Seven previously undescribed seco-abietane and seco-isopimarane type diterpenoids from Biscogniauxia sp. and their biological activities.

Three previously undescribed seco-abietane (1-3) and four undescribed 3, 4 seco-isopimarane diterpenoids (4-7) were isolated from Biscogniauxia sp. 71-10-1-1. Their structures were established through comprehensive spectroscopic analyses, quantum chemical ECD calculations, C NMR chemical shift calculations, and X-ray crystallography. Notably, biscognisecoabietate A (1) represents the first example of an abietane-type diterpenoid featuring simultaneous A-ring cleavage and B-ring rearrangement, which results in a unique 1-(4,4-dimethylpentyl)-5-isopropyl-1-methyloctahydro-1H-indene skeleton. Biscognisecoabietates B-C (2-3) are rare abietane-type diterpenoids characterized by B-ring cleavage between C-6 and C-7, along with decarboxylation at C-6. Biscognisecoisopimaric acids A-B (4-5), together with biscognisecoisopimarate B (6), represent the first examples of 3,4 seco-isopimarane diterpenoids containing a rare 6-oxabicyclo[3.2.1]octane moiety isolated from fungi. In anti-osteoporotic assays, compounds 2-3 and 5-6 exhibited significant activities, with compound 6 demonstrating the most potent effect. In anti-inflammatory assays, compounds 2-6 markedly suppressed the production of the pro-inflammatory cytokine IL-6, whereas compounds 4-7 significantly inhibited TNF-α. In addition, plausible biogenetic pathways for compounds 1-3 are proposed.