Oryzines A & B, Maleidride Congeners from Aspergillus oryzae and Their Putative Biosynthesis

Abstract

<i>Aspergillus oryzae</i> is traditionally used in East Asia for the production of food and brewing. In addition, it has been developed into a suitable host for the heterologous expression of natural product biosynthetic genes and gene clusters, enabling the functional analysis of the encoded enzymes. <i>A. oryzae</i> shares a 99.5% genome homology with <i>Aspergillus flavus</i>, but their secondary metabolomes differ significantly and various compounds unique to <i>A. oryzae</i> have been reported. While using <i>A. oryzae</i> as a host for heterologous expression experiments we discovered two new metabolites in extracts of <i>A. oryzae</i> M-2-3 with an unusual maleidride backbone, which were named oryzine A and B. Their structures were elucidated by high resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) analysis. Their structural relationships with known maleidrides implied involvement of a citrate synthase (CS) and a polyketide (PKS) or fatty acid synthase (FAS) in their biosynthesis. Analysis of the <i>A. oryzae</i> genome revealed a single putative biosynthetic gene cluster (BGC) consistent with the hypothetical biosynthesis of the oryzines. These findings increase knowledge of the chemical potential of <i>A. oryzae</i> and are the first attempt to link a novel product of this fungus with genomic data.