Rhizomatoflavonoid D and Other Flavonoids from the Twigs of Ochna Rhizomatosa as a Potential Inhibitor of HIV-1

Currently, HIV morbidity and mortality in sub-Saharan Africa remain a huge concern and awaiting interventions. Even though the combination antiretroviral therapy (cART) has recorded significant success, drug resistance and limited access to available therapeutics are major factors responsible for the low impact of cART in several African communities. Herein, as part of our continuous effort on the investigation of bioactive metabolites of Ochna rhizomatosa, we report the isolation of a new flavonoid; Rhizomatoflavonoid D (1), alongside with four known ones (2–5). The structures of these compounds were elucidated by using spectroscopic techniques (¹H NMR, ¹³C NMR, HSQC, HMBC, ¹H-¹H COSY, and ROESY) and mass spectrometry. The antiviral activity of the resulting compounds was assessed using deCIPhR assay run in parallel with the Alamar Blue based cytotoxicity assay. This assay revealed a moderate activity for compound 4 (72% inhibition at 2.5 µg/mL) while compound 1 had minimal activity (36% inhibition at 2.5 µg/mL). The prominent inhibitory effect on HIV-1 was showed by compound 4 (IC₅₀ = 3.1 µM). Unfortunately, compound 4 proved to be non-selective as it demonstrated also a CC₅₀ = 5.2 µg/mL (Selectivity index of 1.7). The prominent inhibitory effect on HIV-1 showed by compound 4 (IC₅₀ = 3.1 µM) could be due the presence of a methoxy group at C-7, since this group enhances the lipophilicity of biflavonoids, thereby improving its incorporation into cells.