FIG 3.

Piericidin A1 and the piericidin derivative Mer-A 2026B are the bioactive constituents of prefraction 1772D. (A) Prefraction 1772D was fractionated by HPLC-MS, and the eluent was rescreened to identify the active constituents. Fractions from minutes 31, 32, 43, and 44 contained compounds that inhibited T3SS-driven NF-κB activation in HEK293T cells. The averages and SEM are shown. *, P < 0.05, and **, P < 0.005 (Student t test) relative to HEK293T cells infected with the Δyop6 strain and DMSO treated from two independent experiments. (B) Chromatogram (HPLC trace) of prefraction 1772D. Bioactive 1772D fractions 31, 32, 43, and 44 are boxed and contained compounds with related UV absorbance profiles. mAU, milliabsorbance units. (C) Structures of piericidin A1 and the piericidin derivative Mer-A 2026B identified through standard MS and NMR analyses.