Urushiols, structure

Uridine, biosynthesis of, 1124 Uronic acid, 994 from aldoses, 994 Urushiols, structure of, 600 UV, see Ultraviolet... 

Poison oak Rhus toxicodendron or Toxicodendron toxicaria Anacardiaceae) is nearly always found as a low-growing shrub, and has lobed leaflets similar to those of oak. It is also common throughout North America. There appears considerable confusion over nomenclature, and Rhus radicans may also be termed poison oak, and R. toxicodendron oakleaf poison ivy. Poison oak contains similar urushiol structures in its sap as poison ivy, though heptadecylcatechols (i.e. C17 side-chains) predominate over pentadecylcatechols (C15 side-chains). 

Originally from China, Rhus vernicefera has been under cultivation in Japan since the sixth century AD. The latex is collected in the same way as the rubber plant Hevea brasiliensis. The product is known as urushiol, which consists mostly of dihydric phenols of structures (Fig. 6) and is used as lacquers. 

As is true in the case of other phenolic lipids, urushiol is also a mixture of components varying mostly in the degree of unsaturation. Thus, the urushiol from Rhus vernicefera has structures shown in Fig. 6 [139]. Rhus toxicodendron is also known to give urushiol, but its... 

Although urushiol possesses an interesting structure for transformation into speciality polymers, no attempt has been reported. Notwithstanding its applications in a specified area, it appears that it is not properly put to use as it can be converted to polymers with better properties. The possibilities for such conversions into high-performance polymers are illustrated by cardanol, a phenolic lipid of related structure obtained from Ana-cardium occidentale. 

Pyrolysis also has been utilized for the determination of the structure of unique natural polymers in certain lacquers such as those produced by Rhus vernicifera and Rhus succedanea [2] and utilized as surface coating for wood, porcelain, etc. in Japan. The pyrolysis products of the two lacquer films at 400° C contain respectively laccol and urushiol, and each also contains alkenes, alkanes, alkenylphenols, and alkylphenols. From these results it was possible to assign the following structure for laccol polymer ... 

A similar structure (with 15 carbons on the aliphatic chain) was obtained for urushiol polymer. 

Figure I. Chemical structures of various phenolic lipids (A) sorgoleone, (B) heptadecenyl resorcinol (C) urushiol and (D) anacardic acid.

ABSTRACT This review is concerned with non-isoprenoid phenolic lipids typified by compounds biosynthesised by the polyketide pathway. Botanical, biological and entomological sources of such phenolic lipids are described which contain monohydric phenols, notably cardanol and relatives, dihydric phenols such as cardols, alk(en)ylresorcinols,urushiols and phenolic acids, particularly anacardic acids. Some recently investigated mixed types of dihydric phenolic lipids are included. Separatory methods are briefly reviewed. Synthetic methods for the saturated and unsaturated members of the three main classes of interest in structure/activity studies are summarised. Biological properties of members of the three main classes are given and discussed. 

The structures and formulas of known dihydric phenolic lipids of the urushiol type are presented in Fig. (3). 

Going back lo step 3, yon can now work backward to the structure of urushiol II. 

Considering these findings we here propose a cell structure for the durable Japanese lacquer film the lacquer film is composed of cells or grains of 0.1 ym size packed densely in the film. The cells have plant gum wall with polymerized urushiol inside, and are firmly... 

In this cell structure model, the plant gum provides a protective barrier towards diffusion of oxygen into the polymerized urushiol inside, resulting in and explaining the high durability of Japanese lacquer films. Since the plant gum is hygroscopic, absorption of humidity would break down the barrier characteristics, and thereby causes degradation of the polymerized urushiol in the lacquer film, but a combination with hydrohobic polymerized urushiol results in a cell structure wall of low humidity absorption. 

In order to elucidate the formation of aggregated cell structure made from plant gum and urushiol in Japanese lacquer films proposed above, it is most important to know the interaction between urushiol and plant gum in the sap being treated or in the lacquer in the film formation process. 

The first phase separation concept is well accepted in polymer chemistry formation of the cell structure arises from the larger difference in polarity or cohesive energy between the plant gum and urushiol. 

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