Abstract The 6-(levulinyloxymethyl)-3-methoxy-2-nitrobenzoyl (LMM o NBz) and 2- (levulinyloxymethyl)-5-methoxy-4-nitrobenzoyl (LMM p NBz) groups were developed as novel base-labile protection for the 5′-hydroxy function in solid-phase oligonucleotide synthesis. A comparative study of the LMM o NBz, LMM p NBz and 2-(levulinyloxymethyl)-5- nitrobenzoyl (LMNBz) protecting groups for oligonucleotide synthesis proved strong ...