SNIF-NMR—Part 2: Isotope Ratios as Tracers of Chemical and Biochemical Mechanistic Pathways

Isotope labeling is a privileged source of information on chemical and biochemical mechanisms. In this context, the SNIF-NMR approach, which quantifies non-random distributions of isotopes at the natural abundance level, can be considered as a labeling method devoid of the need for isotopic enrichment [1]. Consequently, in its fields of application, it benefits from specific advantages with respect to conventional labeling methods. In particular, it avoids time-consuming syntheses of selectively labeled precursors, enables all monolabeled isotopomers of a molecular species to be simultaneously compared in identical experimental conditions, and provides a unique strategy for investigating mechanistic pathways taking place in unperturbed conditions. The main limitations are due to the rather poor sensitivity and chemical shift resolution of ²H-NMR (cf. Part 1), which preclude observation of complex metabolites present in very diluted media or available only at the submilligram level.