Naturally occurring sinapic acid and its esters are known to exhibit anti-UV and antiradical properties. Various studies have shown that these properties can be enhanced by increasing the conjugation within the chemical structures. One interesting solution consists in dimerizing these esters to obtain β,β-linked compounds.  Although β,β linkage could be obtained through various procedures in low to average yields, there are drawbacks such as high toxicity of the reagents and no-scalability. To address this, catalytic process using copper (I) in pyridine have been developed and provide the target in average yields; however this procedure remains quite toxic.  In this work, a greener catalytic route to the β,β-disinapate esters has been devised. A design of experiments allowed the production of the dimers in yield as high as 89% while significantly reducing pyridine amount (-97%) by substituting it with Cyrene®, a green polar aprotic solvent. It is noteworthy to mention that reaction time was also reduced by 70% compared to classical copper (I)/pyridine conditions.  Anti-UV absorption of the resulting β,β-disinapate esters in ethanolic solution were measured and compared to that of sinapoyl malate, one natural sunscreen in plants, and to Octinoxate®, the widely used commercial anti-UV in cosmetics. Data revealed not only an increase in UV absorption intensity but also a broader absorption range covering both UV-A and UV-B.  For antiradical assay, ABTS method was used and dimers were benchmarked against BHT, BHA, Trolox® and Irganox 1010®. Results demonstrated that such dimers exhibit high antiradical activity, making them potential substitutes to current fossil-based antiradicals.

Synthesis and evaluation of antiradical and anti-UV properties of new biobased dimers derived from sinapic acid

2019 Spring National Meeting

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