SYNTHESIS OF FLAVONOID SULFATES .1. STEPWISE SULFATION OF POSITION-3, POSITION-7, AND POSITION-4' USING N,N'-DICYCLOHEXYLCARBODIIMIDE AND TETRABUTYLAMMONIUM HYDROGEN SULFATE

The dicyclohexylcarbodiimide-mediated esterification of flavones and flavonols with tetrabutylammonium hydrogen sulfate, resulted in the formation of mono-, di- and trisulfated products. Sulfation occurred mainly at positions 7, 4'' and 3 of the flavonoid skeleton and followed the order 7 > 4'' > 3. Using this method, a number of mono- to trisulfate esters of various naturally occuring flavones and flavonols were synthesized, and their structures verified by spectroscopic methods. This method can be applied to the synthesis of other sulfated natural products, such as steroids and sugars.