Dimethylformamide → Racemic pivaloyloxymethyl 3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

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반응 단계

A solution of 4.2 g. (0.012 mole) of racemic N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 1.3 g. (0.013 mole) of triethylamine and 1.26 g. (0.013 mole) of chloromethylpivalate in 20 ml. dimethylformamide is stirred at 90° C. for 20 hours and then poured into 200 ml. water. The product is extracted into 100 ml. of ethyl acetate and washed with 25 ml. of a saturated sodium bicarbonate solution and 25 ml. of water. After drying over anhydrous magnesium sulfate and filtering, the filtrate is concentrated under reduced pressure to give the N-carbobenzyloxy derivative of the desired ester. This material is dissolved in 100 ml. of absolute ethanol containing 10 ml. of a 9.6 N ethanolic-anhydrous hydrogen chloride solution and hydrogenated with 3 g. of a 10% palladium-on-carbon catalyst at an initial pressure of 35 p.s.i. for 24 hours. After removing catalyst by filtration, the filtrate is concentrated under reduced pressure. The residue is dissolved in 25 ml. of water, made basic with a saturated sodium carbonate solution to pH 8 and the insoluble product extracted with 100 ml. of ethyl acetate. After drying over anhydrous magnesium sulfate and filtering, 5 ml. of 9.6 N ethanolic anhydrous hydrogen chloride solution is added and the solution concentrated under reduced pressure to give 1.5 g. (22.6%) of the hydrochloride of the racemic pivaloyloxymethyl 3-(3,4-dihydroxyphenyl)-2-methylalaninate, homogeneous upon thin layer chromatography [fluorescent silica gel plate developed with a 5-2-3 (by volume) mixture of n-butanolacetic acid-water] Rf = 0.86.

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