Enantiomeric pairs of meroterpenoids from Rhododendron fastigiatum.

Five pairs of optically pure meroterpenoid enantiomers (1a/1b-5a/5b) and two known compounds (6 and 7) were isolated from Rhododendron fastigiatum. Compounds 1a/1b-5a/5b were resolved from naturally scalemic mixtures by chiral HPLC. Their structures were elucidated by spectroscopic methods, X-ray crystallographic experiments, and ECD analyses. Compounds 1a/1b, 2a/2b, 3b, 4a/4b, and 5a/5b were new meroterpenoids with different polycyclic systems. Two enantiomeric pairs (2a/2b and 3a/3b), 6, and 7 exhibited inhibitory effects on protein tyrosine phosphatase 1B (PTP1B) in vitro.