Synthesis of two novel flavonoid derivatives with extended φ-system: Possible UV-B and UV-A sunscreens

Two novel flavonoid derivatives 5 and 6 were synthesized and characterized by IR, ¹H, ¹³C NMR spectroscopy and mass spectrometry. The core structure of the two flavonoids was constructed by applying Baker-Venkataraman rearrangement on 2-Acylphenyl ester intermediate. The two compounds exhibited remarkable UV-visible absorption activities compared to flavone. Flavonoid 5 showed a bathochromic shift of 75.6 nm when the size of the cinnamic acid was increased by phenylbutadienyl group and hence it is a good UVA sunscreen. The 4-nitrostyryl group introduced in the cinnamic acid subchromophore of flavonoid 6 causes the compound to absorb at 308.3 and at 345.8 nm which will make it a broad-spectrum sunscreen.