We report here the synthesis of tricyclic nucleoside analogues via acid-catalyzed cyclization of guanine with 1,1,3,3tetramethoxypropane. The method enables the use of hydroxyl-unprotected antiviral drugs (acyclovir, ganciclovir, and penciclovir), guanosines, oligonucleotide, and triazole-linked nucleoside dimers as substrates. Nucleoside trimer and tetramer were synthesized by derivatization reactions.