Synthesis of N,N-dimethyl-2,4-dinitro-5-fluorobenzylamine and its reactions with amino acids and peptides

A practical synthesis is described for N,N-dimethyl-2,4-dinitro-5-fluorobenzylamine (DMDNFB) and its -d6 analog as an alternative Sangerʹs reagent (DNFB), for purposes of amino acid derivatization detectable by positive mode electrospray ionization mass spectrometry. DMDNFB is comparable to DNFB in its efficiency to derivatize amino acids and peptides. Various DMDNP (d0/d6) derivatives of (modified) lysine were synthesized to evaluate the potential use of isotope-edited LC-ESI-MS as a tool for structural definition of the posttranslational modification of protein-based lysines.