is the most abundant of the dimeric antitumor alkaloids isolated from Catharanthus roseus G. Don. Several species of Strep-tomyces produced a common metabolite of the alkaloid, and S. griseus (UI1158) was incubated with 400 mg of leurosine sulfate to obtain 28 mg of pure metabolite (180). The metabolite was identified as 76 primarily on the basis of its H-NMR spectrum. The mass spectrum indicated that the metabolite contained one oxygen atom more than 75. The H-NMR spectrum contained all of the aromatic proton signals of the vindoline portion of the molecule, and aromatic proton signals for the Iboga portion of the compound occurred as a doublet of doublets... 

Another cultured cell line of Catharanthus roseus (EU4A), which does not produce detectable amounts of vinblastine and other bisindole alkaloids, was also examined for its ability to transform 78 (183). Cell-free extracts of the culture line were prepared, and the 35,000 X g supernatant solution was used. Incubations with 2r-tritioanhydiovinblastine yielded a mixture from which radioactive vinblastine (52) was isolated. The labeled vinblastine was reisolated after unlabeled carrier was added and rigorously purified by successive thin-layer chromatography, reversed-phase HPLC, and crystallization to constant specific activity. Boiled extracts could not produce labeled 52, thus supporting the involvement of enzymes in the conversion process. 

Rniz-May E, Galaz-Avalos RM, Loyola-Vargas VM. (2009) Differential secretion and accumulation of terpene indole alkaloids in hairy roots of Catharanthus roseus treated with methyl jasmonate. Mol Biotechnol 41 278-285. 

The isolation of the antitumor agents vincaleukoblastine (1) and leuro-cristine (2) from Catharanthus roseus (L.) G. Don has proved to be one of the most important developments in both natural product chemistry and the clinical treatment of cancer during the 1960s to 1980s. More alkaloids (over 90) have been isolated from C. roseus than from any other plant, and because of the complexity of the alkaloid mixture this work has required the most advanced isolation and structure determination techniques. The exceptional interest in the broad spectrum of antitumor activity of these compounds has resulted in numerous achievements in the pharmaceutical, clinical pharmacologic, and therapeutical sciences. Simultaneously, strenuous efforts have been made in three areas of the natural product chemistry (i) elaboration of a practical semisynthesis of... 

Because of the previous inaccurate botanical determination of the Madagascan periwinkle, the alkaloids of this plant were formerly considered as Vinca alkaloids, an erroneous subclassification for alkaloids isolated from a plant belonging to the genus Catharanthus. It also should be noted that the alkaloids of C. roseus containing two different (most commonly indole and dihydroindole) alkaloid building blocks were, and sometimes still are, referred to as dimeric indole alkaloids. It is more accurate to use the term binary or bisindole alkaloids, since chemically these alkaloids are not dimers of two equal subunits, but rather comprised of two (bis) different alkaloid building blocks. 

The occurrence of structurally established bisindole alkaloids in Cath-aranthus roseus (L.) G. Don and in the minor species of Catharanthus, namely, C. lanceus (Boj. ex DC.) Pich., C. longifolius Pich., C. ovalis Mgf., C. pusillus (Murr.) G. Don, and C. trichophyllus (Bak.) Pich, is... 

Alkaloids with Unknown Structures Isolated FROM Catharanthus roseus... 

The almost simultaneous discovery of vinblastine (1) by Noble et al. (57) and by Svoboda and co-workers (58) is one of the the most publicized events in alkaloid chemistry. Since its initial discovery, vinblastine (1) has been reisolated from C. roseus several times (47 9,57-60,) and it has also obtained from C. ovalis (32), C. longifolius (33), and C. trichophyllus (60). The large-scale separation of vinblastine (1) and vincristine (2) from C. roseus received attention from pharmaceutical industries, and several procedures for the separation of these alkaloids have been reported in the patent literature (61-71). 

Vincristine (leurocristine) (2) is present in C. roseus in approximately 0.0003% yield, the lowest level of any medicinally useful alkaloid produced on commercial basis. Since the initial isolation of 2 45), its structure elucidation has been reviewed 1,3). The final confirmation of structure 2 and the determination of the absolute configurations of the stereo centers of vincristine (2) were achieved by X-ray crystallography of its methiodide derivative 79,80). 

Chromatographic separation of the post-leurocristine alkaloid fraction of C. roseus yielded amorphous catharanthamine (9) with a molecular... 

The isolation of Catharine (10), C45H54N40,o, mp 271-275°C, an on-colytically inactive alkaloid, has been reported from several Catharan-thus species C. roseus (29-31), C. ovalis (32), and C. longifolius (33). The structure of Catharine (10) has been elucidated by X-ray crystallography (89-91) of its acetone solvate. Catharine (10) can be obtained by mild oxidation of either leurosine (11) (30) or anhydrovinblastine (8) (92-93). In view of the ease of this oxidation, Catharine (10) may be considered as an artifact of the isolation process. 

The amorphous alkaloid vincathicine (24), C46H56N4O9, initially isolated from C. rose us (37), was suspected to contain an oxindole chromophore. No further work was reported on the structure elucidation of 24 until it was observed that vincathicine (24) could be prepared from leurosine (11) by acid treatment (94,95). Efforts followed by the reisolation of vincathicine (24) from C. roseus led to the unambiguous structure elucidation of this alkaloid (94). 

Vindolicine (32) is an unusual alkaloid, isolated from C. roseus (29,53), whose structure reflects the joining of two vindoline units through con-... 

Since the last major review of the biosynthesis of the monoterpenoid indole alkaloids (97), there have been several full and partial 98-104) reviews of various aspects of the work that has been conducted since 1974. Two major developments have dominated the field in this period, namely, the demonstrations that (i) strictosidine (33) is the universal precursor of the monoterpenoid indole alkaloids and (ii) selected cell-free systems of C. roseus have the ability to produce the full range of alkaloid structure types, including the bisindoles. This section traces some aspects of these developments, paying particular attention to work been carried out with C. roseus, and omitting work, important though it may be, on other monoterpenoid indole alkaloid-producing plants, e.g., Rauwolfia, Campto-theca, and Cinchona. 

This overall biosynthetic scheme is summarized in Scheme 7, and it is well to remember that C. roseus is almost alone as a plant in which this whole pathway can be viewed in its entirety, for most indole alkaloid-containing plants produce only one or two of the major alkaloid classes, and not all four. In addition, C. roseus is without doubt the most economically important of the indole alkaloid-containing plants, and thus studies were, and continue to be, driven by the goal of increasing the availability of the commercially significant alkaloids ajmalicine (39), vinblastine (1), and vincristine (2). 

This review of the biosynthesis of the bisindole alkaloids of C. roseus is organized along a developing biosynthetic pathway, as far as possible, and relies on the notion that the most sophisticated studies are those utilizing the purified enzyme systems. Biosynthetic studies on the other monoterpene indole alkaloids are not reviewed here. 

Studies of conditions for the growth of callus tissue of C. roseus were first reported in 1962 (114) by Babcock and Carew, and analytical work commenced when Carew and co-workers (115) demonstrated that in the presence of 0.5 mg/liter kinetin callus tissue grew rapidly and probably produced vindoline (3), as well as a number of other alkaloids. At the same time, a group at Eli Lilly (116) reported an analysis of the alkaloids of crown gall cultures which had been maintained by Hildebrandt s group... 

Leaf organ cultures of C. roseus have also been described 118). A typical 2.5-g fresh weight inoculum produced 29 g fresh weight of leaf material after 35 days dedifferentiated tissue was absent. The alkaloids found included ajmalicine (39), sitsirikine (48), tetrahydroalstonine (39), serpentine (40), and vindoline (3). 

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). 

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