Synthesis, in vitro percutaneous absorption and phototoxicity of new benzylidene derivatives of 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-one as potential UV sunscreens

Abstract A series of 5-(alkoxyphenylmethylene)-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-6-ones ( 1a–i ) were prepared to evaluate their potential cosmetic application as UV sunscreens. All new synthesised compounds were studied for their UV absorption and the relative sunscreening action was determined by sunscreen index values obtained from the UV spectra: compound 1c showed its maximum absorption in the UVB region, compounds 1a and 1d showed their maximum absorption in the UVA–UVB immediate zone, the others in the UVA sunscreen area. Since an ideal sunscreen should show a high extent of substantivity without penetrating the skin, on the basis of UV spectral data, four of them ( 1a , 1d , 1f , 1h ) were evaluated as regards their in vitro percutaneous absorption. Subsequently, the two less absorbed compounds, 1f and 1h , were also assayed for their potential in vitro phototoxicity, by photohemolysis and lipid peroxidation tests. The skin permeation and the phototoxicity data of the studied compounds were compared to the data of 3-(4-methylbenzyliden)bornanone ( 2 ), a commercially available UV filter having a chemical structure similar to the new derivatives. Compounds 1f and 1h were less absorbed than compound ( 2 ) and showed a photoinduced lytic activity which is comparable to that displayed by the marketed compound.