Convergent and rapid assembly of benzonaphthopyranone cores of chartreusin, chrymutasins and hayumicins

Synthesis of the Tetracyclic Spiro-naphthoquinone Chartspiroton

Chartspiroton is a recently discovered naphthoquinone natural product that features a spiro-fused benzofuran lactone. We report its first synthesis via an 11-step linear sequence. The sterically hindered tetra-ortho-substituted biaryl subunit was installed by base-induced ring expansion of a readily available 1,3-indandione. This step also liberated the fully substituted naphthalene core unit at the same time. The unique spiro-fused benzofuran lactone of the natural product was constructed via late-stage oxidation of an advanced naphthoquinone.

Synthesis of C3-epi-virenose and anomerically activated derivatives

A 9-step synthetic route to a protected form of the C3-epimer of virenose from D-fucose is described. C3-epi-virenose is the carbohydrate unit of the bioactive polyketide elsamicin B and part of the carbohydrate unit of elsamicin A. The developed route enabled preparation of anomerically activated forms of this unique C6-deoxy sugar, including derivatives with 1-acetyl, 1-acetylthio, 1-trichloroacetimidate, 1-bromo, and 1-fluoro substituents.

Synthesis of 7-hydroxy-6H-naphtho[2,3-c]coumarin via a TsOH-mediated tandem reaction

A concise and efficient method for the synthesis of 7-hydroxy-6H-naphtho[2,3-c]coumarin using available 1-(2-hydroxyphenyl)-2-phenylethanone and Meldrum's acid has been developed. This transformation involved a tandem aldol reaction/lactonization/Friedel-Crafts reaction to form a lactone ring and a benzene ring. It showed high atom economy with water and acetone as the byproducts. Mechanism studies demonstrated two roles of Meldrum's acid: (i) as the reagent for the tandem reaction, and (ii) as the catalyst for the Friedel-Crafts reaction. Moreover, the hydroxyl group of 7-hydroxy-6H-naphtho[2,3-c]coumarin was further functionalized efficiently by arylethynyl, aryl, and cyano groups to furnish D-π-A compounds with excellent fluorescence emissions (Φ_F = 0.14-0.78).

Annulations with Butenolides and Phthalides: New Entries to Isocoumarins, 3,4-Dihydroisocoumarins, and Benzofurans

The reactions of the anions of butenolides and substituted phthalides with sorbate esters and mono-epoxy sorbate esters furnish isocoumarins, 3,4-dihydroisocoumarins, and benzofurans. The yields range from 41% to 71%.

Bipiperidine conjugates as soluble sugar surrogates in DNA-intercalating antiproliferative polyketides

1,4′-Bipiperidine-1′-carbamate residues were evaluated as sugar surrogates in daunorubicin and chartreusin, yielding water-soluble derivatives and prodrugs with dramatically improved antiproliferative activities.

Naphthopyranones--isolation, bioactivity, biosynthesis and synthesis

The 1H-naphtho[2,3-c]pyran-1-one (naphthopyranone) moiety forms the structural framework of a group of secondary metabolites that have been isolated from a range of organisms including fungi, bacteria, lichen and plants. This review documents the known naturally occurring naphthopyranones - their isolation, biosynthesis and biological activity. A survey of methods reported for the synthesis of naphthopyranone natural products is presented.

Phthalide Anions in Organic Synthesis. A Direct Total Synthesis of Furomollugin

Furomollugin was synthesized in three steps from commercially available starting materials using phthalide annulation chemistry.

Angucyclines: Biosynthesis, mode-of-action, new natural products, and synthesis

Covering: 1997 to 2010. The angucycline group is the largest group of type II PKS-engineered natural products, rich in biological activities and chemical scaffolds. This stimulated synthetic creativity and biosynthetic inquisitiveness. The synthetic studies used five different strategies, involving Diels-Alder reactions, nucleophilic additions, electrophilic additions, transition-metal mediated cross-couplings and intramolecular cyclizations to generate the angucycline frames. Biosynthetic studies were particularly intriguing when unusual framework rearrangements by post-PKS tailoring oxidoreductases occurred, or when unusual glycosylation reactions were involved in decorating the benz[a]anthracene-derived cores. This review follows our previous reviews, which were published in 1992 and 1997, and covers new angucycline group antibiotics published between 1997 and 2010. However, in contrast to the previous reviews, the main focus of this article is on new synthetic approaches and biosynthetic investigations, most of which were published between 1997 and 2010, but go beyond, e.g. for some biosyntheses all the way back to the 1980s, to provide the necessary context of information.