Synthesis of aromatic 13C/2H-α-ketoacid precursors to be used in selective phenylalanine and tyrosine protein labelling

Recent progress in protein NMR spectroscopy revealed aromatic residues to be valuable information sources for performing structure and motion analysis of high molecular weight proteins. However, the applied NMR experiments require tailored isotope labelling patterns in order to regulate spin-relaxation pathways and optimize magnetization transfer. We introduced a methodology to use alpha-ketoacids as metabolic amino acid precursors in cell-based overexpression of phenylalanine and/or tyrosine labelled proteins in a recent publication, which we have now developed further by providing synthetic routes to access the corresponding side-chain labelled precursors. The target compounds allow for selective introduction of C-13-H-1 spin systems in a highly deuterated chemical environment and feature alternating C-12-C-13-C-12 ring-patterns. The resulting isotope distribution is especially suited to render straightforward C-13 spin relaxation experiments possible, which provide insight into the dynamic properties of the corresponding labelled proteins.