Naturally occurring biogenesis

Naturally occurring isocyano compounds are no longer an oddity since their frequent isolation from members of the class of Demospongiae. Their biogenesis has intrigued chemists ever since the first terrestrial isocyano compound (an amino-acid derivative) was described from a micro-organism. All known marine isocyano compounds are terpenoid and their biosynthesis continues to pose an unsolved problem, which is discussed in Chapter 2. 

The synthesis of pyrrolizidine derivatives by condensation of di-(4-oxo-ra-butyl)amine is considered in Section V in conjunction with the biogenesis of naturally occurring pyrrolizidines. 

Biogenetic pathways leading to naturally occurring pyrrolizidine bases were proposed by Robinson, Schopf, and Lukefi (see, e.g., refs. 119-121) in their publications concerned with the biogenesis of alkaloids. The most probable precursors of the pyrrolizidine system are commonly accepted to be ornithine (176), hydroxyomithine (177), and their biogenetic equivalents. It is noteworthy that ( + )- -hydroxy-jV-methylnorvaline (178) (structurally related to ornithine) was isolated... 

Because of their suitable skeletal structure trans-CHD are applicable in the synthesis of compound classes of chemical, biological, and pharmaceutical interest. Regio- and stereoselective epoxidation of either one or two double bonds of 2, for example, opens up an approach to a group of naturally occurring cyclohexane epoxides which have attracted considerable attention because of their unusual structures, biogenesis, and biological activity [15]. 

Full details of an earlier synthesis of chamigrene (161) have been published.95 Further work on the components of the red alga Laurencia nipponica Yamada has resulted in the isolation and structural elucidation (by Y-ray analysis) of the diol (162)96 and spironippol (164).97 The biogenesis of the latter compound can be viewed in terms of an intramolecular cyclization of the diol (163) derivable from the naturally occurring epoxide of 10-bromo-a-chamigrene. 

In 1907, Collie showed that dehydroacetic acid is converted into orcinol (128) on treatment with base. ° It was presumed that this transformation proceeds through triketone (127 equation 148). On the basis of this reaction, Collie suggested the polyacetate biogenesis of naturally occurring phenolic compounds. In later work, it was shown that trione (127) is converted by acid into phenol (128). - 2... 

Information obtained from the above studies will help not only to elucidate the structures of bitumens kerogens and other naturally occurring substances but also to clarify the mechanisms of biogenesis, transformation and metamorphism of all fossil remains existing in nature. A better understanding of the interactions of vanadium complexes... 

Levy and McNutt (1962) have studied the utilization of the naturally occurring pteridine, xanthopterin (CVIII) by a bacterium isolated from soil, hoping to relate some of the intermediates produced to metabolites formed in the normal biogenesis of pteridines. They isolated from cultures of this organism, and identified by ultraviolet... 

Rosenthal, G. A., Bell, E. A. Naturally occurring, toxic nonprotein amino acids. In Herbivores, Their Interaction with Secondary Plant Metabolites (G. A. Rosenthal, D. H. Janzen, eds.), pp. 353-385. Academic Press, New York 1979 Smith, R. L. The Excretory Function of Bile. Chapman and Hall, London 1973 Williams, R. T. The biogenesis of conjugation and detoxication products. In Biogenesis of Natural Compounds (P. Bernfeld, ed.), pp. 589-639. Pergamon Press, Oxford 1967... 

Most protoberberine alkaloids occur in nature as tetrahydroprotober-berines or as quaternary protoberberinium salts. However, in the last few years a number of quaternary iV-methyltetrahydroprotoberberine salts as well as 7V-oxides have been reported. In addition to the usual substitution pattern, the C-8 position may bear a methyl group as in the naturally occurring protoberberine alkaloid ( —)-corytenchirine. Two recently reported retroprotoberberines are TV-methyl- and iV,(9-dimethylmecambridine the chemistry, synthesis, pharmacology, and biogenesis of the protoberberine alkaloids have been reviewed. 

All of the naturally occurring porphyrins and chlorins seem to be derived from the isomer III series. Isomer I uroporphyrin and coproporphyrin have been found, but isomer II has not yet been found. Isomer IV is still chromatographically inseparable from isomer III, and other classic methods of separation would not detect small amounts (10 % ) of the various isomers. The chemical conditions which form a large amount of isomer III are of interest for their possible relation to the biogenesis of these important pigments. 

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