Disaccharide nucleoside antibiotics plicacetin and streptcytosine A (also named rocheicoside A) were effectively synthesized through the common precursor cytosamine. The amosamine and amicetose moieties were efficiently assembled through an α-selective O-glycosylation, and the cytosine nucleus was subsequently introduced through a β-selective gold(I)-catalyzed N-glycosylation. Further microwave-assisted amidation reactions completed the modular syntheses.
Main observation and conclusion
Amicetin and congeners constitute a small family of complex pyrimidine nucleosides, which exhibit strong antibiotic activities against Gram‐positive bacteria and notably against strains of Mycobacterium tuberculosis. Herein, we report chemical synthesis of a series of disaccharide congeners of the amicetin family, including amicetin, plicacetin, and cytosaminomycin A—D. It is the first time for successful synthesis of amicetin, the prototypical member, and cytosaminomycins. The synthetic approach employs glycosyl N‐phenyltrifluoroacetimidate and thioglycoside donors to construct the characteristic aminodeoxydisaccharides consisting of α‐(1→4)‐glycosidic linkage, uses gold(I)‐catalyzed N‐glycosylation to furnish 2‐deoxy‐β‐nucleosides, and finally exploits amidation and global deprotection to complete the syntheses. It is noteworthy that the 3‐O‐protecting group in the 2‐deoxydisaccharide donors is found to be crucial for a successful N‐glycosylation to assemble the cytosaminomycin disaccharide nucleosides.
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