Plasmodium-Resistant Indole Diterpenoid Biosynthesis Gene Cluster Derived from <i>Aspergillus oryzae</i> Was Activated by Exogenous P450 Gene <i>Ast B</i>

Abstract

Synthetic biology is an effective way to activate silent biosynthetic gene clusters. Five new indole diterpenoids (<b>1</b>, <b>2</b>, <b>5</b>, <b>9</b>, and <b>10</b>), together with 10 known derivatives (<b>3</b>, <b>4</b>, <b>6</b>-<b>8</b>, and <b>11</b>-<b>15</b>) were activated from <i>Aspergillus oryzae</i> transformants by an exogenous P450 gene <i>Ast B</i> and obtained under the guidance of molecular networking. Their planar structures were determined by NMR and HR-ESI-MS. The absolute configuration of compound <b>1</b> was determined by single crystal X-ray diffraction, and those of compounds <b>2</b>, <b>5</b> , <b>9</b>, and <b>10</b> were confirmed by comparing the observed ECD with the calculated ECD. HPLC analysis suggested that the BGCs of indole diterpenoids in <i>A. oryzae</i> were activated by exogenous P450 gene <i>Ast B</i>. Compounds <b>1</b>-<b>4</b>, <b>7</b>, <b>8</b>, and <b>11</b> displayed strong activity against chloroquine-sensitive plasmodium strain <i>P.f.</i>3D7 with IC₅₀ values ranging from 0.84 to 2.9 μM. It is the first report that indole diterpenoids have potential antimalarial activity. The structure-activity relationship study showed that the linear indole diterpenoids contribute significantly to the antiparasite activity. Molecular docking studies showed that <b>1</b> and positive control chloroquine were at the center of the active pocket of <i>Pf</i>Hsp90, while <b>11</b> was far from the active site.