Bio-guided isolation of antioxidants from the stems of Dendrobium aurantiacum var. denneanum.

Bio-guided fractionation of the stems of Dendrobium aurantiacum var. denneanum using a 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay, led to the isolation of three 2-glucosyloxycinnamic acid derivates, namely, cis-melilotoside, trans-melilotoside and dihydromelilotoside, respectively. Their structures were elucidated through the analysis of uni- and bi-dimensional NMR, UV, IR and MS data. All these three compounds were first reported from the genus Dendrobium and exhibited potent antioxidant activities.