title: Spiroketals of Pestalotiopsis fici provide evidence for a biosynthetic hypothesis involving diversified Diels-Alder reaction cascades.
abstract: Chloropestolides B-G (1-6), six new metabolites featuring the chlorinated spiro[benzo[d][1,3]dioxine-2,7'-bicyclo[2.2.2]octane]-4,8'-dione (1-3) and spiro[benzo[d][1,3]dioxine-2,1'-naphthalene]-2',4-dione (4-6) skeletons, and their putative biosynthetic precursor dechloromaldoxin (7) were isolated from the scale-up fermentation cultures of the plant endophytic fungus Pestalotiopsis fici . The structures of 1-7 were determined mainly by NMR experiments. The absolute configurations of 1-3 were deduced by analogy to the previously isolated metabolites from the same fungus (9 and 13-18), whereas those of 4, 5, and 7 were assigned by electronic circular dichroism (ECD) calculations. Structurally, the spiroketal skeletons found in 1-3 and 4-6 could be derived from 2,6-dihydroxy-4-methylbenzoic acid with chlorinated bicyclo[2.2.2]oct-2-en-5-one and 4a,5,8,8a-tetrahydronaphthalen-2(1H)-one, respectively. Biogenetically, compounds 1-6 were derived from the same Diels-Alder precursors as the previously isolated 9 and 12-18. In addition, compounds 2 and 3 were proposed as the biosynthetic intermediates of 17 and 16, respectively. Compound 1 was cytotoxic to three human tumor cell lines.
authors.affiliation: State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.forename: Ya
authors.initials: Y
authors.lastname: Cao
authors.forename: Liangdong
authors.initials: L
authors.lastname: Guo
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.forename: Yongsheng
authors.initials: Y
authors.lastname: Che
mesh_terms: D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D013141:Spiro Compounds / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D013237:Stereoisomerism; D013098:Xylariales / Q000737:chemistry*
chemical_list: D013141:Spiro Compounds