Inhibitory Activity of Proanthocyanidins Against Escherichia coli 1-Deoxy-D-Xylulose-5-Phosphate Reductoisomerase

1-Deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) is a key enzyme in the methylerythritol phosphate pathway for terpenoid biosynthesis. Furthermore, it is an ideal target for the screening of novel antibiotics because it is present in causative organisms, but absent from humans. To identify more lipophilic DXR inhibitors from natural resources, we tested the DXR inhibitory activity of five proanthocyanidins in this study. The results indicated that all these compounds specifically restrained the activity of DXR, with procyanid B2 exhibiting a relatively low effect against DXR (IC50 similar to 305 mu M) and procyanid C1 displaying moderate activity (IC50 75.1 mu M). The other three compounds cinnamtannin A2, cinnamtannin B1, and cinnamtannin D1 (IC50 similar to 89.3, 105.0, and 97.8 mu M, respectively) showed DXR inhibitory effects that were slightly weaker than that of procyanid C1. In addition, based on the initial characterization, the structure-activity relationship of this series of compounds against DXR is discussed.