Resorcinolic Lipids, the Natural Non-isoprenoid Phenolic Amphiphiles and Their Biological Activity.

Although phenolic compounds are present in both the plant and animal worlds, most of them are of plant origin.1 This heterogeneous group of natural compounds is still, in many textbooks, described as “secondary metabolites”, which suggests their less important role in cellular physiology and biochemistry. It includes both simple phenols and polyphenols as well as their derivatives. In general, the term “phenol” can be defined chemically as a substance that possesses an aromatic ring bearing a hydroxyl substituent and functional derivatives. The natural plant phenols arise biogenetically from two main pathways: the shikimate pathway, which directly provides phenylpropanoids such as the hydroxycinnamic acids and coumarins, and the polyketide (acetate) pathway, which can produce simple phenols and also lead to quinones. The flavonoids, by far the largest group of phenolics, are derived by combination of these two pathways. Among plant single-ring phenolics the group of various compounds that has recently shown growth is the derivatives described as phenolic lipids or long-chain phenols.2 They are amphiphilic in nature due to the non-isoprenoid side chains attached to the hydroxybenzene ring and are believed to be also derived from the polyketide (acetate) pathway, as, for example, 6-pentadecylsalicylic acid. Non-isoprenoid phenolic lipids are relatively uncommon and can be considered for simplicity as fatty acids, with the carboxyl group replaced by the hydroxybenzene ring. Therefore, they are derivatives of monoand dihydroxyphenols, namely, catechol, resorcinol, and hydroquinone. The biogenetic pathway of these compounds, described in textbooks and recent reviews,2-5 is based on incomplete experimental data supplemented with chemical considerations. The biosynthetic aspects of resorcinolic lipids Volume 99, Number 1 January 1999