Theophylline, silver salt

Because of the great interest in the naturally occurring nucleosides, studies of the synthesis of D-ribosides of purines and pyrimidines have been numerous. The first attempt in this direction was made by Levene and Sobotka146 who condensed the silver salt of theophylline with tri-acetyl- 8-D-ribopyranosyl bromide to obtain what was probably triacetyl-7- 8-D-ribopyranosyl theophylline (LXXVI). Subsequently Hilbert and Rist94 condensed 2,4-diethoxypyrimidine (LXXVII) with triacetyl-0-D-ribopyranosyl bromide (LXXVIII) to form ethyl bromide and 1-triacetyl-D-ribopyranosyl-4-ethoxyuracil (LXXX), which, on deacetylation with hydrogen chloride, gave 1-D-ribopyranosyluracil (LXXIX), an isomer of... 

Direct condensation of 2,3,5-tri-0-benzoyI-/3-D-ribofuranosyl bromide with adenine in acetonitrile at 50 °C leads after deblocking to the 3-/3-D-ribofuranosyladenine (132) (B-68MI40901). Metal derivatives of purines tend to produce 7- or 9-glycosyl derivatives thus the silver salt of 2,8-dichloroadenine with 2,3,5-tri-O-acetylribofuranosyl chloride produces the 9-/3-D-ribofuranosyl derivative (133) (48JCS967, 48JCS1685). However similar reactions with theobromine produce O-glycosides and with theophylline N-7 derivatives (34JCS1639). 

Theophylline also gives a silver salt quantitatively. It is only weakly acidic in water (pK = 8.60—see above aminophylline). In the presence of silver nitrate, it gives a silver monosalt, which precipitates ... 

In the list of the above-mentioned compounds, some of them form silver salts completely only in the presence of ammonia. This is the case for thiourea and also theophylline. The precipitation of thiourea by silver ions might be the result of the following two reactions ... 

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