Modifications chain-length reduction

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

The chain length or carbon number of the starting diol at the first reaction step determines the hydroxyl position with respect to the acid terminus. The position of unsaturation is fixed by selection of acetylenic intermediates which form the Grignard reagent, and the Z isomers are developed from the Lindlar reduction. Modifications of these synthetic methods were used to synthesize a variety of analogs (Bowers et al., in manuscript). 

Long-chain 3-oxoalkanoates with a carbon chain length of 10,14 or 18 C-atoms are also reduced by baker s yeast in >97% ee, but low to moderate yields if the acids are used81-128. If the methyl esters are employed the reactions are much slower and less selective. In addition to substrate modifications, several other methods are known for improving baker s yeast reduction, namely by the selective reduction with or stimulation of one of the reducing enzymes in the cell90-92. 

A major portion of the petroleum used today is derived from lipids of plants deposited in past eons. The structures of most compounds isolated from petroleum suggest a derivation from fatty acids. Various chemical changes have occurred, mostly reduction and decarboxylation, so that most petroleum is comprised of a mixture of odd- and even-chain-length hydrocarbons. Some petroleums have a variety of other compounds that appear to be derived from chemical modification of other types of secondary metabolites. 

The chemical modification of CS biopolymers via reductive amination, to yield alkylated CS derivatives, and further quaternisation result in very efficient antibacterial materials the degree of activity is correlated to the length of the alkyl chain and bacterial strain. The most active CS derivatives are more selective at killing bacteria than the quaternary ammonium disinfectants, cetylpyridinium chloride and benzalkonium chloride, and AMP. Vanillin can be used as a crosslinker of CS nsing this approach, functionalised antimicrobial polymers based on CS, vanillin. Tween 60 and so on may be easily prepared. Imino-CS biopolymer films, prepared by the acid condensation of the amino groups of CS with various aldehydes, can be used as functional biodynamic materials. 

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