Antimicrobial bianthrones from the crinoid Heterometra sp

Antimicrobial resistance is a global public health problem and identification of new chemical scaffolds is important to overcoming this threat. In a recent high-throughput discovery campaign, fractions derived from the organic extract of crinoid, Heterometra sp. (Echinodermata), showed antibacterial activity. Chemical investigation of this extract led to the isolation of three natural products, namely crinemodin bianthrone (1), the new structure 1''-dehydrocrinemodin bianthrone (2), and 1''-hydroxycrinemodin bianthrone (3). Their planar structures were determined through HRESIMS and 1D and 2D NMR analysis while a combination of chemical and chirooptical methods was employed to define their absolute configurations for the first time. Variations in proton chemical shifts as well as instability in DMSO and pyridine were observed for 3. Compounds 1 and 3 showed selective antimicrobial activity against Gram-positive bacterial strains.