Chirality in nature

Although the different enantiomers of a chiral molecule have the same phju ical properties, they usually have different biological properties. For exam pie, the dextrorotatory enantiomer oflimonene has the odor of oranges, ba the levorotatory enantiomer has the odor of lemons. 

The hundreds of different pharmaceutical agents approved for use by the U.S. Food and Drug Administration come from many sources. Many drugs are isolated directly from plants or bacteria, others are made by chemical modification of naturally occurring compounds, and still others are made entirely in the laboratory and have no relatives in nature. 

Those drugs that come from natural sources, either directly or after chemical modification, are usually chiral and are generally found only as a single enantiomer rather than as a racemic mixture. Penicillin V, for example, an antibiotic isolated from theFenicillium mold, has the 2S,5ft,6/ configuration. Its enantiomer, v/hich does not occur naturally but can be made in the laboratory, has essentially no biological activity. 

In contrast to drugs from natural sources, those drugs that are made entirely in the laboratory are either achiral or, if chiral, are often produced and sold as racemic mixtures. Ibuprofen, for example, contains one chirality center, and only the S enantiomer is active as an analgesic and anti-inflammatory agent. The R enantiomer of ibuprofen is inactive, although it is slowly converted in the body to the active S form. Nevertheless, the substance marketed under such trade names as Advil, Nuprin, and Motrin is a racemic mixture of R and S. 

Not only is it chemically wasteful to synthesize and administer an enantiomer that does not serve the intended purpose, many examples are now known where the presence of the wrong enantiomer in a racemic mixture either affects the body s ability to utilize the right enantiomer or has unintended pharmacological effects of its own. The presence of (jR)-ibuprofen in the racemic mixture, for instance, slows substantially the rate at which the S enantiomer takes effect in the body, from 12 minutes to 38 minutes. 

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The introduction of synthetic materials into natural products, often described as adulteration , is a common occurrence in food processing. The types of compounds introduced, however, are often chiral in nature, e.g. the addition of terpenes into fruit juices. The degree to which a synthetic terpene has been added to a natural product may be subsequently determined if chiral quantitation of the target species is enabled, since synthetic terpenes are manufactured as racemates. Two-dimensional GC has a long history as the methodology of choice for this particular aspect of organic analysis (38). 

Mori K (2002) Chirality in the natural world chemical communications. In Lough WJ, Wainer JW (eds) Chirality in natural and applied science. Blackwell, Oxford, p 241... 

CHIRALITY IN NATURE AND INDUSTRY THE PRESENT AND THE FUTURE. ENZYMES AND ANTIBODIES... 

In summary, the origin of the chiral amplification is basically the difference in stability of the homochiral and heterochiral dinuclear Zn complexes. These complexes act as catalyst precursors, but differences in their kinetic behavior also affect the degree of the nonlinear effect. This investigation is probably the first example of elucidation of a molecular mechanism of catalytic chiral amplification (41) and may provide a chemical model of one means of propagation of chirality in nature. 

Although all proteins are complex in structure and chiral in nature, some of them could achieve the status of a chiral selector in liquid chromatography. The complex structures of proteins are the result of the different intramolecular hydrogen-bonding, disulfide bridges, and other types of bonding. All of the proteins used for chiral resolution in liquid chromatography are obtained from animals except for cellobiohydrolase-I. The structures and properties of some of the most commonly used proteins as chiral selectors are discussed herein. 

The existence of chirality in nature is of particular importance in numerous recognition processes, often illustrated by examples detectable by non-spectroscopic methods such as the different orange and lemon odors of R-(+)- and S-(-)-limonene, respectively (Fig. 3) [8]. As such, chiral discrimination is also of considerable consequence in the medical sciences, as often one enantiomer is pharmaceutically active whereas the other may show adverse side effects. A historic example is the anti-emetic activity of one of the enantiomers of thalidomide, while the other can cause fetal damage [9,10]. These considerations highlight the importance of chiral discrimination in the production of biologically active materials, whereas on the other hand, the design of routes to asymmetric synthesis presents an active challenge to synthetic chemists worldwide. 

K. Mori, Chirality in the Natural World Chemical Communications. In Chirality in Natural and Applied Science W. J. Lough,... 

Abstract Understanding the origin of chirality in nature has been an active area of research since the time of Pasteur. In this chapter we examine one possible route by which this asymmetry could have arisen, namely chiral-specific chemistry induced by spin-polarized electrons. The various sources of spin-polarized electrons (parity violation, photoemission, and secondary processes) are discussed. Experiments aimed at exploring these interactions are reviewed starting with those based on the Vester-Ulbricht hypothesis through recent studies of spin polarized secondary electrons from a magnetic substrate. We will conclude with a discussion of possible new avenues of research that could impact this area. 

What is the origin of chirality in nature Most biomolecules can be synthesized in mirror-image shapes. Yet in organisms, amino acids are always left-handed, and sugars are always right handed. The origins of this preference remain a mystery. 

Another aspect of NLE is asymmetric autocatalysis as an event following symmetry breaking in nature. On the origin of chirality in nature, two major mechanisms have been proposed [28]. (1) Chance mechanism To generate an optically... 

A characteristic hallmark of life is believed to be its homochirality .36 In general, it is true, although natural products are not always enantiomerically pure.37 The origin of biomolecular homochirality is discussed in depth by MacDermott.36 Those who are interested to see whether the parity-violating weak force is the cosmic dissymmetry that Pasteur was looking for should read her chapter in the book entitled Chirality in Natural and Applied Sciencd. 

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