Efficient, Baseline Separation of Pyrethrins by Centrifugal Partition Chromatography

Abstract

Pyrethrins are natural pesticides present in the oil extracted from the flowers of Chrysanthemum cinerariaefolium. They are potent ion-channel neurotoxins which have higher selective toxicity for insects compared to mammals. These phytochemicals have an exceptionally safe environmental profile and are an attractive natural alternative to organophosphate insecticides currently used in agriculture. The oil extract contains six pyrethrins compounds, which are structurally related esters. Isolation of reference standards for pyrethrins and their derivatives in multi-gram quantities is a prerequisite for studying toxicity and soil degradation for these natural pyrethrins. Chromatography is difficult because of the high hydrophobicity and close structural similarity. The isolated pyrethrin compounds also have poor stability because they are photosensitive. To facilitate these studies, we have developed a twostep purification process, in which the two groups were first separated by normal phase liquid chromatography on silica gel. The separation of pyrethrin, cinerin, and jasmolin within each group was achieved by centrifugal partition chromatography (CPC). We explored and successfully optimized solvent systems that were subsequently applied to achieve multi-gram scale separation. The pyrethrins I group compounds were separated using a solvent system containing heptane-methanol-acetonitrile (6:1:2, v/v) in ascending mode. The pyrethrins II group compounds were separated using a solvent system containing heptane-terbutylmethyl ether-acetonitrile-water (8:1:5:1.5, v/v) also in ascending mode. In both cases, gram quantities of individual pyrethrins with purity exceeding 99% were produced.