Decorating phenylalanine side-chains with triple labeled ¹³C/¹⁹F/²H isotope patterns

We present an economic and straightforward method to introduce ¹³C-¹⁹F spin systems into the deuterated aromatic side chains of phenylalanine as reporters for various protein NMR applications. The method is based on the synthesis of [4-¹³C, 2,3,5,6-²H₄] 4-fluorophenylalanine from the commercially available isotope sources [2-¹³C] acetone and deuterium oxide. This compound is readily metabolized by standard Escherichia coli overexpression in a glyphosate-containing minimal medium, which results in high incorporation rates in the corresponding target proteins.