A simple and economical method for the production of ¹³C, ¹⁸O-labeled fmoc-amino acids with high levels of enrichment: Applications to isotope-edited IR studies of proteins

Isotope-edited IR of proteins has generated considerable interest. Double labeling with ¹³C and ¹⁸O with high levels of isotopic enrichment is required for residue-specific resolution. Current methods for the preparation of doubly labeled amino acids give modest ¹⁸O enrichment, limiting the utility of the approach. We report a simple and economical method for preparing ¹³C, ¹⁸O-doubly labeled N-(9- fluorenylmethoxycarbonyl)-amino acids with high levels of enrichment for residues that do not require acid-labile side-chain protecting groups.