Spiroketones and a Biphenyl Analog from Stems and Leaves of Larrea nitida and Their Inhibitory Activity against IL-6 Production.

Bioactivity-guided fractionation for the stems of leaves of Larrea nitida Cav., using interleukin-6 (IL-6) inhibitory assay in human mast cells (HMC-1), led to the isolation of three new compounds with an unprecedented skeleton in nature ( 1 - 3 ) and three known compounds ( 4 - 6 ). Their structures were elucidated through extensive spectroscopic analysis. The three new compounds were elucidated as two new spiroketones, nitidaones A ( 1 ), and B ( 2 ) and one new biphenyl analog, nitidaol ( 3 ). The known compounds were identified as nordihydroguaiaretic acid ( 4 ), 7,3',4'-tri- O -methylquercetin ( 5 ) and ayanin ( 6 ). All the isolates were tested for their inhibitory activity against IL-6 production in HMC-1 cells. Of them, compounds 1 , 3 - 6 showed potent anti-inflammatory activity, with IC50 values of 12.8, 17.5, 14.9, 22.9, and 17.8 µM, respectively.