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.
Preparation and activity of guanidinated or acetylated erabutoxins
