This was presented at Prep 2017 in Philadelphia on July 17th, 2017.
Pyrethrins are natural pesticides present in the oil extracted from the flowers of Chrysanthemum cinerariaefolium. These six structurally related esters are potent neurotoxins that interfere with sodium channels in neurons of insects. With low toxicity to mammals and an exceptionally safe environmental profile, there is an increasing use of the oil extract as a natural pesticide. The six pyrethrins are either of trans-chrysanthemic acid (pyrethrins I group) or pyrethric acid (pyrethrins II group). Both groups comprise pyrethrin, cinerin, and jasmolin, with minute differences in the alkyl chain in the alcohol moiety.
Isolation of multi-gram quantities of all six pyrethrins in high purity is a prerequisite to synthesizing derivatives for studying toxicity and soil degradation. High hydrophobicity and close structural similarity between the individual pyrethrins within their groups make this task challenging. As a result, large quantities of these esters have not been commercially available. To facilitate the study, we have developed a two-step purification process, in which the two groups were first separated by normal phase column chromatography on silica gel. For the separation of pyrethrin, cinerin, and jasmolin within each group we applied Centrifugal Partition Chromatography (CPC). We explored and successfully optimized solvent systems that were subsequently applied to achieve multi-gram scale separation. In both cases, gram quantities of individual pyrethrins in purity exceeding 99% were produced.