Npeoc -protecting group

An interesting synthesis of a nucleoside carbonic ester was conducted in excellent yield by reaction with 1 -methyl-3 - [2-(p-nitropheny l)ethoxycarbony 1]-imidazolium chloride (for an analogous introduction of the npeoc-protecting group, see also Section 3.10.1) [2393 as mentioned in Section 3.1.8, methylation of the imidazole unit increases significantly the reaction rate. 

DBU, CH3CN, 140 s. The 2-(4-nitrophenyl)ethyl (Npe) phosphate protective group and the 2-(4-nitrophenyl)ethoxycarbonyl (Npeoc) group are stable to these conditions, but the cyanoethyl group is not. 

This method is used, for example, for the mild introduction of protecting groups like benzyloxycarbonyl (Z), tert-butoxycarbonyl (Boc) and p-nitrophenylethoxycarbonyl (npeoc). 

Some examples for the introduction of amino protecting groups such as 2-(4-nitro-phenyl)ethoxycarbonyl (npeoc) or benzyloxycarbonyl (Z) were already given in the compilation of carbamates produced with imidazolium caiboxylates in Section 4.6.1. 

This group was developed as a 5-protective group in nucleoside synthesis that is compatible with the 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarb onyl (npeoc) groups. It is introduced using the chloroformate (3-83% yield) and is rapidly cleaved with 0.1 M DBU in CH3CN with half-lives of 7-14 s. ... 

Another family of base protecting groups that has found some favor for DNA-RNA synthesis comprises the 2-(4-nitrophenyl), 5 (Npe), 2-(4-nitro-phenyl)ethoxy carbonyl, 6 (Npeoc), groups [22,23] (Fig. 2). They are stable to both weak acids and bases yet can be readily removed with a nonnucleo-philic base such as l,8-diazabicyclo[5.4.0.]undec-7-ene (DBU). Use of these... 

The Npeoc group was introduced for protection of the exocyclic amino functions of nucleic acid bases, but has also been used for simple amines. 

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