Exploring Diversified Abietane Diterpenoids from Leucosceptrum canum with Immunosuppressive and Antifungal Activities

Thirty-nine structurally diversified abietane diterpenoids, including 20 new ones ( 1 – 20 ) and 19 known ones ( 21 – 39 ), were isolated from Leucosceptrum canum . Their structures were elucidated by extensive NMR spectroscopic analysis, ECD calculations, and X-ray diffraction. Notably, compounds 1 and 2 possess the rare 5/6/6- and 5/6-fused ring systems, respectively. Compound 4 is a trinor -abietane diterpenoid featuring a novel 18(4→3)- abeo -9,10- seco -15,16,17- trinor -abietane skeleton, while compounds 11 – 20 and 38 – 39 are abietane diterpenoids with distinct 9,13-endoperoxide stereoconfigurations. Compounds 1, 3, 11 – 20, and 38 – 39 exhibited extensive immunosuppressive activity by inhibiting the proliferation of T cells and the production of cytokine IFN-γ, with IC 50 values ranging from 3.75 to 14.96 μM, and the preliminary structure–activity relationship was summarized. Compounds 4, 34, and 38 – 39 exhibited moderate antifungal activities against Curvularia lunata, Fusarium graminearum, and F. oxysporum, with IC 50 values ranging from 39.4 to 106.6 μM.