Lithocarpic Acids A–N, 3,4-<i>seco</i>-Cycloartane Derivatives from the Cupules of <i>Lithocarpus polystachyus</i>

Abstract

Fourteen new 3,4-<i>seco</i>-cycloartane-type triterpenes, lithocarpic acids A–N (<b>1</b>–<b>14</b>), together with one known compound, coccinetane E (<b>15</b>), were identified from the cupules of <i>Lithocarpus polystachyus</i>. The structures of <b>1</b>–<b>14</b> were determined by spectroscopic data analysis and chemical methods, and the absolute configurations of <b>1</b> and <b>4</b> were defined unequivocally by X-ray crystallography using Cu Kα radiation. Compounds <b>1</b>–<b>15</b> are the first examples of 3,4-<i>seco</i>-cycloartane derivatives isolated from the genus <i>Lithocarpus</i>. Among them, compounds <b>1</b> and <b>2</b>, <b>9</b> and <b>10</b>, and <b>11</b> and <b>12</b> were found to be three pairs of C-24 epimers, while compounds <b>7</b> and <b>8</b> represent the first examples of 3,4-<i>seco</i>-norcycloartane-type triterpenes. Compound <b>1</b>, as the major component of the plant extract, showed potent antibacterial activity against <i>Micrococcus luteus</i> and <i>Bacillus subtilis</i>, with MIC values of 3.1 and 6.3 μg/mL, respectively, as well as inhibitory activity against human and mouse 11β-hydroxysteroid dehydrogenase type 1, with IC₅₀ values of 1.9 and 0.24 μM, respectively