Novel Bisamide Alkaloids Enantiomers from Pepper Roots ( Piper nigrum L. ) with Acetylcholinesterase Inhibitory and Anti-Neuroinflammatory Effects.

The roots of Piper nigrum L. , a seasoning for cooking various types of broths, are renowned for their high nutritional content and potential medicinal benefits. In this study, nine pairs of novel cyclohexene-type bisamide alkaloids ( 1a / 1b-9a / 9b ) were isolated from the pepper roots using molecular network analysis strategies. Their structures were determined by extensive spectroscopic data, electronic circular dichroism (ECD) calculations, and X-ray diffraction analyses. Using an intermolecular Diels-Alder reaction, a strategy for the synthesis of bisamide alkaloids from different monomeric amide alkaloids was developed. Furthermore, these compounds were chirally separated for the first time, and compounds 3a and 5a / 5b showed significant anti-neuroinflammation effects in the models of lipopolysaccharide(LPS)-induced BV2 microglial cells. Meanwhile, compounds 6b and 7a displayed concentration-dependent inhibitory activities against acetylcholinesterase with IC 50 values of 6.05 ± 1.10 and 3.81 ± 0.10 μM, respectively. These findings confirmed that these bisamide alkaloids could be applied in functional food formulations and pharmaceutical products as well as facilitate the further development and usage of pepper roots.