Sesquiterpenes from stigma maydis (Zea mays) as a crop by-product and their potential neuroprotection and inhibitory activities of Aβ aggregation

Maize (Zea mays Linn.) during industrial processing generates a vast amount of residues including stigma maydis, which is generally regarded as a waste and discarded. However, there are great medicine and economic value in the industrial crop wastes. With the aim of fully utilizing the stigma maydis as a valuable source of bioactive components, a phytochemical investigation on stigma maydis was performed, leading to the isolation of five new macrocarpene-type sesquiterpenes (1–5), named stigmenes A-E, along with a known analogue stigmene F (6). The chemical structures of all compounds were unambiguously determined by employing various spectroscopic measurements. Their absolute configurations were confirmed by comparison of the experimental and calculated ECD data. All compounds were screened for the inhibitory effect of amyloid-β (Aβ) aggregation, among which 1 exhibited the most significant inhibitory activity. Molecular docking was used to predict the putative binding mode as the mechanism of action against Aβ aggregation. In addition, neuroprotection against H2O2-induced SH-SY5Y cell injury for all compounds was evaluated, and 5 and 6 were the most active. In total, the results suggest that stigma maydis is a promising and valuable crop waste for the pharmaceutical industry of neurological diseases.