Inhibitors of melanocyte tyrosinase as topical skin lighteners

Methods and formulations are provided to reduce pigmentation in skin, using an array of compounds selected from benzimidazoles, phenylthioureas, phenyltiols, phenylamines, bi- and multicyclic phenols, thiopheneamines, and benzothiamides. The compounds preferably inhibit pigment systhesis in melanocytes through the tyrosinase pathway. The methods can be used for lightening skin, and for treating uneven skin complexions which result from hyperpigmentation-related medical conditions such as melasma, age spots, freckles, ochronosis, and lentigo. The compounds can be used medically or cosmetically.

EXAMPLES 
 Example 1: Benzoimidazolethiols A first class of compounds based upon the template compound benzimidazolethiol (lower left structure) were tested for tyrosinase inhibition, cell culture pigment inhibition, and toxicity, by methods described in Curto, E. V., et al. (1999) &lsqb;25&rsqb;. Results of the tests are given in Table 1. 1 TABLE 1 15 16 ID &num; R 1 R 2 R 3 R 5 R 6 R E P T &egr; &lgr; max 138 NH SH N H H C 0.25 — — 14300 300 140 NH SH N CH3 H C 0.12 2.4 >1000 6300 305 084 NH SH N OCH 3 H C 0.07 1.6 >1000 10000 310 040 S SH N H H C 8 — — 091 S SH N H OCH 2 CH 3 C >1000 >1000 >1000 205 NH &boxH;S N(CO)CH 3 H H C 0.5 8.3 35 098 NH &boxH;Se NH H H C 0.8 14 132 135 NH &boxH;S NH H H N 4 256 >1000 *Inhibition &lsqb;&mgr;M&rsqb; as measured in three assays. Here “E” is the concentration of compound that produces 50% pigment inhibition in the cell-free mammalian-enzyme assay system. “P” is for the concentration of compound that produces 50% inhibition in the mammalian-melanocyte-culture pigment assay system. “T” is the concentration of compound that kills 50% of cells in the manimalian-melanocyte-culture toxicity assay system. The compound extinction coefficient is # &egr; &lsqb;OD/M × cm&rsqb; at the wavelength of maximum absorbency &lgr; max &lsqb;nm&rsqb;. 
 Example 2: Thiophenols A second class of compounds based upon the template compound benzenethiol were tested for tyrosinase inhibition, cell culture pigment inhibition, and toxicity, by methods described in Curto, E. V., et al. (1999) &lsqb;25&rsqb;. Results of the tests are given in Table 2. 2 TABLE 2 17 ID &num; R 1 R 2 R 3 R 4 R 5 E P T &egr; &lgr; max 099 H H OCH 3 H H 53 85 202 3000 265 102 H H H SCH 3 H 0.24 115 126 2300 280 083 H H H NH(CO)CH 3 H 19 82 542 4700 265 103 H H OCH 3 OCH 3 H 8 8 >1000 4300 250 093 H OCH 3 H H OCH 3 500 200 200 2700 305 148 (CO)CH 3 H H NH(CO)CH 3 H 500 30 125 3300 255 inhibition &lsqb;&mgr;M&rsqb; as measured in three assays. Here “E” is the concentration of compound that produces 50% pigment inhibition in the cell-free mammalian-enzyme assay system. “P”is for the concentration of compound that produces 50% inhibition in the mammalian-melanocyte-culture pigment assay system. “T” is the concentration of compound that kills 50% of cells in the mammalian-melanocyte-culture toxicity assay system. The compound extinction coefficient is #&egr; &lsqb;OD/M × cm&rsqb; at the wavelength of maximum absorbency &lgr; max &lsqb;nm&rsqb;. 
 Example 3: Phenylthioureas A third class of compounds based upon the template compound phenylthiourea (lower left structure) were tested for tyrosinase inhibition, cell culture pigment inhibition, and toxicity, by methods described in Curto, E. V., et al. (1999) &lsqb;25&rsqb;. Results of the tests are given Table 3. 3 TABLE 3 18 19 ID &num; R 2 R 3 R 4 R 5 R E P T &egr; &lgr; max 033 H H H H NH 2 2 12 >1000 181 OCH 3 H H H NH 2 >1000 >1000 105 H F H H NH 2 1.52 1.78 >1000 11000 255 104 H OH H H NH 2 4 8 >1000 131 H CH 3 H H NH 2 0.82 2.28 >1000 053 H H OCH 3 H NH 2 8 30 60 049 H H NH(CS)NH 2 H NH 2 4 250 >1000 101 H CH 3 H CH 3 NH 2 250 125 >1000 054 H H H H CH 3 16 16 >1000 *Inhibition &lsqb;&mgr;M&rsqb; as measured in three assays. Here “E” is the concentration of compound that produces 50% pigment inhibition in the cell-free mammalian-enzyme assay system. “P” is for the concentration of compound that produces 50% inhibition in the mammalian-melanocyte-culture pigment assay system. “T” is the concentration of compound that kills 50% of cells in the mammalian-melanocyte-culture toxicity assay system. The compound extinction coefficient is #&egr; &lsqb;OD/M × cm&rsqb; at the wavelength of maximum absorbency &lgr; max &lsqb;nm&rsqb;. 
 Example 4: Miscellaneous A fourth group of miscellaneous compounds of diverse structure were also tested for tyrosinase inhibition, cell culture pigment inhibition, and toxicity, by methods described in Curto, E. V., et al. (1999) &lsqb;25&rsqb;. Results of the tests are given in Table 4. 4 TABLE 4 1 20 2 21 3 22 4 23 5 24 6 25 7 26 8 27 &num; ID&num; E P T &egr; &lgr; max 1 081 5 81 500 1000 275 2 100 32 62 >1000 3 073 >1000 100 >1000 4 079 73 71 472 5 006 110 182 >1000 6 092 79 236 >1000 7 009 98 209 775 8 026 54 153 367 *Inhibition &lsqb;&mgr;M&rsqb; as measured in three assays. Here “E” is the concentration of compound that produces 50% pigment inhibition in the cell-free mammalian-enzyme assay system. “P” is for the concentration of compound that produces 50% inhibition in the mammalian-melanocyte-culture pigment assay system. “T” is the concentration of compound that kills 50% of cells in the mammalian-melanocyte-culture toxicity assay system. The compound extinction coefficient is #&egr; &lsqb;OD/M × cm&rsqb; at the wavelength of maximum absorbency &lgr; max &lsqb;nm&rsqb;. Throughout this application, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 
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