The hydrolysis of 6,7-dichloro-3-nitro-2-naphthoic acid ethyl ester (I) with NaOH in ethanol gives the expected free acid (II), which is treated with diphenylphosphoroazidate and triethylamine in DMF to yield 6,7-dichloro-3-nitro-2-naphthylamine (III). The reduction of (III) with H2 over RaNi in ehanol/ethyl acetate affords the corresponding diamine (IV), which is cyclized with thiocarbonyldi-imidazole (V) in refluxing benzene to give 6,7-dichloro-2,3-dihydro-1H-naphtho[2,3-d]imidazole-2-thione (VI). The methylation of (VI) with methyl iodide in dry DMF yields the corresponding methylsulfanyl derivative (VII), which is condensed with 1-O-acetyl-2,3,5-tri-O-ben-zoyl-beta-D-ribofuranose (VIII) by means of trimethylsilyl trifluoro-methanesulfonate (TMSOTf) and N,O-bis(trimethylsilyl)acetamide (BSA) in dichloromethane affording the benzoylated ribofuranoside (IX). The debenzoylation of (IX) with ammonia in methanol gives the free ribofuranoside (X), which is finally treated with Cl2/CCl4 in methanol to eliminate the methylsulfanyl group.