Prepn of 3,4-dihydroxyphenyl-alpha-amino acids - from 4-hydroxyphenyl-alpha-amino acids

摘要

Prod. acids are prepd. in 70-80% yields by (a) converting a 4-hydroxyphenyl-substd. alpha-amino acid into the corresp. N-acyl-alpha-amino acid; (b) nitrating this to give the corresp. 3-nitro-4-hydroxyphenyl-substd. N-acyl-alpha-amino acid; (c) reducing this to the 3-amino-4-hydroxyphenyl-substd. N-acyl-alpha-amino acid, pref. by catalytic hydrogenation; and (d) diazotising and hydrolysing the diazonium salt, pref. by heating in an aqs. medium contg. Cu (I) and Cu (II) cpds.; and if necessary (e) removing the N-acyl gp. by hydrolysis. Step (a) is pref. acetylation with acetic anhydride in aqs. medium pH 9.5-10.5. The process is esp. useful for converting L-tyrosine into L-dopa, and also for converting alpha-methyl-L-tyrosine into 3-hydroxy- methyl-L-tyrosine.