Isolation of key intermediates during formation of oolongtheanins

Oolongtheanin-3′-O-gallate (2b) was obtained by treatment of (−)-EGCg (1d) with CuCl2. This transformation was achieved over three steps, with the isolation of two intermediates; their chemical structures were determined through derivatization reactions, MS, and 1D/2D NMR techniques. One intermediate was identified as dehydrotheasinensin A (3); the other was identified as the novel dimer pro-oolongtheanin-3′-O-gallate (6). Compound 3 was converted to 6 by heating in aprotic solvent, and compound 6 was converted to 2b by addition of water.