A Survey of Synthetic Routes towards the Pyranonaphthoquinone Antibiotic Pentalongin and Syntheses of the Corresponding Nitrogen Derivatives

A survey through the synthetic possibilities of pentalongin and its derivatives is presented. Pentalongin is the parent compound in the 3,4-dehydropyranonaphthoquinone series and is the active principle of the medicinal plant Pentas longiflora. Attention is paid to eight approaches towards these 3,4-dehydropyranonaphthoquinones. Synthetic methodologies for the corresponding nitrogen analogues are described, focusing on several natural products.