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Investigation of the 95% EtOH extract of stems of Dendrobium findlayanum afforded four new seco-dendrobines, findlayines A-D (1-4); two known dendrobines, dendrobine (5) and 2-hydroxydendrobine (6); and four new phenolic compounds, dendrofindlaphenols A-C (7, 9, and 10) and 6″-de-O-methyldendrofindlaphenol A (8). Compounds 1 and 2 are the first seco-dendrobines possessing a seven-membered lactam moiety, with 3 and 4 derived from the oxidative cleavage of the C-2-C-3 bond of dendrobine. The structures were established using spectroscopic methods and by comparison with literature data. The absolute configurations of 1-4 were confirmed via single-crystal X-ray diffraction data. Cytotoxic activity assays against HL-60, SMMC-7721, A-549, MCF-7, and SW480 human cancer cell lines revealed IC values ranging from 2.3 to 5.3 μM for compound 7, from 19.4 to 34.4 μM for 8, and from 49.4 to 96.8 μg/mL for the EtOAc extract. An assay of the inhibition of NO production with RAW 264.7 cells indicated that 8 had an IC value of 21.4 μM, and the EtOAc extract, 10.5 μg/mL. The EtOAc extract possessed DPPH radical scavenging activity of 69.93% at 100 μg/mL.

2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical cation (ABTS+) is a stable free radical frequently used for estimating the total antioxidant capacity (TAC) of natural products. The existing methods for ABTS+ radical-scavenging activity assays are diverse in pre-diluting solvents and reaction time, which lead to errors in the TAC estimations. To develop an effective and universal method for estimating the ABTS+ capacity accurately and reasonably, five pre-dilution solvents [methanol, ethanol, phosphate buffer (Na 2 HPO 4-NaH 2 PO 4 , 200 mM, pH = 7.4), PBS buffer (Na 2 HPO 4-NaH 2 PO 4-NaCl, 200 mM, pH = 7.4), and distilled water] and different reaction times were investigated in ABTS+ assays of five typical antioxidants. The results showed that the solvent effects were very significant. When using different pre-diluting solvents, different detection wavelengths should be selected. ABTS+ assay could be measured within 2-10 min to obtain a rough result, which was mostly 6 min in the literature. However, full and accurate evaluation of antioxidant reactivity rather than capacity requires recording ABTS+ loss continuously during the whole reaction period. The present study makes a recommendation for estimating the ABTS+ capacity accurately and reasonably.