Stereocontrolled syntheses of deoxyribonucleosides via photoinduced electron-transfer deoxygenation of benzoyl-protected ribo- and arabinonucleosides

The stereocontrolled, de novo syntheses of beta-2'-deoxy-, alpha-2'-deoxy-, beta-3'-deoxy-, and beta-2',3'-dideoxyribonucleosides are described. Strat egically protected ribose, arabinose, and xylose glycosylation precursors w ere synthesized bearing Ca-esters capable of directing Vorbruggen glycosyla tion. The key step is the regioselective deoxygenation of the desired hydro xyl group as either the benzoyl- or 3-(trifluoromethyl)benzoyl derivative. This deoxygenation is accomplished via a photoinduced electron-transfer (PE T) mechanism using carbazole derivatives as the photosensitizer. The synthe ses of the desired deoxynucleoside generally proceed in three steps from a common, readily available precursor.