Combined use of filtered and edited 1 H NMR spectroscopy to detect 13 C-enriched compounds in complex mixtures

• Published in: NMR in biomedicine 2012-11, Vol.25 (11), p.1217-1223
• Main Authors: Howe, P W A, Ament, Z, Knowles, K, Griffin, J L, Wright, J
• Format: Article
• Language: English
• Subjects: Animals; Carbon Isotopes; Complex Mixtures - chemistry; Magnetic Resonance Spectroscopy - methods; Male; Microsomes, Liver - drug effects; Microsomes, Liver - metabolism; Phenacetin - chemistry; Phenacetin - pharmacology; Protons; Rats
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.2791

In conventional metabolism and pharmacokinetic studies, radioactive isotopes are used to identify and quantify the breakdown products of xenobiotics. However, the stable isotope (13) C provides a cheaper and less hazardous alternative. Metabolites of (13) C-enriched xenobiotics can be detected, quantified and identified by (13) C-filtered NMR spectroscopy. However, one obstacle to using (13) C is its 1.1% natural abundance that produces a background signal in (13) C-filtered NMR spectra of crude biological extracts. The signal makes it difficult to distinguish between (13) C-enriched xenobiotics resonances from endogenous metabolites unrelated to the xenobiotic. This study proposes that the (13) C background signal can be distinguished from resonances of (13) C-enriched xenobiotics by the absence of a (12) C component in the xenobiotic. This is detected by combined analysis of (13) C-filtered and -edited NMR spectra. The theory underlying the approach is described and the method is demonstrated by the detection of sub-microgram amounts of (13) C-enriched phenacetin in crude extracts of hepatocyte microsomes.