New Antioxidant Caffeate Esters of Fatty Alcohols Identified in .

The stem bark of black locust ( L.) was extracted, and nine antioxidant compounds (-) were detected by high-performance thin-layer chromatography combined with the radical scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assay, multi-detection, and heated electrospray high-resolution mass spectrometry. For structure elucidation, the methanolic crude extract was fractionated by solid-phase extraction, and the compounds were isolated by reversed-phase high-performance liquid chromatography with diode array detection. The structures of isolated compounds were elucidated by nuclear magnetic resonance and attenuated total reflectance Fourier-transform infrared spectroscopy as well as gas chromatography-mass spectrometry to determine the double bond position. 3--Caffeoyl oleanolic acid (), oleyl (), octadecyl (), gadoleyl (), eicosanyl (), ()-9-docosenyl (), docosyl (), tetracosyl (), and hexacosanyl () caffeates were identified. While has been reported in stem bark, the known , , , , and are described for the first time in this species, and the , , and are new natural compounds. All nine caffeates demonstrated antioxidant activity. The antioxidant effects of the isolated compounds - were quantified by a microplate DPPH• assay, with values ranging from 0.29 to 1.20 mol of caffeic acid equivalents per mole of isolate.