Caractérisation phytochimique et évaluation de l’activité antioxydante de Nicotiana glauca (Solanaceae).

Abstract

Nicotiana glauca Graham (Solanaceae), or tree tobacco, is found in dry arid climates of North America, Africa and Europe. It has been reported to have both toxic and medicinal properties. The main aim of this study was to analyze the phytochemical screening and quantitative estimation of polyphenols, flavonoids and flavonols and identification of the man chemical compounds by LC-ESI-MS/MS of crude extracts from the leaves of N.glauca to evaluate its in vitro antioxidant properties.Three different solvents were used to extract bioactive compound from powdered leaves of N.glauca : dichloromethane(DCM), ethyl acetate (AE) and n-buthanol (n-BuOH). Phytochemical screening showed the presence of polyphenols and comarines in all extracts. Moreover, flavonoids, tannins, steroids and quinones were reported in the AE and n-BuOH extracts. In addition, alkaloids were seen to be present in DCM extract, while saponines and phlobatannins were absent in all extracts. The extracts AE and nBuOH have high total polyphenols (351.55±0.07 mg GAE /g and 284.98 ±0.08 mg GAE /g respectively) compared to their total flavonoids (105.97±0.04 mg QE/g and 164.44±0.07 mg QE/g, respectively) and total flavonols contents (22.41±0.24 mg QE/g and 18.75±0.46 mg QE/g, respectively). The chromatographic identification by LCESI-MS/MS spectrometry, concducted on the DCM, AE and n-BuOH extracts, provided tentative identification of 16 compounds, the majority of which were detected for the first time in this species, including 5 alcaloids, 2 coumarins, 2 flavonoids, 2 monterpens, 4 hydroxycinnamic acid derivatives and one homoserine lactone. Furthermore, The antioxidant capacity was performed using six methods (DPPH, ABTS, DMSO alcalin, Phénantroline, FRAP and CUPRAC). Results using the DPPH method showed strong free radical scavinging activity for three extracts, this activity decreased with increasing concentration in the following order : n-BuOH>AE>DCM. In other assays, all extracts showed good antioxidant activity which decreased with increasing concentration in the following order : AE > n-BuOH > DCM. Extracts were compared with standards : BHT, BHA, Tanic acid and α-Tocopherol. From all these results, n-BuOH extract was selected for the separation of bioactive molecules.this separation using column chromatography (CC).The compound separated was elucidated by the various methods spectral :NMR(1H, 13C), UV and comparison with lettirature valrieus. In parallel, the antioxidant potentiel of the majority compound separeted P* Rutin, was evaluated by the same six methods used previously, showed a very significant antioxidant activity (DPPH :IC50=7.19±0.11µg/mL ; ABTS :IC50=10.12±0.14µg/mL ;DMSOalcalin :A0.5=3.09±0.05µg/mL ;phénantroline: A0.5=33.88±0.23µg/mL ;FRAP :A0.5=56.27±1.56µg/mL andCUPRAP :A0.5=7.55±0.1 8µg/mL).