Natural products have been a source of many pharmaceutical drugs and a number of drugs that are currently used in the treatment of cancer are derivatives of compounds originally isolated from natural products. There is evidence that extracts of Tulbaghia violacea can be used to treat cancer. The activation of apoptosis in cancer cells is a target for the development of novel anti-cancer drugs since one of the characteristics of cancer cells is resistance to apoptosis due to the deregulation of biochemical pathways leading to apoptosis. In fact, many current anti-cancer drugs exert their effects through the activation of apoptosis. Previous studies showed that extracts of T.violacea induce apoptosis in cancer cells and one study reported on the isolation of a compound (methyl-ԃ-D-glucopyranoside), which is responsible for the pro-apoptotic activity of the T.violacea extract. Therefore the aim of this study was to investigate the anti-cancer activity of methyl-ԃ-Dglucopyranoside and extracts prepared from T.violacea. In this study the pro-apoptotic activity of methyl-ԃ-D-glucopyranoside and extracts prepared from T.violacea were investigated on a panel of human cancer cell lines, which included HepG2, MCF7, H157, HT29 and the non-cancerous cell line, KMST6. The induction of apoptosis was evaluated by flow cytometry using several bioassays which measures biochemical events (caspase activation, phosphatidylserine externalisation and reactive oxygen species (ROS) production that is associated with the induction of apoptosis. The results demonstrated that the effects of methyl--D-glucopyranoside on cultured cells are transient and that the cells recover from the effects of methyl--D-glucopyranoside. This suggested thatmethyl-ԃ-D-glucopyranoside is not the compound responsible for the pro-apoptotic bioactivity in the T.violacea extract. This study also showed that cytotoxic and pro-apoptotic bioactivity of the leaf-extract was significantly higher in comparison to the tuber-extract. The bioactivity of the organic solvent extracts (dichloromethane, hexane, methanol and 50% methanol/water) of T.violacea leaves was also significantly higher than water extracts of T.violacea leaves. A comparison of the different organic extracts prepared from the T.violacea leaves showed that the highest activity was observed for the dichloromethane and hexane extracts. In an effort to identify the bioactive compound(s) the dichloromethane extract was subjected to Versaflash® column chromatography. However, due to problems experienced with the solubility of the dichloromethane sub-fractions, these compounds could not be tested for their bioactivity. Palmitone (16-hentriacontanone) was identified as one of the major compounds present in the dichloromethane sub-fractions. This compound was previously shown to have anticonvulsant bioactivity but there is no evidence in the literature that it has anti-cancer or pro-apoptotic activities. Fingerprinting of the methanol extract showed the presence of long chain fatty acid derivatives, flavonoids and allicin derivatives in the methanol extract. Although, this study failed to isolate the pro-apoptotic bioactive compound(s) present in the extracts of T.violacea, it confirmed that extracts of this plant induce apoptosis in cultured human cancer cell lines.

Natural products have been a source of many pharmaceutical drugs and a number of drugs that are currently used in the treatment of cancer are derivatives of compounds originally isolated from natural products. There is evidence that extracts of Tulbaghia violacea can be used to treat cancer. The activation of apoptosis in cancer cells is a target for the development of novel anti-cancer drugs since one of the characteristics of cancer cells is resistance to apoptosis due to the deregulation of biochemical pathways leading to apoptosis. In fact, many current anti-cancer drugs exert their effects through the activation of apoptosis. Previous studies showed that extracts of T.violacea induce apoptosis in cancer cells and one study reported on the isolation of a compound (methyl-ԃ-D-glucopyranoside), which is responsible for the pro-apoptotic activity of the T.violacea extract. Therefore the aim of this study was to investigate the anti-cancer activity of methyl-ԃ-Dglucopyranoside and extracts prepared from T.violacea. In this study the pro-apoptotic activity of methyl-ԃ-D-glucopyranoside and extracts prepared from T.violacea were investigated on a panel of human cancer cell lines, which included HepG2, MCF7, H157, HT29 and the non-cancerous cell line, KMST6. The induction of apoptosis was evaluated by flow cytometry using several bioassays which measures biochemical events (caspase activation, phosphatidylserine externalisation and reactive oxygen species (ROS) production that is associated with the induction of apoptosis. The results demonstrated that the effects of methyl--D-glucopyranoside on cultured cells are transient and that the cells recover from the effects of methyl--D-glucopyranoside. This suggested thatmethyl-ԃ-D-glucopyranoside is not the compound responsible for the pro-apoptotic bioactivity in the T.violacea extract. This study also showed that cytotoxic and pro-apoptotic bioactivity of the leaf-extract was significantly higher in comparison to the tuber-extract. The bioactivity of the organic solvent extracts (dichloromethane, hexane, methanol and 50% methanol/water) of T.violacea leaves was also significantly higher than water extracts of T.violacea leaves. A comparison of the different organic extracts prepared from the T.violacea leaves showed that the highest activity was observed for the dichloromethane and hexane extracts. In an effort to identify the bioactive compound(s) the dichloromethane extract was subjected to Versaflash® column chromatography. However, due to problems experienced with the solubility of the dichloromethane sub-fractions, these compounds could not be tested for their bioactivity. Palmitone (16-hentriacontanone) was identified as one of the major compounds present in the dichloromethane sub-fractions. This compound was previously shown to have anticonvulsant bioactivity but there is no evidence in the literature that it has anti-cancer or pro-apoptotic activities. Fingerprinting of the methanol extract showed the presence of long chain fatty acid derivatives, flavonoids and allicin derivatives in the methanol extract. Although, this study failed to isolate the pro-apoptotic bioactive compound(s) present in the extracts of T.violacea, it confirmed that extracts of this plant induce apoptosis in cultured human cancer cell lines.

<p>Background and objectives: Apoptosis is a process in which a cell programmes its own death. It is a highly organized physiological mechanism in which injured or damaged cells are destroyed. Apart from physiological stimuli however, exogenous factors can induce apoptosis. Many anti-cancer drugs work by activating apoptosis in cancer cells. Natural substances have been found to have the ability to induce apoptosis in various tumour cells and these substances have been used as templates for the construction of&nbsp / novel lead compounds in anticancer treatment. On the other hand, alkylating agents such as cisplatin, cis- [PtCl2 (NH3) 2] have been widely used as antineoplastic agents for a&nbsp / wide variety of cancers including testicular, ovarian, neck and head cancers, amongst others. However, the use of cisplatin as an anticancer agent is limited due to toxicity and resistance problems. The aim of this present study was to screen the leaves of Rhus laevigata, a South African indigenous plant, for the presence of pro-apoptotic and&nbsp / anti-proliferative natural compounds and also to screen newly synthesised palladium based complexes (15 and 57) and a platinum based complex (58) for their antineoplastic&nbsp / activities tested against a panel of cell lines. Results. The results showed that crude methanol extracts from Rhus laevigata as well as the newly synthesised palladium based complexes (15 and 57) and a platinum based complex (58) induced apoptosis in the cell lines tested, as demonstrated by the externalization of phosphatidylserine, mitochondrial membrane permeabilization,caspase-3 activation, and DNA fragmentation. Caski (cervical cancer) and H157 (non small cell lung carcinoma) cell lines treated with the methanol extract from Rhus laevigata however, were more resistant to apoptosis induction. Among the metallocomplexes, complexes 15 and 57, palladium based complexes, were the most active. Conclusion: The methanol extract from the leaves of Rhus laevigata contain pro-apoptotic and antiproliferative natural compound(s), which need to be characterised and elucidated as they could provide the much-needed lead compounds in the fight against cancer. On the other hand the newly synthesized palladium complexes also need further evaluation to&nbsp / see if they can be used as anticancer agents that can overcome the problems associated with cisplatin.</p>

The genus Helichrysum (Asteraceae) consists of approximately 500 species worldwide, with 245 indigenous to South Africa. As a result of the large number of species, the chemistry and biological activity of several species have not yet been investigated. The aim of this project was to investigate the phytochemistry of three species and propose a synthetic route to one of the antibacterial compounds isolated. An extensive literature review regarding the widespread traditional uses, biological activity and phytochemistry of the South African Helichrysum species is provided. From Helichrysum splendidum, a plant used traditionally to treat rheumatism, two monomeric guaianolides and a dimeric guaianolide, helisplendidilactone, were isolated. The stereochemistry of these known compounds was confirmed and the NMR assignments for certain peaks of helisplendidilactone were corrected. An X-ray structure for helisplendidilactone was obtained for the first time. The phytochemistry of Helichrysum montanum was investigated for the first time and new diastereoisomers of known guaianolides were isolated. The phytochemistry of H. splendidum and H. montanum is remarkably similar and supports their morphological classification in the same taxonomic group. The chloroform:methanol extract of H. montanum yielded a new dimeric guaianolide, 13’-epihelisplendidilactone, which is related to helisplendidilactone, as well as three monomeric guaianolides (of which one is a new diastereomer of a known compound). The extract also yielded spathulenol (a sesquiterpene), umbelliferone (a coumarin) and 4’,5,7-trihydroxy-3,3’,8-trimethoxyflavone (a flavonoid). Thirty-five Helichrysum species were screened for antimicrobial activity against six microorganisms and a preliminary cytotoxic assay, which included the use of “normal” and cancer cell lines, was performed. H. excisum was selected for further study based on the fact that it exhibited promising antimicrobial activity and relative low toxicity. Furthermore, with the exception of the essential oil, the phytochemistry of this species has not been investigated. From the aerial parts of H. excisum, five flavonoids, identified as pinocembrin, gnaphaliin, lepidissipyrone, 5-hydroxy-7,8-dimethoxyflavone and isoscutellarein 7-O-b-glucoside were isolated. Four of these flavonoids have an unsubstituted B-ring, a phenomenon often observed in flavonoids isolated from Helichrysum species. The active antimicrobial component of H. excisum has been identified as lepidissipyrone. Owing to the interesting biological activities reported for phloroglucinol a-pyrones and the synthetic challenges associated with these molecules, lepidissipyrone was selected for a synthetic study. Both the flavanone and pyrone moieties present in lepidissipyrone have been successfully synthesised. A successful strategy towards the CH2 linker between the two units has been illustrated. The strategy could be used to synthesise similar phloroglucinol-derived pyrones. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008.

Type II polyketide synthase (PKS) produced natural products have proven to be an excellent source of pharmacologically relevant molecules due to their rich biological activities and chemical scaffolds. Type II-PKS manufactured polyketides share similar polycyclic aromatic backbones leaving their diversity to stem from various chemical additions and alterations facilitated by post-PKS tailoring enzymes. Evidence suggests that post-PKS tailoring enzymes form complexes in order to facilitate the highly orchestrated process of biosynthesis. Thus, protein-protein interactions between these enzymes must play crucial roles in their structures and functions. Despite the importance of these interactions little has been done to study them. In the mithramycin (MTM) biosynthetic pathway the Baeyer−Villiger monooxygenase (BVMO) MtmOIV and the ketoreductase MtmW form one such enzyme pair that catalyze the final two steps en route to the final product. MtmOIV oxidatively cleaves the fourth ring of the mithramycin intermediate premithramycin B (PreB) via a Baeyer−Villiger reaction, generating MTM’s characteristic tricyclic aglycone core and highly functionalized pentyl side chain at position 3. This Baeyer−Villiger reaction precedes spontaneous lactone ring opening, decarboxylation, and the final step of MTM biosynthesis, a reduction of the 4′- keto group catalyzed by the ketoreductase MtmW. Another example of co-dependent post-PKS tailoring enzymes from the gilvocarcin biosynthetic pathway is composed of GilM and GilR. These two enzymes form an unusual synergistic tailoring enzyme pair that does not function sequentially. GilM exhibits dual functionality by catalyzing the reduction of a quinone intermediate to a hydroquinone and stabilizes O-methylation and hemiacetal formation. GilM mediates its reductive catalysis through the aid of GilR that provides its covalently bound FADH(2) for the GilM reaction, through which FAD is regenerated for the next catalytic cycle. A few steps later, following glycosylation related events unique to each gilvocarcin derivative, GilR dehydrogenates the hemiacetal moiety created by GilM to establish the formation of a lactone and the final gilvocarcin chromophore. To achieve a better understanding of post-type II PKS tailoring enzymes and their protein-proteininteractions for the benefit of future combinatorial biosynthetic efforts two specific aims were devised. Specific aim 1 was to investigate the structure of MtmOIV and the role of active site residues in its catalytic mechanism. Specific aim 2 was to integrate the function of GilM and its protein-protein interactionswith GilR that lead to their synergistic activity and sharing of GilR’s bicovalently bound FAD moiety.

Several nucleoside natural product antibiotics from Streptomyces sp. and actinomycetes have recently been shown to target bacterial peptidoglycan cell wall biosynthesis by inhibiting the bacterial translocase I (MraY). The biosynthetic gene clusters for A-90289, liposidomycins and caprazamycins revealed a protein with sequence similarity to proteins annotated as α-KG:taurine dioxygenases (TauD). This enzyme (LipL) is a mononuclear, non-heme, Fe(II) dependent α-keto glutarate (α-KG) :uridine monophosphate (UMP) dioxygenase responsible for the net dephosphorylation and two electron oxidation of UMP to uridine-5’-aldehyde. The postulated reaction coordinates involving the activation of the C-5’ center in UMP and the corresponding formation of uridine-5’-aldehyde are modeled on extensive spectroscopic and structural characterizations of TauD. In this dissertation, the postulated radical mechanism for LipL involving the formation of an unstable hydroxylated intermediate is investigated via the characterization of a key product obtained from the reaction of LipL (and its homolog Cpr19) with a synthetically modified surrogate substrate where the bridging phosphoester oxygen in UMP is replaced with a 5’ C-P bond. We further validate our hypothesis by analyzing the reactions of both LipL and Cpr19 with specifically 2H1 – labeled UMP substrate and confirming the expected products via mass spectrometry. In addition, we explore substrate promiscuity of the enzymes and utilize a set of site specific mutants of Cpr19 as means of gaining better insight into the active site residues. Predictive models for Cpr19 and LipL structures are developed by the combination of experimental results and chemical logic.

No description available.

<p>Early man dabbled with the use of plant extracts to cure ailments. This practice has been passed down from generation to generation and today more than 50% of the world'sdrugs are natural products or derivatives thereof. Scientists have thus established a branch of research called natural product research. This branch of research involves the identification and purification of secondary metabolites with a specific biological activity. The methodology involves the screening of plant products for a specific biological activity, purification of the biologically active natural product by separation technology and structure determination. The biologically active natural products is then further scrutinized to serve as a novel drug or lead compound for the development of a novel drug. This research exploited this research methodology.</p>

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (p. 153-160) Also available on the World Wide Web.

Thesis (Ph.D.)--Victoria University of Wellington, 2008. / Includes bibliographical references.