Branfman A R, McComish M F, Bruni R J, Callahan M M, Robertson R, Yesair D W
Drug Metab Dispos. 1983 May-Jun;11(3):206-10.
A major caffeine metabolite (A1) has been isolated from human urine by a combination of solvent extraction, reverse phase high-pressure liquid chromatography, and silica gel open column chromatography. The chromatographic and spectral properties of A1 are identical with an authentic sample of 5-acetylamino-6-amino-3-methyluracil. A stable isotope-labeling study, in which [2-14C]caffeine in a 1:1 mixture of unlabeled caffeine and [1,3-15N-8-13C] caffeine was administered to subjects, demonstrated that the C-8 carbon of caffeine was lost during the biotransformation to A1. Thus, the acetyl group in A1 does not originate from caffeine. The 1:1 ratio of the mass spectral ions for A1 isolated from the stable isotope study and the specific activity of A1 support caffeine as the principal source of A1. A related metabolite (A2) was too labile for complete purification and structural identification. The chromatographic and mass spectral properties of the degradation product of A2 were identical with those of A1.
通过溶剂萃取、反相高压液相色谱和硅胶开放柱色谱相结合的方法，从人尿中分离出一种主要的咖啡因代谢物（A1）。A1的色谱和光谱特性与5-乙酰氨基-6-氨基-3-甲基尿嘧啶的真实样品相同。一项稳定同位素标记研究中，给受试者施用未标记咖啡因与[1,3-15N-8-13C]咖啡因1:1混合物中的[2-14C]咖啡因，结果表明咖啡因的C-8碳在生物转化为A1的过程中丢失。因此，A1中的乙酰基并非源自咖啡因。从稳定同位素研究中分离出的A1的质谱离子的1:1比例以及A1的比活性支持咖啡因是A1的主要来源。一种相关代谢物（A2）过于不稳定，无法进行完全纯化和结构鉴定。A2降解产物的色谱和质谱特性与A1相同。
