Selenium dehydrogenation

The second alkaloid solanocapsidine, C2gH4404N2, m.p. S05° (approx.), is amorphous. It was used for a selenium dehydrogenation experiment and yielded Diels s hydrocarbon, y-methylci/ciopentenophenanthrene (picrate, m.p. 117°) and a mixture of bases from which 2-methyl-5-ethylpyridine (picrate, m.p. 162°) and 4-methyl-2-ethylpyridine (picrate, m.p. 125°) were isolated. 

On the assumption that the two alkaloids may have a similar structure and, with that reservation, applying the result of the selenium dehydrogenation experiment to the case of solanocapsine, the authors suggest that the annexed formula (p. 670) aeeounts for all the reae ions of this alkaloid so far observed. 

Jacobs and Craig have made an extended study of the selenium dehydrogenation products of cevine and in addition to cevanthrol and eevanthridine have obtained the following thirteen substances Bases, j3-picoline, 5-methyl-2-ethylpyridinc, 5-methyl-2-hydroxyethylpyridine, base, CgHgON (pierate, m.p. 151-2°), base, CgHjgN (pierate, m.p. 150-1°), base, CggHigN, m.p. 233-5° (methiodide, m.p. 285-290°), base, m.p. 229-230° (methiodide, m.p. 295° (dec.) )... 

On selenium dehydrogenation at 340° jervine, like eevine, yields three types of produets. ... 

The selenium-dehydrogenation products of fsorubijervine have not yet been fully examined, but the two structurally significant products, 5-methyl-2-ethylpyridine and a hydrocarbon, m.p. 135-6°, yielding... 

All the erythrophleum alkaloids examined in detail so far are of the same type, viz., acyl esters of either monomethylaminoethanol, e.g., erythrophleine and coumingidine or dimethylaminoethanol, such as cassaine or cassaidine. The acyl substituents are complex, yield 1 7 8-trimethylphenanthrene on selenium dehydrogenation, and contain at least one hydroxyl group, which may be acylated by an aliphatic acid, e.g., coumingine forms three components on hydrolysis. 

Ketohydroxycassanic acid, C20H32O4, has also been used for another mode of degradation by Ruzicka, Dalma and Scott (1941). On oxidation by chromic acid in acetic acid it yields diketocassanic acid, C20H30O4, m.p. 225°, [a]u ° — 44° (EtOH), which forms a methyl ester, m.p. 108°, (EtOH), and is reduced by sodium amyloxide at 220° to cassanic acid, C20H34O2, m.p. 224°, [a]f - - 3° (CHCI3), which on selenium dehydrogenation also yields 1 7 8-trimethylphenanthrene. 

Cleavage of the hetero ring in a number of extended tetrahydro-j8-carboline systems was observed in the course of structural elucidation of tetrahydro-jS-carboline alkaloids. A few examples only will be given. The indole derivative 287 was isolated as one of the products of the selenium dehydrogenation of yohimbine (358 R = and... 

These data indicate a close relationship with ajmalicine, which is supported by chemical evidence. Thus, selenium dehydrogenation gives alstyrine lithium aluminum hydride reduction gives a primary alcohol, akuammigol (I), which possesses a typical indole UV-spectrum, with a deep minimum at 250 m/r. The formulation of this product as an allylic alcohol, stereoisomeric with tetrahydroalstonol, is further shown by its... 

The presence of an ethylidene group in echitamine chloride was also demonstrated by oxidation with periodic acid, which was reported to give acetaldehyde and indole-3-acetaldehyde (78). Alkali fusion and selenium dehydrogenation experiments gave inconclusive results, but the basic fractions were suspected to contain derivatives of jS-carboline (77, 78). Oxidation of echitamine with alkaline potassium permanganate afforded a low-melting base, which was considered to be Nb-methyl-tryptamine (80). 

The only degradations that have so far been carried out with villal-stonine are the drastic ones of potash fusion and selenium dehydrogenation. Alkali fusion yields products characteristic of the indole alkaloids, namely, 2-methylindole, indole-2-carboxylic acid, and a basic fraction which exhibits a typical /3-carboline UV-spectrum a weak base also obtained in this degradation possesses a UV-spectrum closely resembling that of echitamidine. /3-Carboline derivatives, so far unidentified, also appear to be the products of selenium dehydrogenation (35). 

Dehydrogenation of cinchonamine with selenium or palladium-charcoal resulted in fission of the quinuclidine ring and the isolation of dehydrocinchonamine (V), mp 203°, whose spectral characteristics and p/fa were in agreement with its formulation. From the selenium dehydrogenation products, a trace of a crystalline compound was also obtained which, from a single ultimate analysis and UV-spectrum, is considered to be IV (10). 

Huntrabrine methochloride has an ethylidene group, a quaternary IV-methyl, a 5-hydroxyindole chromophore, and a primary hydroxyl group. It underwent a facile Emde degradation, and the resulting tertiary base upon tosylation gave a phenolic-O-tosylate quaternary tosylate. The latter compound, upon selenium dehydrogenation, afforded uncharacterized products, one with a sempervirine-like UV-spectrum and another with a 2-pyridylindole chromophore. All these results are interpreted as supporting the structure XLVI (see Table I) for huntrabrine methochloride (27). 

The structure (XCIIa) of this alkaloid has long been known (Volume II, p. 100) (63,64). Its UV- and IR-spectra as well as a number of chemical reactions clearly indicate that it is 10-methoxyajmalicine. Selenium dehydrogenation yields 5-methoxyalstyrine and the stereochemical criteria as already outlined confirm C/D and D/E trans junctions and a C-19 equatorial methyl. 

Selenium dehydrogenation of rauniticine gives alstyrine similarly obtained from ajmalicine. These alkaloids differ only in that raunitidine is a monomethoxyrauniticine. Their IR-spectra (3.4 p) indicates a C/D trans junction with the C-3-H axial. That the D/E junction is cis follows... 

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