NMR Analysis of Carboxylate Isotopomers of 13C-Metabolites by Chemoselective Derivatization with 15N-Cholamine

A substantial fraction of common metabolites contains carboxyl functional groups. Their C-13 isotopomer analysis by nuclear magnetic resonance (NMR) is hampered by the low sensitivity of the C-13 nucleus, the slow longitudinal relaxation for the lack of an attached proton, and the relatively low chemical shift dispersion of carboxylates. Chemoselective (CS) derivatization is a means of tagging compounds in a complex mixture via a specific functional group. N-15(1)-cholamine has been shown to be a useful CS agent for carboxylates, producing a peptide bond that can be detected via N-15-attached H with high sensitivity in heteronuclear single quantum coherence experiments. Here, we report an improved method of derivatization and show how C-13-enrichment at the carboxylate and/or the adjacent carbon can be determined via one-and two-bond coupling of the carbons adjacent to the cholamine N-15 atom in the derivatives. We have applied this method for the determination of C-13 isotopomer distribution in the extracts of A549 cell culture and liver tissue from a patient-derived xenograft mouse.

Automated summary

This study presents an improved method for chemoselective derivatization of carboxylates using N-15 cholamine for C-13 isotopomer analysis by NMR. The method allows for determination of C-13 isotopomer distribution in extracts from cell culture and animal tissue samples.