Caffeoylquinic Acids, Cytotoxic, Antioxidant, Acetylcholinesterase and Tyrosinase Enzyme Inhibitory Activities of Six Inula Species from Bulgaria Antoaneta Trendafilova,* a Victoria Ivanova, a Miroslav Rangelov, a Milka Todorova, a Gulmira Ozek, b Suleyman Yur, b,c Temel Ozek, b,c Ina Aneva, d Ralitza Veleva, e,f Veselina Moskova-Doumanova, e Jordan Doumanov, e and Tanya Topouzova-Hristova e a Institute of Organic Chemistry with Center of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria, e-mail: trendaf@orgchm.bas.bg b Department of Pharmacognosy, Faculty of Pharmacy, Anadolu University, 26470 Eskişehir, Turkey c Medicinal Plant, Drug and Scientific Research Center (AUBIBAM), Anadolu University, 26470 Eskişehir, Turkey d Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria e Faculty of Biology, Sofia University, ‘St. Kliment Ohridski’, 1164 Sofia, Bulgaria f Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria Chlorogenic (5-CQA), 1,5-, 3,5-, 4,5- and 3,4-dicaffeoylquinic (DCQA) acids were identified and quantified in the methanol extracts of Inula oculus-christi L., I. bifrons L., I. aschersoniana JANKA var. aschersoniana, I. ensifolia L., I. conyza (GRIESS.) DC. and I. germanica L. by HPLC analysis. The amount of 5-CQA varied from 5.48 to 28.44 mg/g DE and the highest content was detected in I. ensifolia. 1,5-DCQA (4.05–55.25 mg/g DE) was the most abundant dicaffeoyl ester of quinic acid followed by 3,5-DCQA, 4,5-DCQA and 3,4-DCQA. The extract of I. ensifolia showed the highest total phenolic content (119.92 � 0.95 mg GAE/g DE) and exhibited the strongest DPPH radical scavenging activity (69.41 � 0.55%). I. bifrons extract was found to be the most active sample against ABTS *+ (TEAC 0.257 � 0.012 mg/mL) and the best tyrosinase inhibitor. The studied extracts demonstrated a low inhibitory effect towards acetylcholinesterase and possessed low cytotoxicity in concentration range from 10 to 300 μg/mL toward non-cancer (MDCK II) and cancer (A 549) cells. Keywords: Inula species, caffeoylquinic acids, antioxidant activity, acetylcholinesterase and tyrosinase inhibition, cytotoxicity. Introduction Chlorogenic acids, mono- and dicaffeoyl esters of quinic acid have attracted the attention of the scientists because of their broad spectrum of bio- logical activities and their health effects, such as antispasmodic, hepatoprotective and choleretic activ- ities, antioxidant, antiviral, antibacterial, anticancer and anti-inflammatory properties, and reduction of the relative risk of diabetes type 2 and Alzheimer’s disease. [1–3] These secondary metabolites are widely distributed in Plant Kingdom and particularly in the species of Asteraceae family. [4] The genus Inula (Asteraceae) comprises about 100 species widespread in temperate regions of Europe, Africa and Asia. Many Inula species are used in traditional medicines throughout the world and reports on their ethnopharmacological applications have been recently reviewed. [5] Plants belonging to this genus have shown to possess various biological activities–anti-inflammatory, antitumor, antibacterial, antitussive, antiproliferative, antioxidant, antidiabetic and hepatoprotective, etc., which were attributed to the abundance of bioactive components mainly sesquiterpene lactones, phenolic acids, and flavonoids. [5–7] Chlorogenic acid and dicaffeoyl esters of quinic acid have been also reported in some Inula species. [5,6,8–25] DOI: 10.1002/cbdv.202000051 FULL PAPER Chem. Biodiversity 2020, 17, e2000051 © 2020 Wiley-VHCA AG, Zurich, Switzerland