The Antiprotozoal Activity of Sixteen Asteraceae Species Native to Sudan and Bioactivity-Guided Isolation of Xanthanolides from Xanthium brasilicum - Nour, Amal M. M.; Khalid, Sami A.; Kaiser, Marcel; Brun, Reto; Abdallah, Wai'l E.; Schmidt, Thomas J. (Planta Medica, 2009)