From Big Medical Encyclopedia

RACEMIC CONNECTIONS (synonym racemic substances, racemates) — the chemicals representing equimolar mix of two enantiomer (i.e. isomers, one of to-rykh is a mirror image of another), each of to-rykh has optical activity; in other words are the chemicals representing equimolar mix of optical antipodes. The problem of division of racemic substances is very important for pharmacology since only one of isomers has often therapeutic activity. E.g., L-DOFA is successfully applied at treatment of parkinsonism (see. Dioksifenilalanin ), whereas at D-DOFA pharmakol. there is no activity, the L-form of sarcolysine is active at treatment of nek-ry types of malignant tumors, the D-form — is inactive etc. R. page have no optical activity since from the enantiomer making them one rotates the plane of polarization of light to the right, another — to the left. The river of page cannot be divided without use of so-called chiral reagents, i.e. the connections capable to react differently with left-handed and dextrorotatory molecules.

Temperatures of melting of both enantiomer are identical, but differ, as a rule, from temperature of melting of a racemate. The racemate can crystallize in the form of mix-crystals.

Usual methods of synthesis, at to-rykh are used the substances which do not have optical activity always lead to formation of racemates. B yole. synthesis with use of enzymes — the proteins which are isomers with very high specificity leads to formation optically of homogenous matters. Under the influence of each specific enzyme only one of two possible enantiomer of a product of enzymatic reaction — amino acid, sugar, alkaloid, etc. is formed. In the course of chemical reaction, in a cut asymmetric carbon atom is mentioned, optically active connections are exposed to partial or full racemization. Nek-ry amino acids contain two asymmetric carbon atoms and can exist in four stereoisomeric forms, i.e. can form treo-and erythro-isomers. The hexoses making important group monosaccharides (see), have four asymmetric carbon atoms and can form eight racemates. Treat such sugars glucose (see), mannose (see) and galactose (see).

See also Isomerases , Isomerism .

Bibliography: Mathieu Ch.-P. and R. Kurs's Pa-niko of theoretical fundamentals of organic chemistry, the lane with fr., M., 1975; M e c of l e r D. Biokhimiya, Chemical changes in living cell, the lane with English, t. 1 — 3, M., 1980.

N. N. Zolotov.