Vitamins are organic compounds that control nutrition in humans and animals in extremely small amounts and are involved in various physiological phenomena in the living body. We have to take vitamins in our diet because they are not produced through biosynthesis. Recently, many vitamins which have a specific physiological activity have been used as medicines. Among them, vitamin E (tocopherol), an oilsoluble vitamin, has been in frequent use in large amounts and for long periods since the 1970s to treat various diseases and has attracted great attention clinically. Clinical information concerning vitamin E is widespread and includes its effects on gynecological internal secretion control against sterility, heart circulation, liver diseases, peripheral blood circulation and thrombosis, 2) drug poisoning and radiation damage, aging, and carcinogenesis. While vitamin E thus has the potential to be a very useful drug, it has some defects as drug such as poor stability and absorbability and accumulation in fat. Vitamin E naturally occurs in two forms, tocopherol and tocotrienol, each having four homologues, a, b, g, and d (Fig. 1). 3) In the work described herein, we have attempted to synthesize vitamin E derivatives (prodrugs) that possess better stability and absorbability and rapidly emerge as vitamin E in the body, by chemically modifying the phenolic hydroxyl group of tocopherol and have examined the pharmacological activity of the resulting derivatives.Chemistry Glycolation of a-and d-homologues was performed according to the Helferich method.4) Each tocopherol (2, 3) and each acetylated sugars (1a-c) was dissolved in nitrobenzene. After adding p-toluene sulfonic acid as a catalyst to the resultant solution, the reactants were allowed to react under an N 2 atmosphere during distillation at 90°C of the solvent at reduced pressure (20 mmHg) to give the intermediate compounds (4a-c, 5a-c). Deacetylation of 4a-c and 5a-c in dry methanol containing sodium methoxide at reflux yielded the desired compounds (6a-c, 7a-c) (Chart 1). 5,6) Results and DiscussionEnzymatic hydrolysis of the glycoside bond is necessary in the body in order that the synthesized tocopherol derivatives can display the physiological activity of vitamin E. A regeneration test was then conducted. Since the compounds synthesized were hardly soluble in water, enzymatic hydrolysis was examined using water-containing organic solvents and cosolvents. Then, stability of b-galactosidase 7) in organic solvents containing 50% water was examined. As a result, the enzyme was found to keep 90% of its activity in tert-butanol containing 30% water, even after 10 h, as shown in Fig. 2. Hydrolysis of 6a and 7a by b-galactosidase was then tested in the mixed solvent. As seen in Fig. 3, the percentage of hydrolysis for 6a was below 50% even after 8 h, showing that the compound is poorly hydrolyzable. On the contrary, 7a, d-tocopherol and a-tocopherol without methyl groups at the 5 and 7 positions, was rapidly hydrolyzed enzymatically. Examination was then carried o...
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