Moracenins

Hypertension is an important risk factor for coronary heart disease and stroke. Since ancient times, hypertensive patients have been treated orally with plant extracts based on folk medicine. However, and despite their in vitro vasodilator effects, little information about the protective effects of flavonoids on hypertension is available in the literature. Flavonoids have been considered as active principles of several antihypertensive plant extracts (e.g. rhamnoglycoside of limocitrin isolated from Citrus limonum, kaempferol 4 -0-glucose and hyperin from Euphorbia maddeni, moracenins from Morus alba, procyanidin glycoside from Rhamnus lycioides) [150,151]. In all cases, only the acute antihypertensive effects after i.v. administration in anaesthetised normotensive and/or hypertensive animals have been described. In addition to the direct vasodilator effects discussed above, the inhibition of angiotensin-converting enzyme reported... 

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. 

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. 

As has been mentioned previously. Hiking and co-workers also isolated four hypotensive compounds from Moms root bark, named then moracenins A-D and proposed structures 26 (76), 25 (75), 121 ... 

More or less simultaneously. Hiking s group revised their original structures 25, 26 and 121 for their moracenins B, A, and C, to 25, 26 and 121, after analysis of the H-NMR spectra of the reduction products of moracenin B octadeuteromethyl ether (25 e) 104). They attributed their erroneous conclusions drawn from NMR evidence on the locations of the benzoyl and phenyl moieties in the methylcyclohex-ene rings of moracenins B, A, and C, to inappropriate irradiation power in the C- H decoupling experiments. 

OsHiMA, Y., C. Konno, H. Hikino, and K. Matsushita Structure of Moracenin B, a Hypotensive Principle of Moms Root Barks. Tetrahedron Letters 21, 3381 (1980). 

---