Novel nucleoside analogs, such as 3-(.beta.-D-Ribofuranosyl)-2-fluoropyridine, 3-(.beta.-D-Ribofuranosyl)-pyridin-2-one, 3-(.beta.-D-Ribofuranosyl)-pyridin-2-(4-nitrophenylethyl)-one, 3-(.alpha.-D-Ribofuranosyl)-2-fluoropyridine, 5-(.beta.-D-Ribofuranosyl)-2-bromopyridine, 5-(.alpha.-D-Ribofuranosyl)-2-bromopyridine, 5-(.beta.-D-Ribofuranosyl)-pyridin-2-one, 5-(.alpha.-D-Ribofuranosyl)-pyridin-2-one, 5-(.beta.-D-Ribofuranosyl)-2-aminopyridine, 5-(.beta.-D-Ribofuranosyl)-pyridin-2-(4-nitrophenylethyl)-one, and 5-(.alpha.-D-Ribofuranosyl)-2-aminopyridine; process for their synthesis and incorporation into polynucleotides.