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A new 2',3'-cis diol protecting group required for the solid-phase synthesis of capped oligonucleotide derivatives.

New 2',3'-cis-diol protecting groups of methylated G-capping reagents required for the solid-phase synthesis of capped oligonucleotide derivatives were designed so as to have a phenylborate skeleton with an alkylaminomethyl substituent and a DMTr group. The former can stabilize the boronic ester function. The latter led to significant enhancement of the solubility of the capping building units and the spectrometric assay of the DMTr cation generated upon acid treatment of capped products on solid supports enabled us to estimate easily the coupling yield of the 5'-capping reaction. The utility of these protecting groups are discussed.