|其他摘要||This dissertation mainly focused on the chemical investigation on five plants from Asclepiadaceae and Araliaceae families: Cynanchum otophyllum, Dregea volubilis, Dischidia esquirolii, Schefflera venulosa, and Heteropanax fragrans. Through various chromatographic methods, 69 natural products were isolated, including 33 new ones. Their structures were determined on the basis of detailed spectroscopic analyses and chemical methods. The AChE inhibitory, anti-fungal and anti-virus activities of some compounds were studied. Moreover, the plant resources of C. otophyllum were evaluated by HPLC analysis.
Chapter 1 The chemical constituents of three plants of Asclepiadaceae and their bioactivities
C-21 steroidal glycosides occurred commonly in the plants of Asclepiadaceae family. These kind of natural steroids possess a pregnane skeleton and some activities on nervous system, such as antiepilepsy and antidepression. Their structures and functions are so similar to those of neurosteroids that they are presumed to be a kind of neurosteroids-like compounds from plants.
The total glycosides from Cynanchum otophyllum (Chinese name: Qingyangshen) have been used for the clinical treatment of epilepsy for more than twenty years in China, and the quality of this phytomedicine was not so stable these years because of the confusion of the original plant materials. Phytochemical studies on the roots of C. otophyllum collected in the northwest of Yunnan province led to the isolation of 15 C-21 steroidal glycosides, including 12 new compounds. The glycosides had qingyangshengenin or caudatin as aglycones and various compositions of sugars, consisting of 3-7 sugar units. The sugar units contained cymarose, oleandrose, digitoxose, thevetose, and glucose. A pair of optically isomeric sugars, D- and L-cymarose was obtained. The aglycones, qingyangshengenin and caudatin were isolated from the acidic hydrolysate of the total glycosides as well. Both the glycosides and aglycones were submitted to the AChE inhibitory assay in vitro, and no obvious activity was observed. Accounting for the problem of plant resources, a HPLC analysis method was established for the quality control of the medicinal materials of Qingyangshen. It is found that one botanical sample known as Qingyangshen by local people contained neither qingyangshengenin nor caudatin.
Dregea volubilis was reported to contain plenty of C-21 steroidal glycosides. By the utilization of open column chromatography and preparative or semi-preparative HPLC, 20 C-21 steroidal glycosides, including 15 new ones were isolated from the stems of D. volubilis collected in Mojiang, Yunnan province. It is interesting that the C-21 steroidal glycosides from D. volubilis possessed a relative stable sugar chain, mostly consisted of two cymarose and one 6-deoxy-3-O-methyl allose. However, the aglycones exhibited a molecular diversity, which may result from the different living environments. The aglycones of these C-21 steroidal glycosides can be devided into four types according to the reduction of the side chain at C-17 and the hydroxyl substitution at C-8. The hydroxyl groups at C-11, C-12 and C-20 can form the ester groups in different ways of combination. Furthermore, there are various ester groups in these compounds, and a novel one named 3-methylvaleryl was discovered. Meanwhile, 3 new lignan glycosides and 2 known triterpene were obtained; these kinds of compounds were isolated from the plants of Dregea genus for the first time. Most of the C-21 steroidal glycosides were valuated for the in vitro AChE inhibitory activity and no positive results were observed.
Eleven compounds were isolated from Dischidia esquirolii, including two new ones. The structure of a known compound was revised by detailed NMR studies. The phytochemical studies revealed that the fresh aerial parts of D. esquirolii mainly contained pentacyclic triterpenes of high oxidization degree and flavonoids. It is interesting that a quinovic acid glycoside which commonly occurred in Rubiaceae family and C-glycoside flavonoids of macro-quantity which are really rare in Asclepiadaceae family were found in this plant. Some of the compounds were submitted to the anti-fungal and anti-virus bioassay and no potent ingredients were found.
Chapter 2 The chemical constituents of two plants of Araliaceae
Opportunistic fungal infections, mainly resulting from Candida, Cryptococcus, and Aspergillus, are life threatening in immuno-deficient patients with cancer, AIDS, diabetes, or organ transplant, etc. The current antifungal drugs have different side-effects in clinical treatment. It is of great importance to find new antifungal agents from natural products with high efficiency and little toxicity.
Some medical plants of Araliaceae family were used to treat fungal infections according to the ancient medicine records. Different extracts of some plants were prepared and submitted to initial anti-fungal bioassay. The results revealed that the water-soluble part of Schefflera venulosa and the fruits of Heteropanax fragrans have potential antifungal activities.
Systematic phytochemical studies on S. venulosa and H. fragrans led to the isolation of 1 novel and 17 known compounds including triterpenoids, flavonoids, lignans, polyphenols, diterpenoids, and etc. The further antifungal activity screening work of the isolated compounds will be carried out in American National Center for Natural Products Research, School of Pharmacy, University of Mississippi.
Chapter 3 Review: C-21 steroidal glycosides in Cynanchum (Asclepiadaceae)
The aglycone of C-21 steroidal glycosides can be divided into two kinds: the normal four-ring pregnane skeleton and the abnormal pregnane skeleton arising from a high oxidization degree. Both of them were contained in the plants of Cynanchum genus. A summary concerned the distribution and modern pharmacological studies of these two types was given here to provide evidences for the chemotaxonomy investigation and the utilization of medicinal plants of Cynanchum.|