Alkaloids possible structures

Besides sesquiterpene lactones, an alkaloid analyzed as CgH14N203 (45), was isolated from the leaves of Arnica montana L. (80). Distinction between the two possible structures 45 (amide-urethane) and 46 (ester + urea) was accomplished by a selective synthesis from prolinamide. 

Clivojuline (195) (10) represents an unusual structural type since it lacks the 9,10-aromatic oxygenation pattern, which is ubiquitious among the other lactone alkaloids. The structure of the related alkaloid cliviahaksine (196) was assigned on the basis of spectral comparisons with 195 although its stereochemistry was not specifically indicated (15). Since cliviaaline (197) was isolated in only very small amounts, its structure was deduced principally from its IR spectrum and its mass spectral fragmentation pattern however, the possibility that it was an artifact was not rigorously excluded (14). 

The above plant yielded haplopine and robustine H. obtusifolium Ldb. yielded skimmianine and evoxine and H. bucharicum Litv. yielded dictamnine, skimmianine, y-fagarine, robustine, haplopine, bucharine, benzamide, and a new alkaloid, bucharamine. Of several possible structures for the latter the more probable is 107 (85). 

Analysis of all the above results led to only two possible structures, A and B, for lythrancines I-IV and lythrancepines I—III. Structure A is preferred because the molecular models show large interactions between the 10-methylene group and the aromatic hydrogen atoms in B and the 13-membered ring is highly strained. X-ray crystallographic studies of lythrancine 101 O-brosylate confirmed stereochemistry A. Thus, the absolute stereochemistry of seven quinolizidine alkaloids was established as 100-103 and 107-109 (104). 

The Panamanian frog Dendrobates pumilio yielded not only pumiliotoxin C (vide ante) but also pumiliotoxins A and B. The instability of pumiliotoxins A and B under acid conditions has interfered with the preparation of a crystalline salt and many years after the isolation of these alkaloids the structural formulas remained unknown. Pumiliotoxins A and B and many related alkaloids are widely distributed in frogs of the genus Dendrobates. Serendipitously, in searching for a different alkaloid, a major alkaloid with a molecular weight of 251 (pumiliotoxin 25 ID) was isolated from the skin of the Ecuadorian poison frog Dendrobates tricolor. It proved to be a simpler analog of pumiliotoxins A and B, but most importantly, it was possible to crystallize the HC1 salt and consequently to derive its structural formula by X-ray diffraction analysis (37). 

The presence of a phenanthroindolizidine ring system can be assumed on the basis of the UV- and mass-spectra. Oxidation of the alkaloid with alkaline hydrogen peroxide yielded m-hemipinic acid as the only isolable product. On the basis of its IR-spectrum and biogenetic considerations, the methoxyl groups can be assigned to the 2,3,6- or 3,6,7-positions on the phenanthroindolizidine system leading to the alternate structures XVa and XVI. It is of interest that racemic forms of both the possible structures have already been synthesized (12, 18). 

Dilute hydrochloric acid converted crinamine to apohaemanthamine (CLXXXIX, R = H), proving that the crinane nucleus was the basic ring system of the alkaloid. Since oxocrinamine was not identical with oxohaemanthamine (CLXXXVIII, R = O), it could not be the Cji epimer of haemanthamine. The most likely structure for crinamine is the Cs methoxy epimer of haemanthamine. This is the only possible structure if allylic rearrangement does not occur during the conversion of crinamine to apohaemanthamine (149b). 

The weakly basic alkaloid, heptaphylline, C18H17O2N (mp 170°) is optically inactive. Exhaustive spectral analysis indicated a carbazole nucleus with hydroxyl and formyl substituents and an isoprenoid side chain. Treatment with polyphosphoric acid generated the isomeric chroman, cycloheptaphylline (mp 250°) so that, of the possible structures, the most likely is XXXVII (54). 

Of all the Senecio alkaloids, the structure of monocrotaline is known with most certainty as a result of the work of Adams and his co-workers over a period of five years or more. The alkaloid monocrotaline (I) is the ester of retronecine vith monocrotalic acid. The structure of the necine portion has been proved conclusively, while the structure of the necic acid portion is considered the most likely of three possible configurations. The position of attachment of the two portions is known with certainty. The... 

Propylein, the other alkaloid of this group, appears to be the sole alkaloid of the beetle Propylaea quatuordecimpmctata Propylein is an amorphous, unstable, laevorotatory base of molecular formula C13H21N which affords precoccinellin on hydrogenation. Since the alkaloid contains one olefinic proton that is in an enamine system (n.m.r., i.r.), three dehydroprecoccinellin structures are possible for propyleia Two of these can be excluded, since propylein exhibits only end absorption in the u.v. It thus appears that in propylein the 7r-electron system of the double bond is so oriented that it cannot interact with the unshared electrons on the nitrogen atom. This leaves only one possible structure (32) for propylein [cf. conformation (33)]. ... 

This amorphous base (C23H28N2O6) was isolated in small amounts from the aerial parts of Vinca major. Its mass spectrum was superimpos-able upon that of carapanaubine and the UV-, IR-, and NMR-data agreed well with a structure of the type XXXIIa-c. The NMR-spectrum of the alkaloid further indicated a pair of o-hydrogen atoms in the aromatic ring. However, a decision could not be made among the three possible structures (31). 

Phanostenine, C19H19O4N, was first described by Tomita (44) as obtained from Stephania sasakii Hayata m.p. 210°, [a] — 36.7° (chloroform). It was subsequently isolated from S. capitata (45) and shown to have the above formula. It has one methoxyl and one hydroxyl, and upon methyla-tion with diazomethane affords an alkaloid shown to be Z-dicentrine (m.p. 160-165°) because when admixed with d-dicentrine there was formed the known dZ-dicentrine (m.p. 176°). Phanostenine can therefore have only one of two possible structures, namely, XVI, with one of the two meth-oxyls replaced by hydroxyl. 

First, the assumption was made that micranthine is unsubstituted at the 5-positions of the isoquinoline nuclei on the basis that no substituents are present in the 5-positions of all known bisbenzylisoquinoline alkaloids. Then, all the possible structures containing a diphenylene dioxide ring, one... 

Alkaloids are structurally very similar to plant growth hormones. Waller and Nowacki critically considered the possibility that alkaloids have a hormonal influence on plant growth. This old hypothesis is still open for discussion examples in literature attempt to both prove and disprove it. The contradictory results derive from the diversity of alkaloids, not to mention plant diversity and that of other organisms producing alkaloids. There are alkaloid-rich and alkaloid-poor plants from the same species. One such plant is Washington lupine Lupinus polyphyllus Lindl.), which is capable of growing under various climatic conditions in both the Northern and the... 

PND was shown to be 10 to 50 times more sensitive than FID (Wink et al. 1982). The other detection method commonly used to obtain further information on the chemical structures was EI-MS. However, even GC-MS data are not always sufficient for the identification of quinolizidine alkaloids, since structural isomers such as tetrahydrorhombifoline and N-methyl-angustifoline were found to have the same retention time and very similar mass spectra but could be distinguished by TLC (thin-layer chromatography) (Balandrin and Kinghorn 1981). From some esters of hydroxylupanine it was not possible to detect the molecular ion (Wink et al. 1982). FD-MS (field desorption) was performed directly on the alkaloid extract to detect the molecular ions of the various bases in the mixture. The identity of the compounds was further confirmed by comparison of their retention indices with the ones of authentic samples. More recently, also CI-MS (isobutane or... 

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