Investigations on centaurea athoa dc. and endemic centaurea polyclada dc. taxa naturally distributed in West Anatolia

The genus Centaurea L. (Asteraceae) is represented by 200 taxa in the flora of Turkey, 110 of which are endemic. Centaurea species are used orally or externally as traditional medicines for various purposes. Bioactivity studies on several Centaurea species have reported antiinflammatory, antimalarial, antiprotozoal, antimicrobial, antiulserogenic and cytotoxic properties. Phytochemical investigations on Centaurea species that are rich in bioactive secondary metabolites are generally resulted in isolation of sesquiterpene lactones, flavonoids and lignan glucosides. In our preliminary studies, the methanol and chloroform extracts from C. athoa and C. polyclada exhibited in vitro antioxidant, anti-inflammatory and cytotoxic activities, which prompted us to start a detailed investigation on these species. In this thesis, the chloroform, methanol and n-butanol extracts obtained from the aerial parts of C. athoa and C. polyclada were studied for their secondary metabolite content. Structures of the compounds purified by chromatographic methods [Open column chromatography (OCC), vacuum liquid chromatography (VLC), solid phase extraction (SPE)] were established using spectral methods [1 and 2 dimensional (1D and 2D) Nuclear Magnetic Resonance spectroscopy (NMR), mass spectroscopy and infrared (IR) spectroscopy]. Fractionation of the chloroform extract from the aerial parts of C. athoa led to the isolation of three elemane-type sesquiterpenes; [athoin (CA-1), 14-O-acetylathoin (CA-2) and methyl 14-O-acetylathoin-12-oate (CA-3)] with a germacrane type sesquiterpene [4'-hydroxypecterolide-14-O-acetate (CA-4)], whereas the n-butanol extract afforded two simple phenolic compounds and two phenolic glucosides [p-hydroxybenzoic acid (CA-5), protocatechuic acid (CA-6), vanillic acid-4-O-b-D-glucopyranoside methyl ester (CA-7) and picein (CA-8)], two phenylpropanoid derivatives [9-O-methyl coniferin (CA-9) and syringin (CA-10)] and a phytosterol [b-sitosterol-3-O-b-D-glucopyranoside (CA-11)]. Fractionation of the chloroform and n-butanol extracts of the C. polyclada aerial parts provided five elemane-type sesquiterpenes [6a,8a,15-trihydroxyelema-1,3,11(13)-trien-12-oic acid (CP-2) and its methyl ester (CP-1), 8a-O-[2'-(hydroxymethyl)-but-2'-enoyl]-6a,15-dihydroxyelema-1,3,11(13)-trien-12-oic acid (CP-3), 13-N-proline melitensin (CP-4) and 13-N-proline-6a,8a,15-trihydroxyelema-1,3-dien-12-oic acid (CP-5)], an eudesmane-type sesquiterpene [1b,6a,8a-trihydroxy-15-oxo-eudesm-11(13)-en-12-oic acid methyl ester (CP-6)], three flavonoids [salvigenin (CP-7), eupatorin (CP-8) and 3'-methoxy eupatorin (CP-9)], a lignan [arctiin (CP-10)], a phenolic glucoside [tachioside (CP-10)] and a phenylpropanoid glucoside [syringine (CP-12)]. The investigation of the aerial parts of C. athoa and C. polyclada afforded six new elemanolide derivatives (CA-1, CA-2, CA-3 and CP-3, CP-4, CP-5) and one new eudesmane (CP-6). Also the germacranolide CA-4 and the eleman derivative CP-1 have been reported from the genus Centaurea for the first time. Antiinflammatory and cytotoxic activities of the isolated sesquiterpenes were investigated on different cell lines. The highest cytotoxic activity against all cell lines (A549, CaCO-2, HeLa, MCF-7, MDAMB231, mPanc-96, PC3, U87MG and HEK293) was observed with the germacranolide 4'-hydroxypecterolide-14-O-acetate (CA-4) isolated from C. athoa by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay. Antiinflammatory activities were studied by iNOS (Inducible nitric oxide synthase) inhibition assay on RAW 264.7 murine macrophage cell line and NF-kB (Nuclear Factor kappa B) inhibition assay on NF-kB luciferase reporter stable HeLa cell line. 4'-hydroxypecterolide-14-O-acetate (CA-4) and 13-N-proline melitensin (CP-4) showed significant inhibitory activities while they had no cytotoxicity on RAW 264.7 cell line.