Isopropyl malate dehydrogenase; part of the gene cluster that mediates the de novo generation of L-homotyrosine from acetyl-CoA and 4-hydroxyphenyl-pyruvate (PubMed:22998630). L-homotyrosine is a building block of echinocandin B, a fungal lipidated cyclic hexapeptide that acts as an antifungal agent (PubMed:22998630). L-homotyrosine 4-hydroxyphenyl-pyruvate first undergoes an aldol-type condensation by htyA with the C-2 of acetyl-CoA followed by the release of CoA to form 2-(4-hydroxybenzyl)-malate (PubMed:22998630). This is followed by isomerization of 2-(4-hydroxy-benzyl)-malate to 3-(4-hydroxybenzyl)-malate by htyD (PubMed:22998630). Thereafter, 3-(4-hydroxybenzyl)-malate undergoes decarboxylation and oxidation to form 2-oxo-4-(4-hydroxybenzyl)butanoic acid, coupled to reduction of NAD(+) to NADH by htyC (PubMed:22998630). The product then undergoes transamination catalyzed by htyB to form L-homotyrosine (PubMed:22998630). (2R,3S)-3-isopropylmalate + NAD(+) = 4-methyl-2-oxopentanoate + CO2 + NADH Binds 1 Mg(2+) or Mn(2+) ion per subunit. Antifungal biosynthesis. Homodimer. Due to their effectiveness as antifungal agents, echinocandin derivatives can be used for the treatment of human invasive candidiasis (PubMed:22998630). Belongs to the isocitrate and isopropylmalate dehydrogenases family.