A novel methodology to access alkynyl nucleoside analogs was elaborated. Highly fluorescent 5-alkynylfuropyrimidines were synthesized (97-46%) and their antiviral properties investigated in vitro . Regiochemistry of the functionalization was achieved with the aid of 5- endo - dig electrophilic halocyclization of acetyl 5- p -tolyl- or 5- p -pentylphenyl-2'-deoxyuridine. Structure of one of the resulting nucleosides, 6- p -tolyl-5-iodo-2'-deoxyribofuranosyl-furo[2,3- d ]pyrimidin-2-one, was confirmed by X-ray crystallography, and its conformation was compared to related nucleosides. Diverse alkynyl substituents were introduced at the heterobicyclic base C-5 position via Sonogashira coupling of 5-iodo-2'-deoxyribofuranosyl-furo[2,3- d ]pyrimidin-2-ones. The resulting compounds had fluorescence emissions of 452 to 481 nm. High quantum yields of 0.53-0.60 were observed for 9-ethynyl-9-fluorenol and propargyl alcohol/methyl ether-modified furopyrimidines. These modified nucleosides, designed in the form of ribose acetyl esters, represent potential tools for fluorescent tagging, studying nucleoside metabolism, 2′-deoxyribonucleoside kinase activity, and antiviral activity. Antiviral assays against a broad spectrum of DNA and RNA viruses showed that in human embryonic lung (HEL) cell cultures some of the compounds showed antiviral activity (EC 50 1.3-13.2 μM) against varicella-zoster virus (VZV). The alkynyl furopyrimidine with two p -pentylphenyl substituents emerged as the best compound with reasonable and selective anti-VZV activity, confirming p -pentylphenyl potency as a pharmacophore.