Chemo-Enzymatic Synthesis of 13C Labeled Complex N-Glycans As Internal Standards for the Absolute Glycan Quantification by Mass Spectrometry
2015
Echeverria, Begoña | Etxebarria, Juan | Ruiz, Nerea | Hernandez, Álvaro | Calvo, Javier | Haberger, Markus | Reusch, Dietmar | Reichardt, Niels-Christian
Methods for the absolute quantification of glycans are needed in glycoproteomics, during development and production of biopharmaceuticals and for the clinical analysis of glycan disease markers. Here we present a strategy for the chemo-enzymatic synthesis of ¹³C labeled N-glycan libraries and provide an example for their use as internal standards in the profiling and absolute quantification of mAb glycans by matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry. A synthetic biantennary glycan precursor was ¹³C-labeled on all four amino sugar residues and enzymatically derivatized to produce a library of 15 glycan isotopologues with a mass increment of 8 Da over the natural products. Asymmetrically elongated glycans were accessible by performing enzymatic reactions on partially protected UV-absorbing intermediates, subsequent fractionation by preparative HPLC, and final hydrogenation. Using a preformulated mixture of eight internal standards, we quantified the glycans in a monoclonal therapeutic antibody with excellent precision and speed.
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