<p>This thesis describes the initial steps towards the use of dipeptidyl acyloxymethyl ketones as a platform to develop molecular imaging (MI) probes for cancer. Initially the synthesis of an AOMK was performed following a literature procedure which resulted in an epimerized product. This issue was addressed by optimizing an alternative method yielding all intermediates in yields similar or better to those reported in the literature (final product yield of 67%). An AOMK derivative that can be used to evaluate target expression levels was synthesized by linking a fluorescent dye to the ε-amine group of lysine in accordance to a literature procedure describing the synthesis of an optical imaging probe in 24% yield. A second generation derivative AOMK was prepared by linking 4-fluoro-benzoic acid to the same amino group yielding a model of a PET MI probe.</p> <p>An endpoint colorimetric assay was developed and optimized to test cathepsin B inhibitors. Due to the fact that the AOMKs exhibit time-dependent inhibition these assay conditions did not prove to be adequate for the assessment of the cathepsin B binding. Steps toward developing a continuous assay that would be better suited for these compounds were achieved. Factors such as the relationship between the formation of the assay product vs enzyme concentration and determination of the Michelis-Menten constant (K_m = 390 ± 30 nM) were established. These parameters can be used to determine the optimal enzyme and substrate concentration that should be used to test the AOMK based probes.</p> / Master of Science (MSc)