Oxidative Cyclization of Morusin

These results suggest that the photo-oxidations may be models for the biogenesis of certein uncommon flavonoids, for example, compound A (31) (32), chaplasin (18) (30), and oxyisocyclointegrin (23) (31), which are supposedly derived in vivo from a 3-prenyl-2 -hydroxy 

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Fig. (7). Reaction mechanism of photo-oxidative cyclization of morusin (3).

Nomura, T., and T. Fukai Studies on the Constituents of the Cultivated Mulberry Tree IV. On the Reaction Mechanism of Photo-oxidative Cyclization of Morusin. Heterocycles 9, 635 (1978). 

Nomura, T., T. Fukai, and M. Katayanagi Oxidative Cyclization of Morusin with Manganese Dioxide. Heterocycles 6, 1847 (1977). 

As described in Chapter III, morusin (3) has been found to be anti-tumor promoter in a two-stage carcinogenesis experiment with teleocidin. Considering the similarity of the structures between morusin (3) and artonin E (7), artonin E (7) was expected to be an anti-tumor promoter. Furthermore we found a novel photo-oxidative cyclization of artonin E (7) as follow photo-reaction of artonin E (7) in CHCI3 containing 4% ethanol solution with high-pressure mercury lamp produced artobiloxanthone (8) and cycloartobiloxanthone (9), and the treatment of artonin E (7) with radical reagent (2,2-diphenyl-1-picrylhydrazyl DPPH) resulted in the same products, Fig. (15), [84]. 

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