Synthesis and characterization of 13C labeled carnosine derivatives for isotope dilution mass spectrometry measurements in biological matrices

Due to the physiological properties of L-carnosine (L-1), supplementation of this dipeptide has both a nutritional ergogenic application and a therapeutic potential for the treatment of numerous diseases in which ischemic or oxidative stress are involved. Quantitation of carnosine and its analogs in biological matrices results to be crucial for these applications and HPLC-MS procedures with isotope-labeled internal standards are the state-of-the-art approach for this analytical need. The use of these standards allows to account for variations during the sample preparation process, between-sample matrix effects, and variations in instrument performance over analysis time. Although literature reports a number of studies involving carnosine, isotope-labeled derivatives of the dipeptide are not commercially available. In this work we present a fast, flexible, and convenient strategy for the synthesis of the 13C-labeled carnosine analogs and their application as internal standards for the quantitation of carnosine and anserine in a biological matrix.