Stereoselective Synthesis of the Ribocitrin Trisaccharide Framework via 1,2‐ cis ‐α‐Selective Ribofuranosylation Using Ribofuranosyl Iodides

Ribocitrin, a natural product isolated from Streptomyces neyagawaensis MF980‐CF1, consists of ( S )‐homocitric acid and a trisaccharide unit, α‐ d ‐ribofuranosyl‐(1→2)‐α‐ d ‐ribofuranosyl‐(1→3)‐ d ‐ribofuranose. Ribocitrin exhibits inhibitory activity against Streptococcus mutans dextransucrase and is therefore considered a potential preventive agent for dental caries. Although ribocitrin exhibits promising biological activity, its structural complexity is anticipated to render chemical synthesis difficult; accordingly, neither the trisaccharide moiety nor the full molecule has been synthesized to date. In this study, we present the first successful synthesis of the trisaccharide framework of ribocitrin via 1,2‐ cis ‐α‐selective ribofuranosylation using ribofuranosyl iodides as glycosyl donors. Both α‐glycosidic linkages were constructed with complete 1,2‐ cis ‐selectivity. The trisaccharide structure was confirmed by comparison of the spectroscopic data of its per‐ O ‐acetylated derivative with those previously reported.