Add time:07/21/2019         Source:sciencedirect.com

A new route for the preparation of radioactively labelled α-methyl l-tyrosine is described. The labelling at the α position has been successfully achieved with 14C-, 11C- (very preliminary, unpublished), and 3H-labelled methyl iodide. A detailed report on 14C-labelling at the α position and the hydrolysis of 4-methoxy α-methyl phenylalanine is presented. The alkylation proceeds via the methylation of the carbanion of N-benzylidene 4-methoxy phenylalanine methyl ester 2. Hydrolysis of 4-O methyl tyrosine 6 to tyrosine 7 by HBr and HI were analysed and used in the optimization of the hydrolysis conditions of 4. Enantiomeric purity of the isolated L-isomer has been found to be 99% as judged by HPLC, radiochemical purity 99%, radiochemical yield 24% and the sp. radioact. 55 mCi/mmol. Pseudo first-order rate constant for the hydrolysis of 14C-labelled α-methyl 4-methoxy phenyl alanine methyl ester was determined, kψ = 6 x 10−2 min−1; t12 1.2 min. Preliminary findings of the 3H- and 11C-radiolabel α-methyl tyrosine (methyl labelled) are also mentioned. For the first time it was shown that α-methyl d,l-tyrosine can be separated into enantiomerically pure α-methyl d- and l-tyrosine using a CHIRALPAK WH column.

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