SYNTHESIS OF 1-(C-11)-LABELED AND 3-(C-11)-LABELED L-LACTIC ACID USING MULTIENZYME CATALYSIS

The synthesis of 1‐ and 3‐11C‐labelled L‐lactic acid from the corresponding racemic 1‐ or 3‐11C‐labelled alanine using a multi‐enzymatic reaction route, is presented. DL‐[1‐11C]Alanine was synthesised by reacting sodium 1‐hydroxy‐ethyl sulfite with hydrogen [11C]cyanide, obtained from [11C]carbon dioxide, and ammonia followed by acid hydrolysis. DL‐[3‐11C]‐Alanine was synthesised by a methylation of a glycine derivative, N‐(diphenylmethylene)‐glycine tert‐butyl ester, with [11C]methyl iodide, obtained from [11C]carbon dioxide, and subsequent hydrolysis. The racemic 1‐ or 3‐11C‐labelled alanine was then converted to pyruvic acid, by D‐amino acid oxidase/catalase and glutamic‐pyruvic transaminase, which was directly reduced to L‐lactic acid by L‐lactic dehydrogenase in a one‐pot procedure. The total synthesis time was 40 minutes, counted from release of [11C]carbon dioxide. The decay corrected radiochemical yields were ca. 80% for L‐[1‐11C]lactic acid, based on hydrogen cyanide, and ca. 60% for L‐[3‐11C]lactic acid, based on carbon dioxide. The radiochemical purities were higher than 99% analysed by HPLC. Copyright © 1990 John Wiley & Sons, Ltd.