Chiral synthesis technique

Regardless of the precise structure of the chosen half southern synthon, the two main problems to be solved are the establishment of the carbon skeleton and the introduction of the necessary chirahty into the molecule. The published approaches have introduced chirality either by resolution, by starting with a chiral precursor, or via use of asymmetric synthesis techniques. The carbon skeleton has been established by use of a wide variety of techniques including the Diels-Alder and other cycloaddition reactions, heteroatom induced cyclizations, intramolecular Michael or Aldol cyclizations, intramolecular ether formation, and radical cyclization. 

Phosphorothioates can be incorporated into DNA sequences by solid-phase synthesis techniques. The chemical synthesis of the monomer imits creates a chiral center at the modified phosphorous atom. These diastereomers can be separated for chemical synthesis, while any enzymatic incorporation results in only the... 

Even the first thermotropic liquid crystals (cholesterol benzoate and cholesterol acetate) were chiral molecules, and their chiral mesophases were observed [2]. Here, the chirality is taken from the chiral pool. Because liquid crystals are needed in gram scales for physical research and technical applications, they should be prepared by short synthetic pathways using easily available starting materials. Thus, synthetic strategies based on the chiral pool are more often used than asymmetric synthesis or chiral separation techniques. 

Clearly, there is a need for techniques which provide access to enantiomerically pure compounds. There are a number of methods by which this goal can be achieved . One can start from naturally occurring enantiomerically pure compounds (the chiral pool). Alternatively, racemic mixtures can be separated via kinetic resolutions or via conversion into diastereomers which can be separated by crystallisation. Finally, enantiomerically pure compounds can be obtained through asymmetric synthesis. One possibility is the use of chiral auxiliaries derived from the chiral pool. The most elegant metliod, however, is enantioselective catalysis. In this method only a catalytic quantity of enantiomerically pure material suffices to convert achiral starting materials into, ideally, enantiomerically pure products. This approach has found application in a large number of organic... 

Chiral epoxides and their corresponding vicinal diols are very important intermediates in asymmetric synthesis [163]. Chiral nonracemic epoxides can be obtained through asymmetric epoxidation using either chemical catalysts [164] or enzymes [165-167]. Biocatalytic epoxidations require sophisticated techniques and have thus far found limited application. An alternative approach is the asymmetric hydrolysis of racemic or meso-epoxides using transition-metal catalysts [168] or biocatalysts [169-174]. Epoxide hydrolases (EHs) (EC 3.3.2.3) catalyze the conversion of epoxides to their corresponding vicinal diols. EHs are cofactor-independent enzymes that are almost ubiquitous in nature. They are usually employed as whole cells or crude... 

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