Novel cytotoxic acylated oligorhamnosides from Mezzettia leptopoda

Activity-guided fractionation of a stem extract of Mezzettia leptopoda usin g human oral epidermoid carcinoma (KB) cells led to the isolation of seven highly acylated oligorhamnosides. Four of these constituents are novel, nam ely, n-octyl 2-O-acetyl-alpha-L-rhamnopyranosyl-(1-->3)-2,4-di-O-acetyl-alp ha-L-rhamnopyranosyl-(1-->3)-4-O-hexanoyl-alpha-L-rhamnopyranoside (mezzett iaside 8) (1); n-octyl 2,3-di-O-acetyl-alpha-L-rhamnopyranosyl-(1-->3)-4-O- hexanoyl-alpha-L-rhamnopyranoside (mezzettiaside 9) (2); n-octyl 2,4-di-O-a cetyl-alpha-L-rhamnopyranosyl-(1-->3)-4-O-hexanoyl-alpha-L-rhamnopyranoside (mezzettiaside 10) (3); and n-octyl 2,3,4-tri-O-acetyl-alpha-L-rhamnopyran osyl-(1-->3)-4-O-hexanoyl-alpha-L-rhamnopyranoside (mezzettiaside 11) (4). Three known compounds were identified as mezzettiasides 2 (5), 3 (6), and 4 (7), respectively, previously isolated from this same plant. The structure s of novel compounds 1-4 were determined by spectroscopic methods. All the isolates were evaluated against a panel of human cancer cell lines in this study, and compounds 1-2 and 4-7 were found to be weakly cytotoxic toward K B and/or human colon and lung cancer cell lines.