Comparative Study On Chiral Separation Of Pyrethroic Acids with Amino and Neutral Cyclodextrine Derivatives

Background: Pyrethroids are used as synthetic insecticides. They have more intensive effects than pyrethrum acid, or natural analogues found in the flowers of Chrysanthenum cinerariaefolium (Fam. Asteraceae). In the pyrethroic acids, both the geometric and chiral isomerisms appear as cumulated, therefore these compounds can be successfully used to study chiral separation.
The aim of the study was to separate by means of positively ionizable selector: permethyl- monoamino-b-cyclodextrin (PMMAbCD), monoamino-b-cyclodextrin (MAbCD) and other neutral b-cyclodextrin derivatives, the enatiomers and diastereomers of permethrinic, deltamethrinic and chrysanthemic pyrethroic acids.
Methods: Pyrethroic acids studied were chrysanthenum, permethrynic and deltamethrinic with pKa values 5,1±0,4. As chiral selectors, we used cyclodextrins: permethyl-monoamino-b-cyclodextrin( PMMAbCD) and monoamino-b-cyclodextrin( MAbCD) particularly the positively charged cyclodextrins. Experiments were carried out on a Hewlett Packard 3DCE system (Hewlett Packard, Waldbronn, Germany) with diode array UV detector at 25 °C. To characterise the separation of enantiomers we used resolution values Rs (calculated by half-width method).
Results: The PMMAbCD at 15 mM is an effective chiral separation agent for pyrethroic acids as it can fully separate all isomers of chrysanthemic, permethrinic and deltamethrinic acids with the exception of trans chrysanthemic acid which was only partially separated.
Conclusion: The best chiral separation agent toward pyrethroic acids studied was found to be permethyl-momoamino-b-cyclodextrin (PMMAbCD). The cis isomers show higher selectivity than trans isomers in the ionized form of acids. Our results show that dissociation alone can not fully explain the appearance of experimental curves, should take into consideration stereochemistry contributions.