Phenolic lipids

Rhodamine 6G long-chain hydrocarbons [169] squalene, a-amyrin [170] methyl esters of fatty acids [171] glycerides [91] sterols [172, 173] isoprenoids, quinones [HI] lipoproteins [174] glycosphingolipids [175] phenolic lipids [176] phosphonolipids [177] increasing the sensitivity after exposure to iodine vapor [178,179]... 

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. 

This is one of the most widely distributed plants cultivated formally to obtain the well-known edible nut popularly known as a cashew nut. The phenolic lipid is only... 

Kaprelyants, A., Suleimenov, M., Sorokina, A., Deborin, G., El-Registan, G., Stoyanovich, F., Lille, Yu., Ostrovsky, D. Structural-functional changes in bacterial and model membranes induced by phenolic lipids. Biological membranes, Vol.4, No.3, (March 1987), pp. 254-261, ISSN 0748-8653... 

Complex phenolics Coumarins, phenolic quinones, lignins, flavonoids, stilbenes, hydrolyzable tannins, condensed (or catechin) tannins, phenolic lipids... 

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... 

J.H.P. Tyman, Non-isoprenoid Phenolic Lipids, in Studies in Natural Products Chemistry, Ed. Atta-ur-Rahman, Elsevier, Amsterdam, Vol.9, p.313. 

Type III synthases, as a whole, employ a wider spectrum of physiological starter molecules than their type I and II counterparts, including a variety of aromatic and aliphatic CoA esters such as coumaiyl-CoA, methyl-anthraniloyl-CoA, as well as the recently identified medium- and long-chain fiitty acyl-CoA ester starters used by certain bacterial and plant type III enzymes involved in the biosyndiesis of phenolic lipids (22, 24, Cook et al., unpublished results). The most extensively studied type III en mie, chalcone synthase (Fig. 4), uses 4-coumaryl-CoA as the starter unit and catalyzes three successive condensation reactions with malonyi-CoA as the extender. Cyclization and aromatization of the linear tetraketide intermediate is performed within the same active site, yielding the final product 4 ,2 ,4 ,6 -tetrahydroxychalcone. 

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

The combination of a root hair specific EST approach and expression analysis was an effective strategy for isolating candidate polyketide synthases potentially involved in sorgoleone biosynthesis. As a result of these efforts, two novel type III polyketide synthases have been identified that preferentially use long chain acyl Co-A s and are potentially involved in sorgoleone biosynthesis. These candidate polyketide synthases can form pentadecatriene resorcinol, an intermediate in sorgoleone biosynthesis. Furthermore, these efforts may aid in the identification of other polyketide synthases responsible for the biosynthesis of phenolic lipids in other plant species. 

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]. 

Besides urushiol, similar natural phenolic lipids, laccol from Taiwan and Vietnam and thitsiol from Thailand and Myanmar, are produced in Southeast Asian countries. They are inexpensive and often used for primer coating. The laccase-catalyzed crosslinking of urushiol, laccol, and thitsiol was examined in the presence of a protein hydrolysate [95]. Laccase (PCL and ML) efficiently catalyzed the crosslinking of urushiol and laccol to produce the film with high gloss surface and hardness. 

This chapter focuses on the use of different methods for isolation of alkylresorcinols. Alkylresorcinols are members of a lipid group called non-isoprenoid phenolic lipids. Different aspects of the extraction by classical methods and supercritical CO2 are discussed. Supercritical CO2 extraction of alkylresorcinols from rye bran is discussed for the first time. As compared to the classical extraction methods, supercritical CO2 gives higher yields and it allows the separation of the crude extrac into long- and short-chain alkylresorcinol homologues. 

AR are amphiphilic phenolic lipid derivatives of 1,3-dihydroxybenzene with an odd-numbered alkyl chain at position S of the benzene ring (I) (figure 1). For example, rye AR are characterized by unbranched alkyl chains with an odd number of carbon atoms (17-2S) attached to position 5 of the phenolic ring (2). AR are composed of mixtures of resorcinol derivatives. Resorcinol derivatives with saturated aliphatic chains represent about 85% of the AR while other resorcinol analogues, including AR with mono- and di-unsaturated aliphatic chains and with keto groups, represent 15% (3). 

For resorcinolic lipids, particularly those with long saturated side-chains, the use of polar solvents is important due to their amphiphilicity. The crude extracts in many cases are subjected to preliminary fractionation/purification either by solvent fractionation/partition or by application of chromatography. For prepurification of the material and its separation from polymerized phenolics, gel filtration on hydrophobic Sephadex or TSK gel is sometimes used. Silica gel is most frequently employed for the separation and/or purification of resorcinolic lipids, notably in some studies with Ononis species (12-14). The array of compounds reported appears partly attributable to methylation or acetylation reactions occurring during column chromatographic separation. An interesting approach for I the pre-purification and selective separation of resorcinolic lipid from phenolic lipids or resorcinolic lipids from impurities has recently been reported. A selective partitioning of different non-isoprenoid phenolic lipids... 

Supercritical CO2 extraction of AR or other phenolic lipids have been only sparcely reported (49,50). The solubility of a compound in a solvent depends on its physico-chemical properties. The ARs present in a crude extract, especially those with consecutive number of carbon atoms in the acyl chain (e.g. Cis and Ci7 homologues in rye alkyiresorcinols) have very similar physico-chemical properties. Therefore, when supercritical CO2 is used, the separation of individual homologues from crude extracts still remains a challenge. Illustrative studies on the extraction of phenolic lipids by supercritical CO2 are given in the following sections. 

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