Liquid chromatography-mass spectrometric analyses of potential antioxidant constituents from zanthoxylum zanthoxyloides leaves: Probing into the role of alkaloids

Abstract

Zanthoxylum zanthoxyloides is a plant used traditionally as food and in medicine, with known antioxidant properties. The study aimed to prepare n-butanol fractions of Z. zanthoxyloides leaves and evaluate their in-vitro antioxidant potential. Vacuum liquid chromatography (VLC) was used to separate the constituents of the n-butanol fraction using gradients of binary mixtures of dichloromethane in methanol (1L) sequentially in the ratios; 9:1 (BF1), 7:3 (BF2), 5:5 (BF3), 3:7 (BF4), and 1:9 (BF5). Three standard antioxidant assay models were adopted for the in-vitro antioxidant activity. Ascorbic acid (53.60%) exhibited superior antioxidant activity relative to the n-butanol sub-fractions; (BF1 14.51%, BF2 24.76%, BF3 10.90%, BF4 6.19% and BF5 23.38%). Meanwhile, BF3 displayed superior reducing potential relative to ascorbic acid using both the TAC and FRAP method (TAC 2.320 ± 0.002; FRAP 2.27 ± 0.002 versus TAC 0.298 ± 0.000; FRAP 0.274 ± 0.002). BF1, BF2, BF4 and BF5 displayed lower reducing potential: TAC 0.202 ± 0.001; FRAP 0.199 ± 0.000, TAC 0.162 ± 0.001; FRAP 0.153 ± 0.001, TAC 0.186 ± 0.002; FRAP 0.174 ± 0.002 and TAC 0.262 ± 0.000; FRAP 0.223 ± 0.003, respectively when compared to ascorbic acid. Several known potential antioxidants were tentatively characterized in the n-butanol sub-fractions by liquid chromatography-mass spectrometry (LC-MS) dereplication. However, a significant number of alkaloids and phenolic compounds unknown for any role in radical scavenging activity (RSA) were detected in n-butanol sub-fractions. Our findings also further probed the possible role of alkaloids in antioxidant cascade.