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Crystal structures of complexes of D-xylose isomerase with deoxysugars have been determined. Deoxynojirimycin is a structural analogue of -pyranose and mimics the binding of these aldose substrates. The structure of this complex supports the hypothesis that an imidazole group catalyzes ring opening of the pyranose. The steric restrictions in the active site of the enzyme prevent a /3-pyranose from binding in the same way. For the reverse reaction with ketoses, the anomeric specificity is less certain. Dideoxyimino-D-glucitol is a structural analogue of the ketose -D-furanose. The binding of the inhibitor dideoxyimino-D-glucitol to the crystals of the enzyme does not mimic the binding of the reactive a-D-fructofuranose. Superposition of the nonphysiological substrate -D-fructofuranose onto the atomic positions of dideoxyimino-D-glucitol is not possible due to the steric restrictions of the active site. However, by utilizing the approximate 2-fold symmetry of the sugar, a stereochemically sensible model is produced which is consistent with other data. In addition to reaction with -D-furanose, the enzyme probably reacts with open ring keto sugars which are present at significant concentrations. Other sugars which resemble furanoses either do not inhibit significantly or are not observed in the crystals bound in a single conformation.

Abstract

Synthetic studies towards the insect antifeedant jodrellin A l a are reported. This work delineates a synthetic strategy that affords a polycyclic epoxy diacetate model compound 2 which contains most of the structural features found in the natural product. This material was also shown to possess mild insect antifeedant activity against Spodoptera littoralis.