Encecalol angelate, an unstable chromene from Ageratum conyzoides L.: Total synthesis and investigation of its antiprotozoal activity

The unstable chromene ester encecalol angelate was synthesized in a six step sequence in 15% overall yield starting with resorcinol. The compound was identified as native constituent of the dichloromethane extract of Ageratum conyzoides L. (Asteraceae). Its activity against Trypanosoma, Leishmania and Plasmodium species was quite low so that it does not represent the chemical principle responsible for the high antiprotozoal activity of the crude extract.