- A reliable Pd-mediated hydrogenolytic deprotection of BOM group of uridine ureido nitrogen
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The benzyloxymethyl (BOM) group has been utilized widely in syntheses of a variety of natural and non-natural products. The BOM group is also one of few choices to protect uridine ureido nitrogen. However, hydrogenolytic cleavage of the BOM group of uridine derivatives has been unreliably performed via heterogeneous conditions using Pd catalysts. One of the undesirable by-products formed by Pd-mediated hydrogenation conditions is the over-reduced product in which the C5-C6 double bond of the uracil moiety was saturated. To date, we have generated a wide range of uridine-containing antibacterial agents, where the BOM group has been utilized in their syntheses. In screening of deprotection conditions of the BOM group of uridine ureido nitrogen under Pd-mediated hydrogenation conditions, we realized that the addition of water to the iPrOH-based hydrogenation conditions can suppress the formation of over-reduced uridine derivatives and the addition of HCO2H (0.5%) dramatically improve the reaction rate. An optimized hydrogenation condition described here can be applicable to the BOM-deprotections of a wide range of uridine derivatives.
- Aleiwi, Bilal A.,Kurosu, Michio
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experimental part
p. 3758 - 3762
(2012/09/25)
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- 176. Nucleosides part LXI: A simple procedure for the monomethylation of protected and unprotected ribonucleosides in the 2′-O- and 3′-O-position using diazomethane and the catalyst stannous chloride
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Intensive studies on the diazomethane methylation of the common ribonucleosides uridine, cytidine, adenosine, and guanosine and its derivatives were performed to obtain preferentially the 2′-O-methyl isomers. Methylation of 5′-O-(monomethoxytrityl)-N 2-[2-(4-nitrophenyl)ethoxycarbonyl]-O 6-[2-(4-nitrophenyl)ethyl]-guanosine (1) with diazomethane resulted in an almost quantitative yield of the 2′-nd 3′-O-methyl isomers which could be separated by simple silica-gel flash chromatography (Scheme 1). Adenosine, cytidine, and uridine were methylated with diazomethane with and without protection of the 5′-O-position by a mono- or dimethoxytrityl group and the aglycone moiety of adenosine and cytidine by the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group (Schemes 2-4). Attempts to increase the formation of the 2′-O-methyl isomer as much as possible were based upon various solvents, temperatures, catalysts, and concentration of the catalysts during the methylation reaction.
- Cramer, Hagen,Pfleiderer, Wolfgang
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p. 2114 - 2136
(2007/10/03)
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