Secondary metabolites function

The first chapter provides an informative introduction to this area of biomimetic natural product synthesis, in particular focusing on the role of electrocyclisation reaction cascades, from K.C. Nicolaou s seminal synthesis of the endiandric acids, to the more recent research carried out on the tridachiahydropyrones and related sacoglossan metabolites. The thesis then sets out to explore the hypothesis that these secondary metabolites function as photo-protective membrane antioxidants, shielding the producing organisms from the damaging effects of UV radiation. 

Low-molecular-weight products, generally secondary metabolites such as alcohols, carboxyhc and an iino acids, antibiotics, and vitamins, can be recovered using many of the standard operations such as liquid-hquid extraction, adsorption and ion-exchange, described elsewhere in this handbook. Proteins require special attention, however, as they are sufficiently more complex, their function depending on the integrity of a delicate three-dimensional tertiaiy structure that can be disrupted if the protein is not handled correctly. For this reason, this section focuses primarily on protein separations. Cell separations, as a necessary part of the downstrean i processing sequence, are also covered. 

With remarkable accuracy, Democritus in the fifth century B.C. set the stage for modem chemistry. His atomic theory of matter, which he formulated without experimental verification, still stands, more or less intact, and encapsulates the profound truth that nature s stunning wealth boils down to atoms and molecules. As science uncovers the mysteries of the world around us, we stand ever more in awe of nature s ingenious molecular designs and biological systems nucleic acids, saccharides, proteins, and secondary metabolites are four classes of wondrous molecules that nature synthesizes with remarkable ease, and uses with admirable precision in the assembly and function of living systems. 

Epoxides are often encountered in nature, both as intermediates in key biosynthetic pathways and as secondary metabolites. The selective epoxidation of squa-lene, resulting in 2,3-squalene oxide, for example, is the prelude to the remarkable olefin oligomerization cascade that creates the steroid nucleus [7]. Tetrahydrodiols, the ultimate products of metabolism of polycyclic aromatic hydrocarbons, bind to the nucleic acids of mammalian cells and are implicated in carcinogenesis [8], In organic synthesis, epoxides are invaluable building blocks for introduction of diverse functionality into the hydrocarbon backbone in a 1,2-fashion. It is therefore not surprising that chemistry of epoxides has received much attention [9]. 

Very large Serine/Threonine kinases and the molecular Target of Rapamycin, a naturally occurring secondary metabolite, TOR proteins function within multiprotein complexes to couple cell growth and stress responses to environmental and developmental cues. 

Theis N and Lerdau, M (2003), The evolution of function in plant secondary metabolites , Int. J. Plant Sci., 164 (3 Suppl.), S93-S102. 

Wink M (1999), Introduction biochemistry, role, and biotechnology of secondary metabolites , in Michael Wink, Functions of Plant Secondary Metabolites and their Exploitation in Biotechnology, Annual Plant Reviews, Academic Press, UK, 3, 1-16. 

Assuming that the metabolic pathways are similar in the biosynthesis of related isocyanoterpenes, these studies remain difficult, due in part to the competitive formation of other secondary metabolites. In addition to the common trio (-NC, NCS, -NHCHO) of the nitrogenous functions found attached to these skeletons, analogs such as -CN, -CNO, and -SCN foreshadow the complexity of identifying and selecting specific precursors to be targeted for incorporation into the family of marine isonitriles. 

Several secondary metabolites are dithiolanes, as for instance the allelochem-icals found in the tropical weed, Sphenoclea zeylanica. Zeylanoxide A is present in two stereoisomeric forms depending on whether the chirality at sulfur is (R) or (5) the latter form is 44 (Scheme 15). Zeylanoxides B are similar but in these cases the oxide function is on the sulfur at the 2 position. These molecules inhibited root growth in rice seedlings as well as the germination of letuce seeds.95... 

Heldt HW and Heldt F. 2005. Secondary metabolites fulfill specific ecological functions in plants. In Plant Biochemistry, 3rd ed. San Diego, CA Elsevier Academic Press, pp. 402-412. 

WINK, M., Functions of Plant Secondary Metabolites and their Exploitation in Biotechnology, Sheffield Academic Press, 1999, 362 p. 

Secondary chemistry differs from primary chemistry principally in its distributional variability and it is this variability that has intrigued ecologists for the past 30 years. Theories [or provisional hypotheses (35)] to account for the structural differentiation and function of secondary metabolites, as well as the differential allocation of energy and materials to defensive chemistry, abound, but they are almost exclusively derived from studies of plant-herbivore interactions (Table 2). This emphasis may be because the function of secondary chemicals in plants is less immediately apparent to humans, who have historically consumed a broad array of plants without ill effects, so alternative explanations of their presence readily come to mind. The fact that animals upon disturbance often squirt, dribble, spray, or otherwise release noxious substances at humans and cause pain leads to readier acceptance of a defensive function [although there are skeptics who are unconvinced of a... 

Bruckner, B. (1992) Secondary Metabolites Their Function and Evolution, Ciba... 

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