2-Arylbenzofuran derivatives

Kinoshita, T. et al.. The isolation of new pyrano-2-arylbenzofuran derivatives from the root of Glycyrrhiza glabra, Chem. Pharm. Bull, 44, 1218, 1996. 

Basnet, P. et al.. Two new 2-arylbenzofuran derivatives from hypoglycemic activity-bearing fractions of Morus insignis. Chemical Pharmaceutical Bulletin, 41, 1238, 1993. 

Five Novel 2-Arylbenzofuran Derivatives, Chalcomoracin, Mulberrofurans... 

Prohibitins isolated so far include eleven flavonoid derivatives, such as albanins A-E (64-68) (71-73), F (25) (74) [ = kuwanon G (55)=mor-acenin B (75)], G (26) (74) [(=kuwanon H (5 )=moracenin A (76)], H (69) (7, morusin (24) (72), kuwanons C (33) (72), and E (42) (73), and three 2-arylbenzofuran derivatives such as albafurans A-C (70-72) (78, 79) (Fig. 16). These prohibitins are obtained from the epidermis and not from the xylem tissue of the shoot, which suggests that the epidermis of the mulberry shoot plays an important role not only as a physical defense structure but also as a chemical defense against pathogens. Details concerned with the Diels-Alder type adducts albanins F (25), G (26), and H (69), will be presented later in this article. 

About thirty phytoalexins have so far been isolated from the mulberry tree. A few differences are observed in the structures of phytoalexins isolated from different parts of the mulberry tree. From the fungus-infected xylem tissue of the shoot, two stilbene phytoalexins were isolated and characterized as oxyresveratrol (73) and 4 -prenyloxyresvera-trol (74) (80). From the acetone extracts of cortex and phloem tissues of the shoot infected with Fusarium solani f. sp. mori, the following phytoalexins have been isolated, twenty-six 2-arylbenzofuran derivatives, moracins A-Z (75-100) (71, 81-83), as well as dimoracin (101) (84), a Diels-Alder type adduct composed of two 2-arylbenzofuran derivatives with isoprenoid substituents. Biogenetically these phytoalexins seem to be derived from moracin M (87) by hydroxylation, methyla-tion, and isoprenylation (Fig. 17). Structures were determined on the... 

From an acetone extract of infected mulberry leaves a new phytoalexin, chalcomoracin (103) (57), was isolated. Compound 103 can be viewed biogenetically as a Diels-Alder type adduct between a chalcone and a dehydroprenyl-2-arylbenzofuran derivative. The isolation of 103 was the first report on a series of optically active Diels-Alder type adducts obtained from the mulberry tree (72). Details of its structure determination will be presented later. 

As described in Chapter IV, a series of 2-arylbenzofuran derivatives have been isolated from the mulberry tree. Tabcasugi et al. isolated a phytoalexin from diseased mulberry leaves and designated it as chal-comoracin (103) 87). In the course of our studies, three novel 2-aryl-benzofuran derivatives, mulberrofurans C (130), F (131), and G (27), were isolated as hypotensive components. Single intravenous injection of 130, 131, or 27 caused a marked depressor effect in rabbits 111, 112). 

Table 4. C-NMR Data of 2-Arylbenzofuran Derivatives (Diels-Alder type adducts chalco-moracin CM, mulberrofurans C, E, F, G, J, and H MC, ME, ME, MG, MJ, and MH)...

Mulberrofuran I (138), [ajo +212°, had molecular formula of C34H24O8 and furnished a pentaacetate (138 a). The UV spectrum of 138 was similar to those of 2-arylbenzofuran derivatives and had maxima at 250 (inflection, 12600), 290 (shoulder, 12600), 330 (shoulder, 20000), and 338 nm (24500). In acid solution the compound showed a red color which faded when neutralized, and exhibited the following bathochromic shifts in the UV spectrum 296 (shoulder, 48900),... 

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. 

A new 2-arylbenzofuran derivative, mulberrofuran R (161) (137), can regarded as a variation of Diels-Alder type adducts such as mulber-rofurans C (130) and J (135). To a new glucosylcoumarin, mulberrosi-de B (162) (138), formula 162 was attributed. 

Fukai, T., Y. Hano, K. Hirakura, T. Nomura, and J. Uzawa Constituents of the Cultivated Mulberry Tree XXVII. Structures of a Novel 2-Arylbenzofuran Derivative and Two Flavone Derivatives from the Cultivated Mulberry Tree Morns Ihou Koidz.). Chem. Pharm. Bull. (Japan) 33, 4288 (1985). 

Nomura, T., T. Fukai, T. Shimada, and I.-S. Chen Constituents of the Cultivated Mulberry Tree XIII. Components of Root Bark of Moms australis. 1. Structure of a New 2-Arylbenzofuran Derivative, Mulberrofuran D. Planta medica 49, 90 (1983). 

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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