Abstract: The invention relates to hitherto unknown derivatives of 6-aminopenicillanic acids of the formula ##SPC1##In which R.sub.1 and R.sub.2 are similar or different aliphatic, cycloaliphatic, aromatic or heterocyclic substituents linked directly or through alkyl groups to the nitrogen atom, or R.sub.1 and R.sub.2 together with the nitrogen atom form a heterocyclic ring, and R.sub.3 is a hydroxyl or substituted hydroxyl group; to pharmaceutically acceptable salts, and to methods for producing these new compounds having a strong antibacterial effect, especially on gram-negative bacteria, to pharmaceutical preparations in dosage unit forms containing the compounds of the invention solely, or in synergistic mixtures with penicillins, and to methods of treating patients with the dosage units.