γ-lactam and γ-lactone-containing sesterterpenoids from Colquhounia coccinea var. mollis with immunosuppressive activity.

Ten previously undescribed sesterterpenoids (1-10), characterized by α,β-unsaturated-γ-lactam and γ-lactone motifs, were isolated from Colquhounia coccinea var. mollis and their structures were elucidated via spectroscopic analyses (1D/2D NMR, HRMS, ECD) and X-ray crystallography. Biological evaluation identified colquhoulactam A (1) as an inhibitor of IFN-γ secretion in T cells, exhibiting an IC50 value of 12.83 μM and superior activity compared to its γ-lactone analogues. Furthermore, plausible biogenetic pathways were proposed to link lactam-bearing colquhoulactams to colquhounoids, underscoring divergent oxidative modifications in terpenoid biosynthesis.