Minor Non-Cytotoxic Enantiomeric Constituents from the Leaves of Morus alba

ObjectivesThe current work aimed to isolate and identify new interesting small-molecule natural products from the leaves of a well-known medicinal plant Morus alba.MethodsThe ethanol extract of M. alba leaves was partitioned between EtOAc and water, and the EtOAc soluble part was fractionated by macroporous resin column chromatograph (CC) eluted with gradient EtOH. The 80% EtOH eluate was subject to silica gel, reversed phase C18, MCI gel and Sephadex LH-20 CC and finally purified by HPLC to afford four minor compounds 1–4, and the racemic 1 and 2 were further separated by chiral columns. Structural elucidation of these isolates was achieved via spectroscopic means especially HR-ESIMS and NMR, with the absolute configurations of new compounds assigned by ECD analyses. The cytotoxic screening was performed by MTT assay.ResultsA pair of new quinone enantiomers (1a/1b), a pair of new stilbenoid enantiomers (2a/2b), a known prenyl stilbenoid (3) and a known dihydrochalcone (4) were isolated and structurally characterized from the leaves of M. alba. They did not show significant cytotoxicity against MDA-MB231, A549, Hela and 4T1 tumor cell lines.ConclusionsThe M. alba leaves represent a rich source of new natural products, and the currently obtained constituents did not exert obvious growth inhibitory activity against the tested tumor cell lines. The bioactivities of the new isolates deserve further exploration in the future.