A series of 33 N-1 side chain-modified analogs of 1-[(2-hydroxyethoxy) methyl]-6- (phenylthio) thymine (1, HEPT) were synthesized and evaluated for their anti-HIV-1 activity. In particular, the influence of substitution of the terminal hydroxy group of the acyclic structure of HEPT and the structural rigidity of this side chain were investigated. Halo (7, 8), azido (9), and amino (10-15) derivatives were synthesized from HEPT via the p-tosylate ...