Biological systems, biogenesis

Metabolism is the series of pathways operating when biological systems synthesize their constituents. Biosynthesis is the experimentally established pathway of formation of secondary metabolites where experimental proof is absent, the term biogenesis is used. 

At around this time, there was much scientific debate about the theory of the origin of species proposed by Charles Darwin (1809-1882), a theory which was to change the world. Darwin himself was very cautious about making statements on biogenesis. It was still too early to answer such questions, because neither results from the science of cell biology nor an extensive knowledge of our planet, the solar system and the cosmos were available. 

Although the terms exobiology and astrobiology really mean the same thing, astro-biology , introduced by NASA in 1995, has become the one of choice. This branch of science reaches from cosmochemistry via biogenesis to all the other themes involving research on traces of life (of whatever sort) on planets and on moons, both within and outside our solar system. 

In the present review, we summarize the occurrence, biogenesis, biological activity, and the chemistry of carbazole alkaloids, which have been classified based on their natural sources, ring system, and substitution pattern. While a comprehensive overview is given on all carbazole alkaloids isolated from natural sources, only their total syntheses published since 1990 are discussed. 

A fascinating area of research linking organic chemistry and biology is the study of the biogenesis of natural products the detailed sequence of reactions by which a compound is formed in living systems, plant or animal. All the isoprene units in nature, it appears, originate from the same compound, isopentenyl pyrophosphate. 

The parent compound of the secoiridoids is secologa-nin (see secoiridoids), the most important intermediate in the biogenesis of alkaloids that are not derived from an amino acid. This includes most indole alkaloids, the ipecac, the Cinchona, and the pyrroloquinoline alkaloids as well as simple monoterpene alkaloids The best known biological property of the I. is their bitter taste. However, bitter principles are mostly not used as pure substances, instead alcoholic extracts are preferred to stimulate appetite (increased secretion of gastric juice). Furthermore, bitter substances are used to modify the taste of pharmaceutical products. Some I. exert various effects on the central nervous system as a consequence of their volatility and lipophilicity, e.g., nepetalactone, iridodial, teucrium lactones, and valepotriates. 

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