Nonribosomal peptide synthetase-like enzyme; part of the gene cluster that mediates the biosynthesis of the isoquinoline alkaloids fumisoquin A, fumisoquin B and fumisoquin C; as well as small amounts of fumipyrrole as a shunt metabolite (PubMed:25582336, PubMed:27065235). The products of the cluster lead to a brown coloration and are important for growth and conidiation (PubMed:25582336). The nonribosomal peptide synthetase-like protein fsqF, which lacks a canonical condensation domain, is required for addition of a serine-derived dehydroalanine moiety to activated tyrosine but is not essential for the subsequent steps leading to isoquinoline formation (PubMed:27065235). A different enzyme, most likely the ATP-grasp enzyme fsqD, is responsible for activation of tyrosine (Probable). Three additional enzymes encoded by the fsq cluster, the N-methyltransferase fsqC, the phenol 2-monooxygenase fsqG and the FAD-dependent oxidase fsqB, catalyze the formation of the isoquinoline ring system in the fumisoquins (PubMed:27065235, PubMed:30194285). FsqB converts the fspF thiolation domain-bound (2S,4S,5S)-2-amino-6-(3,4-dihydroxyphenyl)-4-hydroxy-5-(methylamino)hexanoyl into isoquinoline (PubMed:27065235, PubMed:30194285). The cyclization most likely proceeds via a two-step mechanism, beginning with FAD-dependent oxidation of the methyl group to an iminium species followed by electrophilic attack on the deprotonated phenol (Probable). Secondary metabolite biosynthesis. Expression is positively regulated by the fumisoquins biosynthesis specific transcription factor fsqA (PubMed:25582336). FsqF lacks the condensation domain that is essential for canonical peptide bond formation, and bioinformatic analysis of the vicinity of fsqF did not reveal any genes that could code for a second NRPS or free-standing condensation domain. Prevents the production of fumipyrrole and leads to reduced growth and sporulation, but does not affect virulence in infected mice (PubMed:25582336). Abolishes completely the production of isoquinolines as well as of pyrroles and leads to the production of a single brightly red shunt metabolite, the anthranilic acid-substituted isoquinoline (PubMed:27065235). Belongs to the NRP synthetase family.