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|Title: ||An investigation on the bioactive properties of the chemical components and endophytic fungi of Cephalotaxus oliveri Mast.|
|Other Titles: ||Bi zi san jian shan hua xue cheng fen ji nei sheng zhen jun de sheng wu huo xing yan jiu|
|Authors: ||Zeng, Lingbin ( 曾令斌)|
|Department: ||Department of Biology and Chemistry|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Cephalotaxaceae -- Analysis.|
|Notes: ||CityU Call Number: QK494.5.C4 Z46 2011|
xi, 191 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references (leaves 144-176)
|Abstract: ||It is widely accepted that endophytic fungi are a rich source of active compounds.
Many natural products with diverse bioactivities have been obtained from these fungi,
including ones, such as taxol and podophyllotoxin, which were originally thought to be
isolated from plants. These results imply that endophytic fungi are a potentially large
source of untapped bioactive compounds awaiting exploration.
Cephalotaxus oliveri Mast. is a relic, dioecious plant species and endemic to some
subtropical forests in China. Its richness in harringtonine (HT) and homoharringtonine
(HHT), two phytochemical drugs used to treat leukemia and other cancers is well
established. To date, little information is available on the bioactivities of the chemical
components and the endophytic fungi of C. oliveri. Hence, this plant seems to be a
good candidate to explore the bioactivities of its chemical components and endophytic
fungi, to analyze the chemical profile and their antioxidant activities, to isolate and
identify the endophytic fungi, and evaluate their bioactivity potential, and to search for
HT- and/or HHT- producing strains amongst these fungi, and finally to isolate the pure
active compounds from the endophytic strain with the most potent bioactivities.
Antioxidant activities of C. oliveri as indicated by the DPPH (2,2-diphenyl
-1-picryl hydrazyl), ABTS [2,2'-azinobis (3-ethyl- benzothiazoline-6- sulfonic acid)],
superoxide, reducing power coupled with the total phenolic content assays suggest the
plant has potent antioxidant potentials. The methanol extract had the most potent
activities in DPPH, ABTS and reducing power assays with the highest level of
phenolic content among the test extracts. LC-MS/MS and GC-MS analyses resulted in
the detection of 22 compounds in the methanol extract, among which are 15 phenolic compounds. The considerable antioxidant potentials and high phenolic content suggest
C. oliveri is a rich source of natural phenolic antioxidants.
A total of 101 endophytic fungal strains were isolated from C. oliveri using
successive surface-sterilization, fragment plating and hyphal tip methods. Nineteen
representative strains, identified as either Guignardia (anamorph Phyllosticta) or
Colletotrichum species by 18S rRNA gene sequencing, show evident antioxidant,
anticancer and antimicrobial activities. The phenolic compounds produced by the
endophytes contributed to their antioxidant activities as assessed in DPPH test. Among
the endophytic strains, Guignardia sp. L79 was the most antioxidative and cytotoxic.
LC-MS/MS and GC-MS analyses indicate the presence of four phenolic compounds
including protocatechuic acid, gentisic acid, tyrosol and syringol as secondary
metabolites in Guignardia sp. L79. High yields suggest a promising alternative source
of the four phenolic compounds can be produced by controlled fungal fermentation.
Tyrosol and syringol were isolated from the ethyl acetate extract of Guignardia sp.
L79 culture liquid by bioactivity guide fractionation. Syringol displayed more potent
antioxidant activities than the commonly used synthetic antioxidant BHT in DPPH,
ABTS and reducing power assays, whereas tyrosol exhibited only weak activities in
the three assays. Syringol had overt cytotoxic activities to all the three test cancer cell
lines, while tyrosol exerted significant inhibitory action to KB and HeLa cells. This is
the first report on tyrosol from Guignardia (anamorph Phyllosticta) species and
syringol from endophytes as secondary metabolites.
However, no trace of HT and HHT was detected in the culture filtrates of all the
101 endophytic strains from C. oliveri using HPLC-DAD analysis.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086558|
|Appears in Collections:||BCH - Doctor of Philosophy |
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