CHEMISTRY AND BIOLOGY OF PHENOLICS ISOLATED FROM LEAVES AND WOOD OF Laurus nobilis (Lauraceae) AND FROM THE PEELS OF Punica granatum (Punicaceae)

Abstract

Finding healing power in plants is an ancient idea. People in all continents have long applied poultices and imbibed infusions of hundreds if not thousands, of indigenous plants, dating back to prehistory. Currently, a remarkable percent of all pharmaceuticals dispensed all over the world have higher-plant origins. A world wide interest in phytochemicals has grown up and during the last decades there has been an increasing search for these compounds which have been termed "Natural Products" to use them as drugs. Natural products embrace a wide range of chemical classes among which the class of plant phenols represents the most heterogeneous one (Swain et al., 1977). As plant phenols are those compounds that contain an aromatic moiety with one or more hydroxyl functional groups (Harborne 1973). Several classes of natural products including flavonoids (Markham, 1982), lignins (Brunow 2001), coumarins (Thornes and O’ Kennedy, 1997) and quinones (Bruneton, 1999), are therefore considered as phenolics, but the specific chemistry of each has grown up remarkably and led to their final separation into individual classes. Simple monocyclic phenols and phenyl propanoids, including their dimers, lignans (Ayres and Loike, 1990) are existing in considerable numbers in terrestrial plants. Besides minor phenolic constituents as neolignans (Wagner and Wolff, 1977) are of rare occurrence. Occasionally, phenolic units are also encountered in alkaloids (Nawwar et al., 1995) and even among the terpenoids (Ageta et al., 1988). Interest on the part of pharmacologists has focused on their potential applications for treating human diseases. As plant phenols, including polyphenols are among the most potent and therapeutically promising bioactive substances. Since polyphenolic compounds are well known to exhibit antioxidant properties (Bouchet et al., 1998) and can also act as a direct scavenger molecules (Hagimasi et al., 2000), they can prevent lipid peroxidation and biological damage caused by free radicals formed under oxidative stress. The confirmed antibiotic activity of phenolics in the human body was suggested to result from direct interaction of these plant metabolites with microbes, as concluded from established polyphenol toxicity towards microorganisms in a number of biological experiments (Haslam et al., 1989). It is proved that such interaction, i.e. inhibition of pathogenic bacteria and inactivation of their produced toxins; occu