Total Syntheses and Antibacterial Evaluations of Neocyclomorusin and Related Flavones.

Neocyclomorusin ( 1 ), a natural bioactive pyranoflavone mainly isolated from plants of the Moraceae family, was synthesized for the first time using a Friedel-Crafts reaction, a Baker-Venkataraman (BK-VK) rearrangement, a selective epoxidation, and a novel S N 2-type cyclization as the key steps. The present protocol was also successfully applied for the total synthesis of oxyisocyclointegrin ( 2 ). Structurally related natural products morusin ( 23 ) and cudraflavone B ( 24 ) were also prepared. We investigated the antibacterial activities of these natural compounds against both Gram-negative and Gram-positive strains. The prenylated flavones, morusin ( 23 ) and cudraflavone B ( 24 ), showed comparable activity to ampicillin and kanacycin A against Staphylococcus aureus . Both morusin ( 23 ) and cudraflavone B ( 24 ) showed better antibacterial activities than ampicillin against the Gram-positive bacteria Staphylococcus epidermidis and Bacillus subtilis . Both neocyclomorusin ( 1 ) and oxyisocyclointegrin ( 2 ) displayed disappointing antimicrobial activities against Escherichia coli , Staphylococcus aureus , Staphylococcus epidermidis , and Bacillus subtilis strains.