Water-assisted/water-accelerated photoreaction of trans-TSG from the roots of Polygonum multiflorum.

The photoreaction of 2,3,4',5-tetrahydroxystilbene-2-O-beta-D-glucoside (TSG) has been investigated. Waterassisted/water-accelerated photodimerization of trans-TSG favored the formation of syn-head-to-tail [2 + 2] photocyclobutane under 365 nm irradiation as a result of hydrophobic association and a fluorescent solute-solute aggregate from their excited singlet states. In contrast, irradiation with 254 nm led to [2 + 2] photocycloreversion. The two cyclobutane dimers were first obtained through straightforward photoreaction and identified as multiflorumiside A and multiflorumiside C through the detailed analysis of high-resolution electrospray ionization mass spectrometry and one- and two-dimensional nuclear magnetic resonance. Therefore, trans-TSG should be protected from light and water.