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

Diaporlabanoids A-C (<b>1</b>-<b>3</b>, 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 <i>Diaporthe phaseolorum</i> H3-2 isolated from the Chinese mangrove <i>Ceriops tagal</i>. Their structures, including absolute configurations, were elucidated via spectroscopic data, X-ray crystallography, GIAO ¹³C NMR (DP4+), and electronic circular dichroism (ECD) calculations. Notably, <b>1</b> exhibited fascinating immunosuppressive activity <i>via</i> the inhibition of the CaN/NFAT and PKCθ/NFκB signal transduction pathways.