Figure 3: Synthesis of analogues UA-O-a~UA-O-j from UA.

Reagent and condition: (a) CrO3, H2SO4, acetone, 0 °C, 1 h; (b) R1-CHO, KOH, ethanol, r.t., overnight.

Reagent and condition: (a) CrO3, H2SO4, acetone, 0 °C, 1 h; (b) R1-CHO, KOH, ethanol, r.t., overnight.