New acyclic secondary metabolites from the biologically active fraction of Albizia lebbeck flowers

Abstract

The total extract of Albizia lebbeck flowers was examined in vivo for its possible hepatoprotective activity in comparison with the standard drug silymarin at two doses. The higher dose expressed promising activity especially in reducing the levels of AST, ALT and bilirubin. Fractionation via liquid–liquid partition and reexamination of the fractions revealed that the n-butanol fraction was the best in improving liver biochemical parameters followed by the n-hexane fraction. However, serum lipid parameters were best improved with CHCl3 fraction. The promising biological activity results initiated an intensive chromatographic purification of A. lebbeck flowers fractions. Two compounds were identified from natural source for the first time, the acyclic farnesyl sesquiterpene glycoside1-O-[6-O-α-L-arabinopyranosyl-β-D-glucopyranoside]-(2E,6E-)-farnesol (6) and the squalene derivative 2,3-dihydroxy-2,3-dihydrosqualene (9), in addition to eight compounds reported here for the first time from the genus Albizia; two benzyl glycosides, benzyl 1-O-β-D-glucopyranoside (1) and benzyl 6-O-α-L-arabinopyranosyl β-D-glucopyranoside (2); three acyclic monoterpene glycosides, linalyl β-D-glucopyranoside (3) and linalyl 6-O-α-L-arabinopyranosyl-β-D-glucopyranoside (4); (2E)-3,7-dimethylocta-2,6-dienoate-6-O-α-L arabinopyranosyl-β-D-glucopyranoside (5), two oligoglycosides, n-hexyl-α-L arabinopyranosyl-(1 → 6)-β-D-glucopyranoside (creoside) (7) and n-octyl α-L-arabinopyranosyl-(1 → 6)-β-D-glucopyranoside (rhodiooctanoside) (8); and ethyl fructofuranoside (10). The structures of the isolated compounds were elucidated based on extensive examination of their spectroscopic 1D and 2D-NMR, MS, UV, and IR data. It is worth mentioning that, some of the isolated linalol glycoside derivatives were reported as aroma precursors.