Of mulberrofuran

The C-NMR spectrum is presented in Table 4. When the spectrum of mulberrofuran F (131) is compared with that of chalcomoracin (103), the chemical shifts of the carbon atoms of the 2-arylbenzofuran skeleton, except those of C-3 and C-4, are seen to be similar to those of the corresponding carbon atoms of 103. Moreover, a characteristic singlet signal at 5103.3 suggested the presence of a ketal carbon. The... 

The H-NMR spectra of mulberrofuran I (138) and its pentaacetate (138 a) indicated the presence of a 4 -substituted-6,5 -dihydroxy-3 -oxy-genated-2-arylbenzofuran, 2,4-dihydroxyphenyl, and 4-hydroxy-2-oxy-genated phenyl moieties, thus leading to partial structure (138 ). Analogy with other Diels-Alder type adducts between 4 -dehydroprenyl-2-arylbenzofuran and chalcone such as mulberrofuran C (130), led to... 

Mulberrofuran M (142) 120), an amorphous powder, [a]o -1-15°, had molecular formula C34H22O10, and gave a tetraacetate (142a). The UV spectrum had maxima at 208 (51000), 225 (inflection, 26000), 261 (20000), 299 (inflection, 18000), 323 (shoulder, 28000), 335 (34000) and 350 nm (shoulder, 28000), and was similar to those of other 4 -sub-stituted 6,3, 5 -trioxygenated 2-arylbenzofuran derivatives. The C-NMR spectrum of 142 is listed in Table 5. Hydrolysis of mulberrofuran M with 10% H2SO4 in methanol gave P-resorcylic acid methyl ester and a compound (142 ) were obtained. Considering the spectral data of 142,142 a, and 142, formula 142 was proposed for mulberrofuran M. 

Table 5. C-NMR Data of Mulberrofuran I (13S) and the Related Compounds (Mulberro-furans M, P, Q, Kuwanols A, and B)...

Kuwanon I (152) 132), [a]o —454°, seems to be a Diels-Alder type adduct of dehydromorachalcone A and morachalcone A (120) its stereoisomer kuwanon J (147) 129) was also isolated from the same Morns root bark. Kuwanons K (153) 133), L (154) 133), N (155) 134), O (156) 134), and W (157) 135) seem to be Diels-Alder type adducts of dehydroprenylflavonoids and chalcone derivatives. Kuwanons P (158) 114), Y (144) 123), and X (145) 114), are regarded as Diels-Alder type adducts of a chalcone derivative and dehydroprenylstilbene derivatives, while kuwanon Z (159) 123) seems to be derived from Diels-Alder type adducts, such as kuwanons X (145) or Y (144) through a hemiketal intermediate, as described in the case of mulberrofuran Q... 

Since both 130 and 135 exhibit a positive Cotton effect, as mentioned above, the absolute configuration of mulberrofuran C (130) may be represented by formula (c) in Fig. 57, while that of mulberrofuran J (135) is shown as formula (b) in Fig. 58, based on the exciton chiraUty theory. Finally, the absolute configuration of the three chiral centers in mulberrofuran C (130) may be written as 3"S, 4"R, 5"S which includes the conformation of the cyclohexene ring, discussed earUer in this section, and that of mulberrofuran J (135) as 3" R, 4" R, 5 S (Fig. 59). 

Optical rotations of Diels-Alder type adducts from Morns root bark are summarized in Table 8. The cis-trans adducts exhibit positive optical rotations, while the z [ trans adducts exhibit negative values. Compared with the absolute configuration of 130 and 135, only the configuration at C-3" is different. Consequently, one may conclude that the configuration at the C-3" chiral center influences the sign of the rotation. Hence, the absolute configurations of the cis-trans adducts would be the same as that of mulberrofuran C (130), and those of the d3 -trans... 

Structures of mulberrofurans F (131), G (27), and K (179) have been established by correlation with chalcomoracin (103) and with mul-berrofuran C (130) using a ketalization reaction 91, 112). Therefore, the configuration of the three chiral centers in the methylcyclohexene ring of the ketal compounds is the same as those of 103 and 130. 

Fukai, T., Y. Hano, K. Hirakura, T. Nomura, J. Uzawa, and K. Fukushima Structures of Mulberrofurans F and G, Two Natural Hypotensive Diels-Alder Type Adducts from the Cultivated Mulberry Tree Morns Ikon (Ser.) Koidz.). Heterocycles 22, 473 (1984). 

Structure of Mulberrofuran P, a Novel 2-Arylbenzofuran Derivative from the Cultivated Mulberry Tree (Morns alba l.). Heterocycles 24, 1381 (1986). 

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