Hybrid flavan–flavanones from Friesodielsia desmoides and their inhibitory activities against nitric oxide production

The first phytochemical investigation of Friesodielsia desmoides leaves and twigs led to the isolation and identification of three new hybrid flavan–flavanones, friesodielsones A–C (1–3), together with 18 known compounds (4–21). The structures of compounds 1–3 were elucidated through intensive analysis of spectroscopic data and their absolute configurations at C-2 and C-4 were determined by a combination of 1H NMR and CD spectroscopy. The configuration at C-2′′ is tentatively assigned as 2′′S based on biosynthesis considerations. Compounds 2 and 15 significantly inhibited NO production with IC50 values of 10.21 ± 0.074 and 7.56 ± 0.087 μM, respectively, whereas compounds 11 (IC50 = 28.14 ± 0.024 μM) and 12 (IC50 = 37.21 ± 0.017 μM) were moderate inhibitors.