The present study examines the dynamics of the hop prenylphenol, Desmethylxanthohumol (DMX), by means of quantitative 1H-NMR (qHNMR) in a setting that mimics in vitro and physiological conditions. The experiments provide a comprehensive, time-resolved, and mechanistic picture of the spontaneous isomerization of DMX into congeneric flavanones, including their 1H/2D isotopomers. Formation of the potent phytoestrogen, 8-prenylnaringenin (8PN), suggests that measurable estrogenic activity even of high-purity DMX is an artifact. Together with previously established qHNMR assays including purity activity relationships (PARs), dynamic qHNMR assays complement important steps of the post-isolation evaluation of natural products.