Dauresorcinols A and B, Two Pairs of Merosesquiterpenoid Enantiomers
with New Carbon Skeletons from Rhododendron dauricum
Abstract
Five pairs of new merosesquiterpenoid enantiomers, named dauresorcinols
A−E (1−5), were isolated from the leaves of
Rhododendron dauricum. Their structures were elucidated by
comprehensive spectroscopic data analysis, quantum chemical
calculations,
Rh2(OCOCF3)4-induced
ECD, and single-crystal X-ray diffraction analysis. Dauresorcinols A
(1) and B (2) possess two new merosesquiterpene
skeletons bearing an unprecedented
2,6,7,10,14-pentamethyl-11-oxatetracyclo[8.8.0.02,7.012,17]octadecane
and a caged
15-isohexyl-1,5,15-trimethyl-2,10-dioxatetracyclo[7.4.1.111,14.03,8]pentadecane
motif, respectively. Plausible biosynthetic pathways of
1−5 are proposed involving key oxa-electrocyclization
and Wagner−Meerwein rearrangement reactions. (+)/(−)-1 and
3−5 showed potent α-glucosidase inhibitory activity, 3
to 22 times stronger than acarbose, an antidiabetic drug targeting
α-glucosidase. Docking results provide a basis to design and develop
merosesquiterpenoids as potent α-glycosidase inhibitors.