PubMed · 13111245
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P BERG, W K JOKLIK. 1953-11-28. Transphosphorylation between nucleoside polyphosphates.. https://doi.org/10.1038/1721008a0
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A general synthetic approach to various isoxanthopterin-nucleosides starting from 6-methyl-2-methylthio-4(3H),7(8H)-pterdinedione (1) has been developed. Ribosylation with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose via the silyl-method led to 2 and reaction with 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-alpha-D-ribofuranose using the DBU-method afforded 28. Protection of the amide function at O4 by benzylation to 5 and by a Mitsunobu reaction with 2-(4-nitrophenyl)ethanol to 29 gave soluble intermediates which can be oxidized to the corresponding 2-methylsulfonyl derivatives 8 and 30, respectively. Nucleophilic displacement reactions of the highly reactive 2-methylsulfonyl functions by various amines proceeded under mild conditions to isoxanthopterin-N8-ribo- (11-17) and 2'-deoxyribomucleosides (31-33). Debenzylation can be achieve by Pd-catalyzed hydrogenation (9 to 19) and cleavage of the npe-protecting group (31, 32 to 34, 35) works well with DBU by beta-elimination.
Four D-altritol nucleosides with a 3'-O-tert-butyldimethylsilyl protecting group are synthesized (base moieties are adenine, guanine, thymine and 5-methylcytosine). The nucleosides are obtained by ring opening reaction of 1,5:2,3-dianhydro-4,6-O-benzylidene-D-allitol. Optimal reaction circumstances (NaH, LiH, DBU, phase transfer, microwave irridation) for the introduction of the heterocycles are base-specific. For the introduction of the 3'-O-silyl protecting group, long reaction times and several equivalents of tert-butyldimethylsilyl chloride are needed.
The coupling reaction of acetoxymethoxy ribofuranoside 4 with nucleic acid bases 5a-f to synthesize novel (ribofuranosyloxy)methyl uracil, thymine, cytosine, adenine, guanine derivatives 6a-g respectively in preference to the expected formation of natural nucleosides 2',3',5'-tri-O-benzoyl uridine, methyluridine, cytidine, adenosine and guanosine 7a-g is described. Detailed study of these reactions catalysed by Lewis acids TMSOTf and SnCl4 is described. TMSOTf exhibited selectivity for the formation of ribofuranosyloxy methyl derivatives 6a-g rather than 7a-g. Reason for formation of 6a-g is explained by HSAB principle.