Diastereoisomers


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Diastereoisomers

 

(also called diastereomers), stereoisomers with several asymmetrical centers in which the configuration of some of the asymmetrical atoms coincides and that of others is opposite. In contrast to optical antipodes, in which the configuration of all asymmetrical centers is opposite and which differ from each other only in the sign of optical rotation (with complete coincidence of all other properties) diastereoisomers differ not only in the extent of optical rotation but also in other physical properties, such as melting point and solubility, in some chemical properties (for example, reaction rates). For example, mesotartaric acid is a disastereoisomer with respect both to (-) -tartaric and (+)-tartaric acid, although the two are optical antipodes. The method of splitting racemic compounds into optically active substances is based on the difference in the physical properties of disastereoisomers. For example, if an optically active base acts on racemic acid, the resultant salts will be disastereoisomers and can be separated by ordinary methods such as crystallization, after which optically active acids are regenerated from the salts. Racemic bases are separated in a similar manner.

References in periodicals archive ?
Silymarin consists of at least seven flavonolignans, of which the most prevalent are the diastereoisomers silybin A and silybin B; silibinin consists only of silybin A and silybin B.
We were not able to separate the isomers present in the pheromone volatiles collected from females or synthetic stereoisomers with 2 different chiral columns because the enantiomers of branched aliphatic hydrocarbons do not possess a functional group that permits derivatized into diastereoisomers that could be separated by chromatographic methods or by spectroscopic techniques such as Nuclear Magnetic Resonance (Meierhenrich et al.
It is postulated that the glucose a-anomers bind faster than the [beta\-anomers, but the overall response is poor because the relative abundance of [alpha]-anomers is low and interconversion between the different diastereoisomers is slow.
The hydroboration of 7a (diastereomeric mixture) resulted in 6- and 7-hydroxy methylacetals 8a and 9a, as a sum of 8 regio- and diastereoisomers (ratio of 8a and 9a was 4 : 1), and also 4% of the corresponding 6(S)-hydroxylactol 10.