Corynanthe alkaloids structures

Alkaloids like preakuammicine (Figure 6.79) and akuammicine (Figure 6.75) contain the C10 and C9 Corynanthe type terpenoid units respectively. They are, however, representatives of a subgroup of Corynanthe alkaloids termed the Strychnos type because of their structural similarity to many of the alkaloids found in Strychnos... 

The isolation of cordifoline and related bases led to the prediction of the existence of a common precursor derived by condensation between tryptophan and secologanin. This tetrahydrodeoxycordifoline (TDC) could be (a) a biogenetic cul-de-sac (b) an alternative intermediate to vincoside for some terpenoid indole alkaloids, or (c) the progenitor of a novel range of acidic terpenoid indole alkaloids in which the carboxy group of tryptophan was retained. The last possibility stimulated a search for such alkaloids which was amply rewarded by the discovery in A. rubescens of adirubine (7), 5a-carboxytetrahydroalstonine (102), and 5a-carboxycorynanthine (103), shown to have the tryptophan-based Corynanthe type structures 189,190, and 191, respectively. Surely, with the adoption of modern techniques for... 

This group of alkaloids has two structurally different a. The a of alkaloids found in the genus Cinchona (Ruhiaceae), such as quinine, quinidine, cinchonidine and cinchonine, is L-tryptophan. The j8 is tryptamine and the

[Pg.114]

The stem bark of P. yohimbe (= P. johimbe Corynanthe yohimbe), "yohimbe as it is known in Cameroon, Gabon and Congo is used traditionally as an aphrodisiac and stimulant to prevent sleep (41). The bark contains 1-6% of indole alkaloids, most of which are yohimbane-type alkaloids, the main one being yohimbine [7], which is structurally related to reserpine [8] (89). Yohimbine is a selective inhibitor of a-2- adrenergic receptors and, while at low dose it has hypertensive activity, at high dose it is hypotensive (vasodilation of peripheral vessels). It is the vasodilation of peripheral vessels, and especially vasodilation of the corpus cavemosum, which is the cause of the reputation of yohimbine as an aphrodisiac (90). Tests have shown, indeed, that increased... 

Hydroxy-17-decarbomethoxy-16-dihydro-epiajmalicine (87), Q9H24N2O2, mp 185°C, is a new natural product encountered in the bark of Hunteria zeylanica, a plant endemic to Sri Lanka (78). Structural proof involved the semisynthesis of 87 by oxymercuration of corynantheal. Other indole alkaloids belonging to this class isolated from H. zeylanica included yohim-bol (88) and the new natural product epiyohimbol (89), C19H24N2O, mp 257°C, whose structures were confirmed by comparison with NaBfL reduction products of yohimbone. The fruits of Alstonia macrophylla have... 

Table II tabulates the plant species which contain the complex indole alkaloids. The letters in this table correspond to the various structural types as coded in Figs. 2 and 3. Types I, II, and III are the major variations of the Cfl-Ci 0 unit which, in combination with tryptamine, formally elaborate the three significantly different groups of complex indole alkaloids Corynanthe, Iboga, and Aspidosperma. Such initial classification follows the outline set by Battersby [3, 3a) and others (2, 4, 5). The...

Sarpagine-type indole alkaloids have a structural feature bonding the C-5 and C-16 positions in the Corynanthe-typ monoterpenoid indole alkaloids. This type of compound is distributed not only in Gelsemium plants, but also in many genera in the family of Apocynaceae, Rubiaceae, and Loganiaceae. As shown in Table I, sfac sarpagine-type alkaloids 1-3, 5, 8, and 9 have been isolated from the Gelsemium plants. 

Y. is the main alkaloid of many Aspidosperma species, it also occurs in Rubiaceae such as Corynanthe johimbe i=Pausinystalia) and related trees as well as in some Apocynaceae (e. g., Rauvolfia and Vinca species). Y. is structurally related to the Rauvolfia alkaloids, e. g., reserpine. Y. is the methyl ester of yohimb(in)ic acid (C20H24N2O3, Mr 340.42, mp. 280-300°C). In medicine Y. is used especially in the form of its more water-soluble hydrochloride (decomp. at 302 °C) as a... 

Biogenetic Pathways of the Corynanthe-Aspidosperma and Iboga-type Partial Structures of Monoterpenoid Indole Alkaloids (Carbons indicated by a dotted line may be omitted)... 

Rhynchophylline is composed of tryptamine and a Cjo unit with the corynanthe skeleton. Thus, the partial structure of this alkaloid somewhat resembles those of reserpine (Seaion 2.10) and yohimbine (Section 2.11), although its biological aaivities are different. Unlike reserpine, rhynchophyUine does not cause sedative activity, and, unlike yohimbine, no convulsive activity occurred when it was given to frogs and mice. In addition, unlike reserpine. 

The structure of guettardine (72), isolated from Guettarda heterosepala, suggests that this alkaloid may represent an intermediate between the Corynanthe and cinchonamine types of alkaloids (Herbert, 1986). If so, cleavage of the p-carboline system must precede the formation of the quin-uclidine ring (Fig. 34.20) (Herbert, 1986). 

Most L-tryptophan-derived secondary products still possess the indole ring system of this amino acid. Some compounds, however, are quinoline, pyrrole or benzene derivatives. Additional rings may be present yielding complicated structures, like that of ergoline and / -carboline alkaloids (cf. the formulas of ergotamine, Corynanthe, Strychnos, Iboga and Aspidosperma-type alkaloids). 

B, Iridoid Indole Alkaloids. Most jS-carbolines are derived from tryptamine and the iridoid secologanin (D 6.1.2). In dependence on the structure of the iridoid part alkaloids of the Corynanthe-Strychnos type as well as of the Aspidosperma and Iboga types may be distinguished. The latter are formed by rearrangement of the iridoid part which is shown schematically in Fig. 259 and in detail in Fig. 261. 

Two new indole alkaloids, bisnicalaterine D (1), consisting of an ebumane and a corynanthe type of skeletons, and nicalaterine A (2) were isolated from the bark of Hunteria zeylanica. Their structures were elucidated by various spectroscopic data such as NMR and CD spectra. A series of bisnicalaterines and nicalaterine A showed potent anti-plasmodial activity against P. falciparum 3D7 [28]. 

The alkaloids imder discussion share a common Corynanthe-type nucleus derived from secologanin. Yohimbine is a carbocyclic variant of ajmalicine, and the enzymes that convert deglycosylated strictosidine to yohimbine have not been identified [124, 125]. Strychnine and bmcine are synthesized from the preakuammicine structure by hydrolysis, decarboxylation, and condensation reactions to aldehyde (Wieland-Gumlich), and subsequently reaction with acetyl-CoA to make a hemiacetal form of aldehyde (Wieland-Gumlich) and strychnine and brucine. Brucine is a dimethoxy form of strychnine. Ellipticine is a representative member of pyrido[4,3-b] carbozole alkaloid, and the formation of ellipticine is from ajmalicine (corynanthean skeleton) [126] (Fig. 20.8). 

Loganin is an iridoid glucoside which occupies a central position in the biosynthesis of Corynanthe, Aspidosperma, Iboga, Ipecacuanha, Cinchona, and structurally simpler monoterpene alkaloids. For a review of the extensive researches that led to confirmation of the key role of loganin in alkaloid biosynthesis, see A. R. Battersby, Biochem. Soc. Symp., 29, 157 (1970) A. R. Battersby, Chem. Soc. Spec. Period. Rep., 1, 31 (1971) A. I. Scott, Accts. Chem. Res., 3, 151 (1970). For a useful account of the chemistry of iridoid glucosides see, J. M. Bobbitt and K. -P. Segebarth in Cyclopentanoid terpene Derivatives, Eds., W. I. Taylor and A. R. Battersby, Marcel Dekker, New York, 1969, p 1. 

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