Sesquiterpenoid-Chromone Heterohybrids from Agarwood of Aquilaria sinensis as Potent Specific Smad3 Phosphorylation Inhibitors

Aquilarines A (1) and B (2), two unprecedented sesquiterpenoid-chromone heterohybrids, were isolated from Aquilaria sinensis agarwood. 1 is an alkaloid featuring an unusual pyridine nucleus, and 2 possesses a rare sesquiterpenoid-chromone skeleton via a C–C bond. A plausible biosynthetic pathway for 1 and 2 was proposed. Both 1 and 2 could significantly inhibit the expression of extracellular matrix components, and α-SMA at low concentrations in TGF-β1 induced two types of kidney cells (NRK 52E and NRK 49F) featuring selective inhibition of Smad3 instead of Smad2 phosphorylation, showing their potential in renal fibrosis.