Inverse phosphotriester DNA synthesis using photochemically-removable dimethoxybenzoin phosphate protecting groups

A method has been developed to prepare short DNA sequences using light to deprotect a nucleoside 3'-phosphotriester, generating a phosphodiester useful for coupling with a free 5'-OH-nucleotide. The dimethoxybenzoin group is used as the photochemically-removable protecting group for the 3'-phosphate. Cyanoethyl is most effective as the second protecting group on the phosphodiester. Because the method is directed at the preparation and use of the DNA sequences while still bound to the support, allyl and allyloxycarbonyl protecting groups are used for the nitrogenous bases since, based on the work of Hayakawa and Noyori, they can be removed without cleaving the DNA from the support. Two simple trinucleotides have been prepared in solution using this method. It has been demonstrated that the photochemical deprotection conditions do not lead to the formation of cyclobutane dimers from adjacent T residues.