Structures of Flavonoids Carrying Isoprenoid Substituents

The root bark of the cultivated mulberry tree -hexane 

Cyclomorusin (30) (52), C25H22O6, mp 246-248 °C, was negative in the Gibbs test and gave a characteristic MS fragment ion at m/z 363 (52). The structure was confirmed by oxidation of 24 with manganese dioxide to 30.  

Compound A (31) (52), C25H24O7, mp 258-260 C, afforded a diacetate (31a, negative to FeCla), a triacetate (31b), and a monomethyl ether (31c, positive to FeCls). Treatment of 31 with thionyl chloride in pyridine gave an anhydro product (32), whose H-NMR spectrum 

Kuwanon C (33) (40), C25H26O6, mp 148-150 °C, showed the NMR spectrum shown in Fig. 6. Its structure was confirmed by its oxidation with DDQ which afforded morusin (24) and compound (32). 

Oxydihydromorusin (morusinol, 34) (38, 40), C25H26O7, mp 215-216 C, was isolated from Morns root bark by our group and by Kon-NO et al. Its structure was confirmed by hydration of 24 with methanol-hydrochloric acid. The correlations of the five flavones with isoprenoid substituents (24, 30, 31, 33, and 34) are shown in Fig. 7. 

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