Beta-hairpin peptidomimetics of the general formula (I), cyclo[P1—P2—P3—P4—P5—P6—P7—P8—P9—P10—P11—P12-T1-T2], and pharmaceutically acceptable salts thereof, with P1 to P12, T1 and T2 being elements as defined in the description and the claims, have broad spectrum Gram-negative antimicrobial activity to e.g. inhibit the growth or to kill microorganisms such as Klebsiella pneumoniae and/or Acinetobacter baumannii and/or Escherichia coli. They can be used as medicaments to treat or prevent infections or as disinfectants for foodstuffs, cosmetics, medicaments or other nutrient-containing materials.These peptidomimetics can be manufactured by a process which is based on a mixed solid- and solution phase synthetic strategy.