DL-[Carboxyl-11C]tryptophan, a potential agent for pancreatic imaging; production and preclinical investigations.

In animal studies, DL-(carboxyl-/sup 14/C)tryptophan (DL-Try(C-14)) showed a high specificity for the pancreas, which suggested the potential of DL-(carboxyl-/sup 11/C)tryptophan (DL-Try(C-11)) for clinical pancreatic imaging. The blood clearance and tissue uptake of the amino acid were very rapid, and no carrier effect was observed through a dose of 5 mg/kg. None of three transplanted hamster pancreatic adenocarcinomas that we studied showed a selective uptake of DL-Try(C-14) by the tumor, and none of the three enzymatic regimens investigated gave significant enhancement of the pancreatic specificity. Commercial L-Try(C-14) gave slightly better pancreatic specificity than the analogous racemic compound but without enough improvement to warrant attempts at optical resolution. DL-Try(C-11) was synthesized in amounts up to 325 mCi using a rapid, high-temperature, high-pressure modification of the Buecherer-Strecker amino acid synthesis. Yields ranged from 30 to 60%, and a total of 40 min was required for synthesis and chromatographic purification. DL-Try(C-11) thus appears to have significant potential as a clinical pancreas-imaging agent, particularly when used in conjunction with positron computerized transaxial tomography.