Phytochemical Analysis of a Cytotoxic Fraction of Quassia silvestris using LC‐HR‐ESI‐MSn

Introduction The genus Quassia is a promising source of secondary metabolites with biological potential including antimalarial and cytotoxic activities. Limited data are available on the phytochemistry and pharmacology of Quassia silvestris Cheek & Jongkind, a Cameroonian medicinal plant used to treat various ailments. Objectives To carry out the bioassay‐guided fractionation and LC‐HR‐ESI‐MS analyses of the leaves extract from Q. silvestris; to purify the active fractions and isolate the major compounds using different chromatographic and spectroscopic methods. The obtained compounds will be evaluated for their biological activity. Material and methods Following the cytotoxic screening and LC‐HR‐ESI‐MS profiling of fractions obtained from partition of the methanolic extract of Q. silvestris leaves, the CH2Cl2‐soluble fraction which exhibited the highest cytotoxicity was retained for further investigations. Results Sixteen squalene‐derived metabolites were identified with oxasqualenoid derivatives being the most predominant. Among the isolates, structure elucidation of two new oxasqualenoids quassiols E (1) and F (2), were achieved by NMR (one‐dimensional (1D) and two‐dimensional (2D)) and MS methods. The newly characterised compounds 1 and 2, together with the known tetraol (3) and 3‐oxo‐oleanoic acid (16) displayed moderate cytotoxicity. Conclusion The identification and structural characterisation of highly oxidised squalene derived metabolites from this plant may provide important insight data for further pharmacological investigations. The LC‐HR‐ESI‐MSn method reported here could be developed as a rapid and efficient tool for the analyses of structurally related compounds in the genera Quassia, Simarouba, and Eurycoma of the subfamily Simarouboideae. Copyright © 2016 John Wiley & Sons, Ltd. Following the cytotoxic screening and LC‐HR‐ESI‐MS profiling of fractions obtained from partition of the methanolic extract of Quassia silvestris leaves, sixteen squalene‐derived metabolites were identified with oxasqualenoid derivatives being the most predominant. Among the isolates, structure elucidation of two new oxasqualenoids quassiols E (1) and F (2), were achieved by nuclear magnetic resonance (1D and 2D NMR) and MS methods. The newly characterized compounds 1 and 2, together with the known tetraol (3) and 3‐oxo‐oleanoic acid (16) displayed moderate cytotoxicity.