Diterpenoids and Bisnorditerpenoids from Blumea aromatica

Three new labdane-type Diterpenoids, 6α-O-isovalerylnidorellol (1), (12S)-blumdane (2), and (12R)-epiblumdane (3), and three new bisnorditerpenoids, 6α-O-(3-methyl-2-butenoyl)sterebin A (5), 6α-O-angeloylsterebin A (6), and 6α-O-isovalerylsterebin A (7), plus 17 known compounds were isolated from Blumea aromatica. Their structures of the new compounds were proposed by detailed spectroscopic analysis. The absolute configuration at C-12 of blumdane (2) was determined by the modified Mosher's method. The anti-inflammatory and anti-immunosuppressive effects of these isolated compounds were assessed. Compounds 9, 16, and 23 (at 40 μM) showed a slight suppression of TNF-α production, but no or little effect on the expression of PD-L1 in granulocytic myeloid-derived suppressor cells was observed for all test compounds.