seco-Abietane diterpenoids, a phenylethanoid derivative, and antitubercular constituents from Callicarpa pilosissima

Callicarpa pilosissima (Verbenaceae) is an endemic evergreen shrub that grows in low- to medium-altitude forests throughout Taiwan. Diterpenoids [1], lignanoids [2], flavones [3], and their derivatives are widely distributed in plants of the genus Callicarpa. Many of these compounds exhibit cytotoxic [1], and fish-killing [3] activities. In our studies on the antitubercular constituents of Formosan plants, many species have been screened for in v itro antitubercular activity, and C. pilosissima has been found to be an active species. Investigation of the EtOAc-soluble fraction of the leaves and twigs of C. pilosissima has led to the isolation of six new compounds, including five seco-abietane diterpenoids, 12-deoxy-seco-hinokiol methyl ester (1), 12-deoxy-11,12-dihydro-seco-hinokiol methyl ester (2), callicarpic acid A (3), 9α-hydroxycallicarpic acid A (4), and callicarpic acid B (5), and a phenylethanoid derivative, 4-hydroxyphenethyl tetradecanoate (6), along with 14 known compounds (7-20). 12-Deoxy-11,12-dihydro-seco-hinokiol methyl ester (2), callicarpic acid B (5), and α-tocopherol trimer B (15) exhibit antitubercular activities (MICs ≤ 63.6 µM) against Mycobacterium tuberculosis H₃₇Rv in vitro. This work describes the structural elucidation of 1-6 and the antitubercular activities of the isolates.

Acknowledgements: This work was supported by grant from the National Science Council of the Republic of China.

References: [1] Jones, W.P. et al. (2007)J. Nat. Prod. 70:372–377.

[2] Shao, Y. et al. (2006) Chim. Acta 89:64–72.

[3] Nagai, M. et al. (1973) Yakugaku Zasshi 93:1087–1088.