Fig. 4

Generalized biosynthetic pathways of pyrrolidine-2-one type natural products catalyzed by a polyketide synthase-nonribosomal synthetase hybrid enzyme. The product can have either a pyrrolin-2one or pyrrolidine-2,4-dione depending on whether the reductase domain-catalyzed cyclorelease reaction proceeds via A aldehyde release followed by Knoevenagel condensation or B direct Dieckmann condensation. KS ketosynthase, AT acyltransferase, DH dehydratase, MT methyltransferase, KR ketoreductase, ACP acyl carrier protein, C condensation, A adenylation, T thiolation, R reduction