Two New Compounds from Allii Macrostemonis Bulbus and Their In Vitro Antioxidant Activities.

Two new compounds named 4,4'-bis(-D-glucopyranosyloxy)biphenyl () and spirostane-25(27)-en-2,3-diol-3---D-xylopyranosyl(1→3)--D-glucopyranosyl(1→4)--D-galactopyranoside () were isolated from n-butanol extraction part of 80% ethanol extract of Allii Macrostemonis Bulbus. Alongside these, ten known compounds () were also identified, including a flavonoid glycoside (), seven steroids (-), a nucleoside (), and a phenylpropanoid glycoside () were found. Notably, compounds - were isolated from this plant for the first time. The structures of all compounds were confirmed using high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), 1D, and 2D NMR spectroscopy. Some of these compounds showed strong antioxidant activity, and compound demonstrated the most potent reduction of ferric ions (Fe) with an IC value of 0.59 ± 0.18 mg/mL. Compounds and exhibited the highest scavenging activity against superoxide anion radicals (O·) with an IC value of 0.02 ± 0.01 mg/mL. Additionally, compound displayed substantial scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with IC values of 0.21 ± 0.17 mg/mL and 0.02 ± 0.01 mg/mL, respectively. The discovery of these two new compounds is a reference for identifying Allii Macrostemonis Bulbus quality markers. Moreover, their exceptional antioxidant activity offers a promising avenue for uncovering novel natural antioxidants.