New 3'-, 5'-, 5-bromo-2'-deoxyuridine (3 a-g) and 3'-, 5'-thymidine (4 a-i) analogues with amino acid and peptide residues were synthesized and evaluated for antiviral activity. The influence of long peptide chains, essential amino acids and the effect of this structural modification on the antiviral activity has been also reported. Three 5-bromo-2'-deoxyuridine derivatives containing glycyl-, glycyl-glycyl-and glycyl-gly-cyl-glycyl-residues (3a, 3b, 3c) showed a strong activity against the

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... es virus PsRV and a moderate one vs. HSV-1. The corresponding thymidine analogues were considerably less effective, and only compounds 4d and 4h showed a borderline effect against PsRV