Methods and reagents are provided for synthesizing polynucleotides containing modified deoxyribose residues. Monomeric reagents having the structural formula wherein R1, R2, R3, R4 and R5 are as defined herein, are used to create polynucleotides having nonnucleotidic moieties -A-Z-(R9)n at the 1 position of selected deoxyribose units. The polynucleotides so provided are useful in a variety of hybridization assay formats.