title: Quinolactacins revisited: from lactams to imide and beyond.
abstract: Chemical analysis of a solid phase fermentation of an Australian Penicillium citrinum strain has returned all known examples of a rare class of N-methyl quinolone lactams, quinolactacins A2 (1), B2 (2), C2 (3) and A1 (4), together with the new quinolactacins B1 (5), C1 (6), D1 (7) and D2 (8), and the novel derivatives quinolonimide (9) and quinolonic acid (10). Complete stereostructures were assigned to all these compounds by detailed spectroscopic analysis and chemical interconversion. Carefully controlled and monitored decomposition studies have confirmed that quinolactacins readily undergo C-3 epimerization and oxidation, and under appropriate conditions convert to quinolonimide and quinolonic acid. Mechanisms for key transformations are proposed. The decomposition studies suggested that only quinolactacins A2 (1) and B2 (2) are genuine natural products, with all other isolated compounds being decomposition artefacts. Quinolactacins C1 (6), C2 (3), and the racemic mixture of quinolactacins D1/D2 (8/7) all displayed notable cytotoxic activity.
authors.affiliation: Centre for Molecular Biodiversity, Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Clark
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Capon
authors.forename: Ernest
authors.initials: E
authors.lastname: Lacey
authors.forename: Shaun
authors.initials: S
authors.lastname: Tennant
authors.forename: Jennifer H
authors.initials: JH
authors.lastname: Gill
mesh_terms: D007094:Imides / Q000737:chemistry*; D007769:Lactams / Q000737:chemistry*; D015394:Molecular Structure; D010407:Penicillium / Q000737:chemistry; D011760:Pyrrolidinones / Q000737:chemistry*; D015363:Quinolones / Q000737:chemistry*; D012988:Soil Microbiology; D013237:Stereoisomerism
chemical_list: D007094:Imides; D007769:Lactams; D011760:Pyrrolidinones; D015363:Quinolones; C444201:quinolactacin A2; C521724:quinolactacin B2