Abstract
In 2021, Hawaii will permanently ban the use and sale of octinoxate-based sunscreens as studies have shown serious impacts of such UV filters on the coral reef. This ban, which could be generalized to other countries, highlights the extreme need to offer alternative UV filters that are not only effective in terms of sun protection, but also healthy with regards to human health and the environment. In this context, a wide library of p-hydroxycinnamic esters deriving from naturally occurring sinapic acid has been synthesized using a Knoevenagel–Doebner condensation. The UV filtering activities as well as the antioxidant properties of these sinapic acid esters were then investigated. The results showed promising UVB protection and antioxidant efficacy. A Structure–Activity Relationship (SAR) study on the sinapic acid esters highlighted the need of a free phenol to, as expected, observe antioxidant activity, but also to obtain a higher intensity of protection. Moreover, the nature of the ester moiety also proved to be a key structural feature for the UV absorbance, as higher steric hindrance on the ester moiety leads to more active compounds. The judicious structural design of sinapic esters thus provides promising compounds combining UV protection and antioxidant activity.
Highlights
A high level of sun exposure can lead to sunburn, premature skin aging and, in the worst case, severe forms of skin cancer [1,2,3]
Recentwork workon onthe thehighly highly selective β-β dimerization of sinapic esters highlighted their great potential both as filters and antioxidants. Based on these observations, has highlighted their great potential both as UV filters and antioxidants [26]. Based on these we decided to we focus our efforts on theour synthesis renewable sinapic-acid-based analogues observations, decided to focus effortsofon the synthesis of renewableoctinoxate sinapic-acid-based with dual properties antioxidant)
It is worth mentioning that this two-step procedure was carried out without solvent
Summary
A high level of sun exposure can lead to sunburn, premature skin aging and, in the worst case, severe forms of skin cancer [1,2,3] To offset those negative effects, the use of UV protection is essential. To protect its coral reefs, Hawaii has notably banned the use and sale of sunscreen products containing octinoxate on its territory, starting January 2021 [10]. Such a drastic decision could be taken by many other states in the coming years. Octinoxate is actively challenged for its endocrine disrupting activity, which can have serious effects on humans [11]
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