Novel Daidzein Analogs and Their in Vitro Anti-Influenza Activities

A series of novel isoflavonoids were synthesized based on structural modifications of daidzein, an active ingredient of traditional Chinese medicine (TCM) and evaluated for their anti-influenza activity, in vitro, against H1N1 Tamiflu-resistant (H1N1 TR) virus in the MDCK cell line. Among them, 4-oxo-4H-1-benzopyran-8-carbaldehydes 11a–11g were most promising, and they demonstrated better activities and selectivities comparable to those the reference ribarivin, a nucleoside antiviral agent. 3-(4-Bromophenyl)-7-hydroxy-4-oxo-4H-1-benzopyran-8-carboxaldehyde (11c) displayed the best inhibitory activity (EC50, 29.0 μM) and selectivity index (SI>10.3). Analysis of the structureactivity relationships (SAR) indicated that both the non-naturally-occurring Br-substituted B-ring and appropriate CHO and OH groups on the A-ring might be critical for the activity and selectivity against H1N1 TR influenza viruses.