Piptoside, a novel alkali-labile glucoside from Piptocalyx moorei Oliv.

Abstract

The β-D-glucopyranoside, piptoside, is cleaved by hot dilute acid to glucose and aglucone, the latter being partly converted with loss of carbon dioxide into a furan keto acid. Glucose is also liberated by the action of bases. With sodium methoxide, the aglucone residue rearranges to a pair of isomeric dilactone esters, whereas, with aqueous sodium hydroxide, fission of the carbon chain to (-)-2,3-dimethylsuccinic acid occurs; with alkaline hydrogen peroxide, oxidative chain fission yields a buty- rolactone-4,4-dicarboxylic acid. The structure and partial stereochemistry of each of the products follows from chemical and spectroscopic information. These results, as also those of periodate oxidation, are accounted for by formulation of the aglucone as a system of two spiro-joined γ-lactone rings, one of which is fused to a ketofuranose ring. The reaction products are analogous to well-known products from simple sugars. The hemiacetal hydroxyl group of the ketofuranose remains free in the glucoside and is unusally acidic towards diazomethane, the methyl derivatives not being alkalilabile.    Biogenesis of the aglucone may follow Michael-type addition of a 3-dehydrohexonic acid (of unknown stereochemistry) to angelic acid, or some variant.