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 intermediates

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 57′-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′→5′ internucleotide linkages.