DeepSAT-guided discovery of new eunicellin-type Diterpenoids from Cladiella krempfi and Sinularia ornata.

Guided by HSQC-based DeepSAT technology, six new eunicellin-type diterpenoids litophynols E-J (1-6), together with two known related ones 7-8, were isolated and characterized from the diethyl ether extracts of the soft corals Cladiella krempfi and Sinularia ornata. Among them, compounds 1-3, 7, and 8 were derived from C. krempfi, whereas compounds 4-6 originated from S. ornata. The structures and absolute configurations of these compounds were determined by comprehensive spectroscopic analysis, X-ray crystallography, and time-dependent density dunctional dheory electronic circular dichroism (TDDFT-ECD) calculations. Compounds 1-7 were found to possess a highly oxidized cembrane skeleton featuring a unique C-2-O-C-9 transannular ether bridge. Compound 8 was identified as having a 2,11-cyclized cembrane skeleton with an unusual C-6-O-C-9 ether bridge. All isolates were evaluated for their in vitro anti-inflammatory and antibacterial activities. Compounds 3 and 7 exhibited moderate anti-inflammatory potential by inhibiting nitric oxide (NO) production in LPS-induced RAW264.7 macrophages. In an in vitro antibacterial assay, compound 4 inhibited the growth of Streptococcus agalactiae GSB with an MIC value of 25 μM. Notably, it also exhibited significant inhibition of Staphylococcus aureus SS119-induced hemolysis. Preliminary structure-activity relationship (SAR) analysis indicated that substitutions at C-8 and C-13, particularly the presence of a free hydroxy group at C-8, played a critical role in modulating the antibacterial activity of eunicellin-type diterpenoids. These findings not only expanded the structural diversity of marine-derived eunicellin-type diterpenoids but also highlighted their potential as promising drug leads.