Hypotensive Constituents, Kuwanons G and

The root bark of the cultivated mulberry tree was extracted successively with n-hexane, benzene, and methanol. Intravenous injection of the methanol extract, 1 mg-20 mg, showed a dose-dependent decrease in arterial blood pressure in pentobarbital-anesthetized rabbits 94). The extract was fractionated successively by silica gel column chromatography, polyamide column chromatography, silica gel preparative TLC, and HPLC leading to isolation of kuwanons G (25) 33) and H (26) 34) (Fig. 4). Intravenous injections of both compounds (0.1-3.0 mg/Kg) showed an almost equally transient dose-dependent decrease in arterial blood pressure in anesthetized rabbits (95). 

In parallel with our findings in the preceding paragraph. Hiking and co-workers isolated as two hypotensive compounds from Moms root bark which they named moracenins B (25) (75) and A (26) (76), while Masamune and co-workers isolated two prohibitins of mulberry shoot which they named albanins F (25) and G (26) 74). By direct comparison kuwanon G was found to be identical with moracenin B and albanin F, and kuwanon H with moracenin A and albanin G (96). Structure determinations of these compounds were carried out by the three research groups independently. 

Structure elucidation of these two compounds by our group will be discussed first 33, 34, 97). 

In order to confirm this deduction and the proposed regioselectivity of the Diels-Alder type reaction between a chalcone and a dehydropren-ylphenol, two model compounds 115 and 116 were prepared in 46% resp. 25% yield by a Diels-Alder reaction between /ra 5-chalcone and 3-methyl-l-phenyl-l,3-butadiene (250 °C, 5h). Their structures were established by X-ray crystallography and are shown in Fig. 24. The H-NMR spectra of 115 and 116 were compared with those of alcohols 117 and 118 obtained by reduction. Signals of the protons on the relevant carbon atoms of alcohols 117 and 118 were shifted by 1.16 ppm and 1.61 ppm to higher field than the corresponding signals in 115 and 116, as shown in Fig. 25. 

Kuwanon H (26), an amorphous powder, [a]o — 536°, had a molecular formula C45H44O11. The UV spectrum was similar to that of kuwanon C (33). The MS of 26 showed fragments at w/z 420 (111) and 205 (119). Treatment of 26 with dimethyl sulfate gave a hexamethyl ether 26 a and octamethyl ether 26 b. The hexamethyl ether was pyro-lyzed to give 2 -hydroxy-3 -y,Y-dimethylallyl-2,4,4 -trimethoxychalcone (=morachalcone A trimethyl ether, 120 a), a sample of which was synthesized by reaction of 2 -hydroxy-3 -y,Y-dimethylallyl-4 -methoxyace-tophenone with 2,4-dimethoxybenzaldehyde. The C-NMR spectrum is listed in Table 3. From the spectral data, the difference between kuwanons G (25) and H (26) is the presence of a prenyl group at the C-24 position of 26. 

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