Structural Determination of Two Active Compounds That Bind to the Muscarinic M 3 Receptor in Beer

Background: It is known that beer accelerates gastrointestinal motility in humans. Our previous studies showed that beer congener stimulates gastrointestinal motility by directly stimulating the muscarinic M 3 receptor. Further, we isolated 2 active compounds (compounds A and B) from beer by liquid chromatography. The objective of the present study was to identify the 2 active compounds that bind to the muscarinic M 3 receptor in beer. Methods: Structural analyses of the active compounds were performed by fast atom bombardment mass spectra, 1 H‐nuclear magnetic resonance (NMR), and 13 C‐NMR spectroscopy. Active compounds were chemically synthesized from p ‐coumaric acid and agmatine as starting materials. Binding activity to the muscarinic M 3 receptor was used to confirm the activity of the synthetic compounds. Results: It was identified that 2 active compounds had the same structural characteristics: stereoisomers ( cis ‐isomer and trans ‐isomer), molecular weight=550 and molecular formula=C 28 H 38 N 8 O 4 . Trans ‐isomer (compound B) was identified as the known substance hordatine A, a kind of phytoalexin in barley, and cis ‐isomer (compound A) was found to be a novel compound (tentatively referred to as aperidine). Both naturally present and chemically synthesized aperidine (compound A) and hordatine A (compound B) were demonstrated to have potent binding activities to the muscarinic M 3 receptor. Conclusions: The 2 active compounds isolated from beer, namely aperidine (compound A) and hordatine A (compound B), have structurally and functionally been identified as active entities of binding to the muscarinic M 3 receptor.