Chemical Composition of the Hazelnut Kernel (Corylus avellana L.) and Its Anti-inflammatory, Antimicrobial, and Antioxidant Activities

The chemical composition of hazelnut kernels (Corylus avellana L.) and their COX-2 inhibitory, antimicrobial, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical-scavenging activities were investigated. Six previously undescribed indoleacetic acid glycosides, hazelnutins A–F (1–6), and five known compounds (7–11) were isolated from the hazelnut kernels. The structures of compounds 1–6 were successfully identified by high-resolution-electrospray ionization-mass spectrometry and NMR data, and their absolute configurations were established by electron-capture detector spectroscopy analyses in corporation with quantum chemical calculations. Furthermore, the absolute configurations of compounds 7 and 8 were unambiguously confirmed for the first time. Compounds 8–11 were discovered in hazelnut kernels for the first time. Compounds 1–5 inhibited COX-2 expression with inhibition rates ranging from 36.10 to 64.08%. Compounds 3, 4, and 8 could inhibit the proliferation of Candida albicans. Compound 11 exhibited potent antioxidant activity against ABTS and DPPH with IC50 values of 11.22 and 13.21 μmol/L, respectively. Compounds 8 and 10 exhibited moderate antioxidant activity against ABTS.