Diels-Alderase; part of the gene cluster that mediates the biosynthesis of the tetramic acid Sch210972, a potential anti-HIV fungal natural product that contains a decalin core (PubMed:26360642). The PKS module of cghG together with the enoylreductase cghC catalyze the formation of the polyketide unit which is then conjugated to 4-hydroxyl-4-methyl glutamate (HMG) by the condensation domain of the cghG NRPS module (PubMed:26360642). One unique structural feature of Sch210972 is the tetramic acid motif proposed to be derived from the non-proteinogenic amino acid HMG, by a Dieckmann-type condensation catalyzed by the reductase domain of cghG (PubMed:26360642). The aldolase cghB catalyzes the aldol condensation of 2 molecules of pyruvic acid to yield the intermediate 4-hydroxyl-4-methyl-2-oxoglutarate (HMOG), which can then be stereoselectively transaminated by an unidentified enzyme to form HMG (PubMed:26360642). The Diels-Alderase cghA then uses the Dieckmann product released by cghG as substrate and catalyzes the Diels-Alder cycloaddition to form the decalin ring of Sch210972 (PubMed:26360642). CghA also suppresses the nonenzymatic formation of the alternative stereoisomer (PubMed:26360642). (2S)-3-[(2S)-3,5-dioxo-4-[(2E,4R,6R,8E,10E,12E)-4,6,12-trimethyltetradeca-2,8,10,12-tetraenoyl]pyrrolidin-2-yl]-2-hydroxy-2-methylpropanoate = sch 210972 Secondary metabolite biosynthesis. Belongs to the Diels-Alderase family.