Unravelling the antifungal and antiprotozoal activities and LC-MS/MS quantification of steroidal saponins isolated from Panicum turgidum .

Bioassay-guided investigation of Panicum turgidum extract resulted in the identification of seven steroidal saponins (Turgidosterones 1-7). They were evaluated for their in vitro antifungal, antileishmanial, and antitrypanosomal activities. Turgidosterone 6 was the most active antifungal against Candida albicans and Candida neoformans (IC 50 values of 2.84 and 1.08 μg mL -1 , respectively). Turgidosterones 4-7 displayed antileishmanial activity against Leishmania donovani promastigotes with IC 50 values ranging from 4.95 to 8.03 μg mL -1 and against Leishmania donovani amastigote/THP with IC 50 values range of 4.50-9.29 μg mL -1 . Activity against Trypanosoma brucei was also observed for Turgidosterones 4-7 with an IC 50 values range of 1.26-3.77 μg mL -1 . Turgidosterones 1-3 did not display any activity against the tested pathogens. The study of structure-activity relationships of the isolated saponins indicated that the antifungal, antileishmanial, and antitrypanosomal activities are markedly affected by the presence of spirostane-type saponins and the elongation of the sugar residue at C-3. To quantitatively determine the most abundant active ingredient in Panicum turgidum extract, a single run, sensitive, and highly selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been applied under positive and negative modes. The obtained results showed that compound 5 was the most abundant (95.93 ± 1.10 mg per gram of dry Panicum turgidum extract ), followed by 6 (52.51 ± 1.05 mg gm -1 ), 4 (32.71 ± 0.48 mg gm -1 ), and 7 (13.19 ± 0.50 mg gm -1 ). Docking of these saponins against the Candida albicans oxidoreductases and Leishmania infantum trypanothione reductase active sites revealed their potential to effectively bind with a number of key residues in both receptor targets.