Beta-hairpin peptidomimetics of the general formula (I), and pharmaceutically acceptable salts thereof, with P, X, Q., and optionally L being elements as defined in the description and the claims, have 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 and/or Pseudomonas aeruginosa and/or Enterobacter cloacae. 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.