Steroid glycosides of the roots ofCapsicum annuum. II. The structure of the capsicosides

Abstract

Two tigogenin glycosides and two diosgenin glycosides have been isolated from a methanolic extract of the roots of bush red pepper. An attempt to isolate the individual spirostanol glycosides directly was unsuccessful. These compounds have very similar structures. For their separation, acetylation and epoxidation of the double bond of the aglycon, diosgenin, in the corresponding glycosides was performed. The derivatives obtained were purified by chromatography. To establish the complete chemical structure of each capsicoside we used both chemical and physical methods; complete and partial acid hydrolysis, methylation followed by methanolysis, IR spectroscopy, mass spectroscopy, etc. It was shown that capsicoside A₂ is (25R)-5α-spirostan-3β-ol 3-O-β-D-galactopyranoside, capsicoside B₂ is (25R)-5α-spirostan-3β-ol 3-O-[O-β-D-glucopyranosyl(1→4)-β-D-galactopyranoside], capsicoside A₃ is (25R)-spirost-5-en-3β-ol 3-O-β-D-galactopyranoside, and capsicoside B₃ is identical with funkioside C.