Pyrethrum is a natural insecticide extracted from Tanacetum cinerariifolium. Six esters, the pyrethrins, are responsible for the extract's insecticidal activity. The oxidative degradation of pyrethrins through contact with aerial oxygen is a potential cause of pyrethrin losses during pyrethrum manufacture. Described here is the first investigation of the autoxidation chemistry of the six pyrethrin esters isolated from pyrethrum. It was found that pyrethrins I and II, the major pyrethrin esters present in pyrethrum, undergo autoxidation more readily than the minor pyrethrin esters, the jasmolins and cinerins. Chromatographic analysis of pyrethrin I and II autoxidation mixtures showed some correlation with a similar analysis performed on extracts from T. cinerariifolium crop, which had been stored for 12 weeks without added antioxidants. Two pyrethrin II autoxidation products were isolated, characterized, and shown to be present in extracts of stored T. cinerariifolium crop, confirming that autoxidation of pyrethrin esters does occur during crop storage.

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The synthesis of a set of monofluorinated, difluorinated, and non-fluorinated N-acetylated-β3-arginine esters, potential inhibitors of trypsin-like proteases, is described. Elaboration to the target compounds from previously reported enantiopure precursors derived from 3-hydroxypropanal involved 6–7 steps and was achieved in 48–65 % overall yield. The α,α-difluoro-β3-arginine derivative was found to be particularly prone to hydrolysis. Three β3-arginine derivatives were tested for their ability to inhibit trypsin, the α,α-difluoro compound being assayed in the form of a carboxylate zwitterion.