Of resorcinolic lipids

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... 

Dihydric phenolic lipids of the cardol type are the most abundant in plant, fungal and bacterial kingdoms. The first species in which the members of the title subclass of phenolic lipids, resorcinolic lipids, were found was Ginkgo biloba (Ginkgoaceae) [6,9,10,17]. Later, the presence of resorcinolic lipids (5-n-alk(en)ylresorcinols) was shown also in other species, first, in the Anacardiaceae [14], which is an important source of various phenolic lipids, not only of alkylresorcinols but also of alkylphenols and alkylcatechols. For example, the cashew and the processing of cashew nuts are the main source of phenolic lipids for the formaldehyde-polymer industry. Aspects of Anacardium occidentale in relation to synthesis, semi-synthesis and chemical industry have been reviewed Tyman [1,11,14] as well as a recent book [2]. 

Another plant family in which the occurrence of resorcinolic lipids was demonstrated is the Gramineae family. The pioneering work of Wenkert has demonstrated the existence of substantial amounts of 5-n-alkylresorcinols in wheat bran [93]. Later, the occurrence of resorcinolic lipid in rye [94] and barley [95] has been shown, compared with other families [96-98] and also shown among lower plants. A number of further studies have been concerned with the determination, localization and characterization of various resorcinolic lipids present in cereal grains [99-103]. Later, the occurrence of resorcinolic lipids has been demonstrated in an increasing number of plant sources. 

Since 1969 the existence of resorcinolic lipids has been demonstrated in microbial organisms [24]. Leprosols, are resorcinolic lipids derivatives which have been identified in Mycobacterium leprae. Later the occurrence of simple 5-alkylresorcinols has been demonstrated in strains of soil bacteria from Azotobacter [104-107] and Pseudomonas families [104-111]. Bacterial resorcinolic lipids have been thought to be related exclusively to the transformation of vegetative cells into their dormant forms, cysts [106]. However, our previous studies on other Azotobacter and Pseudomonas strains [107], as well as recent, unpublished data indicate the occurrence of resorcinolic lipids also in vegetative cells, non-... 

The amount of resorcinolic lipids in plant and microbial sources varies considerably depending on the source. The most prominent source of resorcinolic lipids (cardol and methylcardol), as well as of other phenolic lipids, is the oil obtained from extraction of the shell of cashew nuts, Anacardium occidentale, (up to 20% of resorcinolic lipids). The oily extract from the roasting of cashew nuts (Cashew Nut Shell Liquid) is one of the most important sources of these compounds for formaldehyde polymerisation in industry [1,2,11,114], Other plant sources contain amounts of resorcinolic lipids that vary from 0.01% to 0.1% with rye grains as the richest [101,115-120] while bacterial sources, depending on the family and strain contain up to 6% of various resorcinolic lipid derivatives [105]. 

The structures of over 120 identified natural resorcinolic lipid homologues are presented in Table 4 and Fig. (4) which lists the formulae of resorcinolic lipids and relevant references to previous and current studies. 

It is worth noting that in many cases some of the resorcinolic lipids present in biological material still remain structurally uncharacterised. For instance, chromatographic analysis of acetone extracts from cereal grains shows the presence of at least 4 other components that probably belong to the group of resorcinolic lipids. Two of them have been identified as 5-(2-oxoalkyl) resorcinol and 5-(2-oxoalkenyl) resorcinols [178] and the another as a 5-(2-hydroxyalkyl) resorcinol [181]. 

These results and those now discussed which show the ability of resorcinolic lipids to incorporate and modulate phospholipid bilayer properties, suggest a possible similar role in biological membrane-related enzymatic activities. It has been demonstrated that at a concentration of 10 5 M, long-chain resorcinolic lipids, caused a decrease of apparent acetylocholinesterase activity in the erythrocyte membrane while simultaneously stimulating the activity of Ca2+-dependent ATPase [348]. The inhibition of erythrocyte acetylcholinesterase has been also observed for other phenolic lipids (Stasiuk and Kozubek - unpublished work) and a similar effect of one of the homologues, namely tridecylresorcinol shown towards Na+-K+ ATPase [157]. a-Glucosidase and aldolase were also inhibited by resorcinolic lipids isolated from cashew [283]. 

Similar inhibitory activity was observed for cobra venom phospholipase A2 and the mixture of bacterial alkylresorcinols in lecithin black lipid membrane and phospholipid emulsion systems. Almost complete inhibition (95%) of the enzyme studied was observed at a concentration of about 8 mM of resorcinolic lipids [351]. 

Interaction of resorcinolic lipids with phospholipids, bilayer and biological membranes... 

It should be stressed that due to very high values of buffer-membrane partition coefficients and low CMC values, the effect of resorcinolic lipids injected into the external medium is different from the effect observed when they were present internally in the membrane. For instance, the same homologues that are highly hemolytic when injected into erythrocyte suspension are not lytic when injected in the form of phosphatidylcholine-resorcinolic lipid liposomes, which indicates that direct exchange of resorcinolic lipids between membranes is limited. 

It should be mentioned that in many cases direct comparisons of reported biological effects are very difficult. Due to amphiphilic properties, a significant part of the effect of resorcinolic lipids is related to their interaction with membranous structures and the hydrophobic domains of proteins and therefore, the molar ratios rather than absolute concentrations should be used as a actual measure. The importance of this fact is clearly observed, e.g., in the studies of hemolytic concentration dependence on the number of erythrocytes used in the tests and in the time dependence of this process [387]. 

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