The bacterial enzyme undecaprenyl pyrophosphate synthase (UppS) is present in most prokaryotes and is needed for bacterial survival. UppS produces the essential lipid carrier, bactoprenyl monophosphate (BP). BP is critical for the structural integrity of cell membranes, the supply and storage of energy, and antibacterial resistance. Therefore, a greater understanding of this enzymes active site would provide insight into an important target for new therapeutics directed at pathogenic microorganisms. This study investigated the specificity and selectivity of UppS through the modification of its natural substrate, farnesyl diphosphate (FPP). Previous studies utilized mutations of specific residues within the active site, however, mutating protein sequences can have deleterious effects on structure that can often be difficult to recognize. Altering a natural UppS substrate allows a more controlled investigation of the active site. Herein, a group of carefully selected halogenated aromatics were chosen to synthesize in order to test the selectivity of the enzyme based on size, electronegativity, and shape. The effect of the tags' shape on enzyme activity was investigated through the appendage of the halogen in the para position of an aniline ring appended to the end of the molecule. The effect of size and electronegativity on enzyme activity was also investigated using halogenated-aniline rings coupled to the molecular probes. The analogues used were formed via a five-step synthesis process that includes reductive amination and diphosphorylation reactions. The halogenated FPP analogue 4BrGPP was tested with UppS from the organism Staphylococcus aureus.