Nonribosomal peptide synthetase; part of the gene cluster that mediates the biosynthesis of aspergillic acid, a hydroxamic acid-containing pyrazinone with aliphatic side chains that originates from leucine (Leu) and isoleucine (Ile) (PubMed:29674152). Aspergillic acid has antibiotic properties and was shown to be lethal to mice (PubMed:29674152). The first step in the pathway is the production of deoxyaspergillic acid via a condensation between the Ile amine and the Leu carboxylic acid, followed by a reductive release from the protein forming the dipeptide aldehyde NH(2)-Leu-Ile-CHO, which could undergo an intermolecular cyclization resulting in a dihydropyrazinone (PubMed:29674152). As the NRPS asaC lacks a condensation domain, it is improbable that it is responsible for condensation of Leu and Ile (PubMed:29674152). One possibility is that asaC acts on a previously condensed dipeptide and functions as a Leu-Ile reductase to yield deoxyaspergillic acid (PubMed:29674152). After asaC forms deoxyaspergillic acid, the cytochrome P450 asaD oxidizes the pyrazinone to the hydroxamic acid-containing bioactive metabolite aspergillic acid (PubMed:29674152). The hydroxylase/desaturase asaB can then convert aspergillic acid to hydroxyaspergillic acid (PubMed:29674152). Both aspergillic acid and hydroxyaspergillic acid can form complexes with iron producing ferriaspergillin analogs (PubMed:29674152). Secondary metabolite biosynthesis. Expressed during the earliest stages of maize kernel infection (PubMed:23834374). NRP synthetases are composed of discrete domains (adenylation (A), thiolation (T) or peptidyl carrier protein (PCP) and condensation (C) domains) which when grouped together are referred to as a single module (By similarity). Each module is responsible for the recognition (via the A domain) and incorporation of a single amino acid into the growing peptide product (By similarity). Thus, an NRP synthetase is generally composed of one or more modules and can terminate in a thioesterase domain (TE) that releases the newly synthesized peptide from the enzyme (By similarity). Occasionally, epimerase (E) domains (responsible for L- to D-amino acid conversion) are present within the NRP synthetase (By similarity). AsaC contains an amino acid adenylation domain (A), a peptidyl carrier protein (PCP) domain with a phosphopantetheine prosthetic group, and a short-chain dehydrogenase/reductase terminus (R), but it does not have an identifiable condensation (C) domain required for the formation of peptide bonds during non-ribosomal peptide synthesis (PubMed:29674152). Abolishes the production of ferriaspergillin and aspergillic acid (PubMed:29674152). Belongs to the NRP synthetase family.