Chemical synthesis of labelled intermediates in cyanogenic glucoside biosynthesis

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Abstract
Chemical syntheses of [UL‐ 14C]‐labelled N‐hydroxytyrosine, p‐hydroxyphenylpyruvic acid oxime, p‐hydroxyphenylacetaldoxime, and p‐hydroxyphenylacetonitrile in high yields from L‐[UL‐14 C]‐tyrosine are described. These syntheses involve initial conversion of L‐tyrosine to p‐hydroxyphenylpyruvic acid, which then is allowed to react with hydroxylamine to form p‐hydroxypheny lpyruvic acid oxime. N‐Hydroxytyrosine is obtained from the latter by reduction with sodium cyanoborohydride, and is oxidatively decar‐boxylated to p‐hydroxyphenylacetaldoxime by treatment with ammonia. Finally, p‐hydroxyphenylacetonitrile is obtained by dehydration of the aldoxime with thionylchloride. All synthesized compounds were identified by combined GLC/MS of their trimethylsilyl derivatives. The commercial availability of several specifically labelled 14C, 2H, and 3H tyrosines and of 2H and 3H sodium cyanoborohydride makes the method equally useful for synthesis of various specifically labelled compounds.