Modelling the controlled release of toxins in a rumen environment

Pimelea poisoning in grazing cattle has been a long-time pestilence for the pastoral industry throughout arid regions of inland Australia.1 The causative native Pimelea species have been confirmed with the secondary metabolite simplexin, a daphnane orthoester, being extracted and identified as the principal toxin. There is no effective prevention or remedy for Pimelea poisoning, however naïve calves have previously been demonstrated to develop detoxification capability following prolonged low-dose simplexin intake. In parallel with the ongoing search for potential rumen microflora able to decompose simplexin, a variety of biocomposites are being manufactured by encapsulating Pimelea plant material or a crude simplexin extract in biodegradable and biocompatible polyesters, aiming to develop a slow sustained toxin release mechanism via hypothesised surface erosion (Figure 1). In this project, a method to quantify simplexin within these biocomposites was established and validated utilising solid phase extraction combined with UHPLC-Q-Orbitrap MS/MS. Based on this assay, the release kinetics of simplexin from these complex systems when exposed to rumen environment in vitro and in vivo will be revealed. The effects of factors such as matrix formulation, matrix geometry, filler dimensions, types and crystallinity of the polymeric material on microscopic and macroscopic biodegradation patterns and the resulting in vitro releasing behaviour of simplexin will be investigated. Mathematical models reflecting the underlying mass transport mechanism of simplexin will be ultimately built from the simplest assumptions to increasing complexity as needed to deliver robust prediction, which holds the potential to guide the development of new intra-ruminal devices with tailored releasing performances

Insect chemistry and chirality

Examination of the chemistry of a number of Australian insect species provided examples of unusual structures and encouraged determinations of their absolute stereochemistry by stereocontrolled syntheses and chromatographic comparisons. Inter alia, studies with the fruit-spotting bug (Amblypelta nitida), certain parasitic wasps (Biosteres sp.), the aposematic shield bug (Cantao parentum), and various species of scarab grubs are summarized. The determination of enantiomeric excesses (ee's) for component epoxides, lactones, spiroacetals, and allenes are described. Stereochemical and related aspects of the biosynthesis of spiroacetals in certain fruit-fly species (Bactrocerae sp.) are also presented