Tautomeric cinnamoylphloroglucinol-monoterpene adducts from Cleistocalyx operculatus and their antiviral activities

Abstract

Guided by ¹H NMR spectroscopic experiments using the characteristic enol proton signals as probes, three pairs of new tautomeric cinnamoylphloroglucinol-monoterpene adducts (1–3) were isolated from the buds of Cleistocalyx operculatus. Their structures with absolute configurations were established by spectroscopic analysis, modified Mosher’s method, and quantum chemical electronic circular dichroism calculation. Compounds 1–3 represent a novel class of cinnamoylphloroglucinol-monoterpene adducts featuring an unusual C-4–C-1′ linkage between 2,2,4-trimethyl-cinnamyl-β-triketone and modified linear monoterpenoid motifs. Notably, compounds 1–3 exhibited significant in vitro antiviral activity against respiratory syncytial virus (RSV).

Keywords:

• Myrtaceae
• cinnamoylphloroglucinol-monoterpene adduct
• Cleistocalyx operculatus
• antiviral activity
• absolute configuration

Disclosure statement

The authors declare no competing financial interest.

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China (Nos. 82293681(82293680), 82321004, 82204234, and 82003610), the Guangdong Basic and Applied Basic Research Foundation (Nos. 2022B1515120015 and 2021A1515111021), the Key-Area Research and Development Program of Guangdong Province (No. 2020B1111110004), the China Postdoctoral Science Foundation (No. 2021M701440), and the Science and Technology Projects in Guangzhou (202102070001).