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Heated Sunless Tanning for Rapid Color and Other Topics: Literature Findings
By: Charles Fox, Independent Consultant
Posted: May 27, 2010, from the June 2010 issue of Cosmetics & Toiletries.
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Self-emulsifying bath compositions: Kao Corp. disclosed a self-emulsifying bath composition that forms a uniform milky emulsion when combined with water.5 The composition includes a liquid hydrocarbon oil, glycerin, at least two different nonionic surfactants with a hydrophilic-lipophilic balance range of 8.5–16 HLB, and water. The composition was found to have good storage stability; an example is shown in Formula 2.
Tyrosinase inhibitors: Eastman Chemical Co. has incorporated 5-hydroxy-2-methyl-4H-pyran-4-one esters as novel tyrosinase inhibitors in skin-brightening cosmetic compositions.6 The company also has disclosed how to make and use the compositions.
Kojic acid (50.0 g; 352 mmol), a tyrosinase inhibitor with an EC50 of 17.0 muM, was carefully added in portions over a period of 30 min to a stirring solution of 150 mL thionyl chloride containing 100 mL hexane. After an additional 3.5 hr of stirring, chlorokojic acid (50.9 g; 90% yield) was produced from the mixture and this acid was found to be a more potent inhibitor of tyrosinase than kojic acid, with an EC50 of 6.8 muM.
Chlorokojic acid (20.0 g; 125 mmol) was then added in portions to water (60 mL) and heated to approximately 50°C. To the water and chlorokojic acid mixture, zinc dust (16.2 g) was carefully added in portions, and concentrated hydrochloric acid (37 mL) was added dropwise over 60 min. The reaction was vigorously stirred for an additional 3 hr and excess zinc was removed. The resulting allomaltol was found to be a more potent inhibitor of tyrosinase than kojic acid, with an EC50 of 3.4 muM.
Finally, allomaltol (600 mg; 4.76 mmol) was diluted with approximately 20 mL of anhydrous tetrahydrofuran (THF) and stirred to afford a solution. Trimethylamine (833 mul; 6.33 mmol) was added dropwise to the allomaltol and THF, and the contents were stirred for approximately 5 min. Acetic anhydride (641 mul; 5.00 mmol) was then added dropwise, capped and stirred at RT. Once complete, the reaction mixture was concentrated under reduced pressure, and the contents were purified by silica gel chromatography to afford 650 mg of 6-methyl-4-oxo-4H-pyran-3-yl acetate (3.87 mmol; 81% yield), which exhibited an EC50 of 106 muM.