Enantiomeric Pairs of Meroterpenoids with Diverse Heterocyclic Systems from Rhododendron nyingchiense.

Eight enantiomeric pairs of new meromonoterpenoids (1a/1b-8a/8b) and four known compounds (9-12) were isolated from Rhododendron nyingchiense. Their structures were established by spectroscopic methods, quantum chemical calculations, and X-ray crystallography. The enantiomeric pairs were acquired from scalemic mixtures by chiral-phase HPLC and showed diverse heterocyclic frameworks. Compounds 1a/1b possess a rare 6/7/5/5 heterocyclic system, and 2a/2b incorporate a new 6/6/3/5 heterocyclic system featuring a quinone motif. Compounds 3a/3b represent the first meroterpenoids with a 6/6/5 ring system from the Rhododendron genus. Putative biosynthetic pathways of these compounds are proposed. Compounds 1b, 2a-4a, 8a, 8b, and 11 exhibited weak inhibitory effects on PTP1B, with IC50 values ranging from 5.7 ± 0.5 to 61.0 ± 4.8 μM.