Diaporlabanoids A–C, Immunosuppressive Dinorlabdane Diterpene Alkaloids with an Unprecedented Carbon Skeleton from Mangrove Endophytic Fungus Diaporthe phaseolorum H3-2

Diaporlabanoids A-C (1-3, respectively), three highly modified dinorlabdane diterpene alkaloids featuring an unprecedented succinimide-containing 6/6/6/5/5-fused pentacyclic skeleton, were obtained from endophytic fungus Diaporthe phaseolorum H3-2 isolated from the Chinese mangrove Ceriops tagal. Their structures, including absolute configurations, were elucidated via spectroscopic data, X-ray crystallography, GIAO 13C NMR (DP4+), and electronic circular dichroism (ECD) calculations. Notably, 1 exhibited fascinating immunosuppressive activity via the inhibition of the CaN/NFAT and PKCθ/NFκB signal transduction pathways.