Labeling of Unnatural Amino Acids with ^99mTc and Tissue Distribution of the Labeled Products in Mice

Abstract

The selective affinity of amino acids for pancreas, due to its high rate of protein synthesis, has prompted us to synthesize new radio-labeled amino acids for pancreatic imaging. Labeling of 19 unnatural amino acids with ^99mTc was tried in the usual way, and 10 labeled products were obtained with low yields. The highest distribution of radioactivity from all these labeled amino acids, which had been injected intravenously into mice, was found in the kidney, whereas little activity was found in the pancreas. Their low distributions in stomach suggest little dissociation of the labeled amino acids into ^99mTcO₄^- in mice. It is presumed that these labeled amino acids behave unlike their original amino acids in the body.