Anacardic acid, phenolic lipid

In the phenolic lipids such as the alkylphenols from Anacardium occidentals, semi-synthetic transformations have been described which exploit the functionality of the component phenols, cardanol, cardol and anacardic acid (ref. 104). A number of reactions are shown for... 

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

This is one of the most widely distributed plants cultivated to obtain cashew nut. The phenolic lipid is only a by-product known as cashew nut shell liquid (CNSL). The nut, attached to the base of the cashew nut apple consists of an ivory-colored kernel covered by a thin brown membrane (testa) and enclosed by an outer porous shell, the mesocarp which is about 3 mm thick with a honey-comb structure where the reddish brown liquid (CNSL) is stored [91]. The major components of CNSL are a phenolic acid, anacardic acid, a dihydric phenol, cardol with traces of mono hydric phenol, cardanol, and 2-methyl cardol [92-95]. 

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. 

Subsequently, this approach to the synthesis of C15 phenolic lipids consisted in the route ArCi - ArCis. It has proved generally convenient for the synthesis of the unsaturated anacardic acids. From the methodological view it is also an aspect of the use of acyclic intermediates discussed in the next section since the starting material ethyl 2-methoxy-6-methylbenzoate is prepared from ethyl acetoacetate. 

In the marine environment there has been the first reported occurrence of so-called antifouling (namely, anticrustaceous activity) by (15 0)-anacardic acid. Thus bioassay-directed fractionation of the dichloromethane extract from twigs of Ozoroa insignis containing the phenolic lipid, was used with larvae from Artemia salina as a model to investigate the activity [296]. 

A wide range of botanical and biological families are sources of phenolic lipids. Notable classes of compounds present are certain dihydric phenols (the cardols), phenolic acids (the anacardic acids) and a variety of... 

Since cardanols can be obtained from anacardic acids and cardols from orsellinic acids, the methods outlined have a general applicability to a range of phenolic lipids. Reference has been made largely to the phenols of the Anacardiacae but the methods are likely to be applicable to other phenolic systems, and those with methylene-interrupted structures at different side-chain positions. Alkynes and phosphorans have both proved invaluable in synthetic studies but attention should be drawn to the very elegant use of ailenic compounds in the polyethenoid (arachidonic) series (ref. 168) which has a potential application with phenolic lipids. Methods for the synthesis of leukotrienes are also relevant for the methylene group-interrupted structures of phenolic lipids (169). 

CNSL used in polymerisation with formaldehyde as for example in friction dusts may not require elaborate analysis. Nevertheless interest in the industrial chemical uses of phenolic lipids has led to a study of quantitative methods of analysis by a variety of chromatographic methods. For cashew phenols these were first based on GLC. Thus the (15 3), (15 2), (15 1) and (15 0) constituents of methyl anacardate, cardol and cardanol have been separated by GLC on PEGA columns (ref.206), the free phenols (anacardic acid as methyl anacardate) by GLC on SE30 (ref207) and the hydrogenated anf fully methylated phenols on Dexsil and PEGA columns (ref.208). A further number of stationary phases have been investigated... 

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