The citrus mealybug, Planococcus citri (Risso) is a common pest in the Southern U. S. and the Mediterranean. Two alternative syntheses of the female sex pheromone, (1R)-(+)-cis-2,2-dimethyl-3-isopropenyl-cyclobutane methanol acetate, have been developed. Key transformations include an allylic oxidation of (1R)-(+)-alpha-pinene to (+)-R-verbenone, oxidative decarboxylation using RuCl(3)-NaIO(4), and methylenation with Zn/CH(2)Br(2)/TiCl(4).
Hammett study was carried out on the tributyltin hydride reduction of substituted benzyl bromides. Electron-withdrawing groups facilitate the reaction, whereas electron-releasing groups have little or no impact on the rate. This unusual effect creates a discontinuity in the Hammett plot. Electron-withdrawing groups stabilize both the free radical and polar character of the transition state. Electron-releasing groups, however, stabilize the free radical character but destabilize the polar character of the transition state.
Chitosan is an abundant naturally occurring biopolymer that is biocompatible, of low toxicity and is well suited as a carrier for a range of active agents. Restrictions imposed by this biopolymers unique solubility requirements make if difficult to process. One approach to an internal setting system is to employ the water-soluble blocked isocyanate hexamethylene-1,6-di(aminocarboxysulphonate) (HDACS) in order to cross-link the chitosan and form microspheres in situ utilizing simple emulsion systems. Chitothane microspheres are capable of delivering active agents at controlled release rates and offers a viable alternative to external set methodologies utilizing aldehydes or similar cross-linking agents.
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