Studies On Chemical Constituents And Bioactivities

Lichen Usnea longissima (Usneaceae) is widely distributed throughout the northern temperate zones, especially the subarctic and coastal rainforests of Europe, Asia, and North America. It has been used in traditional Chinese medicine, and Mongolian and Tibetan folk medicine for the ailments treatment, such as phlegm-heat, malaria, asthma, carbuncles, headache, blood in stool, and ascariasis with effects of relieving expectorant and panting, clearing heat and relieving toxicity, and dispelling dampness.Previous phytochemical and biological investigations of U. longissima, which was not systematic and extensive yet, revealed the presence of mono-substituted phenyls, depsides, anthraquinones, dibenzofurans, and terpenoids. One of its primary constituent, usnic acid (UA) belonging to the dibenzofurans, showed significant activities of anti-tumor, anti-inflammatory, and antibacterial. However, the clinical application was limited to some extent due to its low solubility, poor dissolution, especially its side effects on the liver and skin. In order to seek for the UA derivatives and clarify the bioactive ingredients and mechanisms of U. longissima, a combination of proton NMR-guided fractionation and systematic investigation was conducted in addition to its biological evaluation. Concisely, the thesis consists of the following parts.The review section describes a progress on phytochemical investigation and synthetic modification of UA derivatives, along with its bioactivities. The summarized data showed that 54 UA derivatives were isolated from natural resource, and 100 derivatives have been synthesized by various modification approaches. The biological and pharmacological studies revealed that these UA derivatives showed a variety of activities including antitumor, anti-inflammatory, anti-viral, anti-oxidative, and cytotoxicity.The major part of this these is the phytochemical investigation of U. longissima, which were undertaken through various chromatogramphic methods, and the structures were elucidated on the basis of spectral analysis and physiochemical properties. Totally,26 compounds were identified from the EtOAc soluble part of the ethanol extract of U. longissima, including usenamines A-F (1-6), usone (7), and isousone (8). Among them, usenamines B-F, usone, and isousone were new compounds, two ones were isolated as natural products for the first time, and six ones were isolated from Usneaceae family for the first time. Many UA derivatives, such as 2,3, and 6-8 possess unique ethoxy substituents at C-4a in its molecules, so further experiment was performed to demonstrate that 2,3,7, and 8 were not artifacts.The biological part describes an evaluation of these constitutents screened by various activities. The results showed that compounds 1,2, and 8 showed inhibitory effects against the growth of human hepatoma HepG2 cells with their IC50 values of 6.0-53.3μM compared with methotrexate as the positive control, with its IC50 value of 15.8 μM. The susceptibility against a variety of bacteria and fungi, including Escherichia coli, Candida albicans, Bacillus subtilis, Mycobacterium smegmatis, Trichophyton, and Aspergillus, were tested, however, only 7 and 8 displayed weak inhibitory activities against fungi T. rubrum spp., both with minimum inhibitory concentration (MIC) values of 16.0 μg/mL. In addition, three compounds (22,24, and 25) showed significant in vitro anti-inflammatory activities against NO production in RAW264.7 macrophages with IC50 value of 3.93-6.77 μM.Overall, the current study clarified the potential basis, to some extent, of its anti-tumor, anti-fungi, and anti-inflammatory activities. Furthermore, the preliminary mechanism of anti-tumor effect had also been preliminarily explored. The perspective of this folk medicine needs more effort on the discovery of UA derivatives and other bioactive constituents with less side effects. In brief, this study provided modern chemical and pharmacological evidence for the traditional Chinese medicine U. longissima toward its development and utilization.