Analogues of alpha-aminoisobutyric acid with various alkyl groups as potential tumour imaging agents; effects of chain length on tumour and normal tissue specificity.

Eight 14C-labelled analogues of alpha-aminoisobutyric acid (AIB) were synthesized using the modified Bucherer technique to investigate their tissue distribution in Ehrlich tumour bearing mice. A structure-activity relationship within a series of AIB analogues was found; increasing the chain length of R and R' produced a progressive decrease in tumour and a dramatic decrease in normal tissue uptake. AIB and alpha-amino-2-methyl-butanoic acid (AMB) were found to have higher tumour uptake than the other six analogues; and AMB and alpha-amino-2-ethyl-butanoic acid (AEB) showed higher tumour to tissue uptake ratios than the other six analogues, significantly so for liver, stomach, heart, and small intestine. These results indicate that AMB may be a potential tumour seeking agent for emission computed tomography.