Methyl anacardate

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... 

The structures of anacardic acid, cardol, cardanol, and 2-methyl cardol are given in Fig. 9. Each component... 

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]. 

A series of heterocyclic derivatives of (15 0)-anacardic acid have been synthesised to investigate their activity as inhibitors of human cyclooxygenase-2 enzyme (COX-2) and towards (COX-1). Great selectivity of 5-(methoxy)-2-[(2-hydroxy-6-pentadecylphenyl)-methyl]-thio]-lH-benimidazole towards COX-2, compared with COX-1, was found [292],... 

The use of open-chain precursors for obtaining the benzenoid ring in anacardic and orsellinic acids has proved a fruitful approach. Ethyl 2-methoxy-6-methylbenzoate (synthesised through the Michael addition of ethyl acetoacetate virith but-2-en-al, followed by cyclisation and aromatisation), has been alkylated in an aprotic solvent after formation of the carbanion with lithium di-isopropylamide (refs. 113,114) to give the anacardic after hydrolysis and demethylation (a). In a similar way ethyl 2,4-dimethoxy-6-methylbenzoate (ethyl orsellinate), (formed from ethyl acetoacetate and ethyl crotonate followed by cyclisation aromatisation and methylation (ref. 115)), has been alkylated (ref. 116, 117). In this way the C.,5 orsellinic acid precursor [R = C14H29 in route (b)] of the component phenols in Anacardium occidentale has been synthesised (ref. 118) and the method indirectly affords another route to the cardol series. 

A chemical/chromatographic method has been used to determine the first double bond position in the unsaturated anacardic acid constituents of Pistacia vera (ref. 9). The isolated constituent was methylated, dihydroxylated with performic acid, hydrolysed to remove some formate ester, oxidised with potassium periodate in acidic solution and the aldehydes formed reduced with sodium borohydride to the primary alcohols (refs. 226). The retention time of the aromatic product methyl 2-methoxy-6-(8-hydroxyoctyl)benzoate (C8 side chain) was compared with those of the Cl, C3, C7 and CIO synthetic analogues and from the linear plot of retention time against methylenic carbon chain length, the double bond could be readily assigned to the 8-position. Nevertheless mostly on account of limited sample availability and the time involved in purely synthetic verification. 

Anacardic add after methylation and conversion (ref. 226) to 2-methoxy-6-(8-hydroxyoctyl)benzoic acid has been transformed, as depicted iin the preceding scheme, to a compound at first considered to be a dimer but later concluded to be a twelve-membered lactone related to lasiodiplodin (ref. 292). 

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-... 

Compound C. The mass spectrum again showed the common anacardic acid ions, and a molecular ion of m/z 362, which suggested that Compound C was a C21 saturated anacardic acid. The nmr spectrum also indicated that C was saturated, and the terminal methyl signal at 80.85ppm was complexed and represented 6 protons. Hence C was identified as a C21 branched chain anacardic acid, and by comparison with the nmr spectra of iso and anteiso branched chain fatty acid standards, the terminal methyl signal was identical to the terminal methyl resonance of an anteiso group, thus C is in all probability the C21 anteiso saturated anacardic acid. 

This ambiguity was easily solved by the nmr spectrum, which showed that the terminal methyl signal (50.86ppm) was a simple 3 proton triplet, which hence proved that the double bond was located at the co6 position. In addition coupling constants of 5.2 and 5.0Hz indicated that the the double bond was cis. Hence E is identified as the cis 23(06 unsaturated anacardic acid. 

Compound F. A molecular ion at m/z 376 and the knowledge that the retention time of F was slightly earlier than G, which was already known as the C22 straight chain saturated anacardic acid, strongly suggested that Compound F was a C22 branched chain saturated anacardic acid. The nmr of the terminal methyl signal (50.83ppm) showed it contained 6 protons, and was split into a simple doublet, consistent with an iso type end chain. Hence F is the C22 iso saturated anacardic acid. 

Compound K. The mass spectrum was practically identical to that of compound J, with the same molecular ion at m/z 390, but with a slightly later hpic retention time, and hence it was thought likely that K was a C23 straight chained saturated anacardic acid. Confirmation of this was provided from the nmr spectrum which showed a simple three proton terminal methyl triplet at 50.89ppm, as well as the absence of any signals in the vinyl region. Hence K is the C23 straight chain saturated anacardic acid. 

Compound N. The spectrum showed the compound had a molecular weight of 418, consistent with a C25 saturated anacardic acid. Nmr analysis showed that the splitting of the terminal methyl group (50.83ppm multiplet, 6 protons) was complex and identical to the terminal methyl group splitting in the nmr spectrum of the anteiso standard. Hence N is in all probability the C25 anteiso saturated anacardic acid. 

Before doing this, however, it is useful to briefly consider the biosynthesis of anacardic acids. It is believed that anacardic acids are synthesized from long chain fatty acids via a modification of the methyl salicylate synthetase scheme (11. 12). In effect a fatty acid, such as palmitate (Cie) is elongated by six carbons by the addition of three acetate units in a series of condensation and dehydration steps, followed by ring closure and aromatization to form a C22 saturated anacardic acid (5. 10. U ). Similarly, margaric acid (C17) is synthesized to a C23 saturated anacardic acid. A comparative study on the biosynthesis of anacardic acids in resistant and susceptible plants, using fatty acid precursors will be the subject of a separate publication. 

Anacardic acid Cardol Cardanol 2-Methyl cardol... 

CNSL is obtained as a by-product of the cashew nut industry, mainly containing anacardic acid 80.9%, cardol 10-15%, cardanol, and 2-methyl cardol (Fig. 10). CNSL occurs as a brown viscous fluid in the shell of cashewnut, a plantation product obtained from the cashew tree, Anacardium oxidentale (Bhunia, et al., 2000). CNSL is used in the manufacture of industrially important materials such as cement, primers, specialty coatings, p)aints, varnishes, adhesives, foundry core oils, automotive brake lining industry, laminating and rubber compounding resins, epoxy resins, and in the manufacture of anionic and non-ionic surface active agents. CNSL modified phenolic resins are suitable for many applications and perform improved corrosion and insulation resistance. 

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