Site-selective direct arylation of unprotected adenine nucleosides mediated by palladium and copper: insights into the reaction mechanism |
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Authors: | Thomas E Storr Andrew G Firth Karen Wilson Christoph G Baumann |
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Institution: | a Department of Chemistry, University of York, Heslington, York YO10 5DD, UK b Department of Biology, Area 10, University of York, Heslington, York YO10 5YW, UK c Replizyme Ltd, Genesis 2 Building, York Science Park, Heslington, York Y010 5DQ, UK |
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Abstract: | Reaction conditions facilitating the site-selective direct aryl functionalisation at the C-8 position of adenine nucleosides have been identified. Many different aromatic components may be effectively cross-coupled to provide a diverse array of arylated adenine nucleoside products without the need for ribose or adenine protecting groups. The optimal palladium catalyst loading lies between 0.5 and 5 mol %. Addition of excess mercury to the reaction had a negligible affect on catalysis, suggesting the involvement of a homogeneous catalytic species. A study by transmission electron microscopy (TEM) shows that metal containing nanoparticles, ca. 3 nm with good uniformity, are formed during the latter stages of the reaction. Stabilised PVP palladium colloids (PVP=N-polyvinylpyrrolidone) are catalytically active in the direct arylation process, releasing homogenous palladium into solution. The effect of various substituted 2-pyridine ligand additives has been investigated. A mechanism for the site-selective arylation of adenosine is proposed. |
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Keywords: | Direct arylation Purines C-C Bond formation Palladium Copper(I) salts |
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