The present invention describes a process for the production of an N-α-amino-hydroxyphenylacetyl or an N-α-aminophenylacetyl β-
lactam antibiotic comprising an IPNS-catalysed conversion of a precursor
tripeptide hydroxyphenylglycyl-cysteinyl-
valine (HpgCV) or phenylglycyl-cysteinyl-
valine (PgCV), respectively, to the N-hydroxyphenylglycyl or the N-phenylglycyl β-
lactam antibiotic, respectively. The
tripeptide HpgCV or the
tripeptide PgCV may further be prepared by contacting the amino acids hydroxyphenylglycine (Hpg) or phenylglycine (Pg), cystein (C) and
valine (V) with a non-ribosomal
peptide synthetase (NRPS) to effect formation of the tripeptide HpgCV or the tripeptide PgCV, the NRPS comprising a first module M1 specific for Hpg or Pg, a second module M2 specific for C and a third module M3 specific for V An IPNS is further provided having an improved activity in this conversion, as well as an NRPS catalysing the formation of the tripeptides. Also a host
cell is provided capable of fermentatively producing β-
lactam antibiotics with N-α-amino-hydroxyphenylacetyl or an N-α-aminophenylacetyl side chains.