A Chemical–Biological Study Reveals C₉‑type Iridoids as Novel Heat Shock Protein 90 (Hsp90) Inhibitors

The potential of heat shock protein 90 (Hsp90) as a therapeutic target for numerous diseases has made the identification and optimization of novel Hsp90 inhibitors an emerging therapeutic strategy. A surface plasmon resonance (SPR) approach was adopted to screen some iridoids for their Hsp90 α binding capability. Twenty-four iridoid derivatives, including 13 new natural compounds, were isolated from the leaves of <i>Tabebuia argentea</i> and petioles of <i>Catalpa bignonioides</i>. Their structures were elucidated by NMR, electrospray ionization mass spectrometry, and chemical methods. By means of a panel of chemical and biological approaches, four iridoids were demonstrated to bind Hsp90 α. In particular, the dimeric iridoid argenteoside A was shown to efficiently inhibit the chaperone in biochemical and cellular assays. Our results disclose C₉-type iridoids as a novel class of Hsp90 inhibitors