2 ,3 -0-Isopropylidene guanosine, preparation

Mono-isopropylidene derivatives of adenosine and guanosine have also been prepared by Levene and Tipson. They are probably, likewise, the 2,3-isopropylidene derivatives, but their structures have not yet been proved. 

Chemical Synthesis.—Purine nucleoside 5 -monophosphates enriched with or 0 on the phosphate group are conveniently prepared by treating phosphorus pentachloride in dry triethyl phosphate with one equivalent of the appropriately labelled water to give PO]- or P 0]P0Cl3, which is not isolated but mixed with adenosine or guanosine in the same solvent. Work-up of the resulting 5 -phos-phorodichloridate in similarly labelled water permits the formation of pO]-or P 0]AMP (or GMP) in fair yield with good enrichment. The 5 -monophos-phates of the 5 -C-methyl uridines derived from 6-deoxy-D-allose and 6-deoxy-L-talose have been prepared via phosphorylation of the 2, 3 -0,0-ethoxymethyl-idene derivative of the nucleosides (1) with -cyanoethyl phosphate and DCC or TPS-Cl. The same method has been used to phosphorylate iV -benzoylated 2, 3 -0,C -isopropylidene derivatives of various 5 -C-alkyladenosine species (2) and also 4 -allyladenosine (3) as part of a study in which derivatives of AMP... 

Samples of 5-amino-l-(P-D-ribofuranosyl)imidazole and its 5 -phosphate (AIR), labelled separately with in each of the three nitrogen atoms, have been prepared from 2,3-0-isopropylidene-P-D-ribofuranosylamine by Shaw s methodology, and similar methods were used to make the a-isomer of AICA riboside and hence a-guanosine from the isoxazole (12),3l and also in the preparation of the imidazole phosphonate (13). The novel mesoionic nucleoside (14) and its 2 -deoxyanalogue have been prepared from ribofuranosylhydrazine derivatives.32... 

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