Stereochemical assignment and first synthesis of the core of miharamycin antibiotics.

The relative configuration at C-6' of nucleoside antibiotic miharamycin A has been elucidated by NMR spectroscopy and proved to be S. The total synthesis of miharamycin B has also been investigated, which has led to the unprecedented construction of its core. The bicyclic sugar moiety has been elaborated by means of a SmI(2)-based keto-alkyne coupling. Elongation of its C-6 position towards a bicyclic sugar amino acid and conversion into a suitable glycosyl donor enabled efficient N-glycosylation with 2-aminopurine to take place to afford the nucleosidic part of miharamycin B. Final peptide coupling with arginine afforded the skeleton of miharamycin B. Unfortunately, attempts to deprotect this scaffold failed to afford the complex nucleoside antibiotic.