This invention relates to a novel class of 4,5,6,7-substituted non-nucleoside, non-phosphorylatable pyrrolo[2,3-d]pyrimidines which exhibit both significantly lower levels of cytotoxicity and superior antiviral activity than known nucleoside, non-nucleoside, and non-nucleoside, non-phosphorylatable pyrrolo[2,3-d]pyrimidine derivatives, particularly against human DNA viruses such as cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1). These compounds are represented by the following formula: wherein: R4 is —NR1R2 or oxo; R5 is —CN, or —CSNR1R2, or —CONR1R2; R6 is —H, or halo, or —NR1R2; wherein R1 and R2 are independently —H or an aliphatic group; and R7 is of the formula R3—Ar, wherein R3 is an aliphatic group and Ar is an unsubstituted aryl or an aryl independently substituted with halo, nitro, amino, or aliphatic groups; provided that when R5 is a —CN or —CSNH2, and R6 is a —H or —NH2, and Ar is a —C6H5 or a phenyl substituted with only one aliphatic group, R3 is an aliphatic group other than methyl such that —R3— is not a —CH2—; and pharmaceutically acceptable salts, prodrugs and derivatives thereof.