On-line screening and identification of antioxidant phenolic compounds of Saccocalyx satureioides Coss. et Dur

Abstract

Saccocalyx satureioides Coss. et Dur is an endemic plant from northern Sahara used in folk medicine. The purpose of the work is to investigate the radical scavenging capacity of this species which was never presented in the relevant literature yet. Hydro-ethanol extract (8:2) of the air-dried aerial parts of the species were subjected to chloroform, ethyl acetate and n-butanol extractions. These three extracts were evaluated for their free radical scavenging activities based on the ABTS•+ assay. On-line HPLC-ABTS+ was also applied to screen the extracts and subsequent micro-plate based fractionations followed by spectroscopic analysis (HRMS, UV, NMR: 1H, 13C, COSY, NOESY, HSQC and HMBC) were applied to identify the chemical structure of the free radical scavengers. Seventeen compounds were identified: piceol 1, vanillin 2, ferulic aldehyde 3, 3,3′-bis (3,4-dihydro-4-hydroxy-6,8-dimethoxy-2H-1-benzopyran) 4, 3,3′-bis (3,4-dihydro-4-hydroxy-6-methoxy-2H-1-benzopyran) 5, dimethylcaffeic acid 6, balanophonin 7, 7-methyl-sudachitin 8, caffeic acid 9, p-coumaric acid 10, isoscutellarein-7-O-[β-d-allopyranosyl-(1→2)]-β-d-glucopyranoside 11, isoscutellarein-7-O-[β-d-allopyranosyl-(1→2)]-6″-O-acetyl-β-d-glucopyranoside 12, isoscutellarein-7-O-[6″′-O-acetyl-β-d-allopyranosyl-(1→2)]-β-d-glucopyranoside 13, quercetin 14, isoscutellarein-7-O-[6”’-O-acetyl-β-d-allo pyranosyl-(1→2)]-6”-O-acetyl-β-d-glucopyranoside 15, apigenin-7-O-[6”-trans-p-coumaroyl]-β-d-glucopyranoside 16 and sideritiflavone 17. These compounds were the dominant free radical scavengers in the species and their Trolox equivalent antioxidant capacities (TEAC) were determined. Quercetin 14 and caffeic acid 9 were the most active components (TEAC: 34. 41 and 31.93μg/mL respectively), these results were validated by offline antioxidant DPPH and ORAC assays. All these compounds are described for the first time in the genus Saccocalyx whereas compounds 1, 3, 16 are described for the first time in the Lamiaceae family.