Nucleosides and nucleotides. Part 212: Practical large-scale synthesis of 1-(3-C-ethynyl-β-d-ribo-pentofuranosyl)cytosine (ECyd), a potent antitumor nucleoside. Isobutyryloxy group as an efficient anomeric leaving group in the Vorbrüggen glycosylation rea

A practical synthetic route to the antitumor nucleoside, 1-(3-C-ethynyl-β-d-ribo-pentofuranosyl)cytosine (ECyd, ) from 1,2-O-isopropylidene-d-xylofuranose () has been developed. Since most of the compounds were obtained as crystals, the target ECyd was prepared without any chromatographic purification in 31% overall yield from compound . The isobutyryloxy group was found to be an effective leaving group at the anomeric position of the 3-β-C-ethynyl glycosyl donors in the key Vorbrüggen glycosylation reaction. Using a similar procedure without chromatographic purification, the uracil congener EUrd [1-(3-C-ethynyl-β-d-ribo-pentofuranosyl)uracil (), which also has a potent antitumor effect, was synthesized from in 39% overall yield.