Corynantheic acid

The data given in the table for corynanthine are due to Foumeau and Fiore. Raymond-Hamet later found that corynanthine on alkaline hydrolysis gave a dextrorotatory acid, which Scholz confirmed and identified its methyl ester as yohimbine and suggested that corynanthine is a stereoisomeride of yohimbine. Fourneau and Benoit have confirmed that corynanthine on acid hydrolysis gives 1-corynanthic acid (m.p. 284°, [a]i) — 85-9° pyridine), but on alkaline hydrolysis, even in the cold, some racemisation occurs and the resulting acid is of low lasvo-rotation. They also point out that both yohimbine and corynanthine yield yohimbone on dehydrogenation cf., p. 504) and are probably stereoiso-merides. 

A series of publications appeared regarding the transformation of corynanthe-type alkaloids to yohimbane derivatives (285-287). The saponification of cory-nantheine (52) in methanol yielded a complex mixture of corynantheic acid (588), two C-16-epimer acetal acids (589), and demethoxycarbonylcory-nantheine (590). All four compounds upon hydrolysis in acid resulted in cory-... 

Yohimbine Yohimbine is methyl ether ( )-2a-hydroxyyohimban-la-carboxylic acid (12.2.16). It is isolated from the plants Corynanthe johimbe and Rauwolfia serpentina [60,61], It is also synthesized [62-66],... 

The indole nucleus can change during the synthesizing reaction into quinoline nucleus (Figure 32). Moreover L-tryptophan, the precursor, provides both /3-carboline and pyrroloindole nuclei. Iboga, Corynanthe and Aspidosperma nuclei also originate from L-tryptophan (Figure 32). Alkaloids with nuclei derived from this amino acid tend to be very active compounds with a relatively widespread provenance in nature (Table 10). 

Battersby and Co-workers (25-28), Money et al (29) and Leete et al (30) all reported the specific incorporation of [2- C] mevalonic acid and [2- C] geraniol into representative examples of the corynanthe, aspidosperma and iboga groups of alkaloids, and in each case the distribution of radioactivity was in full agreement with the monoterpene hypothesis developed by Thomas (23) and Wenkert (2U), and according to the biogenetic isoprene rule that monoterpene are formed in nature by suitable modification of geranyl pyrophosphate (31). 

Yohimbine, (16a,I7a) 17-Hydroxyyohimban-I6-carboxylic acid methyl ester quebrachine corynine aphro-dine, C, HuNiOJ mol wt 354.43. C 71.16%, H 7,39%, N 7.90%, O 13.54%. Indole alkaloid with a,-adrenergic blocking activity. Found in Corynanthe johimbe K. Schum., Rubiaceae and related trees, also in Rauwolfla serpentina (L.) Benth., Apocynaceae Raymond -Hamet. J. Pharm. Chim. 

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... 

Intramolecular ene reactions. Use of Lewis acid catalysts (particularly FeCL, 15,156 16,190-101) has greatly extended the usefulness of intramolecular ene cy-clization. Thus a new diastereoselective route to corynanthe-type alkaloids involves the ene cyclization of 1 to tr s-indolo[2,3-a]-quinolizidine (2), a precursor to methyl corynantheate (3) by demethoxycarbonylation. SnCU (1 equiv.) is the only common Lewis acid that is useful for this particular ene cyclization, and even so, it also requires the presence of trifluoroacetic acid (1.5 equiv.). 

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... 

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). 

Wanner, M. J., Claveau, E., van Maarseveen, J. H., Hiemstra, H. (2011). Enantioselec-tive syntheses of corynanthe alkaloids by chiral Br0nsted acid and palladium catalysis. Chemistry - A European Journal, 17, 13680-13683. 

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