Inhibition Assay: Antibacterial activity as measured by the minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations of compounds are well known (see., e.g., National Committee for Clinical Laboratory Standards 2000 Performance standards for antimicrobial disk susceptibility tests: approved standard, 7th ed. M2-A7, vol. 20, no. 1, Committee for Clinical Laboratory Standards, Wayne, Pa.).
Enzyme Inhibition Assay: Heterocyclic analogs of propargyl-linked inhibitors of the third generation analogs were evaluated in enzyme inhibition assays, assessed for S. aureus and S. pyogenes inhibition, and evaluated for mammalian cell toxicity.
Spectrophotometric Enzyme Assay: Compounds were evaluated in spectrophotometric enzyme assays using ChDHFR-TS and hDHFR. Inhibition constants (IC50) were measured (see Table 4). The lead compound, X, has an inhibition constant of 38 nM and modest selectivity (8-fold). All of the biphenyl compounds are more potent than the initial lead compound X and exhibit greater selectivity for the pathogenic enzyme. The most potent racemic compound, D(rac), a 5′-biphenyl derivative, is also the most selective of the racemic compounds (944-fold). The single R enantiomer of this 5′-biphenyl analog is the most potent (1.1 nM) and most selective (1273-fold) of all known compounds tested against the Cryptosporidium DHFR enzyme.
Inhibition of human recombinant dihydrofolate reductase using dihydrofolate as substrate measured every 30 secs over 6 mins by UV/visible spectrophotometer in presence of NADPH
Inhibition of recombinant human DHFR assessed as reduction in NADPH oxidation using dihydrofolate as substrate preincubated for 5 mins followed by substrate addition
Inhibition of recombinant human DHFR assessed as reduction in NADPH oxidation using dihydrofolate as substrate by fluorescence spectrophotometric analysis