Photostability and phototoxicity studies of a promising UVA filter for sunscreens: 1-(2-hydroxyphenyl)-3-(4-methoxyphenyl)-1,3-propanedione.

A few years ago, the 2-hydroxy-4´-methoxy dibenzoylmethane (DBM11) molecule was synthesized and studied as a replacement for avobenzone (AVB, butyl methoxydibenzoylmethane) because of the latter's instability under UVA radiation. These studies, conducted in absolute ethanol with an estimated UV irradiance of 8,56 mW/cm², demonstrated almost zero decomposition of DBM11. Thus, it is a promising candidate for use as a UVA chemical filter. However, further studies must be conducted to verify its photostability once formulated into an emulsion and to establish its toxicological profile. The first aim of this work was to scale up the synthesis of DBM11 to allow its formulation into an emulsion, which is required for the evaluation of its photostability under standardized UV irradiation conditions (close to ISO 24443), as required for sunscreen testing in the cosmetic industry. Additionally, in vitro phototoxicity assessments were conducted, with slight modifications to improve reproducibility, in accordance with OECD guidelines. These results demonstrate that DBM11 exhibits promising photostability and a favourable toxicological profile, making it a potential candidate for use as a UVA filter.