Stability of 5-acetamido-6-formylamino-3-methyluracil in buffers and urine.
The caffeine metabolite 5-acetamido-6-formylamino-3-methyluracil (AFMU) and its product of spontaneous deformylation 5-acetamido-6-amino-3-methyluracil (AAMU) were synthesized. Their ultraviolet absorption spectra differed significantly from each other and wavelengths of absorption maximum and molar extinction coefficients varied with pH. The changes of the absorption spectrum parameters of AFMU and AAMU with pH indicated that they ionized with pK(a) of 5.7 and 8.3, respectively. The spontaneous deformylation of AFMU in solutions of different pH and urine were investigated spectrophotometrically and by high-performance liquid chromatography. The data showed the following: (a) AFMU transformed uniquely to AAMU; (b) deformylation obeyed first-order kinetics under the different conditions tested; (c) the half-life of AFMU varied between 7.8 and 36 h between pH 9.0 and 2.0 at 24 degrees C, with a maximum of 150 h at pH 3.0; (d) AFMU deformylated below pH 2.0 and above pH 10.0 with a half-life of less than 4.6 h; (e) half-lives of AFMU in urine were 57 and 12.5 h at 24 and 37 degrees C, respectively, comparable to those in buffers at equivalent pH and temperature. The results are discussed in relation to the mechanism of deformylation and the use of caffeine as a probe drug for NAT2 phenotyping.
Wong
Pierre
P
Department of Oncology, McGill University, McIntyre Medical Science Building, Suite 701, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6. pwong@med.mcgill.ca
Villeneuve
Gérald
G
Tessier
Vicky
V
Banerjee
Kris
K
Nedev
Hinko
H
Jean-Claude
Bertrand J
BJ
Leyland-Jones
Brian
B
D002021:Buffers; D002851:Chromatography, High Pressure Liquid; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007700:Kinetics; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014498:Uracil / Q000031:analogs & derivatives* / Q000032:analysis* / Q000652:urine
D002021:Buffers; D007202:Indicators and Reagents; D014498:Uracil; C036692:5-acetylamino-6-formylamino-3-methyluracil