Biogenetic Considerations

The presumed mechanism for the transformation of anhydrovobasinediol to koumine is as follows  

However, the proposed in vivo transformation of anhydrovobasinediol to gelsemine might involve a series of more extensive alterations of the molecular skeleton which presumably would include (1) oxidation of the 2,7 double bond, (2) an acid-induced 2,7 shift, and (3) allylic rearrangement of the C-20 ethylidene side chain to a C-20 vinyl, so that a humantenine-type precursor 

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Biogenetic considerations [71], and a correlation of all polypropionates from pulmonate molluscs led to revision of the relative stereochemistry of pectinatone (20) and nor-pectinatone (21), metabolites of the pulmonate Siphonaria pectinata [72, 73] the point had already been questioned by Oppolzer s synthesis [74] and was definitively confirmed by two independent X-ray diffraction studies [71, 75] of pectinatone (20). 

Biogenetic Considerations. The structural novelty of ervafoline-ervafolidine... 

The real breakthrough toward synthesis of vinblastine and, in fact, the first significant laboratory preparation of binary indole-indoline alkaloids with the natural C-16 -C14 PARF configuration, was due to the work of the Potier-Langlois team at Gif (38,39 for reviews, see Refs. 40 and 41), buttressed by results obtained by the Kutney group in Vancouver (42,43,44), and the efforts of Atta-ur-Rahman and associates in Karachi. Their basic idea, which relied on the biogenetic consideration that binary indole-indoline alkaloids are formed in plants by the union of vindoline... 

Biogenetic considerations of the carbazole alkaloids isolated from other sources have led to a different view about the genesis of these alkaloids. Without exception, to date, all of the biogenetic proposals of the carbazole alkaloids isolated from other sources have indicated L-tryptophan has a progenitor. 

Miyaconitine and miyaconitinone, two highly oxygenated alkaloids, were isolated from the Japanese species A. miyabei Nakai in 1946 (129). On the basis of chemical and spectral data (54,129-132) and biogenetic considerations, structures 140 and 141 were assigned to miyaconitine and miyaconitinone, respectively. 

An interesting attempt to synthesize the ervafoline ring system was inspired by biogenetic considerations.136 Since the desired pandoline unit was not available, the condensation was studied between (318) (prepared by hydrolysis and decarboxylation of tabersonine, followed by Aa-methylation) and (319) (prepared by Polonovski reaction of 20-ep/-pandoline Nb-oxide, followed by trapping of the immonium ion with cyanide). The product (320) results from condensation of the... 

The attempts at degradation thus having failed, the structure of gelsemine (IX) was eventually elucidated by the X-ray analysis of gelsemine hydrochloride and hydriodide (78). Independently and simultaneously, the same structure was proposed by Conroy and Chakrabarti (79) on the basis of biogenetic considerations, together with some new evidence, mainly derived from the NMR-spectra of gelsemine and its derivatives. 

The structure of callichiline, apart from recognition of its chromo-phoric moiety which must include the carbonyl and methoxy groups, is practically unknown it has no W-methyl and is apparently not identical with any of the other indole alkaloids (about a dozen) with the same UV-spectra. If the functional group analyses are correct, biogenetic considerations would suggest that the formula be revised to C21H22-24N2O3. 

Woodward s synthesis of strychnine stands out as a major synthetic achievement (156). The plan of this synthesis was also strongly influenced by biogenetic considerations, but no short cuts were taken, and the synthesis proceeds step by step, at all stages fully under control. 

Arango GJ, Cortes D, Cassels BK et al (1987) Alkaloids of the Annonaceae. Part 80. Azafluorenones from Oxandra cf. major and biogenetic considerations. Phytochemistry 26 2093-2098... 

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). 

In order to confirm the structures of solanapyrones, chemical synthesis of these phytotoxins were attempted based on biogenetic consideration [55], The retro synthesis envisaged intramolecular Diels-Alder reaction of the achiral polyketide triene (a), a key intermediate, which is further divided into a pyrone moiety (b) and a diene moiety (c). The moieties a and b were prepared from dehydroacetic acid and hexadienyl acetate, respectively. Aldol condensation of the aldehyde (72) with the dithioacetal (73) gave a dienol, which was further converted to a triene (74). The intramolecular Diels-Alder reaction of 74 in toluene at 170-190 °C for 1 hr in a sealed tube yielded a mixture of the adducts (75) and (76) in a ratio of 1 2. This product ratio depends on the solvents, i.e. in water (1 7), and should be useful in differentiating between artificial and enzymatic reactions in biosynthetic studies. Removal of the thioacetal groups in 75 and 76 yielded solanapyrone A (67) and D (70) in a ratio of 3 5. Though solanapyrone D (70) had not been isolated from the natural resources at this stage, the structure and stereochemistry were confirmed by H NMR spectrum. 

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