Alkaloids of Undetermined Structure

A list of these alkaloids is given in Table II. This compilation does not include alkaloids of the same category which were reported in Volume VI and for which no additional information has been published. The listing of alkaloids in this table is somewhat arbitrary. Several of the alkaloids classified in preceding sections have been assigned on the basis of weak or equivocal data such as similar IR-spectra. Many of the alkaloids cited in Table II have not been subjected to modern criteria of purity and may prove to be mixtures. 

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A list of the Daphniphyllum alkaloids is given in Table I. In addition to two alkaloids of undetermined structure, neodaphniphylline (28) and neoyuzurimine, both of which have been isolated in very small quantities (Vol. X, p. 556, and Vol. XII, p. 472), three more structurally unknown alkaloids (alkaloids Ax and A2, and yuzurimine-D) have been obtained from the bark and leaves of D. macropodum (14, 21). In particular, the carbon skeletons of the alkaloids Aj and A2 seem to be considerably different from those of the other alkaloids cited in parts A-E, on the basis of their spectral data. 

Quite recently, three new alkaloids were isolated as minor components from the fruits of the plant Daphniphyllum teijsmanni Zollinger and their structures also determined on the basis of their physical and chemical data (43). In addition, the structure of yuzurine,9 one of the alkaloids of undetermined structure (see Section II, F), was also elucidated by means of an X-ray crystallographic analysis of its methiodide (44). 

Finally, an alkaloid of undetermined structure was studied to demonstrate the utility of these methods. The FABMS of the alkaloid was first determined, followed by derivitization of the alkaloid to its bismethiodide (MeI/Me2CO - room temperature), and subsequent determination of the FABMS of the derivative. The unknown alkaloid exhibited fragmentation characteristic of a type A aporphine-benzylisoquinoline alkaloid with one methoxy and one hydroxy group in... 

The presence of alkaloids of undetermined structure has been recorded for the following cacti ... 

From Ma Huang there have also been isolated a volatile basic compound, benzylmethylamine, by Chen, Stuart and Chen (151) and ephedine, and an alkaloid of undetermined structure, by Chou and Chu (152). Wolfes (153) showed that the European ephedras contain the same alkaloids as the Chinese species. 

Alkaloids (pyrazolinc derivatives) and some others of undetermined structure have been reported from several genera. The family is known chemically for the cucurbitacins-loxic steroidal substances. In this study, 106 samples in 73 species were tested two were already known to contain alkaloids, Momordica charantia (2/11) and M. foeiida (1/2). Other positives included Coccinea addensis (1/3), Cucumis anguria, C. zeyheri, Cucurbita foelidissi-ma (2/3), Echinocystis macrocarpa, Marah macrocarpa, Melothria cordala, Momordica cissoides, M. repens (1/2), Peponium macke-nii, Trichosanthes sp. 

THE PHYSICAL CONSTANTS OF AMABYLLIDACEAE ALKALOIDS OP UNDETERMINED STRUCTURE AND THEIR PRODUCTS OF TRANSFORMATION AND DEGRADATION... 

On the basis of the chemistry and NMR-spectra, the hydroxyl group in vincamine and 11-methoxyvincamine is regarded as being axially substituted (18). Some alkaloids of as yet undetermined structure may... 

Treatment of napelline with dilute mineral acid results in rapid isomerization to isonapelline (42, 43). The structure of isonapelline was represented as 36 with undetermined stereochemistry at C-16. Recently, we established the stereochemistry of the C-16 methyl group in the related alkaloid, cuau-chichicine, an acid-catalyzed rearrangement product of garryfoline. By analogy, the acid-catalyzed rearrangement of napelline to isonapelline should result in a C-16 /1-methyl group in isonapelline. Thus structure 37 can be assigned to isonapelline. 

The total synthesis of dihydrolycorine (38), the sole hydrogenation product of lycorine (6 R1 + R2 = CH2, R3 = R4 = H) and an alkaloid in its own right, has been reported.27 Scheme 3 shows how treatment of the Diels-Alder adduct (33) with methanol gave a mixture of two half-esters which were directly subjected to Friedel-Crafts cyclization to give the indanone ester (34) and a rearrangement product. Attempted Schmidt ring expansion on (34) failed, but a prior reduction-oxidation sequence followed by treatment with sodium azide and hydrolysis produced the desired lactam (35) and an isomeric compound whose structure remains undetermined. Lactam (35) was readily converted into a chain-extended... 

Since the greater majority of plants still remain to be examined, the taxonomic distribution of alkaloids cannot be fixed with any certainty, and their total number and occurrence can only be guessed. About one thousand are now known, the structures of many of them being still undetermined (179). The chemistry of the flora of only a few regions of the world has been intensively studied (Australia Webb (180) Siberia Sokolov (181) ). It is estimated that 10% to 20% of all plants contain alkaloids, but such estimates are uncertain to the extent that our analytical methods often fail to detect traces. Improved methods have led to the finding of nicotine in tomatoes (182) and of alkaloids in... 

Rauwolscine gires colour leactions like those of yohimbine and the absorption curves of the hydrochlorides of the two alkaloids are very similar. Heated to 300°j5 mm. rauwolscinic acid forms barman (p. 490) and 3-ethylindole and on fusion with potassium hydroxide decomposes into indole-2-carboxylic acid, isophthalic add, barman and an unidentified indole derivative.. Rauwolsdne itself on distillation with zinc dust produces barman, 2-methylindole (scatole) and isoquinoline. It is suggested that the alkaloid has the skeletal structure suggested by Scholz (formula XIV, p. 508) for yohimbine, the positions of the hydroxyl and carbomethoxy groups being stUl undetermined. 

Most cybndricines are related to cylindridnes A and B, which are almost always the major constituents of mixtures from spedes collected from various sites on the Tasman coast. Structural analysis was done by chemical spectroscopy and interconversion. Lepadiformine is related to cylindricine C, but with a different configuration at the jimction between indolizidine and cydohexane the final structure of this atypical alkaloid was confirmed by several total syntheses and X-ray analysis of its hydrochloride group (Abe, Aoyagi, and Kibayashi, 2000 Greshock and Funk, 2001 Sim, Sim, and Weinreb, 2001,2002 Weinreb, 2003). Lepadiformines B and C differ from lepadiformine A only in the carbon chains linked to the tricyclic system. Two other alkaloids related to lepadiformine A, polycitorols A and B, were isolated from an undetermined asddian of the family Polycitoridae of Indonesian origin (Issa et al, 2005). All currently known structures are presented in Figure 28.23. 

Upenamide represents a new structural type of mac-rocydic alkaloid containing a spirooxaquinobzidinone. Isolated from an undetermined species of the genus Echinochalina harvested in Indonesia, upenamide is not cytotoxic to the usual cell lines (P388, A549 and HT29). A biosynthetic scheme for this atypical alkaloid has been proposed (Jimenez et al., 2000a). 

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