Nature structural diversity

Chain metasilicates Si03 formed by comersharing of Si04 tetrahedra arc particularly prevalent in nature and many important minerals have this basic structural unit (cf, polyphosphates, p, 528), Despite the apparent simplieily of their structure motif and stoichiometry considerable structural diversity is encountered because of the differing conformations that can be adopted by the linked tetrahedra. As a result, the repeat distance along the c -axis can be (1). 

Natural monomers and polymers present a scenario where they have a structural diversity and complexity that, with appropriate chemical modifications, and taking information from modern techniques of molecular and process designs could be utilized for transforming them into high-value polymers. This was exemplified by showing the example of a natural monomer, cardanol. 

Cytochrome P450 enzymes have been the subject of a number of recent reviews in which their mechanism and scope of action are covered in much detail [1, 6, 10, 11]. The reader is referred to these articles for a more thorough account of the mechanism and reactivity of cytochrome P450 enzymes, while we present a few representative examples of cytochrome P450-catalyzed epoxidation below. The enzymes we chose are all involved in the biosynthesis of polyketide natural products. Polyketides are a large, structurally diverse family of compounds and have provided a wealth of therapeutically useful drugs and drug leads. 

The carotenoids are the most widely distributed group of pigments, occur naturally in large quantities, and are known for their structural diversity and various functions. The carotenoids constitnte a widespread class of natural pigments that occur in all three domains of life in the eubacteria, the archea, and the eucarya. Carotenoids are ubiquitous organic molecules, but they are not produced by the human body. They have been fonnd to be essential to human health based on the nutritional understanding of vitamin A (retinol) and (i-carotene. ... 

Isoprenoids or terpenoids are a large class of naturally occurring organic compounds with tremendous chemical and structural diversity. They are organic materials produced in the HMG-CoA (3-hydroxy-3-methyl-glutaryl-CoA) reductase pathway... 

Since the first description was only two decades ago, combinatorial biosynthesis has advanced from a limited set of proof-of-principle experiments into a more mature scientific discipline. To reach the maximal potential of natural product structural diversity, the combination of this approach with other established and emerging technologies will ultimately provide access to a rich variety of unnatural natural products with improved properties or new biological activities for future drug discovery and development. 

Hamann, M.T. (2003) Enhancing marine natural product structural diversity and bioactivity through semisynthesis and biocatalysis. Current Pharmaceutical Design, 9, (11) 879-889. 

A microwave-driven Sonogashira coupling step is involved in the total synthesis of azaphilones, a structurally diverse family of natural products containing a highly oxygenated bicyclic core and a quaternary center. Porco and his colleagues have described the alkynylation of densely functionalized bromobenzaldehydes with... 

A feature of the metal-ion chemistry of these large ring macrocycles is thus the structural diversity which may occur from one system to the next. This diversity can result directly from small changes in the structure of the cyclic ligand and is also aided by the inherent flexibility of the large rings involved. It is clearly also influenced by the nature of the other ligands available for complex formation. 

The well balanced electronic and coordinative unsaturation of their Ru(II) center accounts for the high performance and the excellent tolerance of these complexes toward an array of polar functional groups. This discovery has triggered extensive follow up work and carbenes 1 now belong to the most popular metathesis catalysts which set the standards in this field [3]. Many elegant applications to the synthesis of complex target molecules and structurally diverse natural products highlight their truely remarkable scope. 

Although structurally-diverse as evidenced above, the insecticidal pyrethroids still conform to a unique, operationally-defined, structure-activity relationship based on the physical characteristics and three-dimensional shape of the entire molecule conforming to those originally evidenced in the natural pyrethrins [13]. From this relationship, it becomes apparent that there is no single molecular aspect or reactive moiety that serves as a true toxophore for the pyrethroids and that their actions at target sites are dependent upon the entire stereospecific structure of these insecticides [1]. 

N-diazeniumdiolates spontaneously dissociate at physiological pH to release nitric oxide (NO) by stable first order kinetics with half-lives ranging from 2 s to 20 h [209, 210]. They are blessed with many attributes that make them an especially attractive starting point for designing solutions to important clinical problems, namely they are stable as solids, have structural diversity, a controlled rate of release of NO on hydrolysis, and a rich derivatization chemistry that facilitates targeting of NO to specific sites of need, a critical goal for therapeutic uses of a molecule with natural bioeffector roles in virtually every organ [208]. 

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