Towards symmetry driven and nature inspired UV filter design

In plants, sinapate esters offer crucial protection from the deleterious effects of ultraviolet radiation exposure. These esters are a promising foundation for designing UV filters, particularly for the UVA region (400 – 315 nm), where adequate photoprotection is currently lacking. Whilst sinapate esters are highly photostable due to a cis-trans (and vice versa) photoisomerization, the cis-isomer can display increased genotoxicity; an alarming concern for current cinnamate ester-based human sunscreens. To eliminate this potentiality, here we synthesize a sinapate ester with equivalent cis- and trans-isomers. We investigate its photostability through innovative ultrafast spectroscopy on a skin mimic, thus modelling the as close to true environment of sunscreen formulas. These studies are complemented by assessing endocrine disruption activity and antioxidant potential. We contest, from our results, that symmetrically functionalized sinapate esters may show exceptional promise as nature-inspired UV filters in next generation sunscreen formulations.


Supplementary Figure 4: Absorbance region of DES in various solvents.
Ultraviolet/visible spectra of diethyl 2-(4hydroxy-3,5-dimethoxybenzylidene)malonate (DES, ~1 μM) in, C12-15 alkyl benzoate (magenta), ethanol (blue) and cyclohexane (green). We note the cut off in absorption of DES in alkyl benzoate below 300 nm, as the absorption of alkyl benzoate saturates the spectrometer. The time-delay is plotted linearly from -0.5 to 10 ps then as a log scale from 10 to 100 ps. b) Evolution associated difference spectra from the sequential global fit of the TAS of DES in cyclohexane photoexcited at 325 nm. c) Selected TAS at specific Δt highlighting the absorption at 380 nm (8 ps, blue) and lack of a photoproduct (2 ns, orange). To account for the chirp of our probe pulse, a third order polynomial is included within the fitting algorithm. Additionally, the fit is convoluted with an instrument response function (IRF) to account for the temporal resolution of our pulses, whose value is taken from Gaussian fits of the solvent-only time zero response (see Supplementary Figure 8).

Supplementary Methods
The critical wavelength for a sunscreen is defined as the wavelength at which the integrated area underneath the spectral absorbance curve reaches 90% of the total area between 290 and 400 nm 1 .
To attain the critical wavelengths of DES, ES and avobenzone (Avo), UV/visible spectra of each compound were taken in ethanol using a UV/visible spectrometer (Cary 60, Agilent Technologies). These spectra are shown in Supplementary Fig. 12. The area under each absorption curve between 290 and 400 nm was determined using the cumulative trapezoidal method function in MATLAB (R2017b), which is defined mathematically as follows: where λ0 = 290 nm < λ1 < … < λN-1 < λN = 400 nm, and Δ is the interval between each wavelength datapoint. The critical wavelength was then assigned to be the value where 90% of the total area resides under the curve. The critical wavelength is marked by a vertical line in Supplementary Fig. 12.
The successful synthesis of DES was confirmed by 1 H NMR; the assignments of the peaks are given as follows: For the endocrine disruption measurements, cell culture material was from Life Technologies (Cergy-Pontoise, France) except the 96-well Cell star plates, which were from Greiner Labortechnic (Poitiers, France). Luciferin (sodium salt) and geneticin were purchased from Promega (Charbonnières, France). R1881 was from NEN Life Science Products (Paris, France). Estradiol, SR12813, hygromycin and puromycin were purchased from Sigma Aldrich (Saint-Quentin Fallavier, France). Stock solutions were made in dimethyl sulfoxide (DMSO) at 10 mM and dilutions from this stock solution were prepared in a culture medium.
HELN and HELN hER cells were already described. 2 Briefly, Hela cells were stably transfected with the ERE-Globin-Luciferase-SVNeomycin plasmid, with or without the pSG5-hER-puromycin plasmid leading to the HELN and HELN hER-cell lines. HG5LN and HG5LN PXR cells were already described. 3 The Hela cells were stably transfected with the GAL4RE5-Globin-Luciferase-SVNeomycin plasmid, with or without the pSG5-GAL4(DBD)-hPXR(LBD)-puromycin plasmid leading to the HG5LN and HG5LN-hPXR cell lines. Agonistic activities of HELN hER and HG5LN hPXR cells were tested in the presence of increasing concentrations (10nM-10M) of DES. Results were expressed as a percentage of maximal luciferase activity. Maximal luciferase activity (100%) was obtained in the presence of 10 nM E2 for ER, and 3 M SR12813 for PXR. Antagonistic assays were performed using a concentration of agonist yielding approximately 60-85% of maximal luciferase activity. The antagonistic activity of DES tested at (10 nM -10 M) was determined by co-incubation with the agonist E2 at 0.1nM for ERα, and the agonist SR12813 at 100 nM for PXR.
DES was also tested for non-specific modulation of luciferase expression on the HELN and HG5LN cell line, which are devoid of hER and hPXR. DES showed non-specific induction of luciferase expression at 10 M.