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Pancreas Specificity of Iodo and Bromo Aliphatic Amino Acid Analogs: Concise Communication

State University of New York at Buffalo and Roswell Park Memorial Institute, Buffalo, New York

Correspondence: For reprints contact: H. F. Kung, Dept. of Nuclear Medicine, SUNY/Buffalo, VA Hospital, 3495 Bailey Ave., Buffalo, NY 14215.

ABSTRACT

Isosteric replacement of a methyl group by a halogen atom (bromine or iodine) in natural compounds often does not impair chemical or biologic properties. Iodo and bromo aliphatic amino acid analogs have been synthesized and studied for possible use as pancreas imaging agents.

Rather than using the short-lived gamma-emitting isotopes of bromine suitable for scanning, we prepared the C-14-labeled compounds. The valine analog, ß-bromo--aminobutyric acid, was synthesized from [¹⁴C] L-threonine, and its distribution was studied in rats. Contrary to expectations, this compound showed neither pancreatic uptake nor any other amino acid behavior. The failure of this bromo-for-methyl substituted compound to be biologically active is rather surprising, in view of the good match in physical properties and previous success in analog localization.

Iodo analogs of leucine (-iodo--aminopentanoic acid) and valine (ß-iodo--aminobutyric acid) have been prepared with I-125 labels. These compounds proved to be quite unstable and were rapidly deiodinated.

It is clear that these bromo and iodo analogs of aliphatic amino acids are not useful as pancreas-localizing agents.