Asteltoxins I–T: Polyketides from a Plant Endophytic Strain of <i>Pochonia bulbillosa</i>

Asteltoxins I-T (<b>1</b>-<b>12</b>), 12 asteltoxin-type polyketides, together with four known analogues (<b>13</b>-<b>16</b>), were isolated from an endophytic fungus <i>Pochonia bulbillosa</i> KNI755. Their structures, including absolute configurations, were determined by extensive spectroscopic analysis, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculations. Compound <b>1</b> featured a tetrahydro-2<i>H</i>-pyran-linked asteltoxin heterodimer incorporating a clavatol unit. Compounds <b>2</b> and <b>3</b> demonstrated unique tetrahydro-1,4-oxazine-linked asteltoxin heterodimers comprising a diphenyl ether unit. Compounds <b>4</b>-<b>7</b> presented unusual 1,4-dioxane-linked asteltoxin heterodimers also containing a diphenyl ether unit. Compounds <b>1</b>-<b>7</b> were immunosuppressive against concanavalin A (ConA)-induced T cell proliferation and lipopolysaccharide (LPS)-induced B cell proliferation with EC₅₀ values ranging from 9.2 to 26 μM and from 6.3 to 27 μM, respectively. Compound <b>1</b> exhibited inhibitory activity against the HCT116 human cancer cell line with an IC₅₀ value of 10 μM.