Photo-Oxidative Cyclization of Morusin

Two isomers of morusin monomethyl ether, 2 -0-methylmorusin (24 e) and 4 -0-methylmorusin (24 f), are formed on methylation of 24 with ethereal diazomethane in isopropyl alcohol and could be distinguished from each other by the Gibbs test. When a solution of 24 e was irradiated, starting material was recovered unchanged, but irradiation of 24f, gave morusinhydroperoxide monomethyl ether (49a). The structure of 49 was established as follows. The UV spectrum (X- ax 280 and 335 nm) resembled that of compound A (31) rather than that 

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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). 

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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