Heteroyohimbine-Yohimbine Group, and Related Oxindoles

The structure and relative stereochemistry of akagerine (75 a) have been confirmed by X-ray crystal structure analysis. 6,7-Dihydroflavopereirine (75b) is among the constituents of Strychnos usambarensis roots.  

In the corynantheine series dihydrocorynantheine, hirsuteine, hirsutine, and dihydrocorynantheine pseudo-indoxyl have been isolated from samples of Uncaria attenuata ssp. attenuata dihydrocoryantheine and epw//o-corynantheine were found in the related subspecies bulusanensis. This is the first recorded occurrence in nature of epia//o-corynantheine and dihydrocorynantheine pseudoindoxyl.  

Reagents i, DMF, non-aqueous work-up ii, kv iii, (C02Et 2-K0Bu -C6H6 iv, dil. HCl v, tryptamine-AcOH-116 °C, 3 h vi, HQ-AcOH, high temperature. 

Pleiocarpamine has been found in the bark of Alstonia vitiensis (Seeman) var. novo ebudica monachino, and 10-methoxygeissoschizol, a-yohimbine, and alstonine in the leaves and stems of Rauwolfia obscura the stems also contain tetrahydroal-stonine and an anhydronium base which, unfortunately, decomposed in the mass spectrometer and was obtained in insufficient amount for structure elucidation. 

Mamatas-Kalamaras, T. Sevenet, C. Thai, and P. Potier, Phytochemistry, 1975,14, 1637. 

Nauclea latifolia. la Isodolichantoside and 16-ep/-diploceline are new epimers of known bases which have been reported416 to occur in the root bark of Strychnos gossweileri. 

Ajmalicine and vallesiachotamine are amongst the alkaloids produced by cultures of cell lines 943,426 953,426 and 200 GW of Catharanthus roseus ia the first two of these cell lines also produced yohimbine and isositsirikine, while cell lines 953 and 200 GW also produced strictosidine lactam. 

A number of new extractions of intact plants, or specific organs of plants, have also been recorded. Geissoschizine occurs, together with aricine, pleiocarpamine, 10-methoxypleiocarpamine, 19,20-dehydroadirubine acetate, and sixteen other 

Recent extractions440 of the leaves of Cinchona ledgeriana have resulted in the isolation of quinamine (previously observed), 3-ep/-quinamine, aricine, and a new alkaloid which may prove to be stereoisomeric with quinamine. 11-Hydroxy-pleiocarpamine occurs in Vinca erecta 4b and herbacine and herbaine in V. herbacea.44c Yohimbine appears to be the major alkaloid of the trunk bark of Pausinystalia macroceras, in which it occurs with four other alkaloids of this group.44d Pleiocarpamine occurs in association with nine alkaloids of the aspidospermine-eburnamine group in the stem and root bark of Hunteria elliottii (Stapf.) Pichon.44e 

A new weak base, neonor-reserpine, from Rauwolfia vomitoria, is regarded as a stereoisomer of psuedoreserpine 45 since the new base appears to have the epiallo stereochemistry, it must differ from pseudoreserpine in the stereochemistry at one or more of the positions C-16, C-17, and C-18. 

Corynantheine-Heteroyohimbine-Yohimbine Group, and Related Oxindoles. A comprehensive review of the alkaloids of Uncaria species provides a valuable summary of the considerable number of investigations reported on the alkaloid content and the chemotaxonomy of UrKoria, and it also includes Ridsdale s revision of the genus, which has resulted in the recognition of 34 species-a considerable reduction and simplification when compared with the 120 recorded in the Kew Index. 

The tertiary base A °-(-)-isositsirikine (60b), corresponding to diploceline (60a), is one of twenty-five alkaloids isolated from the seeds of Aspidosperma album (Vahl) R. Ben. Two others are (+)-sitsirikine and 16-cpi-sitsirikine. 

The non-polar alkaloid fractions of Strychnos dale de Wild, and 5. elaeocarpa Gilg. ex Leeuwenberg contain the same five, closely related, alkaloids, of which akagerine (60c) may be regarded as the parent base. The other four are 17-O-methylakagerine (60d), kribine (60e), which is the internal hemi-acetal of 

17-epi-akagerine, and the two epimeric 21-O-methyl ethers [(60f) and (60g)] of kribine. As expected from these formulations, kribine, which is a mixture of two epimers, affords the ethers (60f) and (60g) on methylation (MeOH-HCl), and is transformed into akagerine (60c) by treatment with acid (acetone-HCI-HjO). In view of the ease of these interconversions, and the fact that methanol and acid were used in the extraction procedure, it may well be that the methyl ethers (60d), (60f), and (60g) are artefacts. 

The major alkaloid of the allegedly toxic fruits of S. usambarensis has been identified as desmethoxycarbonyl-dihydrogambirtannine.  

Whether the dienamine (67) actually participates in this reaction at an alumina surface remains to be proved however, it appears not to be an intermediate in analogous reactions in solution, according to the recent studies of Brown and Leonard,53 which have added further clarification to the processes occurring in the biomimetic syntheses from strictosidine. 

Brown s one-pot synthesis54 affords mainly (19S)-heteroyohimbine alkaloids (e.g. tetrahydroalstonine) by a kinetically controlled process involving preferential formation of an ( )-alkene (61 ) from the initially formed dienamine 

The mechanism of formation of the (19i )-bases was studied by means of 2H and lsO experiments. In D20, at pH 6, strictosidine gives the monodeuterio-compounds (71) and (72), as expected, but whereas the proportion of (72) increases with time, no further deuterium is incorporated. Hence cathenamine does not revert in acid to the dienamine (67). Evidently cathenamine is protonated to 

Reagents i, / -Glucosidase, pH 7.0 ii, acetylation iii, tryptamine iv, NaBH3CN v, POCl3 vi, NaBH4 

The root and stem bark of Strychnos decussata (Pappe) Gilg. contain akagerine, 17-O-methylakagerine, and three new alkaloids, i.e. 10-hydroxy-21-O-methylkribine (79a) and its 21-epimer (79b) and 10-hydroxy-O-methyl-akagerine (80) 56 these alkaloids may be responsible for the muscle-relaxant properties of extracts of the bark of this plant. 

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C. Corynantheine-Heteroyohimbine-Yohimbine Group and Related Oxindoles... 

Monoterpenoid Alkaloids.—Corynantheine-Heteroyohimbine- Yohimbine Group, and Related Oxindoles. The leaves of Strychnos decussata (Pappe) Gil. contain a new glycosidic alkaloid for which the gross structure (78) has been proposed 52 so far, nothing is known about its stereochemistry. Nevertheless it seems distinctly possible that this alkaloid is a close biosynthetic relative of vallesiachotamine. 

Corynantheine-Heteroyohimbine-Yohimbine Group, and Related Oxindoles.— The chemotaxonomic significance of the pattern of... 

Monoterpenoid Alkaloids.—Corynantheine-Heteroyohimbine-Yohimbine Group, and Related Oxindoles. The first recorded extraction of the leaves and twigs of Peschiera laeta Mart, has yielded geissoschizol, a base not previously found in the Peschiera genus. Antirhine and, to a lesser extent, its quaternary Nb-metho-derivative, occur in the bark of Strychnos camptoneura Gilg. et Busse and in Amsonia elliptica, which also contains tetrahydrosecamine, pleiocarpamine,... 

Monoterpenoid Alkaloids. — Corynantheine - Heteroyohimbine - Yohimbine Group, and Related Oxindoles. Details of the AT-ray crystal structure determination of borreline (92) have now been published,and the species from which it was isolated has been identified as Borreria capitata R. et P. A second alkaloid from this species, borrecapine (93), has a similar structure but, in place of the second methyl group in borreline, borrecapine contains an isobutenyl group which completes the monoterpenoid unit of the non-tryptamine part of the molecule. 

Monoterpenoid Alkaloids.— Yohimbine-Corynantheine-Heteroyohimbine and Related Oxindoles) Group. Holeinine ° from Bleekeria vitiensis ° (and Ochrosia sandwicensis) is isoreserpiline metho-salt the former source contains, inter alia, 10,11 -dimethoxyalstonine. ... 

During the past two decades a great number of papers have been published on the isolation, structure elucidation, synthesis and transformation, biogenesis, chemotaxonomy, and pharmacology of indole alkaloids. In this chapter we summarize the new results that appeared from 1968 to mid 1984 for the cory-nantheine-yohimbine group of monoterpene indole alkaloids with greater emphasis on their chemistry, excluding the related oxindoles and heteroyohimbines. 

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