Urushiol methylation

Phenols occur widely throughout nature and also serve as intermediates in the industrial synthesis of products as diverse as adhesives and antiseptics. Phenol itself is a general disinfectant found in coal tar methyl salicylate is a flavoring agent found in oil of wintergreen and the urushiols are the allergenic constituents of poison oak and poison ivy. Note that the word phenol is the name both of the specific compound hydroxybenzene and of a class of compounds. 

In earlier syntheses of the methyl ethers of (15 1)-cardanol (ref. 136) and urushiol (ref. 137) it is doubtful if the products were stereochemically pure. Nonetheless this work represents the first progress towards obtaining unsaturated methyl ethers of the phenolic lipids. Early difficulties centred on the lack of specificity in the reduction of the triple bond, in the removal of the protective group on the phenolic OH without affecting the double bond and, before kinetic and thermodynamic control was used, on lack of steric control in the Wittig reaction. 

The cleavage of urushiol by catechol-2,3-dioxygenase has been studied (ref. 324) and the oxidation of anacardic aldehyde to urushiol with manganeses dioxide (ref. 325), an alternative to the Dakin reaction descibed some years ago (ref. 88). Experiments on the methylation of urushiol (refs. 88,89) Indicate that the 3-hydroxyl group reacts preferentially under mild conditions. Hydrogenated urushiol, 1,2-dihydroxy-3-pentadecylbenzene, reacted similarly to form 1-methoxy-2-hydroxy-3-... 

The removal of urushiol, when regarded as an offensive chemical, can be simply effected by the use of hypochlorites (ref. 329). In a rather more subtle way the induction of tolerance to poison ivy urushiol has been established by epicutaneous applications of the analogue 5-methyl-3-n-pentadecylcatechol (1,2-dihydroxy-4-methylpentadecylbenzene) (ref. 330). 

The finally obtained lacquer usally contains 3% water. The content of water in the lacquer or the sap under treatment seems to correlate to the activity of laccase. Furthermore, from a study of a model reaction with 4-tert-butyl-o-quinone and methyl linoleate, it is found that the existence of water and its content may influence the coupling reaction rate of the urushiol quinone (2), and the ratio of the C-C and C-0 coupling of the urushiol quinone(2). ... 

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