1.3- Dimethyl-8 xanthosine

By 1923 Levene had experimentally confirmed these conclusions since, by treatment of xanthosine with diazomethane, he obtained the l, 3 -dimethyl derivative (ribosyl-theophylline) confirming that neither... 

Urinary excretion of modified nncleosides, originating from tiansfer-RNA, may be nsed as a biomarker for tnmonrs and AIDS. Dudley et al. [54-57] reported method development for the analysis of urinary nucleosides by LC-MS. Initially, LC-MS conditions were optimized [54]. In positive-ion ESI-MS, detection limits were achieved ranging from 7 pmol for tubercidin to 110 pmol for uridine. Next, a comparison was made between GC-MS, LC-MS on an ion-trap instrament, and capillary LC-MS on a triple-quadmpole instmment [55]. These methods proved complementary rather than that just one could be selected as optimal. Therefore, in the next study [56], all three techniques were applied to identily the unexpected 5 -deoxycytidine in the urine of a patient suffering with head and neck cancer. In another study [57], they demonstrated the detection of dA, 1-methyl-dA, xanthosine, 7V-l-methyl-dG, 7V-2-methyl-dG, 7V-2,7V-2-dimethyl-dG, A-2,7V-2,A-7-trimethyl-dG, inosine, and 1-methylinosine in urine samples from various cancer patients. 

A variant of the previous reaction was utilized for the synthesis of the l,3-dimethyl-8(/3-D-ribofuranosyl)xanthosine 515 the ethyl 2,5-anhydro-o-allonodithioate derivative 512 was cyclocondensed with 5,6-diamino-l,3-dimethyluracil (513) followed by removal of the 0-protective group of 514 (86MI4) (Scheme 138). 

Iodonueleosides. A soln. of xanthosine, N-iodosuccinimide, and n-butyl disulfide, as catalyst, in dimethyl sulfoxide allowed to stand 17 hrs. at room temp. 

Fig. 8.8 Biosynthetic pathway for tropane and purine alkaloids, (a) Tiopane alkaloid ODC ornithine decarboxylase, PMT putrescine Ai-methyltransferase). (b) Purine alkaloid XMT xanthosine W-methyltransferase/7-methylxanthosine synthase, XN 7-methylxanthosine nucleotidase, MXMT 7-methylxanthine Ai-methyltransferase/theobromine synthase, DXMT dimethyl-xanthine Ai-methyltransferase/caffeine synthase) (Adopted from Ref. [15])...

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