Secondary metabolites from the root of Ehretia longiflora and their antitubercular activity

Ehretia longiflora Champ. ex Benth. (Boraginaceae) is a medium sized deciduous tree, distributed in south China, Indochina, and in forests from low elevations to 750m of Taiwan [1]. The methanolic extract of the root of this plant showed antitubercular activity against Mycobacterium tuberculosis H37Rv in vitro. The aim of this study is the isolation of chemical constituents and antitubercular activity. Bioassay-guided fractionation of the ethyl acetate-soluble layer from the root of this species led to the isolation of four new compounds, including one quinonoid: ehretiquinone (1); one triterpenoid: ehretiolide (2); one alkaloid: ehretilonine (3); one acetamide: ehretilonamide (4), together with nineteen known compounds, of which three compounds, comprising of 1-(4-methoxyphenyl)-4-phenylbutane-2,3-diol (5), ehretiquinonone (6), (2S,3S)-1,4-bis(4-methoxyphenyl)butan2,3-diol (7), were first isolated from nature. The structures of these isolates were elucidated by spectral analysis. Among these isolates, 1, 5 and 8 exhibited antitubercular activity against M. tuberculosis H37Rv in vitro, showing MIC values of 25.0, 30.0 and 50.0µg/mL, respectively. The clinically use antitubercular agent, ethambutol, was used as a positive control. Antitubercular activity assay of the isolates are still in progress.

Fig.1: Compounds 1-7

References: 1. Hsiao JY, Liu HY (1998) Flora of Taiwan, Editorial Committee of the Flora of Taiwan, Taipei.