Oleanane Triterpenoids from the Leaves of <i>Gymnema inodorum</i> and Their Insulin Mimetic Activities

Abstract

During an effort to find insulin mimetic compounds, the leaves of <i>Gymnema inodorum</i> were shown to have a stimulatory effect on glucose uptake in 3T3-L1 adipocyte cells. Bioassay-guided fractionation on a 70% ethanol extract of <i>G. inodorum</i> was applied to yield two new (<b>1</b> and <b>2</b>) and two known (<b>8</b> and <b>9</b>) oleanane triterpenoids with a methyl anthranilate moiety together with five further new oleanane triterpenoids (<b>3</b>-<b>7</b>). The chemical structures of all isolates were determined based on their spectroscopic data, including IR, UV, NMR, and mass spectrometric analysis. The isolated compounds (<b>1</b>-<b>9</b>) were determined for their stimulatory activities on glucose uptake in differentiated 3T3-L1 adipocyte cells using 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-d-glucose (2-NBDG) as a fluorescent-tagged glucose probe. Three compounds (<b>3</b>, <b>5</b>, and <b>9</b>) showed stimulatory effects on the uptake of 2-NBDG in 3T3-L1 adipocyte cells. Chemicals with a methyl anthranilate moiety have been considered as crucial contributors of flavor odor in foods, and quantitative analysis showed the content of compound <b>8</b> to be 0.90 ± 0.01 mg/g of the total extract. These results suggest that the leaves of <i>G. inodorum</i> have the potential to be used as an antidiabetic functional food or tea.