Nucleosides XI.: Synthesis and antiviral evaluation of 5′-alkylthio-5′-deoxy quinazolinone nucleoside derivatives as S-adenosyl-L-homocysteine analogs

4-Amino-1-(beta-D-ribofuranosyl)quinazolin-2-one (3) was prepared by a direct glycosylation of 4-aminoquinazolin-2-one (7) using the Vorbruggen's silylation method and provided exclusively the beta-anomer. This quinazoline nucleoside and its 2',3'-O-isopropylidene derivative (9) did not undergo the coupling reaction with dialkyl disulfides in the presence of tri-n-butylphosphine unless their 4-amino groups were protected by N,N-dimethyl-aminomethylidene. This approach provides a viable alternative synthetic route to 5'-alkylthio-5'-deoxy nucleosides.