Etude phytochimique et pharmacologique d’une espèce endémique saharienne de la famille des Convolvulaceae

Abstract

Convolvulus trabutianus Schweinf. & Muschl is an endemic plant from northern Sahara used in folk medicine. The purpose of this work is the phytochemical and pharmacological investigation that led to the isolation of the molecules responsible for the radical scavenging capacity of this species. The CHCl3, AcOEt and n-BuOH soluble parts of the hydro-ethanol extract (8:2) of the aerial parts were evaluated for their free radical scavenging capacity by on-line (HPLC-ABTS•+) assay. The obtained data were confirmed off line by TEAC and ORAC assays. A subsequent fractionations by HPLC reverse phase followed by spectroscopic analysis (HRMS, UV, NMR: 1H, 13C, COSY, HSQC and HMBC) were applied to identify the structure of the active compounds. Twenty three compounds of different categories were identified, among which nine phenolic acids: ferulic acid ethyl ester 2, p-coumaric acid ethyl ester 6, caffeic acid ethyl ester 10, vanillic acid 11, ferulic acid 12, alfrutamide 13, 4-hydroxy -benzoic acid 14, p-coumaric acid 15, caffeic acid 16, two phytosterols: stigmasterol 3 and beta-sitosterol 4 as a mixture (73% and 27%, respectively), four coumarins: 7-O-prenylscopoletin 5, isoscopoletin 7, scoparone 8 and scopoletin 9, two quinic acids: 3,5-di-caffeoylquinic acid 21 and 4,5-di-caffeoylquinic acid 22 and six flavonoids: chrysoeriol 1, astragalin 17, vicenin-2 18, isoscutellarein 6-C-β-Dglucopyranosyl 19, nicotiflorin 20 and vitexin 23. All the extracts showed a significant antioxidant activity on-line. The most active compounds were caffeic acid ethyl ester 10, caffeic acid 16, 3,5-di-caffeoylquinic acid 21 and 4,5-dicaffeoylquinic acid 22. These results were validated off-line by ORAC and TEAC assays. Four compounds: 1, 5, 18 and 19 were described for the first time from the Convolvulaceae family, whereas compounds 2, 6, 8, 10, 13 and 21 were new for the genus Convolvulus. These results show a rich chemical composition and varied in secondary metabolites more precisely the phenolic compounds which have exhibited a very high antioxidant activity.