Genome-Guided Discovery of Pretilactam from Actinosynnema pretiosum ATCC 31565

Abstract

<i>Actinosynnema</i> is a small but well-known genus of actinomycetes for production of ansamitocin, the payload component of antibody-drug conjugates against cancers. However, the secondary metabolite production profile of <i>Actinosynnema pretiosum</i> ATCC 31565, the most famous producer of ansamitocin, has never been fully explored. Our antiSMASH analysis of the genomic DNA of <i>Actinosynnema pretiosum</i> ATCC 31565 revealed a NRPS-PKS gene cluster for polyene macrolactam. The gene cluster is very similar to gene clusters for mirilactam and salinilactam, two 26-membered polyene macrolactams from <i>Actinosynnema mirum</i> and <i>Salinispora tropica</i>, respectively. Guided by this bioinformatics prediction, we characterized a novel 26-membered polyene macrolactam from <i>Actinosynnema pretiosum</i> ATCC 31565 and designated it pretilactam. The structure of pretilactam was elucidated by a comprehensive analysis of HRMS, 1D and 2D-NMR, with absolute configuration of chiral carbons predicted bioinformatically. Pretilactam features a dihydroxy tetrahydropyran moiety, and has a hexaene unit and a diene unit as its polyene system. A preliminary antibacterial assay indicated that pretilactam is inactive against <i>Bacillus subtilis</i> and <i>Candida albicans</i>.