Plants of the Genus Syzygium (Myrtaceae): A Review on Ethnobotany, Medicinal Properties, and Phytochemistry

Plants have been used as therapeutic agents since the start of civilization. In many developing countries, herbal medicinal systems remain important in the treatment of many ailments. Ayuvedic medicine is still commonly practiced within India with an estimated 85% of Indians still using crude plant preparations for the treatment of wide variety of diseases and ailments [79]. Traditional Chinese medicine (TCM) and African medicinal systems also account for major portion of healthcare in their populations. Even in countries where allopathic/Western medicine is dominant, medicinal plants still make significant contributions. Furthermore, many people are returning to herbal medicine systems due to the perception that natural medicines are often a safer alternative than allopathic drugs. Individuals are also seeking treatments for diseases, which have not yet been remedied by modern medicine. Many of the prescription drugs currently marketed for a wide variety of ailments were originally isolated from plants and/or are semi-synthetic analogues of phytochemicals. It has been estimated that approximately 25% of all prescription drugs currently in use are of plant origin [122, 194]. Furthermore, 75% of new anticancer drugs marketed between 1981 and 2006 were derived from plant compounds [122]. Traditional plant-based medicines are generally used as crude formulations (e.g., infusions, tinctures and extracts, essential oils, powders, poultices, and other herbal preparations). Modern natural product drug discovery generally focuses on isolating and characterizing the individual phytochemical components with the aim of producing an analogue with increased bioactivity/bioavailability. Such studies have given rise to many useful drugs such as quinine (from Cinchona spp.), digoxin (from Digitalis spp.) as well as the anticancer drug paclitaxel (from Taxus brevifolia Nutt.) and vincristine and vinblastine (from Vinca rosea). However, the bioactivities observed for crude extracts are often much enhanced or even entirely different to those seen for the individual components [32, 81]. Crude plant extracts may contain hundreds, or even thousands, of different chemical constituents that interact in complex ways. Often it is not known how an extract works, even when its therapeutic benefit is well established. Thus, phytochemical and mechanistic studies of traditional medicines may be complex, and it is often difficult to assign single compound/bioactivity relationship.