Bis-spirolabdane Diterpenoids from <i>Leonotis nepetaefolia</i>

Abstract

Ten new bis-spirolabdane diterpenoids, leonepetaefolins A–E (<b>1</b>, <b>3</b>, <b>5</b>, <b>7</b>, <b>9</b>) and 15-<i>epi</i>-leonepetaefolins A–E (<b>2</b>, <b>4</b>, <b>6</b>, <b>8</b>, <b>10</b>), together with eight known labdane diterpenoids (<b>11</b>–<b>18</b>) as well as two known flavonoids, apigenin and cirsiliol, were isolated from the leaves of <i>Leonotis nepetaefolia</i>. The structures of the new compounds were determined on the basis of 1D- and 2D-NMR experiments including ¹H, ¹³C, DEPT, ¹H–¹H COSY, HSQC, HMBC, and NOESY. The absolute configuration of an epimeric mixture of <b>1</b> and <b>2</b> was determined by X-ray crystallographic analysis. The compounds isolated were evaluated for their binding propensity in several CNS G-protein-coupled receptor assays in vitro