Structure and Metabolic-Flow Analysis of Molecular Complexity in a 13C-Labeled Tree by 2D and 3D NMR

Improved signal identification for biological small molecules (BSMs) in a mixture was demonstrated by using multidimensional NMR on samples from 13C‐enriched Rhododendron japonicum (59.5 atom%) cultivated in air containing 13C‐labeled carbon dioxide for 14 weeks. The resonance assignment of 386 carbon atoms and 380 hydrogen atoms in the mixture was achieved. 42 BSMs, including eight that were unlisted in the spectral databases, were identified. Comparisons between the experimental values and the 13C chemical shift values calculated by density functional theory supported the identifications of unlisted BSMs. Tracing the 13C/12C ratio by multidimensional NMR spectra revealed faster and slower turnover ratios of BSMs involved in central metabolism and those categorized as secondary metabolites, respectively. The identification of BSMs and subsequent flow analysis provided insight into the metabolic systems of the plant. Markierte Bäume: Mehrdimensionale NMR‐Spektroskopie und Isotopenmarkierung ermöglichen die umfassende Analyse niedermolekularer Substanzen in dem Baum Rhododendron japonicum. Dabei wurden unerwartete Moleküle identifiziert und Informationen über ihre Stoffwechselwege gesammelt.