Chemical Constituents of the Ficus elastica Leaves and Their Antioxidant Activities

Abstract

Ficus elastica Roxb. Ex Hornem also known as rubber tree, is a tree species belonging to the Moraceae family. This plant grows profusely without any agronomic management and survives well under extreme environmental conditions such as high temperature and limited water supply. F. elastica possesses antimicrobial activity and the leaves extract is used for the treatment of skin infections and skin allergies, as well as a diuretic agent. In addition, several chemical constituents from F. elastica have been investigated. 1 Previously, we reported the antioxidant activities of compounds from the leaves of F. microcarpa and F. callosa . 2,3 In our screening project for antioxidant activities from Ficus species, the leaves of F. elastica was found to exhibit significant antioxidant activities. As part of our continuing research into the biological activities of F. elastica leaves, we report herein the isolation, structural elucidation, and evaluation of antioxidant activities of extracts, as well as two new compounds, ficuselastic acid (2) and (1'S,6'R)-8-O-β-Dglucopyranosyl abscisate sodium (7), along with twelve known compounds from the leaves of F. elastica. Compound 2 was obtained as a white amorphous powder and its molecular formula was determined to be C14H16O6 by ESI-MS at m/z 279 [M–H] – (negative) and HR-ESI-MS at m/z 279.0858 (Calcd C14H15O6 for 279.0874). The 1 H-NMR spectrum of 2 showed signals for a secondary methyl at δH 1.23 (d, 7.0), an acetyl methyl at δH 2.04 (s), an oxygenated proton at δH 5.19 (m), and an olefinic proton at δH 6.19 as listed in Table 1. The 13 C-NMR and DEPT spectra of 2 revealed seven non-protonated carbons, consistent with two carbonyls (δC 172.7 and 174.9) and five olefinics (δC 105.2, 122.3, 139.1, 161.9, and 164.9), together with seven pro