GB1040169A - Process for the preparation of l-(-)-ª‡-methyl-ª‰-(3,4-dihydroxy-phenyl)-alanine - Google Patents

Abstract

L - ( - ) - a - Methyl - b - (3,4 - dihydroxyphenyl) - alanine is prepared by reacting D,L-a - amino - a - (3,4 - dimethoxybenzyl) - propionitrile with an isocyanatoacetic acid C1-C3 alkyl ester, the D,L-a -(3,4-dimethoxybenzyl)-a -(o - carbalkoxymethyl - ureido) - propionitrile obtained is treated with an aqueous mineral acid, the D,L-5-(3,4-dimethoxybenzyl)-5-methyl-hydantoin-3-acetic acid thus obtained is resolved with the use of an optically active form of threo-1 - phenyl - 2 - aminopropan - 1,3 - diol and the separated L - ( - ) - 5 - (3,4 - dimethoxybenzyl)-5-methyl-hydantoin-3-acetic acid converted by alkaline and/or acidic saponification into L-( - )-a - methyl - b - (3,4 - dihydroxyphenyl) - alanine. The resolution may be carried out in a C1-C3 alcohol or a mixture of C1-C3 alcohols as solvent. It may be effected (a) by using 1/2 mol. L - (+) - threo - 1 - phenyl - 2 - aminopropane - 1,3-diol per mol. of racemate, and separating the precipitated L - (+) - threo - 1 - phenyl - 2 - amino - propan - 1,3 - diol salt of L - ( - ) - 5 - (3,4 - dimethoxybenzyl) - 5 - methyl hydantoin - 3 - acetic acid, or (b) by separating out the D - ( - ) - threo - 1 - phenyl - 2 - aminopropan - 1,3 - diol salt of D - (+) - 5 - (3,4 - dimethoxybenzyl) - 5 - methylhydantoin-3-acetic acid by the addition of 1/2 mol. of D-( - )-threo-1-phenyl-2-aminopropan-1,3-diol per mol. of racemate, the L-(+)-threo-1 - phenyl - 2 - aminopropan - 1,3 - diol salt of L - ( - ) - 5 - (3,4 - dimethoxybenzyl) - 5 - methyl-hydantoin-3-acetic acid being recovered from the filtrate by the addition of 1/2 mol. L-(+)-threo-1 -phenyl-2-aminopropan-1,3-diol, the salt in both cases being converted to the free L-( - ) - acid by acidification.