Flavonoids and Acid-Hydrolysis derivatives of Neo-Clerodane diterpenes from Teucrium flavum subsp. glaucum as inhibitors of the HIV-1 reverse transcriptase–associated RNase H function

Bioassay-guided fractionation of the ethyl acetate extract from Teucrium flavum subsp. glaucum, endowed with inhibitory activity towards the HIV-1 reverse transcriptase–associated RNase H function, led to the isolation of salvigenin (1), cirsimaritin (2) and cirsiliol (3) along with the neo-clerodanes teuflavin (4) and teuflavoside (5). Acid hydrolysis of the inactive teuflavoside provided three undescribed neo-clerodanes, flavuglaucins A-C (7-9) and one known neo-clerodane (10). Among all neo-clerodanes, flavuglaucin B showed the highest inhibitory activity towards RNase H function with a IC50 value of 9.1 μM. Molecular modelling and site-directed mutagenesis analysis suggested that flavuglaucin B binds into an allosteric pocket close to RNase H catalytic site. This is the first report of clerodane diterpenoids endowed with anti-reverse transcriptase activity. Neo-clerodanes represent a valid scaffold for the development of a new class of HIV-1 RNase H inhibitors.