Methyl quadrangularates A - D and related triterpenes from Combretum quadrangulare

Abstract

From the MeOH extract of leaves of Combretum quadrangulare, fifteen new cycloartane-type triterpenes, methyl quadrangularates A - D (14) and N - P (8, 6, 12), methyl 24-epiquadrangularate C (5), quadrangularic acid E (9), 23-deoxojessic acid (10), 1-O-acetyl-23-deoxojessic acid (11), quadragularols A (7) and B (13) and norquadrangularic acids B (14) and C (15) were isolated together with two known cycloartane-type triterpenes, methyl 23-deoxojessate (16) and 4β, 14α-dimethyl-5α-ergosta-9β, 19-cyclo-24(31)-en-3β-hydroxy- 4α-carboxylic acid (17). Betulinic acid (18), β-sitosterol (19), kamatakenin (20), isokaempferide (21), 5,7,4'-trihydroxy-3,3'- dimethoxyflavone (22) and 5,4'-dihydroxy-3,7,3'-trimethoxyflavone (23) were also obtained from the same extract. The structures of the new compounds were elucidated on the basis of spectral analysis and chemical conversions. All the isolated compounds were tested for their cytotoxicity towards highly liver metastatic murine colon 26-L5 carcinoma cells, and the cycloartane-type triterpenes showed various degrees of cytotoxicity, whereas all the flavonoids possessed strong cytotoxicity with ED50 values equal to or less than 6 μM.