Abstract
This review deals with developments of new types of protecting groups for suger hydroxyl groups in nucleic acid chemistry. The details of introduction of an orthoester type of acid-lablie protecting group, 1, 3-benzodithiol-2-yl (BDT), into primary and secondary alcohols are described. This group is applied to synthesis of DNA and RNA fragments and also used as precusor of the methyl group for the synthesis of 5-carboxymethyl aminomethy 1-2'-O-methyluridine recently discovered from E. Coli tRNA. Two kinds of 4, 4', 4 ''-trisubstituted trityls, tris (benzoyloxy) trityl (TBTr) and tris (levulinyloxy) trityl (TLTr), are described in detail as base-labile and hydrazine-labile protecting groups, respectively, for primary alcohols. The 4, 4', 4'' -tris (4, 5-dichlorophthalimido) trityl (CPTr) group derived from a dye, pararosaniline, is introduced as useful 5'-hydroxyl protecting group which can be easily removed by one step treatment with hydrazine. A successful application of this group to the synthesis of a branched RNA is also shown. Finally, the versatile utility of a new functionalized trityl, 3- (imidazol-1-ylmethyl) -4', 4''-dimethoxytrityl (IDTr), which serves as not only 5'-hydroxyl protecting group but also catalytic site for condensation, is reviewed.
