Studies on Resin Glycosides. II. Unhomogeneity of "Pharbitic Acid" and Isolation and Partial Structures of Pharbitic Acids C and D, the Major Constituents of "Pharbitic Acid"

Abstract

"Pharbitic acid" (I), the component glycosidic hydroxyfatty acid of pharbitin, was found to be a mixture of two minor and two major constituents, pharbitic acids A, B, C (II) and D (III). II and III were isolated by silica gel chromatography of their p-phenyl phenacyl esters and subsequent saponification. II, mp 120-129°, [α]_D -51.4°, C₄₄H₇₈O₂₆·10H₂O, is composed of ipurolic acid, two moles each of D-glucose and L-rhamnose and one mole of D-quinovose, and III, mp 140-145°, [α]_D -63.8°, C₅₀H₈₈O₃₀·2H₂O, has another mole of L-rhamnose. Oxidation of I with Na₂Cr₂O₇ and treatment with AcONa in boiling Ac₂O both followed by acid hydrolysis provided respectively 10-hydroxytridecan-2-one (VI) and 11-hydroxytetradec-2-enoic acid (VII) as the sole ether soluble product indicating that II and III are 11-O-oligosides of ipurolic acid. On oxidation with NaIO₄ and subsequent acid hydrolysis, III provided D-quinovose, while II yielded none, and partial hydrolyses of I, II and III yielded equally monoglucoside (XI), [α]_D -16.2°, C₂₁H₄₀O₉·H₂O, diglucoside (XII), mp 114-116°, [α]_D -23.6°, C₂₇H₅₀O₁₄·1/2 H₂O, and rhamnodiglucoside (XIII), [α]_D -25.7°, C₃₃H₆₀O₁₈·H₂O. On the basis of the above results together with those of gas chromatographic analyses of aglycones and component monosaccharides of the permethylates of II, III, XII and XIII, II and III are assigned the structures either one of IIa-c and IIIa-c, respectively.