14CH labelled ferulic and sinapic acids have been synthesized through an enzymic methylation of caffeic and 5-hydroxyferulic acids using labelled S-adenosyl methionine as donor. The methyltransferases involved which were extracted from stems of Poplar catalyse these reactions with a good efficiency. A purification procedure of 14C S-adenosyl methionine is described which allows the recycling of 14CH donor. The yield of the overall process is therefore greatly improved. This method allows the synthesis of products with high specific radioactivity. 3 14 CH3 3 RESUME Les acides fgrulique et sinapique marques au 14C s u r le groupement m6thyle ont &ti! synth6tis6s par voie enzjrnatique A partir des acides caf6ique et 5-hydroxyf6rulique en utilisant la S-adenosyl m6thionine radioactive comme donneur de 14CH3. Le biocatalyseur utilis6, la 0-methyltransfbrase, est issu de tiges de Peuplier. Dans les conditions optimales de la reaction, cette enzyme est capable d'assurer la formation des deux acides ph6noliques avec un rendement int6ressant.
La mise au point d'un protocole de purification du donneur de 14CH permettant sa rGutilisation, am6liore la rentabilitg de ce mode de synthese dont l'int6rGt consiste en l'obtention de produits d'activit6 sp6cifique 6lev6e.