Editorial [Hot topic: Natural Products (Guest Editors: Wei-Shuo Fang and Junzeng Zhang)]

Natural products have been used for thousands of years in human history for prevention and treatment of diseases, or for maintaining general wellness. Bioactive natural products are also the important sources of many current therapeutic agents, either in original forms or derivatives made from the natural lead compounds. During the past decades, new tools and strategies such as the combinatorial chemistry, high-throughput screening and computer-aided drug design have been introduced into drug discovery and development process and this certainly helps accelerating the pre-clinical studies in pharmaceutical industry. On the other hand, however, pharmaceutical industry is still in great need of the unique chemical diversity and biological relevancy observed in the natural products, resulting from millions of years' evolution. The chemical diversity of natural products comes from the biodiversity of organisms on earth. As such, the topics for the two themed issues (issues 16 and 17) would reflect this type of diversity and cover natural products from microbes to higher plants and from marine to terrestrial environment. In this issue, six reviews are presented. The first review by Ghosh et al. focuses on antitumor antibiotics such as CC-1065, duocarmycin, and yatakemycin. The mode of actions of these natural products and their chemically synthesized analogs are reviewed, followed by the coverage of progress in bioconjugation and prodrug formation as examples to extend the scope of drug development from natural products. Also related to microbial diversity, Li et al. discussed the potential of exploiting this genetic reservoir based on metagenomics research and its implication in drug discovery from numerous non-culturable microorganisms. Marine natural products are the most exciting source of novel compounds in drug discovery nowadays. Chakraborty et al. highlighted recent research on some of the anticancer natural products from various families of marine organisms. Marinebased low molecular weight and oligomeric chitosan and their biological activities are also reviewed by Yin et al., and their potential application as nutraceutical ingredients for chronic diseases discussed. In the area of reviews covering bioactive natural products from terrestrial plants, Acuna et al. provided a comprehensive coverage of polyisoprenylated benzophenones from Clusiaceae and their various biological activities such as antioxidant, antiinflammation, antimicrobial, and cytotoxic, and the related cellular and molecular mechanisms. Pentacyclic triterpenoids and saponins are common natural products presented in herbs of traditional medicines, their apoptosis-inducing activity and the structure-activity relationships and the potential antitumor application are reviewed and discussed by Wang et al. We would like to thank Dr. Allen B. Reitz, for the invitation to be the Guest Editor of this special issue. We wish to offer our sincere appreciation to all the contributors for their dedication and hard work.