Pleospdione, A Tricyclic Natural Product with Dense Oxygenation at the A-Ring: Total Synthesis and Incongruity of the Originally Assigned Structure and its C3-Epimer

Abstract

Previously we developed a promising synthetic approach to complex polycyclic natural products, including aromatic polyketides derived from the type-II polyketide biosynthesis. The approach consists of three key steps; (1) cycloaddition or cyclocondensation of nitrile oxide for assembling the carbon skeleton having an isoxazole as a 1,3-diketone equivalent, (2) benzoin cyclization for stereoselective ring fusion with an angular hydroxy group, and (3) oxidation of isoxazolium salt for installing an additional angular hydroxy group in stereoselective manner. As a synthetic exercise to highlight the utility of this approach, the first total syntheses of the proposed structure of pleospdione (1) and its C3-epimer (3-epi-1) have been achieved. The synthesis has proved the efficiency of the strategy as an entry into polyketide-derived complex architectures.At the same time, it was revealed that neither 1 nor 3-epi-1 represent the true structure of the natural product by incongruity of the NMR spectra.

Applications of [4+2] Anionic Annulation and Carbonyl-Ene Reaction in the Synthesis of Anthraquinones, Tetrahydroanthraquinones, and Pyranonaphthoquinones

“…The structures of few recently isolated hydroanthraquinones, i.e., 1 – 6 , are displayed in Figure . − A good majority of them display interesting biological activities, such as antibacterial activity, antitumor activity, cytotoxicity, anticancer activity, etc (Figure ). However, very few synthetic strategies have been reported. ,, …”

Total Synthesis and Structure Assignment of Saptomycin H

“…Scheme shows successful implementation of the total synthesis. For the removal of the methyl protection for the phenol in 5 , we used a set of conditions, which worked fine. , Thus, methyl ether 5 was treated with MgI 2 ·OEt 2 (CH 3 CN, 50 °C, 1 h, 81%) to give phenol 24 without touching two acetals. Azide 24 was converted to dimethylamine 26 by employing the Staudinger reaction (PMe 3 , H 2 O, THF, rt, 24 h) followed by reductive N -dimethylation (HCHO aq, AcOH, NaBH 3 CN, CH 3 CN, rt, 2 h).…”

Hydroxylamine-Mediated Anthrapyranone Formation, Solving 5-exo/6-endo Issue toward Synthesis of Pluramycin-Class Antibiotics

“…Scheme shows the synthesis of 2 . To remove the methyl ether, tetracycle 25 was treated with MgI 2 ·OEt 2 (CH 3 CN, 50 °C), and acetylation of the resulting phenol gave acetate 29 . Acid hydrolysis of two acetals in 29 gave the corresponding quinone diol 30 , in which the secondary alcohol was selectively mesylated, giving mono -mesylate 31 .…”