1.7- Dimethylxanthine caffeine metabolite

Recent research has begun to characterize the presence of ECs in a variety of waste sources (e.g., wastewater treatment plants, onsite septic systems, etc.) to better understand their potential pathways into the environment. Although data on transformation products for emerging contaminants is more limited when compared to other compounds, such as pesticides, a growing number of methods to detect such transformation products are being developed and select compounds have been found in a variety of waste sources, including wastewater treatment plants [7,67,74-78], septic systems [13,79], landfills [80], and animal manure [81,82]. For example, in a study of waste from wastewater treatment plants [75] and septic systems [13] (Tables 2-3), 1,7-dimethylxanthine (caffeine metabolite), 4-nonylphenol diethoxylate and... 

Boeckx et al. found that the advantage of the assay mentioned, over methods based on reversed-phase separations, was that silica gel columns used in combination with a simple extraction had a longer life than reversed-phase columns used in combination with a direct injection of deproteinized samples. To avoid the interference of 1,7-dimethylxanthine, a caffeine metabolite, in the analysis of theophylline in biological fluids, Van Aerde et al.165 developed a separation on silica gel. As the mobile phase, chloroform - dioxane - formic acid (99.5 4.5 0.01) was used. 

Kimura M, Yamazaki H, Fujieda M, Kiyotani K, Honda G, Saruwatari J, Nakagawa K, Ishizaki T, Kamataki T (2005) CYP2A6 is a principal enzyme involved in hydroxylation of 1,7-dimethylxanthine, a main caffeine metabolite, in humans. Drug Metab Dispos 33 1361-1366... 

Although xanthines such as theophylline (Figure 6.61) are electroactive, " the relatively high potentials (for example +1.2 V vs Ag/AgCl) that are required means that ED offers little advantage over UV detection, particularly if the eluent is chosen to ensure resolution of the caffeine metabolite 1,7-dimethylxanthine. 

Five caffeine metabolites (5-acetylamino-6-fbmiylamino-3-methyluracil, 1-methyl- and 1,7-dimethylxanthine, 1-methyl- and 1,7-dimethyluric acid) were extracted from urine and separated on a C g column (A = 280nm). In addition, nine other related compounds (e.g., 3- and 7-methyhiric acid, 3- and 7-methyl-xanthine, and 1,3,7-trimethylxanthine) were also studied with these compounds using a 12/1/87 methanol/acetonitrile/water (0.05% acetic acid) mobile phase [376]. Concentration ranges of 4-100 pM were used. Peak shapes were very good and most peaks were well resolved. Elution was complete in <35 min. 

Midha, K.K., Sved, S., Hossie, R.D., and McGilveray, I.J., High performance liquid chromatographic and mass spectrometric identification of dimethylxanthine metabolites of caffeine in human plasma, Biomed. Mass. Spectrom., 4,172,1977. 

The key metabolites of caffeine (a trimethylxanthine) found in plasma, are the dimethylxanthines paraxanthine, theophylline, and theobromine the monomethylxanthine 1-methylxanthine the C-8 oxidized monomethylxanthine 1-methyluric acid and the ring oxidized uracil 5-acetyl-amino-6-amino-3-methyluracil. 

Fig. 2. Caffeine and some metabolites TMX, trimethylxanthine DMX, dimethylxanthine MMX, monomethylxanthine...

Closely related methylxanthines include theophylline (1,3-dimethylxanthine), theobromine (3,7 dimethylxanthine) and paraxanthine (1,7-dimethylxanthine). Theobromine is found primarily in chocolate. These derivatives of caffeine are important because they are pharmacologically active and also are the common metabolites of caffeine. 

Antioxidant activities of caffeine (1,3,7-trimethylxanthine) and its main metabolites was compared. Caffeine, 1,7-dimethylxanthine, and 3,7-dimethylxanthine did not show any peroxyl radical-scavenging capacity at concentration up to 100 fxM. Flowever, the relative antioxidant activities (with respect to Trolox) of 1-methyl-xanthine and 1-methyluric acid were 0.82 and 0.58, respectively (L9). 

There are two commonly used and robust methods for phenotyping. The first one measures caffeine (1,3,7-methylxanthine) and its N-demethylated metabolite 1,7-dimethylxanthine (paraxanthine) in a plasma or saliva sample collected within 5 to 7 hours post caffeine dosing (Fuhr and Rost 1996). The second one uses the assay of the metabolites 1-methylurate... 

Theobromine and theophylline are metabolites of caffeine in the horse (M. S. Moss, 1977), and theobromine is frequently ingested with caffeine as a result of the contamination of pelleted horse feed with cocoa husk. Theophylline may also occur as a result of administering aminophylline for respiratory problems. Caffeine appears occasionally in greyhound urine as a result of the widespread practice of giving tea prior to racing. Theobromine, theophylline, and 1,7-dimethylxanthine are all metabolites of caffeine in the horse and man but tiieir proportions vary greatly between the species. In human sport, the upper limit on the urinary concentration of caffeine has recently been set at 15 xg/ml. 

Disposition in the Body. Rapidly absorbed after oral administration bioavailability almost 100%. Metabolic reactions include V-demethylation and oxidation to uric acid derivatives. About 85% of a dose is excreted in the urine in 48 hours with up to 40% of the dose as 1-methyluric acid, 10 to 15% as 1-methylxanthine and up to 35% as 5-acetylamino-6-formylamino-3-methyluracil and 5-acetylamino-6-amino-3-methyluracil other metabolites excreted in the urine include theophylline, 1,7-dimethylxanthine (paraxanthine), 7-methylxanthine, and 1,3-dimethyluric acid. Less than 10% is excreted in the urine as unchanged drug. The extent of V-acetylation is genetically determined. Caffeine, theophylline, theobromine, and paraxanthine are found in plasma from dietary sources especially coffee, tea and cocoa. An average cup of coffee or tea contains approximately 100 mg of caffeine. 

Fig. 11.2. Separation of some xanthine derivatives and urinary metabolites Column uBondapak C18 (300x4 mm ID), mobile phase acetonitrile - 0.1 M disodium hydrogen phosphate and 0.1 M sodium dihydrogen phosphate in water (2 38), flow rate 1.5 ml/min, detection UV 254 nm. Peaks 1, uric acid 2, creatinine 3, 1-methyluric acid, 3-methyluric acid and 7-methyluric acid 4, xanthine 5, 7-methylxanthine 6, 1,3-dimethyluric acid 7, 3-methyl-xanthine 8, 1-methylxanthine 9, theobromine 10, 8-chlorotheophyl1ine 11, theophylline and 1,7-dimethylxanthine (paraxanthine) 12, dyphylline 13, caffeine, (reproduced with permission from ref. 80, by courtesy of Clinical Chemistry)...

Methylated xanthines like caffeine are degraded in humans and rats by oxidative removal of methyl groups [10], Thus caffeine goes to 1,7-dimethylxanthine and 1-methylxanthine [11]. After the first demethylation there is an alternate pathway producing 5-acetylamino-6-formylamino-3-methyluracil. This pathway is more active in people with a more active acetylation system [12, 13]. There are individual, quantitative differences in the activity of this pathway in humans. In rats a major metabolite is... 

Hotchkiss, S.A. Caldwell, J. High-performance liquid chromatographic assay for theophylline and its major metabolites in human urine. J.Chromatogr., 1987, 423, 179—188 Kester, M.B. Saccar, C.L. Mansmann, H.C., Jr. A new simplified microassay for the quantitation of theophylline in serum by high-performance liquid chromatography. J.Liq.Chromatogr, 1987, 10, 957-975 [LOD 100 ng/mL extracted metabolites, caffeine, dimethyluric acid, dimethylxanthine, methylxanthine]... 

Caffeine is usually absorbed rapidly, especially in the small intestine, and overcomes the blood/brain barrier without problems. The bioavaUability is greater than 90%. The drug is deactivated in the liver by cytochrome P 450 enzymes. The methyl groups are an essential part of the pharmacophore. After their oxidative removal, caffeine loses its activity. The primary metabolites are theophylline, theobromine and 1,7-dimethylxanthine. 

Methylxanthines and methyluric acids are secondary plant metabolites derived from purine nucleotides (Figure 6.59). The most well-known methylxanthines are caffeine (1,3,7-trimethylxanthine) and theobromine (3,7-dimethylxanthine), which occur in tea (Camellia sinensis. Camellia ptilophylla, and Camellia taliensis) [242,243], coffee (Coffea arabica, Coffea canephora) [244, 245], cacao (Theobroma cacao) [246], and a number of other nonalcoholic beverages of plant origin Ilex paraguariensis, Paullinia cupana. Cola species and Citrus species [247-249]... 

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