FIG. 4.

IC₅₀ determination for protein synthesis inhibitors. The titration of representative 4H-pyridopyrimidines is shown. REP321436 (A) and REP321437 (B) exhibited IC₅₀s of 3.7 and 4.9 μM, respectively, in A/T reactions. The reactions were carried out as described in Materials and Methods, with the concentrations of the compounds ranging from 0.4 to 400 μM. Positive controls were assays in which there were no antibiotics and approximately 1,000 pmol of phenylalanine was synthesized. The curve fits and IC₅₀s were determined using XLfit (version 4.1; IDBS) as part of Microsoft Excel.