In the courses of our search for bioactive natural products on TRAIL resistance-overcoming activity, the active EtOAc extract from the bark of Celtis tetrandra was chemically investigated. The fractionation of the extract resulted in the isolation of flavanols; (+)-afzelechin (1), (-)-epiafzelechin (2), (-)-catechin (3), and two new flavanol dimers; (-)-epiafzelechin-(4α8)-(-)-catechin (4) and (-)-epiafzelechin-(4α 8)-(-)-epicatechin (5). All isolated compounds 1-5 were tested for their TRAIL resistance-overcoming activity against AGS cells at the concentrations from 5-20 µM. It is likely that the flavanol dimers 4 and 5 exhibited weak activity in the range of the concentration of 10-20 µM as compared with the standard.
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