Anti-inflammatory neoclerodane diterpenoids with diverse oxacyclic frameworks from Croton laui

Inflammation underlies numerous chronic diseases, and plant-derived clerodane diterpenoids have emerged as promising anti-inflammatory agents. Phytochemical investigation of the bark of Croton laui, an ethnomedicinally significant plant, afforded thirty-six previously undescribed neoclerodane diterpenoids, crolatinoids D-Z and AA-AM (1-36), together with twenty-four known analogues (37-60). Structurally, these metabolites feature a rich assortment of five- and/or six-membered oxacyclic ring systems formed through eight distinct oxygen-bridging patterns (12,20-, 17,20-, 15,16-, 19,20-, 18,19-, 6,18-, 3,19-, and 2,20-), encompassing ether, lactone, furan, hemiacetal, and acetal functionalities. Notably, compounds 1-4 possess an unprecedented 17,20-ether bridge, giving rise to a distinctive 6/6/5/5 fused heterocyclic framework. In anti-inflammatory assays, seven compounds inhibited NO production by over 50% at 20 μM, with compound 59 exhibiting the most potent activity (IC₅₀ = 2.98 ± 0.06 μM). Mechanistic studies revealed that 59 exerts its effects through dual inhibition of the NF-κB and MAPK pathways, and its in vivo efficacy was validated in a zebrafish inflammation model. These findings substantially expand the chemical diversity of neoclerodane diterpenoids and identify 59 as a promising lead for anti-inflammatory drug development.