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|Title: ||Reactions and computational studies of andrographolide analogues with glutathione and biological nucleophiles|
|Other Titles: ||Chuan xin lian nei zhi tong xi wu yu gu guang gan tai deng sheng wu qin he ji de fan ying he ji suan yan jiu|
|Authors: ||Zhang, Zhiqiang (張智強)|
|Department: ||Department of Biology and Chemistry|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2007|
|Publisher: ||City University of Hong Kong|
|Notes: ||xvii, 184 leaves : ill. 30 cm.|
Thesis (Ph.D.)--City University of Hong Kong, 2007.
Includes bibliographical references.
CityU Call Number: QK495.A1655 Z43 2007
|Abstract: ||The aims of this work were to investigate the reactivity of the alpha methylene
lactone moiety of andrographolide and its analogues to nucleophiles of biomolecules,
and to explore the structural activity relationship of these compounds. The efforts were
focused on search for molecular targets that react well with andrographolide.
Andrographolide is a diterpenoid component isolated from Andrographis paniculata
which is a traditional herbal medicine claimed to be effective against an array of diseases.
Here, only the anticancer activity of andrographolide was pursued in this study. It is well
documented that the anticancer activity of andrographolide is due to the alpha methylene
lactone. Alkylation of biological nucleophiles, especially sulphydryl groups, by the α,β-
unsaturated carbonyl structure in a Michael addition, has been regarded as the major
reaction which lead to the cytotoxic effect of the alpha methylene lactone structure of
Reactions between andrographolide and L-cysteine were studied at 37°C in different
pH values by indirectly monitoring the free sulphydryl group of cysteine.
Andrographolide was able to scavenge the thiol group and the reaction rates were
enhanced with the pH value at the range from 6.0 to 7.0. This result indicates that
andrographolide can interact with the thiol group in biomolecules. In order to reveal the
interaction between andrographolide and biomolecules, the bimolecular reaction between
andrographolide and glutathione was investigated under a condition mimicking in vivo
environment. Stoichiometric analysis indicates that the reaction between these two
reactants is 1 to 1 at pH 7.0. The reaction rate followed a second-order kinetic. Using a
micro-liquid-liquid extraction method followed by HPLC separation, two major products were isolated and identified, their chemical structures were determined as 14-deoxy-12-
(glutathione-amino)-andrographolide and 14-deoxy-12-(glutathione -S-yl)-
When computational chemistry was applied to explore the structural reactivity of
andrographolide and its analogues to L-cysteine in both gaseous and aqueous phases, it
was found that the 16-carbonyl, 12,13-olefin bond and 14-hydroxyl on the alpha
methylene lactone of the andrographolide are the key structural moieties which are
responsible for the activity of andrographolide. The trend of the computational reactivity
of these pharmacophores was in good agreement with the cytotoxicity of their parent
compounds reported in experimental literatures. When the reactivity of some natural
compounds, such as several sesquiterpenes and diterpenes, was modeled using similar ab
initio method, it was found that the calculated results were also in good agreement with
the bioactivity of these natural compounds reported in literatures. Based on the above
studies, potential macromolecules were envisaged to be proteins or peptides which
possess a cysteine residue near its active site. Therefore, the CAAX motif of proteins of
CENP-E and CENP-F were investigated based on quantum chemistry calculation.
Besides the thiol group, andrographolide has been reported to interact with amino group
of biomolecules. However, the computational results indicate that the reactivity of
andrographolide with amine was lower comparing with thiol group.
Our experimental works confirm that andrographolide did react with nucleophiles
via a Michael reaction at the unsaturated lactone moiety of andrographolide. By using
HPLC, the reactants were isolated and identified. Thus, the computational studies
described in this thesis provide good evidence of structural activity relationship for
andrographolide and its analogues to protein molecule.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2268807|
|Appears in Collections:||BCH - Doctor of Philosophy |
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