Abstract: Disclosed herein are peptides of the formulaY--R.sup.1 --R.sup.2 --R.sup.3 --R.sup.4 --R.sup.5 --R.sup.6 --R.sup.7 --R.sup.8 --R.sup.9 --Zwherein R.sup.1 to R.sup.9 are designated amino acid residues; Y is hydrogen or lower alkanoyl, or Y is the hexapeptide radical W-lle-R.sup.10 -Ser-R.sup.11 -Val-R.sup.12 wherein W is hydrogen or lower alkanoyl and R.sup.10, R.sup.11 and R.sup.12 are designated amino acid residues, or Y is a fragment of the hexapeptide radical wherein from one to five of the amino acid residues (i.e. Ile to Val) may be deleted serially from the amino terminus of the hexapeptide radical; and Z is hydroxy, amino, lower alkylamino or di(lower alkyl)amino. The peptides inhibit bacterial ribonucleotide reductase and are indicated for preventing or ameliorating bacterial infections.

Abstract: Disclosed herein are peptides of the formulaY--R.sup.1 --R.sup.2 --R.sup.3 --R.sup.4 --R.sup.5 --R.sup.6 --Zwherein R.sup.1 to R.sup.5 are designated amino acid residues; R.sup.6 is Phe, homoPhe or an amino acid residue derived from 2-amino-3-cyclohexylpropionic acid, 2-amino-3-(4-(lower alkoxy)phenyl) propionic acid or 2-amino-3-(4-halophenyl)propionic acid; Y is Phe, desamino-Phe, (lower alkanoyl)-Phe, p-haloPhe, Tyr, desamino-Tyr or (lower alkanoyl)-Tyr, or Y is the decapeptide radical W--Val--R.sup.7 --Ser--R.sup.8 --R.sup.9 --Thr--Glu--R.sup.10 --Ser--Phe wherein W is hydrogen or lower alkanoyl and R.sup.7 to R.sup.10 are designated amino acids residues, or Y is a fragment of the decapeptide radical wherein from one to nine of the amino acid residues (i.e. Val to Ser) may be deleted serially from the amino terminus of the decapeptide radical; and Z is hydroxy, amino, lower alkylamino or di(lower alkyl)amino.