Branched-chain sugar nucleosides. III. 9-(3-Deoxy-3-C-methyl-β-D-allofuranosyl and ribofuranosyl)adenine

Abstract

Condensation of triphenylphosphinemethylene (Wittig reagent) with 5-O-benzyl-1,2-O-isopropyl-idene-α-D-erythro-pentafuranos-3-ulose and with 1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranos-3-ulose (1) afforded 5-O-benzyl-1,2-O-isopropylidene-3-deoxy-3-C-methylene-α-D-ribofuranose in 36% yield and 1,2:5,6-di-O-isopropylidene-3-C-methylene-α-D-ribo-hexofuranose (2) in 55% yield, respectively. A detailed study of the affect of reaction conditions on the yield of the unsaturated sugar is described. Hydrogenation of 2 proceeded stereoselectively to yield 4 which was hydrolyzed selectively to the 1,2-O-monoisopropylidene derivative 5. Benzoylation of the latter gave 6 which was converted by acetolysis to the 1,2-diacetate 7. Condensation of this compound with 6-benzamidochloromercuripurine in the presence of titanium tetrachloride followed by deblocking with methanolic sodium meth-oxide, yielded 9-(3-deoxy-3-C-methyl-β-D-allofuranosyl)adenine (10) in 48% yield based on 7. Sodium metaperiodate oxidation of 10, followed by sodium borohydride reduction of the aldehydo derivative, afforded 9-(3-deoxy-3-C-methyl-β-D-ribofuranosyl)adenine (11) in 85% yield.