Tautomeric cinnamoylphloroglucinol-monoterpene adducts from and their antiviral activities.

Guided by H NMR spectroscopic experiments using the characteristic enol proton signals as probes, three pairs of new tautomeric cinnamoylphloroglucinol-monoterpene adducts (-) were isolated from the buds of . Their structures with absolute configurations were established by spectroscopic analysis, modified Mosher's method, and quantum chemical electronic circular dichroism calculation. Compounds - represent a novel class of cinnamoylphloroglucinol-monoterpene adducts featuring an unusual C-4-C-1' linkage between 2,2,4-trimethyl-cinnamyl--triketone and modified linear monoterpenoid motifs. Notably, compounds - exhibited significant antiviral activity against respiratory syncytial virus (RSV).