Fig. 5. Conformational analysis of sesquiterpene lactones. (A) 2D chemical structures of alantolactone and atractylenolide I. (B) Geometry optimized 3D structures of alantolactone (green) and atractylenolide I (cyan) were aligned based on their lactone rings. (C) Schematic diagram for determining the torsion angle between sesquiterpene skeleton-lactone ring (S-L torsion angle). We calculated Van der Waals (VdW) strains in SH2 binding pocket for alantolactone (D) and atractylenolide I (E). Putative VdW strains were visualized as red flat cylinders. (F) Geometry optimized 3D structures of sesquiterpene lactones were aligned based on their lactone rings. Sesquiterpene lactones, namely alantolactone, isoalantolactone, and parthenolide, which demonstrated over 50% inhibitory effects on STAT3 activation, are shown in green. (G) Correlation between S-L torsion angles and relative p-STAT3 at 10 μM of nine sesquiterpene lactones.
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