Abstract
In the presence of an arylboronic acid and a hydrogen atom transfer mediator under photoredox conditions, furanoside derivatives undergo site-selective redox isomerizations to 2-keto-3-deoxyfuranosides. Experimental evidence and computational modeling suggest that the transformation takes place by abstraction of the hydrogen atom from the 2-position of the furanoside-derived arylboronic ester, followed by C3–O bond cleavage via spin-center shift. This mechanism is reminiscent of the currently accepted pathway for the formation of 3′-ketodeoxynucleotides by ribonucleotide reductase enzymes.
Highlights
The transformation of ribonucleotides to 20-deoxyribonucleotides, catalyzed by ribonucleotide reductase enzymes, is a crucial process in DNA biosynthesis and repair
Diverse organoboron acids (3a–3m) were evaluated as catalysts for the redox isomerization of b-ribofuranoside 1a in the presence of Ir(III) photocatalyst 4 and quinuclidine as hydrogen atom transfer (HAT) mediator (Scheme 2).8a The catalyst structure– activity relationships for this transformation were markedly different from those of our previously reported C–H alkylation reaction of carbohydrates;[5] diphenylborinic acid 3a, the optimal co-catalyst for the latter reaction, was inactive, as was heterocyclic diarylborinic acid 3b,15 but the use of phenylboronic acid led to the formation of 2-keto-3-deoxyfuranoside 2a in 8% yield
The results of additional optimization experiments illustrating the effects of changing the solvent, HAT mediator and catalyst loadings, and control experiments demonstrating the importance of each element of the catalyst system, are provided in the Electronic supplementary information (ESI).†
Summary
The transformation of ribonucleotides to 20-deoxyribonucleotides, catalyzed by ribonucleotide reductase enzymes, is a crucial process in DNA biosynthesis and repair. Site-selective redox isomerizations of furanosides using a combined arylboronic acid/photoredox catalyst system†
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