Bioisosteric substitution of the thiourea (3, 5, 7, 9) and urea (10) moiety of PETT compounds with sulfamide (1), cyanoguanidine (2, 4) and guanidine (6, 8) functionalities, and replacement of the phenethyl group with benzoylethyl group (compounds 11–20) have been studied. Synthesis and antiviral activities are described.