O-prenylated acylphloroglucinol derivatives from Hypericum densiflorum

The Hypericum genus (family Clusiaceae), is a rich source of prenylated acylphloroglucinol derivatives. These prenylated acylphloroglucinol derivatives are structurally diverse and exhibit a wide range of biological activities which include anti-HIV, anticancer, antioxidant, antiviral, antibacterial, anti-inflammatory, and anti-depressant effects. Previous studies of Hypericum densiflorum have afforded three O-geranylated acylphloroglucinol derivatives, which show anticancer, antioxidant and COX-2 inhibitory activities [1], in addition to inhibition of biofilm production and growth of Gram-positive bacteria, including MRSA [2]. In the current study, further phytochemical investigation of an acetone extract of H. densiflorum, collected in Pennsylvania, USA, has resulted in the purification of three new O-prenylated acylphlorglucinols, named densiflorone A-C. Densiflorone A contains an isoprenyl group and densiflorones B and C each contain an oxidized geranyl group. The ¹H NMR spectrum of each compound contained a sharp singlet between 12 and14 ppm, attributed to a phenolic proton hydrogen bonded to an acyl carbon. Signals at 5.9 and 6.1 ppm in each spectrum suggested the presence of two aromatic protons in a meta relationship. ¹H NMR signals for methylene protons between 4.2 and 4.7 pmm, accompanied by ¹³ NMR signals between 65 and 66 ppm, indicated that the isoprenyl and geranyl groups of densiflorones A-C were linked to an oxygen on the phloroglucinol core. ¹H and ¹³C NMR assignments were corroborated by 2D NMR spectroscopic data. The structures were further confirmed by mass spectrometric data.

Acknowledgements: The National Science Foundation is acknowledged for financial support.

Keywords: Hypericum densiflorum, anticancer, 1D and 2D NMR.

References:

[1] Henry GE, Campbell MS, Zelinsky AA, Liu Y, Bowen-Forbes CS, Li L, Nair MG, Rowley DC, Seeram NP. Bioactive acylphloroglucinols from Hypericum densiflorum. Phytother Res 2009; 23: 1759 – 1762

[2] Sarkisian SA, Janssen MJ, Matta H, Henry GE, Laplante KL, Rowley DC. Inhibition of bacterial growth and biofilm production by constituents from Hypericum spp. Phytother Res 2012; 26: 1012 – 1016