Synthesis of oltgonucleotides with sequences identical with or analogous to the 3′-end of 16S ribosomal RNA of Es cherichia coli: preparation of m62A-C-C-U-C-C and A-C-C-U-C-m42C via phosphotriester intermediates1

The synthesis of two fully-protected hexanucleotides (11a and 11b) via a phosphotriester approach, which is based on the use of two types of protecting groups for the internucleotide linkages, i.e. one 2,2,2-tribromo-ethyl at the 5'-terminus and four 2-chlorophenyl groups for the remaining linkages, is reported. The hexanucleotides 11a and 11b, assembled via a block-wise two-step phosphotriester method, can be deblocked conveniently to give the two hexamers 12a and 12b containing only 3'leads to5' internucleotide linkages.