Alstonia structure

Two other alkaloids 47 and 48 were isolated in addition to Neooxygambirtannine 44 (67T3129). Anhydroalstonatine from Alstonia venenata is a closely related structure (77IJC(B)183) (Scheme 18). 

Deplancheine (7) was isolated first from the stem and bark of Alstonia deplanchei van Heurck and Muell. Arg. by Husson et al. (14). The structure of this novel type of alkaloid has been established from spectral evidence the trans annellation of rings C and D is supported by the presence of characteristic Bohlmann bands in the IR spectrum and also by the chemical shift of the C-3 proton below 3.7 ppm. The ethylidene side chain was also indicated by the H-NMR spectrum [8 1.52 (3H, d, J =6 Hz), 5.30 (1H, q, J = 6 Hz)] and its E configuration was confirmed by regio- and stereospecific total synthesis (14). 10-Methoxydeplancheine (8) has been found in the leaves of Alstonia lanceolifera... 

Deplancheine (82), from the stem bark of Alstonia deplanchei van Heurck et Miill.-Arg., is an indoloquinolizidine alkaloid of a novel type in which the three-carbon unit that is normally attached to C-15 is missing.620 The structure (82) was deduced from its spectroscopic properties, and has been confirmed by two independent syntheses (Scheme 10).62° 6 It is of some interest that racemic (82) had been prepared,62c and its configuration established, some six years before its isolation from natural sources. 

At present, little can be said concerning the structure of villalstonine, except that it appears to be the first dimeric base in the Alstonia series. Its constituent chromophores are probably z-unsubstituted indole and dihydroindole nuclei these may be contained in tetra- and hexahydro-/3-carboline ring systems, but not even this can yet be regarded as established. The speculation that villalstonine may be regarded as composed of C19 and C21 units, the latter bearing the essential structural features of coronaridine (35), seems somewhat hasty on the basis of the published data. (See note added in proof, p. 201.)... 

Nordman, C. E., and Nakatsu, K. Interpretation of the Patterson function of crystals containing an unknown molecular fragment. The structure of an Alstonia alkaloid. J. Amer. Chem. Soc. 85, 353-354 (1963). 

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. 

A number of novel nitrogenous derivatives have also been obtained in recent years from several Malaysian plants. An unusual nitrogenous compound angustimaline was obtained from Alstonia angustifolia [192]. The spectral data led to the structure 321 which showed that angustimaline retains all the features of the non-indole portion of a type-B macroline unit except for the presence of an additional oxygenated carbon. It is probably derived from fragmentation of a macroline-type precursor, possibly alstophylline or its oxindole. 

Echitoveniline (102), 11-methoxyechitoveniline (103), and 11-methoxyechitovenidine (104) are three new alkaloids from the fruits of Alstonia venenata R. Br. (135,136), although the leaves are a better source of 103. In consonance with these structures, ester exchange with sodium methoxide affords (-)-19R-minovincinine (80) from 102, and (—)-19/ -ll-methoxyminovincinine, a minor alkaloid of Vinca minor (137), from 103 and 104. 

Alstonerine " from Alstonia muelleriana (82) is a structural type first recognised as one half of the dimeric indole alkaloid villalstonine. The oxindole analogue pf this structural type has been known for some time. 

The monomeric cleavage base alstophylline (221) occurs naturally in Alstonia macrophylla Wall. Macroline (215) was previously isolated from villalstonine (213). The cleavage ketone, C20H26O2N2, has been assigned structure (222) based on the following considerations it is an indole and contains... 

Zeyer s alkaloid was almost certainly an impure sample of the bisbenzylisoquinoline berbamine (1), the principal alkaloid of the plant, but nearly a century went by before it was reisolated from sassafras and its structure fully elucidated (2. Shortly after Zeyer s study, a second alkaloid, alstonine (2), was obtained in an impure form from another Australian plant, Alstonia constricta (Apocynaceae) [3]. This work was also done in Germany, and a similar period elapsed before the complete structure and stereochemistry of alstonine were established [4,443],... 

When NMR and mass spectrometry became available, a large number of alkaloids from various apocynaceous plants were investigated (e.g. species of the genera Alstonia, Aspidosperma, Conopharyngia, Gabunia, Hunteria, Iboga, Oncinotis, Rauwolfia, Vinca). Villalstonine was the first bisindole alkaloid whose structure was elucidated by mass spectral analysis. 

In a study23 of the minor alkaloids of Alstonia constricta the structure (13) for alstonidine was confirmed and the stereochemistry deduced from a detailed n.m.r. examination. The absence of a complex overlapping pattern for aliphatic hydrogens in such / -carbolines facilitates a complete analysis (see ref. la and below). This study also showed vincamajine, 17-0-(3,4,5-trimethoxycinnamoyl)-vincamajine, 17-0-(3,4,5-trimethoxybenzoyl)quebrachidine, and alstonilidine (14) to be present. The structure of the last was again susceptible to n.m.r. analysis... 

As well as macralstonine71" and others, a new alkaloid,716 alstonisidine, has been isolated from Alstonia muelleriana. The structure (80) suggested for this dimer rests on spectral measurements, principally the presence of several ions in its mass spectrum which have the same mass numbers as characteristic fragment ions of authentic macroline and ajmaline alkaloids, the formation of a mono-0-acetate, of a triol with lithium aluminium hydride (fission of N—C—O), and the detection of formaldehyde after acid treatment. Formaldehyde was also detected after a model acid treatment of quebrachidine (81) and it is suggested that this rather surprising result can be explained, for both the dimer, believed to contain a quebrachidine unit, and for quebrachidine itself as shown [arrows in (81) and (82)]. 

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... 

Of the 12 alkaloids belonging to this group occurring in Sri Lankan flora, 11 were encountered in Alstonia macrophylla Wall, of the family Apocynaceae, and the remaining alkaloid was isolated from Taberrtaemon-tana divaricata (L.) Br. ex Roem et Schult. of the same family. Six of the alkaloids were found to be new. Vincamajine (101) and its new derivative, 19-hydroxyvincamajine (102), are two alkaloids of the ajmaline subgroup present in A. macrophylla (82). The structure of 102 was elucidated with the aid of IR, H NMR, and low-resolution MS data. A. macrophylla also... 

Alstonisidine (alkaloid A) [C42H48N4O4 mp 325° [a] — 234° (EtOH)] was first isolated by Elderfield and Gilman from the aerial bark of Alstonia muelleriana 48) but its structure (56) has only recently been elucidated 39). The indoline portion of this structure resembles macroline (57) and may well be derived from it or from a common precursor the second unit is related to quebrachidine (58) and the linkage between the two components is of a novel kind. 

The structure of villalstonine (XIV), the principal alkaloid of Alstonia macrophylla, has recently been elucidated (28-32), mainly owing to the brilliant investigations of Hesse, Schmid, Taylor, and their collaborators (29, 30) their conclusions have been triumphantly confirmed by an independent X-ray crystal structure determination (31). Alkaloid B, one of the constituent bases of A. muelleriana Domin. (33), has been shown to be identical with villalstonine (31), the early work on which (see Volume... 

In another remarkable contribution on the Alstonia alkaloids Hesse, Schmid, Taylor, and their collaborators have very recently discussed in detail the chemistry of macralstonine, for which the structure XLI is proposed (10). The molecular formula C43H52N4O5, mol. wt. 704,... 

Several of the chapters in volume XIV of the Manske series The Alkaloids are of relevance to indole alkaloid chemistry thus, as well as the chapter " on unclassified alkaloids and those of unknown structure, there are reviews of oxindole alkaloids, alkaloids of Mitragyna and related genera, Picralima and Alstonia species, and Cinchom and Elaeocarpus alkaloids. 

Only two members of this group are known, both from Alstonia species. They are alkaloid C (XVII) from A. muelleriana Domin (A. villosa Benth.) whose structure was determined by X-ray methods (68) and alstophylline (XVIII) from A. macrophylla Wall, whose structure was deduced largely from mass spectral data (69). Alstophylline is also... 

Anhydroalstonatine, a new alkaloid from the bark of Alstonia venenata, is a bright red, zwitterionic indolic base which is tentatively formulated as (101), i.e. as a 9-methoxy-5,6-dehydro-neo-oxygambirtannine. In consonance with this structure, reduction of anhydroalstonatine by means of sodium borohydride gave a tetrahydro-/3-carboline base, regarded as (102) the positions of the methoxy and methoxycarbonyl groups in (101) and (102) are based principally on the presence of two ABX systems of aromatic protons in the n.m.r. spectra of both compounds, and on the u.v. absorption of (102). 

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