ENZYMATIC-SYNTHESIS OF [1-C-11] PYRUVIC-ACID, L-[1-C-11]LACTIC ACID AND L-[1-C-11]ALANINE VIA DL-[1-C-11]ALANINE

Abstract

Pyruvic and lactic acids are both normal metabolites in the myocardium. The radiolabeled substrates permit in vivo metabolic investigations. L-[1-11C]Lactic acid was prepared enzymatically from [1-11C]pyruvic acid by way of DL-[1-11C]alanine, using remote, semiautomated procedures. The DL isomers of alanine were prepared by a modification of the Bucherer-Strecker reaction from no-carrier-added (NCA) H [11C]cyanide. The enantiomer mixture was transformed to [1-11C]pyruvic acid by successive elution through columns of immobilized D-amino acid oxidase (D-AAO)/catalase and immobilized L-alanine dehydrogenase (L-AID) or L-amino acid oxidase (L-AAO/catalase). [1-11C]-Pyruvic acid was subsequently converted to L-[1-11C]lactic acid by passage through a L-lactic dehydrogenase (L-LDH) column. L-[1-11C]Alanine and [1-11C]-pyruvic acid were separated chromatographically by way of a cation-exchange column (AG50W-X2, H+ form). Typically the synthesis time was 35-40 min after cyclotron production of H [11C]cyanide (400 mCi) with radiochemical yields of 25 mCi (25%) for L-[1-11C]lactic acid, 35 mCi (29%) for [1-11C]pyruvic acid and 20 mCi (20%) for L-[1-11C]alanine. The use of immobilized enzymes eliminates the possibility of protein contamination and assures the production of sterile, pyrogen-free products, allowing for rapid and effective regio- and stereo-specific transformations.