Comparative Metabolite Profiling of Four Citrus Peel Cultivars via Ultra-Performance Liquid Chromatography Coupled with Quadrupole-Time-of-Flight-Mass Spectrometry and Multivariate Data Analyses

Citrus plants are one of the most economical fruit bearing trees grown worldwide for their medicinal use as well as for the flavor and food industry. This study attempts to characterize the metabolome difference in polyphenols of four Citrus species fruit peels; C. reticulata Blanco cv. Egyptian, C. sinensis (L.) Osbeck cv. Olinda Valencia, C. aurantiifolia Swingle cv. Mexican and C. paradisi Macfad. cv. Duncan via ultra-performance liquid chromatography coupled with quadrupole-time-of-flight-mass spectrometry platform. A total of 163 metabolites were characterized of which 28 were detected for the first time in Citrus cultivars including eight coumarin derivatives, three cinnamic acids conjugates, one polymethoxyflavone, 5 O-glycosides, 2 C-glycosides, three flavone-di-O-glucosides and six acetyl sugar derivatives of luteolin and kaempferol in addition to oxygenated and methylated fatty acids. Flavonoids amounted for the most abundant secondary metabolites class in the studied Citrus peels. The relative variability among these Citrus peels was estimated using clustering analysis with flavonoids accounting for cvs. segregation. Hierarchical clustering analysis revealed the chemical similarity of C. reticulata, C. sinensis and C. paradise peels and being distant them from that of C. aurantiifolia. To the best of our knowledge, this study provides the first report for metabolite compositional differences in these four Citrus peels.

Investigation of Phenolic Constituents of Carduncellus eriocephalus Boiss. var. albiflora Gauba and their Biological Activities

The total ethanolic extract (TEE) of Carduncellus eriocephalus Boiss. var. albiflora Gauba showed antioxidant, antihyperglycaemic, and antihyperlipidaemic activities, which were attributed to the n-butanol fraction (BF). Chemical investigation of the BF led to the isolation of a new flavonoid, kaempferol-3- O-β-D-galactopyranoside-6″-sulfate (16), and a phenyl propenyl glycoside, 1-β-D-glucopyranoside-3-phenyl-2-propenol (rosin) (6), which is reported for the first time in the family Asteraceae. Chrysoeriol (1), 3′- O-methylorobol (2), luteolin (3), quercetin (4), myricetin (5), kaempferol 3- O-α-L-arabinopyranoside (7), kaempferol 3- O-β-D-glucopyranoside (8), quercetin 3- O-β-D-glucopyranoside (12), luteolin 7- O-β-D-rutinoside (13), quercetin 3- O-β-D-rutinoside (14), apigenin 7- O-β-D-rutinoside (15), and 3,5-dicaffeoylquinic acid (17) were isolated for the first time from the genus Carduncellus, in addition to apigenin 7- O-β-D-glucopyranoside (9), chryseriol 7- O-β-D-glucopyranoside (10) and luteolin 7- O-β-D-glucopyranoside (11), which have been previously reported for C. eriocephalus.

Flavonoid Constituents of Carduncellus Mareoticus (Del.) Hanelt and their Biological Activities

The total ethanolic extract (TEE) of Carduncellus mareoticus (Del.) Hanelt showed antioxidant and antihyperlipidemic activities, which were attributed to the ethyl acetate fraction (EAF). Also TEE showed potent cytotoxic activity against a cervix cancer cell line (IC50 = 5 μg/mL) and moderate activity against a breast cancer cell line. Chemical investigation of EAF led to the isolation of a new flavonoid, 8-hydroxy-5-methoxyluteolin 7- O-β-D-glucopyranoside (11), along with ten known metabolites (1–10). Three of these compounds, isorhamnetin 3- O-β-D-glucopyranoside (7), luteolin 3′- O-β-D-glucopyranoside (8), and eriodictyol 7- O-β-D-glucopyranoside (9) are reported for the first time from the genus Carduncellus, and two compounds, chrysoeriol 7- O-β-D-glucopyranoside (6), and luteolin 7- O-β-D-glucopyranoside (10), for the first time from C. mareoticus. The rest of the isolated compounds, chrysoeriol (1), luteolin (2), quercetin (3), kaempferol 3- O-α-L-arabinopyranoside (4), and kaempferol 3- O-β-D-glucopyranoside (5) have been previously reported from the genus.