Phytochemical Investigation of Bioactive Compounds from White Kidney Beans (Fruits of Var. ): Identification of Denatonium with Osteogenesis-Inducing Effect

var. (Leguminosae), commonly known as "white kidney bean", is a twining perennial vine whose fruit has been used as a popular food worldwide owing to its high nutritional content, in terms of proteins, carbohydrates, fats, and vitamins. As part of our ongoing study to investigate novel bioactive components from various natural resources, a phytochemical investigation of the extract of var. fruits resulted in the isolation of three phenolic compounds () and one dipeptide (). The chemical structures of the compounds () were determined through 1D and 2D nuclear magnetic resonance spectroscopy and high-resolution-liquid chromatography-mass spectrometry; they were identified as denatonium (), -ferulic acid ethyl ester (), eugenin (), and α-L-glutamyl-L-Leucine (). Intriguingly, denatonium () is known to be the most bitter chemical compound. To the best of our knowledge, denatonium () was identified from natural sources for the first time, and compounds were reported for the first time from var. in this study; however, compound turned out to be an artifact produced by an extraction with ethanol. The isolated compounds were tested for their regulatory effects on the differentiation between osteogenesis and adipogenesis of mesenchymal stem cells (MSCs). Compound slightly suppressed the adipogenic differentiation of MSCs, and compounds and stimulated osteogenic differentiation, unlike the negative control. These findings provide experimental evidence that compounds and may induce the osteogenesis of MSCs and activate bone formation.