Mulberry, Diels-Alder type adduct

Keywords biosynthesis of mulberry Diels-Alder-type adducts, moraceae... 

The compounds structurally similar to the mulberry Diels-Alder type adduct have also been isolated from the other species of the plants of the family Moraceae. Brosimones A (26) [41], B (27) [14] and D (28) [14] have been isolated from Brosimopsis oblongifolia, a Brazilian moraceous plant (Figure 7). They are expected to be formed through the same way as the mulberry Diels-Alder type adducts. Of these compounds, compound (26) is a unique adduct which may be formed through an intramolecular [4+2] cycloaddition reaction of the isoprenyl portion and the a, -double bond of the chalcone slceleton of compound (28) (Figure 8). Artonins C (29) [42], D (30) [42] and I (31) [43] isolated from Artocarpus heterophyllus, an Indonesian moraceous plant, can also be regarded... 

As described above, the stereochemistries of the mulberry Diels-Alder type adducts could be divided into the following two groups one is an all-trans in relative configuration and the other is a cis-trans configuration. All-trans type adduct may correspond to an exo-addition product in the Diels-Alder reaction of a chalcone and a dehydroprenylphenol, whereas a cis-trans type adduct corresponds to an endo-addition product in the reaction. 

Absolute stereochemistries of the mulberry Diels-Alder type adducts were confirmed by the circular dichroism (CD) spectroscopic evidence and by X-ray analysis [26, 52, 53]. 

Optical rotations ([a]o) of typical mulberry Diels-Alder type adducts are summarized in Table 1. The all-trans type adducts exhibit negative optical rotation, while the cis-trans type adducts exhibit positive values. Considering the absolute stereocheml-... 

As described in section 2, some cell strains of Moras alba callus tissues induced from the seedlings or the leaves have a high productivity of the mulberry Diels-Alder type adducts. The yields of major adducts chalcomoracin (21) and kuwanon J (11) by the cell strains are about 100 - 1000 times more than those of the intact plant [32]. The biosynthesis of the mulberry Diels-Alder type adducts has been studied with the aid of the excellent cell strains. 

Incorporated as a dienophile. These results strongly indicate that dehydrogenation at the isoprenyl portion of (48) followed by a [4 2]cycloaddition reaction with the a, p-double bond of another molecule of isoprenylchalcone leads to the formation of the Diels-Alder type metabolites. Furthermore, the Diels-Alder type metabolites from the precursory chalcones (47), (48), and (53) are all optically active, having the same stereochemistries as those of )cuwanon J (11) and chalcomoracin (21). This fact revealed the [4 + 2]cycloaddition step to be enzymatic. Administration of O-methylated precursory chalcone to the M. alba cell cultures has thus demonstrated that optically active mulberry Diels-Alder type adducts such as 11 and 21 are biosynthesized through an enzymatic intermolecular [4 + 2Jcycloaddition reaction. 

Moms alba L. (cell cultures) Mulberry Diels-Alder type adducts Kuwanon J (405) kuwanon Q (406) kuwanon R (404) kuwanon V (407) mulberrofuran E (426) chalcomoracin (425) mulberrofuran C (424). Antibacterial activity against MRSA and moderate cytotoxicity against five human cancer cell lines. Gunawan and Rizzacasa, 2010[262]. 

Nomura T., Hano Y., Ueda S. Studies on the Optically Active Diels-Alder Type Adducts From Mulherry Tree Int. Congr. Ser. 1998 1157 379 390 Keywords mulberry tree, optically active Diels-Alder type adducts from mulberry tree... 

Mulberry tree is a rich source of intermolecular Diels-Alder type adducts coiq>rising two molecules of isoprenylphenols [26]. This article describes the chemistry of the Diels-Alder type adducts from moraceous plants and the biosynthesis of the adducts in Morus alba cell cultures. 

V. Diels-Alder Type Adducts of the Cultivated Mulberry Tree.115... 

Other Diels-Alder Type Adducts of Cultivated Mulberry Tree. 147... 

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. 

From the root bark of the cultivated mulberry tree and Morns cell cultures, thirty-two Diels-Alder type adducts have so far been isolated and their structures characterized. In this section, the Diels-Alder type adducts, other than those discussed previously are described. 

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). 

Ikuta (nee Matsumoto), J., T. Fukai, T. Nomura, and S. Ueda Constituents of the Cultivated Mulberry Tree XXXV. Constituents of Morns alba l. Cell Cultures. (1). Structures of Four New Natural Diels-Alder Type Adducts, Kuwanons J, Q, R, and V. Chem. Pharm. Bull. (Japan) 34, 2471 (1986). 

Hirakura, K., T. Fukai, Y. Hano, and T. Nomura Constituents of the Cultivated Mulberry Tree 20. Constituents of the Root Bark of Morns Ikon. 2. Kuwanon W, a Natural Diels-Alder Type Adduct from the Root Bark of Morns Ikon. Phytochemistry 24, 159 (1985). 

Hano, Y., H. Kohno, S. Suzuki, and T. Nomura Constituents of the Cultivated Mulberry Tree XXXVII. Constituents of the Chinese Crude Drug Sang-Bai-Pi Morus Root Bark) VIII. Structures of Sanggenons E and P, Two New Diels-Alder Type Adducts from the Chinese Crude Drug Sang-Bai-Pi Morus Root Bark). Heterocycles 24, 2285 (1986). 

Some interesting plant phenolics of stilbene and 2-phenylbenzofuran types have been identified as phytoalexins of the mulberry tree (Moms alba) (19, 107, 112, 113). Of particular interest are the oligomeric compounds chalcomoracin (10) and dimoracin (12), which may be considered to be Diels-Alder adducts of morachal-cone (11) and dehydromoracin (9). However, the adducts are optically active, unlike some other natural products that are proposed to be Diels-Alder adducts. 

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