Penicisteckins A–F, Isochroman-Derived Atropisomeric Dimers from Penicillium steckii HNNU-5B18

Penicisteckins A-D (1-4), two pairs of atropodiastereomeric biaryl-type hetero- and homodimeric bis-isochromans with 7,5'- and 7,7'-linkages and a pair of atropodiastereomeric 2-(isochroman-5-yl)-1,4-benzoquinone derivatives [penicisteckins E (5) and F (6)], were isolated from the Penicillium steckii HNNU-5B18. Their structures including the absolute configuration were determined by extensive spectroscopic and single-crystal X-ray diffraction analysis and TDDFT-ECD calculations. Both the bis-isochromans and the isochroman/1,4-benzoquinone conjugates represent novel biaryl scaffolds containing both central and axial chirality elements. The monomer anserinone B (8) exhibited potent antibacterial activities against Staphylococcus aureus ATCC 29213 and methicillin-resistant Staphylococcus aureus with minimal inhibition concentration values ranging from 2 to 8 μg mL-1. Plausible biosynthetic pathways of 1-6 are proposed, which suggest how the absolute configurations of the isolates were established during the biosynthetic scheme.