Design of a Photostabilizer Having Built‐in Antioxidant Functionality and Its Utility in Obtaining Broad‐spectrum Sunscreen Formulations†

Abstract

Di-2,2'-diethylhexyl-3,5-dimethoxy-4-hydroxy-benzylidenemalonate (INCI name diethylhexyl syringylidene malonate, DESM), the target photostabilizer, was synthesized in one step by condensation of 3,5-dimethoxy-4-hydroxy benzaldehyde (Syringaldehyde) with di-2,2'-diethylhexyl malonate. Photostability data in sunscreen formulations showed that DESM is photostable and improves the photostability of avobenzone significantly when compared to control (without a photostabilizer). Photostable broad-spectrum sunscreen formulations with high SPF (>30) have been achieved by combining avobenzone, DESM and UV-B sunscreens, such as homosalate, octisalate or other UV-B sunscreens. It seems that (a) triplet-state energy transfer from avobenzone to DESM and (b) scavenging of reactive species are responsible for the observed stabilization of avobenzone. In vitro study of the two formulations containing DESM clearly showed critical wavelength of well over 370 nm and can thus be categorized as broad-spectrum sunscreens. DESM does not have any contribution to in vivo SPF; instead it boosts SPF by about 5 units in high-SPF products. DESM was found to be an excellent singlet-oxygen quencher, thereby reducing photodegradation of avobenzone caused by singlet oxygen. In short, the multiplicity of effects and formulation benefits seen with DESM makes it an ideal choice as a unique antioxidant photostabilizer for a variety of cosmetic products targeting young and mature skin alike.

Combination of retinyl palmitate and UV-filters: Phototoxic risk assessment based on photostability and in vitro and in vivo phototoxicity assays

“…Available substances are not completely efficient to neutralize free radicals generated by avobenzone photofragmentation (Chatelain and Gabard, 2001 Abbreviations: 3T3 NRU-PT, 3T3 Neutral Red Uptake Phototoxicity Test; BMTZ, bemotrizinol; BZP-3, benzophenone-3; AVO avobenzone, butyl methoxydibenzoylmethane; DNA, deoxyribonucleic acid; DMSO, dimethyl sulfoxide; DMEM, Dulbecco's Modification of Eagle's Medium; F1-F4, formulations 1-4; F1RP-F4RP, formulations 1-4 containing Retinil Palmitate; IC50, half maximum inhibitory concentration; HPLC, High Performance Liquid Chromatography; ICDRG, International Contact Dermatitis Research Group; LOQ, limit of quantitation; MPE, mean photo effect; MED, minimal erythema dose; OCT, octocrylene; OMC, octyl methoxycinnamate; OECD, Organisation for Economic Co-operation and Development; PBS, phosphate buffered saline; PIF, photo irritant factor; ROS, reactive oxygen species; RP, retinyl palmitate; UV, ultraviolet; UVA, ultraviolet A; UVB, ultraviolet B; k, wavelength. Bemotrizinol (bis-ethylhexyloxyphenol methoxyphenyltriazine, k = 280-380 nm) is a UV-filter, but it also shows promising results as an avobenzone photostabilizer (Chatelain and Gabard, 2001). It is able to absorb UV photons and it has been shown to improve the photostability of sunscreen formulations containing the combination octyl methoxycinnamate/avobenzone (Chaudhuri et al, 2006). Photostability evaluation studies are usually performed using quantitative separation techniques as High Performance Liquid Chromatography (HPLC) Deflandre and Lang, 1988;Berset et al, 1996).…”

Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps

“…There are several studies about how improvement of photostability may be obtained, e.g. with nanoparticle encapsulation of EHMC [23], liposphere preparation of BMDBM [24] or a combination with diethylhexyl syringylidene malonate and BMDBM [25]. These findings are very interesting and will hopefully lead to an improvement in photostability in commercial available products.…”

Review of sunscreen and the emergence of non-conventional absorbers and their applications in ultraviolet protection

“…Photostabilizers have also been shown to exhibit antioxidant properties. Chaudhuri et al showed that diethylhexyl syringylidene malonate can be used as a photostabilizer for avobenzone as well as an effective antioxidant [5]. Synthetic antioxidants are also a possibility.…”