David K. Stumpf

Antifungal eudesmanoids from Parthenium argentatum x P. tomentosa

Abstract Investigation of guayule resin for antifungal activity has led to the isolation and characterization of six eudesmane-type sesquiterpenoids, five of which are new: 2-methoxy-eudesma-1,4,6-trien-3-one (argentone); 2-methoxy-15-nor-eudesma-1,4,6-trien-3-one (15-nor-argentone); 2-methoxy-15-hydroxy-eudesma-1,4,6-trien-3-one (15-hydroxy-argentone); 2-methoxy-eudesma-1,4,6-trien-3,8-dione (8-oxo-argentone); 2-methoxy-15-nor-eudesma-1,4,6-trien-3,8-dione (8-oxo-15-nor-argentone); and the previously identified 11-hydroxy-eudesma-4-en-3-one (carissone). Their structures were elucidated by one- and two-dimensional NMR spectroscopy and mass spectrometry. After 6 weeks all inhibited the growth of Aspergillus fumigatus (ATCC-13073) at 1.0 mg ml− 1 and complete inhibition of A. niger (UA-172-1) for 2-methoxy-eudesma-1,4,6-trien-3-one and 2-methoxy-15-nor-eudesma-1,4,6-trien-3-one. At 0.25 mg ml− 1 2-methoxy-eudesma-1,4,6-trien-3-one demonstrated 100% control against A. fumigatus and 80% control against A. niger.

Lesquerella fendleri seed oil content and composition: Harvest date and plant population effects

Abstract Yield losses of Lesquerella fendleri L. seeds, caused by shattering and seed oil content reduction by excessive desiccation could be minimized by the appropriate choice of harvest dates. However, no information is available on harvest dates to maximize economic returns at any planting density. This research was undertaken to study the effects of harvest dates and plant populations on oil yield and composition in L. fendleri. Mechanically seeded field plots of L. fendleri were thinned at 103 days after sowing (DAS) to density treatments of 250,000, 500,000, 750,000, 1,000,000, and an nonthinned control of 1,500,000 plants/ha. These plants were grown in 1993–1994 at The University of Arizona, Maricopa Agricultural Center in central Arizona, and were harvested at 203, 229, 243, and 264 DAS. Eight fatty acids, which make up 87–96% of mature seed oil, were investigated. These included palmitic (C16: 0), palmitoleic (C16: 1), stearic (C18: 0), oleic (C18: 1), linoleic (C18: 2), linolenic (C18: 3), lesquerolic (C20: 1-OH), and auricolic (C20: 2-OH) fatty acids. Generally, seed at the earliest harvest of 203 DAS had lower concentrations of palmitoleic, stearic, oleic, lesquerolic, and auricolic acids, and lower total oil content than those harvested at 229, 243, and 264 DAS. Also at 203 DAS, the 750,000 plants/ha treatment produced the highest fatty acid content yield, although both this oil and that from the 1,000,000 plants/ha treatment lacked auricolic acid. During this period, the major contributing fatty acids to oil content were oleic, linoleic, linolenic, and lesquerolic. Harvest at 229 DAS resulted in an increase in oil content for all treatments except the 750,000 plants/ha. Lesquerolic acid was the dominant oil for the nonthinned control. At 243 DAS, higher oil contents were observed in the 250,000, 750,000, and 1,000,000 plants/ha densities, with lesquerolic acid again the dominant fatty acid. At final harvest (264 DAS), lesquerolic acid content was virtually the same among the density treatments. No significant differences for seed yield, fatty acid composition or content were found among plant populations. The seed yield averaged over all population densities was 1344 kg/ha with a fatty acid content of 21.9%, giving an oil yield 267 kg/ha (calculated as total fatty acid content).

Determination of latex content in guayule

Abstract An analytical method for evaluating the latex content of guayule ( Parthenium argentatum Gray) is presented. This aqueous based extraction process requires only five grams of stem material and can be performed without harvesting the entire plant. To evaluate this extraction method, latex yield and quality is compared to that from Soxhlet extractions with pentane: acetone (82: 18 v/v). Gel permeation chromatography indicates that the latex extracted using this method is devoid of lower molecular weight rubber coproducts.

Semisynthetic guayule latex with reduced allergenicity

Abstract Semisynthetic latices were prepared batchwise using solvent-swollen rubber extracted from guayule ( Parthenium argentatum ). Emulsification of the extracted rubber with anionic surfactants followed by vacuum desolventization yielded stable, low-resin products. The swollen guayule rubber had a low protein content (2.3 μ g/g dry rubber). As a consequence, the semisynthetic latices had protein contents (11–20 μ g/g dry rubber) significantly lower than that of native guayule latex (129 μ g/g dry rubber) isolated directly from the shrub. More importantly, these semisynthetic latices and the dipped films prepared from compounded latices contained none of the protein allergens associated with either Hevea brasiliensis latex or native guayule latex.