Synthetic and Biological Studies of Juglorubin and Related Naphthoquinones

Juglorubin, juglorescein, and juglocombins A/B are naturally occurring naphthoquinone dimers isolated from Streptomyces sp. These dimers are proposed to be biogenetically derived from juglomycin C, a monomeric naphthoquinone isolated from the same Streptomyces sp. In this study, the dimerization of a juglomycin C derivative, a key step in the total syntheses of these natural products, was investigated. Juglorubin was synthesized from the minor product of the dimerization via the formation of the juglocombin A/B stereoisomers. A mechanism for the dimerization reaction as well as a plausible biosynthetic pathway to obtain juglorubin from juglomycin C is proposed. Furthermore, the antibacterial and cytotoxic activities of five synthetic compounds were evaluated. Among the compounds tested in this study, 1′-O-methyljuglocombin B dimethyl ester and juglomycin C exhibited antibacterial activity against Bacillus subtilis. 1′-O-Methyljuglocombin B dimethyl ester and juglomycin C showed cytotoxicity against human ...