Dihydroxy phenolic lipids

Dihydric phenolic lipids are the most abundant phenolic lipids. They are of the cardol-or urushio 1-type, i.e. with hydroxyl groups in the metha position (1,3-dihydroxy) or in the ortho (1,2-dihydroxy) position respectively. Urushiol-type, dihydroxy phenolic lipids, are practically restricted to the Anacardiaceae family (Rhus genus) of poisonous plants. The most well-known are poison ivy, poison oak and the Indian marking nut. The sap from various plants belonging to Anacardiaceae from which Japanese, Chinese, Burmese, Formosan and Vietnamese lacs is one of the richest source of these phenols. The occurrence of dihydric phenolic lipid of the urushiol type is depicted in Table 3. 

Fig. (3). Structures of known dihydric phenolic lipids Of urushiol (1,2-dihydroxy) type...

It is a lipophilic compound which removes intercellular lipids that are covalently linked to the cornified envelope surrounding epithelial cells [3]. It also enhances penetration of other agents. Resorcinol (m-dihydroxy benzene) is structurally and chemically similar to phenol. It disrupts the weak hydrogen bonds of keratin [4]. Lactic acid is an alpha hydroxy acid which causes corneocyte detachment and subsequent desquamation of the stratum corneum [5]. 

Higher plant resorcinolic lipids include very simple homologues of the orcino 1-type (l,3-dihydroxy-5-methylbenzene) phenols and a variety of homologues that are derivatives with the ring, chain or both ring and chain modified. Resorcinolic lipid molecules have a dual, aromatic and acyclic character. In most cases the side chain in resorcinolic lipids is odd numbered, which is relevant with regard to their possible biosynthetic pathway. 

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