Centaurea lycaonica is a local endemic species from the Centaurea L. genus. The Centaurea species has a wide range of usage in treating diseases in folk medicine. There are limited biological activity studies on this species in the literature. This study investigated enzyme inhibition and antimicrobial activity, antioxidant effect, and chemical content of extract and fractions of C. lycaonica. Enzyme inhibition activity was tested by α-amylase, α-glucosidase, and tyrosinase enzyme inhibition methods and antimicrobial activity by the microdilution method. The antioxidant activity was investigated using DPPH^•, ABTS^•+, and FRAP tests. The chemical content was determined by LC-MS/MS. The methanol extract showed the highest activity for α-glucosidase and α-amylase, even surpassing the positive control acarbose, with IC₅₀ values of 56.333 ± 0.986 and 172.800 ± 0.816 μg/mL, respectively. Additionally, the ethyl acetate fraction also exhibited high activity for α-amylase with an IC₅₀ value of 204.067 ± 1.739 μg/mL and tyrosinase with an IC₅₀ value of 213.900 ± 1.553 μg/mL. Moreover, this extract and fraction were found to have the highest total phenolic and flavonoid contents and antioxidant activity. Additionally, LC-MS/MS analyses of active extract and fraction revealed mainly the presence of phenolic compounds and flavonoids. In silico molecular docking and molecular dynamics simulation studies of determining compounds apigenin and myristoleic acid, common in CLM and CLE extracts and active against α-glucosidase and α-amylase, were performed. In conclusion, methanol extract and ethyl acetate fraction showed potential enzyme inhibition and antioxidant activity as a natural agent. Molecular modeling studies corroborate the findings of in vitro activity analyses.

Diabetes mellitus (DM) is one of the globally worst killer diseases. In this study, the in vitro and in vivo antidiabetic activity and antioxidant capacity were determined and the phytochemical analyses were carried out on flower extract and sub-extracts of Rhaponticoides iconiensis. The in vitro antidiabetic activity was tested with α-amylase and α-glucosidase enzyme inhibition methods and an in vivo OGTT test in healthy and alloxan-induced rats. Although, the antioxidant activity was investigated with DPPH^●, ABTS^●+ and FRAP tests, the phytochemical composition analysis was carried out by LC-MS/MS. The highest α-glucosidase and α-amylase activity even from positive control acarbose were found in the ethyl acetate sub-extract of R. iconiensis (IC₅₀ = 11.737 ± 0.823 µg/mL and 84.247 ± 0.721 µg/mL, respectively). This sub-extract also was active according to the results of in vivo tests. Moreover, the highest antioxidant activity on DPPH^● (IC₅₀ = 0.126 ± 0.002 mg/mL), FRAP (at a concentration of 1 mg/mL equivalent to 3112.052 ± 2.023 mmol Fe²⁺) and ABTS^+● (at a concentration of 0.5 mg/mL equivalent to 0.608 ± 0.005 µM Trolox) tests. In addition, LC-MS/MS analyses of the active sub-extract revealed mainly the presence of patuletin, patuletin 3,7-diglucoside, naringin and 3,4-dicaffeoylquinic acid detected in the active sub-extract. In silico molecular docking and dynamics simulations studies were performed on these compounds with α-amylase and α-glucosidase enzymes for protein–ligand interactions and stability.

Cousinia is one of the widespread genera of Asteraceae family. This study aims to evaluate the biological activities and phytochemical compositions of C. iconica extracts. The antioxidant effects of the extracts were investigated on DPPH^•, ABTS^+•, and iron chelating methods, and the inhibition effects were tested on α-amylase, α-glucosidase, and tyrosinase, as well as AChE, and BChE enzymes. The quantitative and qualitative determinations of the compounds of the extracts were carried out by LC-MS/MS. As a result, the highest TPC (271.65 ± 3.32 mg GAE/g_extract), and TFC (4.79 ± 0.06 mg QE/g_extract) were found in C. iconica ethyl acetate (CIE) sub-extract. The highest antioxidant activity on DPPH^• (IC₅₀ = 90.397 ± 0.575 µg/mL) was shown in C. iconica methanol (CIM) extract. The highest ABTS^+•, and iron chelating activities were found in CIE with IC₅₀ = 70.70 ± 0.38, and 615.10 ± 2.47 µg/mL, respectively. The highest α-amylase, and tyrosinase activities were found in CIE, and C. iconica n-butanol sub-extract (CIB) with 864.57 ± 0.68, and 475.21 ± 6.22 µg/mL IC₅₀ values, respectively. AChE, and BChE activities were observed as the highest in CIB (IC₅₀ = 426.50 ± 3.78 µg/mL), and CIM (IC₅₀ = 330.54 ± 0.79 µg/mL), respectively. According to LC-MS/MS analyses, rutin, and cynarin were determined as the main constituents of CIM, and CIE. This is the first report that these biological activities and phytochemical compositions of C. iconica were investigated.