Purines, pyrimidines, and imidazoles. Part 45. Stereospecific syntheses of some 1-D-ribofuranosyl- and 1-D-xylofuranosyl-uracil derivatives

Ethyl N-[α-acetyl-β-(5,6-O-isopropylidene-D-glucofuranosylamino)acryloyl]carbamate and the corresponding α-ethoxycarbonyl derivative have been prepared from 5,6-O-isopropylidene-D-glucofuranosylamine with ethyl N-(α-acetyl-β-ethoxyacryloyl)carbamate and ethyl N-(α-ethoxycarbonyl-β-ethoxyacryloyl)carbamate, respectively. Ethyl N-[α-acetyl-β-(4,6-O-isopropylidene-L-sorbosylamino)acryloyl]carbamate was similarly prepared from 4,6-O-isopropylidene-L-sorbosylamine, which was produced as a crystalline toluene-p-sulphonate from L-sorbosylamine, acetone, dimethoxypropane, and toluene-p-sulphonic acid.The anomeric ratios of α- and β-2′,3′-O-isopropylidene-5-cyanouridines obtained from ethyl N-(α-cyano-β-ethoxyacryloyl)carbamate and 2,3-O-isopropylidene-D-ribofuranosylamine in aqueous solution have been found to vary with base concentration. Ethyl N-(α-cyano-β-dimethylaminoacryloyl)carbamate did not react readily with either 2,3-O-isopropylidene-D-ribofuranosylamine or 3,5-O-isopropylidene-D-xylofuranosylamine, whereas the corresponding α-acetyl derivative with the xylosylamine gave 5-acetyl-1-(2,3-O-isopropylidene-α-D-xylofuranosyl)uracil and with the ribosylamine gave 5-acetyl-2′,3′-O-isopropylideneuridine; in each case only one anomer was formed. Mechanisms accounting for the stereospecificity of these reactions are proposed.