Stereochemical determination of four 10-membered ring resorcylic acid lactones from the desert plant endophytic fungus Chaetosphaeronema hispidulum

Four 10-membered ring resorcylic acid lactones (RALs) including a new compound hispidulactone F ( 1 ) and three known analogs hispidulactone B ( 2 ), 2 R , 4 R -sonnerlactone ( 3 ), and 2 R , 4 S -sonnerlactone ( 4 ) were isolated from the special bioenvironmental desert plant endophytic fungus Chaetosphaeronema hispidulum . The structure of the new compound hispidulactone F ( 1 ) was determined by extensive spectra analysis including HR-ESI-MS, NMR ( 1 H, 13 C, 1 H- 1 H COSY, HSQC, and HMBC). Hispidulactone F ( 1 ) and hispidulactone B ( 2 ) were a pair of stereoisomers at C-3, whereas 2 R , 4 R -sonnerlactone ( 3 ) and 2 R , 4 S -sonnerlactone ( 4 ) were another pair of stereoisomers at C-4. The stereochemistries of the hydroxyl groups at C-3 in 1 and 2 , and at C-4 in 3 and 4 were first determined by modified Mosher’s reactions. Thus, the absolute configuration C-3 in hispidulactone B ( 2 ) was not right in our previous report, and was rectified to be R . Compounds 1 and 4 were evaluated for their cytotoxic effects on the proliferation of HepG2. The possible biosynthetic pathway of compounds 1 – 4 was also presented.