title: Structure, absolute configuration, and conformational study of 12-membered macrolides from the fungus Dendrodochium sp. associated with the sea cucumber Holothuria nobilis Selenka.
abstract: Dendrodolides A-M (1-13), 13 new 12-membered macrolides, were isolated from Dendrodochium sp., a fungus associated with the sea cucumber Holothuria nobilis Selenka, which was collected from the South China Sea. The structures of the dendrodolides were elucidated by means of detailed spectroscopic analysis and X-ray single-crystal diffraction. The absolute configurations were assigned using the modified Mosher method, exciton-coupled circular dichroism (ECCD), electronic solution and solid-state circular dichroism (ECD) supported by time-dependent density functional theory (TDDFT) ECD calculations, and X-ray analysis. A detailed conformational analysis of the 13 derivatives indicated that the conformation of the flexible macrolide ring plays a decisive role in their chiroptical properties. Thus, it is highly recommended to apply advanced levels of theory and to avoid simple comparison of ECD spectra to determine the absolute configurations of these derivatives. In an in vitro bioassay, compounds 1-5, 7-9, 11, and 12 exhibited different levels of growth inhibitory activity against SMMC-7721 and HCT116 cells. This is the first report of 12-membered macrolides from the fungus of the genus Dendrodochium . The coisolation of four pairs of epimers is extremely interesting and indicates the complexity of β-ketoreductase stereospecificity in the biosynthesis of enigmatic iterative fungal polyketides.
authors.affiliation: Research Center for Marine Drugs and Department of Pharmacology, School of Pharmacy, Second Military Medical University, 325 Guo-He Road, Shanghai 200433, People's Republic of China.
authors.forename: Peng
authors.initials: P
authors.lastname: Sun
authors.forename: Dong-Xiao
authors.initials: DX
authors.lastname: Xu
authors.forename: Attila
authors.initials: A
authors.lastname: Mándi
authors.forename: Tibor
authors.initials: T
authors.lastname: Kurtán
authors.forename: Tie-Jun
authors.initials: TJ
authors.lastname: Li
authors.forename: Barbara
authors.initials: B
authors.lastname: Schulz
authors.forename: Wen
authors.initials: W
authors.lastname: Zhang
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray; D018942:Macrolides / Q000737:chemistry* / Q000302:isolation & purification; D003904:Mitosporic Fungi / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D012616:Sea Cucumbers / Q000737:chemistry*
chemical_list: D018942:Macrolides