Antitumor Agents, 75. Synthesis of Cytotoxic Anthraquinones Digiferruginol and Morindaparvin-B

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Abstract
A simple and efficient synthesis of digiferruginol (4) and morindaparvin-B (10) is described. Marschalk reaction of 1-hydroxyanthraquinone afforded 1-hydroxy-2-methylanthraquinone (2). Treatment of 2 with N-bromosuccinimide and benzoyl peroxide led to 1-hydroxy-2-bromomethylanthraquinone (3), which was converted to 4 with AgNO3 in quantitative yield. Methylation of 1,5-dihydroxyanthraquinone yielded a diemthyl ether (6), which was partially demethylated with boron trifluoride to a difluoroboron chelate (7). Treatment of 7 with alkaline HCHO and sodium dithionate gave rise to 1-hydroxy-2-hydroxymethyl-5-methoxyanthraquinone (9). Cleavage of the 5-methyl ether of 9 with born tribromide furnished 10.