7-Functionalized 7-Deazapurine Ribonucleosides Related to 2-Aminoadenosine, Guanosine, and Xanthosine: Glycosylation of Pyrrolo[2,3-d]pyrimidines with 1-O-Acetyl-2,3,5-tri-O-benzoyl-d-ribofuranose

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Abstract
The Silyl−Hilbert−Johnson reaction as well as the nucleobase−anion glycosylation of a series of 7-deazapurines has been investigated, and the 7-functionalized 7-deazapurine ribonucleosides were prepared. Glycosylation of the 7-halogenated 6-chloro-2-pivaloylamino-7-deazapurines 9b−d with 1-O-acetyl-2,3,5-tri-O-benzoyl-d-ribofuranose (5) gave the β-d-nucleosides 11b−d (73−75% yield), which were transformed to a number of novel 7-halogenated 7-deazapurine ribonucleosides (2b−d, 3b−d, and 4b−d) related to guanosine, 2-aminoadenosine, and xanthosine. 7-Alkynyl derivatives (2e−i, 3e−h, or 4g) have been prepared from the corresponding 7-iodonucleosides 2d, 3d, or 4d employing the palladium-catalyzed Sonogashira cross-coupling reaction. The 7-halogenated 2-amino-7-deazapurine ribonucleosides with a reactive 6-chloro substituent (18b−d) were synthesized in an alternative way using nucleobase−anion glycosylation performed on the 7-halogenated 2-amino-6-chloro-7-deazapurines 13b−d with 5-O-[(1,1-dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-d-ribofuranosyl chloride (17). Compounds 18b−d have been converted to the nucleosides 19b−d carrying reactive substituents in the pyrimidine moiety. Conformational analysis of selected nucleosides on the basis of proton coupling constants and using the program PSEUROT showed that these ribonucleosides exist in a preferred S conformation in solution.

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