The distomer is an enantiomer

Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

 in an optically active compound. It is often the case that only a single one of the enantiomers contains all of the wanted bioactivity, the distomer

Distomer

The distomer is an enantiomer in an optically active compound. It is often the case that only a single one of the enantiomers contains all of the wanted bioactivity, the distomer is often less active, has no disired activity or may even be toxic....

 is often less active, has no disired activity or may even be toxic.

In some cases the eudysmic ratio

Eudysmic ratio

The Eudysmic ratio is a common term in pharmacology, chemistry, and molecular biology. The eudysmic ratio describes the difference in pharmacologic activity between the two enantiomers of a drug....

 is so high that it is desired to separate out the two enantiomers instead of leaving it as a racemic

Racemic

In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...

 product.

It is often possible that the distomer is not simply completely inactive and actually antagonizes

Antagonist

An antagonist is a character, group of characters, or institution, that represents the opposition against which the protagonist must contend...

 the effects of the eutomer

Eutomer

The eutomer is the molecular chiral enantiomer having the desired bioactivity, e. g. as as an active ingredient in a drug. On the other hand the enantiomer of the eutomer having the undesired bioactivity is called distomer....

.