Unusual Anti-allergic Diterpenoids from the Marine Sponge Hippospongia lachne.

Hipposponlachnins A (1) and B (2), possessing an unprecedented tetracyclo [9.3.0.0 ^2,8 .0 ^3,7 ] tetradecane ring system, and the probable biogenetic precursor [3, (1R*,2E,4R*,7E,10S*,11S*,12R*)-10, 18-diacetoxydolabella-2,7-dien-6-one] of 1‒2 were isolated from the South China Sea marine sponge Hippospongia lachne. The structures of the novel compounds were determined using integrated spectroscopic methods in combination with single-crystal X-ray diffraction analysis. Compounds 1‒2 showed potent inhibitory activity on the release of β-hexosaminidase, a biomarker for degranulation, as well as the production of pro-inflammatory cytokine IL-4 and lipid mediator LTB ₄ in DNP-IgE-stimulated RBL-2H3 cells.