Acacia melanoxylon

The natural occurrence of promelacacinidins was until recently restricted to the heartwoods of Prosopis glandulosa and Acacia melanoxylon. The investigations of the heartwood constituents of A. caffra and A. galpinii also revealed the presence of a limited number of promelacacinidins (Table 11.11) as well as mixed di- and trimeric proteracacinidin or promelacacinidins (see Table 11.10). 

Malacacidin Acacia melanoxylon (Fabaceae) CDPK (8), MLCK (>167),... 

Heartwoods of many tropical species are rich in tannins. The basie unit in some of these structure is considered to be derived from flavan-3,4-diols and related compounds, for example melacacidin from Acacia melanoxylon (Hathway, 1962), the structure of which is shown in Figure 2.17. The stereochemistry of the flavan-diols has been the subject of much study by Roux and his collaborators (Fengel and Wegener, 1984). 

Foo, L.Y. Isolation of [4-0-4]linked Biflavanoids form Acacia melanoxylon. First Examples of a New Class of Single Ether Linked Proanthocyanidin Dimers. J. Chem. Soc., Chem. Commun., 1505 (1989). 

The presence of monomeric proanthocyanidins or flavan-3,4-diols in plants has long been known. In hot acid, almost all flavan-3,4-diols are converted to the corresponding an-thocyanidin. The first structure determined for a member of this class of compounds was that of melacacidin (27) from Acacia melanoxylon (Fig. 12.11). Flavan-3,4-diols do not possess an affinity for collagen substrates and, hence, lack tanning properties. Some flavan-3,4-diols are modified to... 

The responsible sensitisers are not yet known. One of the allergenic constituents seems to be anthothecol, found in K, anthotheca up to 0.03% (Morgan and Orsler 1967). In addition, K. anthotheca and K, ivorensis contain the weak sensitiser 2,6-dimethoxy-i,4-benzo-quinone (see Acacia melanoxylon). 

Dimethoxy-i,4-benzoquinone is an allergen in more than 50 different plants and wood species, e.g., mahogany, macore, sipo, wenge, oak, beech, elms, and poplar. With acamelin, it is one of the allergens of Acacia melanoxylon. Sensitization can occur in woodworkers such as carpenters, joiners and sawyers. 

Correia O, Barros MA, Mesquita-Guimaraes J (1992) Airborne contact dermatitis from the woods Acacia melanoxylon and Entandophragma cylindricum. Contact Dermatitis 27 343-344 Lamminpaa A, Estlander T, Jolanki R, Kanerva L (1996) Occupational allergic contact dermatitis caused by decorative plants. Contact Dermatitis... 

Two teracacidol-catechin dimers linked (4)ff->8) and (4)ff- 6) have been synthesized, but these compounds have not been reported as natural products (27, 28). A melacacidol-(4a- 6)-melacacidol dimer isolated from the heartwood of Prosopis glandulosa (mesquite) occurs in low concentration together with the oxidatively coupled flavan-3-ols described previously (174). Foo (103) has recently isolated a melacacinidin-(4a->6)-isomelacacidin dimer from Acacia melanoxylon, the first natural product that has the 2i ,3i ,4i -(2,3-d5-3,4-c/5)-stereochemistry. However, only its 2R,3R,4S (2y3-cis-3,4-t ans) diastereoisomer was obtained by synthesis. 

Foo L Y 1986 A novel pyrogallol A-ring proanthocyanidin dimer from Acacia melanoxylon. J Chem Soc Chem Commun 236-237... 

Foo L Y, Wong H 1986 Diastereoisomeric leucoanthocyanidins from the heartwood of Acacia melanoxylon. Phytochemistry 25 1961-1965... 

King F E, Bottomley W 1954 The chemistry of extractives from heartwoods. Part XVII. The occurrence of a flavan-3,4-diol (melacacidin) in Acacia melanoxylon. J Chem Soc 1399-1403... 

Foo L Y 1987 Configuration and conformation of dihydroflavonols from Acacia melanoxylon. Phytochemistry 26 813-817... 

Schmalle H W, Hausen B M 1980 Acamelin, a new sensitizing furano quinone from Acacia melanoxylon. Tetrahedron Lett 21 149-152... 

Hausen BM, Schmalle H 1981 The sensitizing capacity of naturally occurring quinones. Part VI. Quinonoid constituents as contact sensitisers in Australian blackwood Acacia melanoxylon R. Br.). Brit J Ind Med 38 105-109... 

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