Nanaomycins, structure

Nanaomycin A 103 and deoxyfrenolicin 108 are members of a group of naphthoquinone antibiotics based on the isochroman skeleton. The therapeutic potential of these natural products has attracted considerable attention, and different approaches towards their synthesis have been reported [65,66]. The key step in the total synthesis of racemic nanaomycin A 103 is the chemo-and regioselective benzannulation reaction of carbene complex 101 and allylacety-lene 100 to give allyl-substituted naphthoquinone 102 after oxidative workup in 52% yield [65] (Scheme 47). The allyl functionality is crucial for a subsequent intramolecular alkoxycarbonylation to build up the isochroman structure. However, modest yields and the long sequence required to introduce the... 

Isochroman-5,8-diones (300) were prepared by oxidation of 5,8-dimethoxy-isochromans with AgO and nitric acid (82SC279). This system is present as a structural moiety in some natural quinones, such as eleutherin (51HCA561), kalafungin (68MI1), nanaomycins (75MI2, 75MI3 76CC320), and other compounds. 

Quinone is a key structural motif found in a wide variety of biologically active compounds, including those from natural sources (Figure 8.1). Nanaomycin A is a naphthoquinone derivative fused with a pyran ring, which possesses a potent inhibitory activity against fungi. 

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