Novel N-substituted derivatives of acyclovir (la) were synthesized and evaluated for their antiviral, antimetabolic, and antitumor cell properties in vitro. Monomethylation of la at positions 1, 7, and N-2 gave compounds 2-4, respectively. When positions 1 and N-2 were linked together by an isopropeno group, the tricyclic 9-[(2-hydroxyethoxy) methyl]-1, N-2- isopropenoguanine (5) was obtained. Compound 5 was then further methylated at ...