HIGH-FIELD DEUTERIUM NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC MONITORING OF THE PHARMACOKINETICS OF SELECTIVELY DEUTERATED BENZOIC-ACID IN MAN

The stable isotope tracer technique using C-13 labeling of substrates followed by NMR spectroscopy of biofluids has been widely used in meta bolic investigations, whereas the use of H-2 labeling and H-2 NMR spec troscopy has been extremely limited. The applicability of the high-fie ld H-2 NMR spectroscopy (14.1 T, 92 MHz H-2 frequency) in a simple pha rmacokinetic problem has now been investigated using selectively deute rated benzoic acid (BA) as a model. [7-C-13,2,6-H-2(2)]BA was synthesi zed for use as a tracer to compare the efficiency and sensitivity of H -2 and C-13 labeling. The urinary excretion of [7-C-13,2,6-H-2(2)]hipp uric acid (HA) formed from orally administered [7-C-13,2,6-H-2(2)]BA ( 250 mg) was followed by 92-MHz H-2 and 150-MHz C-13 NMR spectroscopy ( only 10 min accumulation time) following concentration of urine by a f actor of 10, using a standard for quantitation. The heights of resonan ces for (13)C7 and (2)H2,6 were used to calculate the [7-C-13,2,6-H-2( 2)]HA concentration. The lower limit of detection using this H-2 NMR a pproach was approximately 60 nmol/ml and was found to be comparable wi th that of the C-13 NMR approach where the quaternary carbon (C7) was labeled. The administered [7-C-13,2,6-H-2(2)]BA was found to be quanti tatively biotransformed to HA and excreted in urine within 4 h by both NMR approaches. The H-2 NMR approach using a high-field NMR spectrome ter is potentially useful and practical for pharmacokinetic research o n small molecules whose H-2 resonances are relatively sharp since the procedures are very simple and convenient. (C) 1994 Academic Press, In c.