Semi-synthesis and NMR spectral assignments of flavonoid and chalcone derivatives

Previous investigations of the aerial parts of the Australian plant Eremophila microtheca and Syzygium tierneyanum resulted in the isolation of the antimicrobial flavonoid jaceosidin (4) and 2,6-dihydroxy-4-methoxy-3,5-dimethyl chalcone (7), respectively. In this current study, compounds 4 and 7 were derivatized by acetylation, pivaloylation, and methylation reactions. The final products, 5,7,4-triacetoxy jaceosidin (10), 5,7,4-tripivaloyloxy jaceosidin (11), 5,7,4-trimethoxy jaceosidin (12), 2,6-diacetoxy-4-methoxy-3,5-dimethyl chalcone (13), 2-hydroxy-4-methoxy-6-pivaloyloxy-3,5-dimethyl chalcone (14), and 2-hydroxy-4,6-dimethoxy-3,5-dimethyl chalcone (15) were all fully characterized by NMR and MS. Derivatives 10 and 13 have been previously reported but were only partially characterized. This is the first reported synthesis of 11 and 14. The natural products and their derivatives were evaluated for their antibacterial and antifungal properties, and the natural product, jaceosidin (4) and the acetylated derivative, 5,7,4-triacetoxy jaceosidin (10), showed modest antibacterial activity (32-128 mu g/ml) against Staphylococcus aureus strains. Copyright (c) 2016 John Wiley & Sons, Ltd.