Atropisomer

Atropisomerism is a special case of axial chirality. In atropisomers is rotamers in which the rotation is a covalent single bond restricted by bulky substituents such that conformers can be isolated. For a definition of M. Oki the half-life of the isomerization must be ( conversion of a rotamer to the other ) at a given temperature more than 1000 seconds.

1922 first described the phenomenon of " atropisomerism " by Christie and Kenner, who could 2'- diphenic separate the isomers of 6,6 ' -dinitro -2,. Atropisomerism can also be observed with sterically demanding α - subsituierten styrenes. Where such atropisomers yet an additional chiral center, so diastereomeric atropisomers can be easily detected by NMR spectroscopy.

Stereochemistry and nomenclature

Atropisomers are enantiomers which can be separated and - like other enantiomers - usually have the same chemical and physical properties, except the amount of rotation. In a chiral environment, ie in a chemical reaction with an enantiomer of another chiral compound, show atropisomers - like other enantiomers - different properties and effects. Including the physiological properties of atropisomers are usually different. With regard to the nomenclature, the rules of the Cahn -Ingold -Prelog system are applied and describes the configuration of the chiral axis as Ra or Sa or in accordance with the helix nomenclature with the descriptors P ( Plus ) or M ( minus) described the stereochemistry.

Examples

Individual compounds are used in order to carry out stereoselective synthesis reactions as a chiral auxiliary. Well-known examples of this is the use of BINAP or BINOL in asymmetric synthesis.

A practical example of the importance of the herbicide metolachlor Atropisomeric.

Another example is the drug telenzepine, occurs in the atropisomerism. Telenzepine contains a stereogenic C -N bond with restricted free rotation. In neutral aqueous solution, the half-life for racemization about 1000 years. The enantiomers were separated and examined. The ( )-isomer is about 500 times more active than the (-)- isomer at the muscarinic receptor in rats.

Metolachlor

Telenzepine