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]. Cosnzet. Sci. 1 56, 135-148 (March/April 2005) A new long-chain UV absorber derived from 4-tert-butyl-4'-methoxydibenzoylmethane: Absorbance stability under solar irradiation F. WETZ, C. ROUTABOUL, A. DENIS, and I. RICO-LATTES, Laboratoire des Interactions Moleculaires et Reactivite Chimique et Photochimique, CNRS U MR 5623, Universite Paul Sabatier, 31062 Toulouse Cedex 4 (F. W., I.R.-L.), and Bioderma, 75 Cours Albert Thomas, 69447 Lyon Cedex 03 (C.R., A.D.), France. Accepted for publication February 16, 2005 Synopsis A new UV filter, the l-(4-tert-butylphenyl)-2-decanyl-3-(4' -methoxyphenyl)-propane 1,3-dione called ClO­ DBM, was prepared by grafting a ten-carbon aliphatic chain to the a-carbonyl position of 4-tert-butyl-4' - methoxydibenzoylmethane (BM-DBM). 1 UVA absorption efficiency of a cosmetic preparation containing this new filter, called ClO-DBM, was tested and compared to an identical preparation containing BM-DBM. The two preparations were irradiated under a 150-W xenon lamp or exposed to natural sunlight. The originality of this new filter resided in that its UVA absorbance appeared during the irradiation of the molecule. Moreover, although the molar absorption coefficient of ClO-DBM in the UVA domain was lower than that of BM-DBM, its absorption showed much more photostable behavior under both methods of irradiation. After two hours of sunlight exposure, the preparation containing the BM-DBM lost 85% of its UVA absorbance, whereas the UVA absorbance of the preparation containing ClO-DBM showed a decrease of 3% in comparison to the maximum absorbance obtained after 30 minutes of irradiation. Also, after two hours of exposure to natural sunlight, the UVA absorbance of the preparation containing ClO-DBM remained above its initial value (before the irradiation began). INTRODUCTION Exposure to ultraviolet (UV) radiation plays a causal role in acute and chronic skin damage. Skin photoaging has been connected with UVA light. Moreover, UVA irra­ diation generates free radicals, inducing different types of degradation to cellular DNA, lipids, and proteins. It is now commonly recognized that UVA as well as UVB irradia­ tion is involved in the development of skin cancer. This is particularly clear for squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs) in Caucasian people (1). Fur- Address all correspondence to I. Rico-Lattes. 1 Patent: FR 2 857 663 (17 July 2003, France (PCT request)). 135