隨著個人計算機運算能力的快速發展，虛擬藥物篩檢已被廣泛運用。目前運用於計算機輔助藥物虛擬篩選的化合物數據庫多為人工合成的數據庫，而用於天然產物藥物篩選的數據庫則較少報道。為了加速天然化合物的虛擬篩選，我們建立了包含約8000個天然產物的數據庫。他們中的大多數為傳統中藥。 / 為了驗證天然產物數據庫的可用性，其被用於篩選乙酰膽鹼酯酶抑製劑。該數據庫成功地確定了美國藥品監督管理局所批準的乙酰膽鹼酯酶抑製劑，如石杉鹼甲和他克林，表示該天然產物數據庫可以用於藥物虛擬對接篩選。 / 除了已知的乙酰膽鹼酯酶抑製劑，十二種植物化學物（大黃酸，大黃素，蘆薈大黃素，大黃酚，花椒毒素，珊瑚菜素，別異歐前胡素，歐前胡素，紫草素，乙酰紫草素，異戊紫草素和β，β-二甲基丙烯酰紫草素）被確定為新的乙酰膽鹼酯酶抑製劑。澱粉樣蛋白聚集可以導致神經細胞死亡；本研究中新發現的乙酰膽鹼酯酶抑製劑乙酰紫草素能夠阻止澱粉樣蛋白的聚集。除此之外，乙酰紫草素及其衍生物可以對抗過氧化氫誘導的神經細胞凋亡。其抗凋亡的活性作用是通過抑制活性氧的產生，以及保護線粒體膜電位的損失所實現的。亞鐵血紅素加氧酶在其神經細胞保護作用中起重要作用。 / 趨化因子受體4為跨膜G蛋白偶聯受體（GPCRs）。 CXCR4已被確定為一個新治療以及預防腫瘤轉移的新靶點。本研究利用分子對接篩選，從天然產物數據庫篩選選出CXCR4拮抗劑。通過分子對接和基於細胞的測定，黃芪甲苷，羥基紅花黃色素A和水飛薊賓已被確定為CXCR4拮抗劑。抗轉移的研究表明，黃芪甲苷和水飛薊賓抑制CXCL12誘導乳腺癌細胞的遷移和侵襲。此外，水飛薊賓也抑制CXCL12誘導的人臍靜脈內皮細胞管形成。另一方面，羥基紅花黃色素A對乳腺癌細胞的增殖表現出較強的抑製作用，因此很難進行抗轉移實驗。 / With the rapid advances in personal computing power, virtual drug screening has become increasingly popular. While there are numerous databases for synthetic compounds, there are few natural product databases that are specifically for in silico docking studies. To facilitate virtual docking on natural compounds, in-house Natural Products Database has been established, which contains approximately 8,000 naturally occurring chemicals so far. Most of them are documented Traditional Chinese Medicines. / In order to validate the usefulness of the database, in silico screening of acetylcholinesterase inhibitors (AChEIs) by virtual docking was performed. The database successfully identified the FDA-approved AChEIs such as huperzine and tacrine, indicating the in-house database is workable for natural products docking screening. / Apart from well-known AChE inhibitors, twelve phytochemicals (emodin, aloe-emodin, chrysophanol, rhein, xanthotoxin, phellopterin, alloisoimperatorin, imperatorin, shikonin, acetylshikonin, isovalerylshikonin and β, β-dimethylacrylshikonin) were identified as AChE inhibitors in this study that were not previously reported. Amyloid aggregation leads to toxic species that cause neuronal cell deaths, it was found that the newly identified AChEIs acetylshikonin and shikonin are able to prevent amyloid aggregation. A series of cell-based analysis were conducted for in vitro evaluation of the neuroprotective activities of the newly identified AChEIs. Acetylshikonin and its derivatives was found to prevent apoptotic cell death induced by hydrogen peroxide in human and rat neuronal SH-SY5Y and PC12 cells at 10 μM. Acetylshikonin exhibited the most potent anti-apoptotic activity through inhibition of reactive oxygen species (ROS) generation as well as protection of the loss of mitochondria membrane potential. Furthermore, acetylshikonin upregulates hemooxygenase 1(HO-1) which is a key step mediating its anti-apoptotic activity from oxidative stress in SH-SY5Y cells. / The C-X-C chemokine receptor type 4 (CXCR4) belongs to the class A family of seven transmembrane G protein-coupled receptors (GPCRs). CXCR4 has been identified as one of novel target against metastasis. A search for natural CXCR4 antagonists was conducted from natural product database by molecular docking for anti-metastasis study. Astragaloside IV, hydroxy safflower yellow A and silibinin have been identified as novel CXCR4 antagonists by both molecular docking and characterized by various cell-based assays. Anti-metastasis study showed that astragaloside IV and silibinin inhibited CXCL12-induced migration and invasion in breast cancer cells. In addition, silibinin also inhibited CXCL12-induced tube formation in human umbilical vein endothelial cells. On the other hand, hydroxy safflower yellow A exhibited a strong cytotoxicity on breast cancer cell proliferation, which is difficult to conduct anti-metastasis experiments. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Yan. / Thesis (Ph.D.) Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 230-250). / Abstracts also in Chinese.

Natural product synthesis is one of the most creative branch of chemistry in terms of its boundless scope for innovation and has stimulated several generations of synthetic organic chemists. With advancement in the technology, particularly in the isolation and purification techniques, high-field NMR and X-ray crystallography, it has become fairly routine to isolate and assign the structures, high-field NMR and X-ray crystallography, it has become fairly routine to isolate and assign the structures, even to those complex molecules, which are available only in microscopic quantities from natural sources. Concurrently, one has witnessed tremendous advances in the availability of new synthetic methodologies with high region-, stereo-, and enantiocontrol for one or multiple C-C bond formations and rapid generation of molecular complexity. These developments have rekindled interest with total synthesis of natural products as platforms for testing and validating new reactions and strategies. Many natural products exhibit wide range of biological activities and thus provide good leads in drug discovery but quite often such bioactive compounds are obtained only in minute quantities from Nature. Hence, there is need to synthesize them to obtain requisite quantities and build diversity around their scaffold to further explore their therapeutic potential. Thus, natural product synthesis combines both intellectual challenge and possible application for human wellbeing. Our research group is actively engaged in the synthesis of structurally complex, bioactive natural products and as a part of this endeavour, total syntheses of several bioactive compounds have been accomplished in our laboratory in recent past. The present thesis has also evolved around the ongoing theme directed towards natural product synthesis and is organized under three chapters. Chapter I: Total synthesis of (+)-1S-Minwanenone Chapter II: Enantioselective total synthesis of the bioactive natural product (+)-Sch 642305. Chapter III: Enantiospecific total synthesis of 6-epi-(-)-Hamigeran B.

The goal of this project was the development of a computer-based system using artificial intelligence to classify the limonoids, protolimonoids and triterpenoids isolated from the family Meliaceae by the Natural Products Research Group of the University of Natal, Durban. A database of samples was obtained between 1991 and 1996, part of which time the author was a member of the group and isolated compounds from Turraea obtusifolia and Turraea floribunda. Over and above the problem of complexity and similarity in structures of the above mentioned natural products, are other difficulties. These include very small amounts of sample being isolated producing very weak peak signals in the C-13 NMR spectra, extraneous peaks in the NMR spectra due to different impurities and instrument noise, non-reproducible spectra due to the pulsed Fourier transform intervals and the nuclear Overhauser effect, impure samples often isolated as stereoisomeric mixtures or as mixed esters and superposition of peak signals in the NMR spectra due to carbons in the same environment within the same compound. These factors make identification by traditional computational and expert systems impossible. As a result of these shortcomings, the author has developed a novel approach using artificial neural network techniques. The artificial neural network system developed used real data from the 300 MHz NMR spectrometer in the Department of Chemistry, Durban. The system was trained to discriminate between limonoids, triterpenoids and flavonoids/coumarins from the C-13 NMR spectra of pure, impure and unseen compounds with an accuracy of better than 90%. Further differentiation of the glabretals from the rest of the protolimonoids as well as from the rest of the triterpenoids showed similarly significant results. Finally, individual limonoid discrimination within the limonoid dataset was extremely successful. Apart from its application to the extractives from Meliaceae, the methodology and techniques developed by the author can be applied to other sets of extractives to provide a robust method for the spectral classification of pre-identified natural products. / Thesis (Ph.D.)-University of Natal, Durban, 1998.

Total synthesis of natural products is of contemporary interest in organic synthesis. One of the useful ways to synthesize the natural products is to originate from inexpensive chiral pool compounds abundantly available in nature. In this context, our research group is actively involved in the use of tartaric acid as the four carbon four hydroxy building block in the synthesis of a number of natural products of therapeutic importance. Our strategy relies on the utility of γ-hydroxy amides derived from tartaric acid involving a controlled addition of Grignard reagents and stereoselective reduction. We were successful in application o f this useful building block for the synthesis of a variety of natural products possessing varied functional groups (Chart-1). derived from tartaric acid in the synthesis of oxylipins such as pinellic acid and diyne containing natural products. Chapter 1 of the thesis describes the total synthesis of (+) pinellic acid 6 and (Z,8S,9S,10R)-8,9,10-trihydroxyoctadec-6-enoic acid 10. Key strategy in the synthesis of pinellic acid is elaboration of the aldehyde 3, derived from the γ-hydroxy amide 2 via Horner-Emmons-Wadsworth reaction to yield the α,β-unsaturated ketone 4. Stereoselective reduction of the ketone with (R)-BINAL-H produced the alcohol with requisite stereochemistry which was further extended to pinellic acid 6 (Scheme 1). Wittig homologation of the aldehyde 8 derived from γ-hydroxy amide 7 is the key step for the synthesis of the (Z,8S,9S,10R)-8,9,10-trihydroxyoctadec-6-enoic acid 10. Second chapter of the thesis deals with total synthesis of diyne containing natural products. In the first part of this chapter enantioselective synthesis of possible diastereomers of heptadeca1-ene-4,6-diyne-3,8,9,10-tetrol, a structure proposed for the natural product isolated from Hydrocotyle leucocephala, is accomplished. The alkyne precursors 13 and 14 were synthesized from the α-hydroxy ester 12 derived from γ-hydroxy amide 11 while the alkyne 17 is synthesized from the masked tetrol 16 derived from lactol 15 which was obtained from D-ribose. yne to assemble the diyne unit which was further elaborated to heptadeca-1-ene-4,6-diyne3,8,9,10-tetrol (Scheme 3). It was found that the NMR spectral data of the putative structure assigned for the natural product did not match with any of the diasteromers that were synthesized. This establishes that the structure proposed for the natural product is wrong and requires revision. OH OH OH 18 OH OH 19 OH OH 20 OH OH Scheme 3: Synthesis of diastereomers of heptadeca-1-ene-4,6-diyne-3,8,9,10-tetrol. [Part of this work is published: Prasad, K. R.; Swain, B. J. Org. Chem. (in press)] Second part of this chapter deals with the synthesis of panaxytriol 26 and panaxydiol 28. Key reaction in the synthesis of panaxytriol and panaxdiol is the coupling of bromoalkynes 25 and 27 with 3-silyloxy pent-1-en-4-yne and further elaboration to the triol and diol. The required alkynes were synthesized from the primary alcohol 24 which was obtained from the γ-hydroxy amide 11 involving a series of simple synthetic operations. (Scheme 4). (For structural formula pl see the abstract file)

First chapter of the thesis describes the desymmetrization of the bis-dimethyl amide 1 derived from tartaric acid with vinyl Grignard reagents and subsequent reduction of the resultant -keto amides 2a-c to the -hydroxy amides 3a-c. Application of the -hydroxy amides 3a-c in the total synthesis of bio-active natural products such as gabosines, crassalactone C and anamarine is described in the subsequent sections. In section A of the first chapter, application of the -hydroxy amides 3a-b to the total synthesis of gabosine A 4, gabosine F 5 and gabosine H 6 was described. Key strategy in the synthesis was the use of ring closing metathesis (RCM) reaction. Incidentally, the total synthesis of gabosine H 6 was not only accomplished for the first time but the synthesis also ascertained the absolute stereochemistry of the natural product. During the course of the synthesis of gabosine A 4, an unprecedented formation of a unique 14-membered macrocycle 7 was observed. Incisive studies were conducted to elucidate the reaction sequence for the formation of the macrocyle 7. It was found that the formation of the macrocycle 7 was through a tandem cross-metathesis/intramolecular hetero Diels-Alder reaction. Section B of chapter 1 delineated the utility of the -hydroxy amide 3a in the total synthesis of (–)-crassalactone C 8a. Crassalactone C 8a is a cinnamoyl derivative of styryllactone natural product goniofufurone and was found to possess marginal in vitro cytotoxic activity. Pivotal strategies in the synthesis include the use of bis-cinnamoyl ester 10a in the ring closing metathesis reaction which also evades the selective cinnamoylation of the benzylic hydroxy group. Section C of Chapter 1 deals with the total synthesis of (+)-anamarine 11. While the - hydroxy amide 3a was employed to synthesize an important intermediate 12 enroute to the synthesis of anamarine, to mitigate the number of steps in the synthesis, the -hydroxy amide 13 was employed for the synthesis of (+)-anamarine 11. Key reactions in the total synthesis include the use of 1,3-dithiane as a surrogate for the methyl group, Brown’s allylation and ring closing metathesis. In second chapter of the thesis, formal total synthesis of iriomoteolide 3a 16 is presented. Iriomoteolide 3a 16 is a unique 15-membered marine macrolide isolated by Tusda’s group from the Amphidinium strain HYA024, with impressive in vitro cytotoxic activity against human lymphoma cell line DG-75 (IC50 0.08 g/mL) and Raji cells (IC50 0.05 g/mL). Salient features of the synthesis include the synthesis of the chiral aldehyde 19 from the oxazolidinone 17 and the use of -keto phosphonate 20 derived from D-(–)-tartaric acid in the Horner-Wadsworth-Emmons olefination reaction to construct the C1-C10 fragment 23 of iriomoteolide 3a 16. Synthesis of the C10-C18 fragment 29 was accomplished from the butyrolactone 24 using Keck allylation and olefin cross metathesis reactions as key steps. Ring closing metathesis of the ester 30, followed by selective deprotection of the primary TBS group afforded the key intermediate 31, the transformation of which to iriomoteolide 3a 16 is known in literature.

The thesis entitled “Enantiospecific total synthesis of indole alkaloids eburnamonine, aspidospermidine, quebrachamine, henrycinols A and B and synthesis of azepino[4,5-b]indolones” is divided into three chapters. In the first chapter, a unified strategy for the enantiospecific total synthesis of monoterpene indole alkaloids (+)-eburnamonine (1), (–)-aspidospermidine (2) and (–)-quebrachamine (3) is described. The chiral pool synthesis commenced with (S)-ethyl lactate 4, which was elaborated to the allylic alcohol 5. Johnson-Claisen orthoester rearrangement of the allylic alcohol 5 furnished the key chiral building block 6 possessing a quaternary stereogenic center. Pictet-Spengler cyclization of tryptamine with the corresponding aldehydes obtained by appropriate functionalization of the chiral building block 6 and ring closing metathesis were the key reactions employed en route the total synthesis of the indole alkaloids 1–3 (Scheme 1). Scheme 1. Unified strategy for the synthesis of monoterpene indole alkaloids (+)-eburnamonine (1), (–)-aspidospermidine (2) and (–)-quebrachamine (3). The second chapter of the thesis pertains to the synthesis of azepino[4,5-b]indolones 7 via Brønsted acid mediated intramolecular cyclization of unsaturated tryptamides 8. Various ,-unsaturated acids 9 derived from different -hydroxy esters 10, were converted to the corresponding unsaturated tryptamides 8 and subjected to the optimized reaction conditions. The results of the study indicated that -substituted unsaturated secondary tryptamides derived from (S)-ethyl lactate were the most effective in undergoing an intramolecular cyclization to furnish the corresponding azepino[4,5-b]indolones 7, possessing a quaternary stereogenic center in good yields. The presence of an alkenyl moiety in the quaternary center allowed the functionalization of these compounds and was subsequently employed to access the ABCD core 11 of tronocarpine and the tetracyclic cores 12 of some iboga alkaloids. The loss of chirality in the formation of the azepino[4,5-b]indolones indicated that the reaction proceeds predominantly by an SN1 pathway. During the course of the study an interesting formation of an azonino[5,4-b]indolone 13 by a competing SN1 pathway and a tetracyclic azepino[4,5-b]indolone 14 via a cascade cyclization were noticed (Scheme 2). Scheme 2. Synthesis of azepino[4,5-b]indolones 7 possessing a quaternary stereogenic center. The first total synthesis of two new indole alkaloids, henrycinols A (15) and B (16) which were isolated from the plant Melodinus henryi CRAIB is described in the third chapter of the thesis. The key reaction in the synthetic sequence is the Pictet-Spengler cyclization of L-tryptophan methyl ester 17a and the aldehyde 18 derived from D-tartaric acid which leads to the installation of all the stereogenic centers present in the natural products. Interestingly, a switch in the diastereoselectivity of the reaction was observed by varying the substituent on the amine in L-tryptophan methyl ester 17. When L-tryptophan methyl ester 17b possessing an N-allyl substitution was employed, the desired 1,3-trans tetrahydro--carboline 19b could be obtained in good yields, which was subsequently elaborated to the natural products 15 and 16 (Scheme 3). Scheme 3. Total synthesis of henrycinols A (15) and B (16).

This thesis investigates a total synthesis of the incednine aglycon by utilising alkenylsilane reagents to assemble the pentaenyl and tetraenyl systems through cross-coupling reactions. The early chapters develop methodology to access both cyclic alkenylsiloxanes and functionalised (E)-alkenylsilanes by the controlled hydrogenation of alkynylsiloxanes and silylolefination of aldehydes, respectively, and culminate in the synthesis of a C6-C13 bis(alkenylsilane)incednine fragment (Scheme 1). The C1-C5 and C14-C23 coupling partners are synthesised in three and ten steps from propargyl alcohol and L-alanine methyl ester through phosphorous-based olefination strategies. In the final chapter we describe our first generation approach to incednine which entails orthogonal cross-couplings to construct the C5-C6 and C13-C14 bonds (Scheme 2).

This thesis describes studies towards the total synthesis of manzamine A (9), a marine alkaloid. Two routes are presented. The first route applied a novel palladium-catalysed arylative allene spirocyclisation cascade to the synthesis of manzamine A (9). In the first generation, a short route was developed to access the tricyclic ACE core 263a in only nine steps. The second generation applied the palladium-catalysed cascade to a similar system which utilised non-terminal allene pro-nucleophile 450 in an attempt to access a homologated derivative of the ACE core. The second route relied on a diastereoselective Michael addition between nitro-olefin 473 and 8,5-fused ring system 146 comprising rings C and E of manzamine A (9). Further elaboration of the Michael addition product enabled the synthesis of tetracyclic ABCE core precursor 464 to be carried out and preliminary investigations into ring B formation were investigated.

This thesis focuses upon pacidamycin, a member of the uridyl peptide antibiotics, a family of antibiotics which exhibit an, as yet, clinically unexploited mode of action, against MraY. The Goss group has previously demonstrated the ease of accessing N and C-termini analogues of pacidamycin utilizing precursor directed biosynthesis. The central diamino acid is key to pacidamycin's activity, yet little work has been carried out, to date, to investigate the SAR around this moiety. Particularly this thesis describes work toward generating pacidamycin analogues using the complementary tools of organic synthesis and biosynthesis. Chapter 1 introduces natural compounds and their importance in clinical use, provides a brief overview of the history of antibiotics and focuses on the urgent need for new antibiotics displaying new chemical architectures and possessing novel modes of action. This chapter also introduces uridyl peptide antibiotics and overviews the SAR studies around these unusual peptides, focusing on pacidamycin in particular. Diaminobutyric acid is central to these structures and a discussion of a selection of published methods to synthesis α, β-diaminobutyric acid (DABA) is also presented. Chapter 2 describes the synthesis of DABA and two analogues, in which the C-methyl moiety has been substituted by an ethyl or a cyclopropyl group. The mutasynthesis approach utilised in the attempt to generate novel pacidamycins and discussion around the results observes is also described. Chapter 3 demonstrates a three step one-pot reaction to access 1,3-disubstituted urea molecules. The chapter starts with a brief overview of previously established methods in the literature to access these useful molecules, and then moves towards a discussion about the reaction optimisation. The chapter also describes a family of analogues generated utilising this novel approach; and exploring the use of these analogues in the mutasynthesis of pacidamycin. In order to access the desired pacidamycin analogues with the modified diamino acid residue, it was determined that it is currently not possible to use a mutasynthesis approach, instead an approach of total synthesis needed to be employed. Chapter 4 describes this total synthesis. The C- terminal urea motif was generated using a novel 1-pot phosphine free route developed during this study. To access the central native (2S, 3S)- DABA, a variation of the route of Merino et al's via Garner's aldehyde was initially utilised. Subsequently, a shorter and more flexible approach from Soloshonok et al via a Ni (II) Schiff base complex of glycine was adopted. Unpublished results from the Goss group have shown that the 2',3'dihydroxy uridine analogues in pacidamycin conferred broader spectra of activity. Work towards the synthesis of these analogues has been conducted. The order of assembly of the peptide and the nucleoside fragments was in alignment with Boojamra et al's approach. If the de-protection chemistry had worked according to plan, this would have resulted with a synthesis that is at least 6 steps shorter and higher yielding then Boojamra's. The introduction in this chapter reports the various methods previously reported in the literature for the total synthesis of pacidamycin. A discussion about the current progress in the total synthesis highlighting the difficulties faced is also shown. Chapter 5 demonstrates utilising semi-synthesis as a useful tool to generate novel pacidamycins by applying a Pictet-Spengler reaction on pacidamycin 4. This chapter starts with an overview of this phosphate mediated Pictet-Spengler reaction. In addition, a discussion about the large-scale fermentation of Streptomyces coeruleorubidus, the wild type producer of pacidamycin, and the generation of pacidamycin analogues utilising a semi-synthesis approach is also presented. Chapter 6 describes the future work following on from this study building upon each of the above chapters.

Gilvocarcin V (GV) belongs to the angucycline class of antibiotics that possesses remarkable anticancer and antibacterial activities with low toxicity. Gilvocarcin exhibits its light induced anticancer activity by mediating crosslinking between DNA and histone H3. When photo-activated by near-UV light, the C8 vinyl group forms a [2+2] cycloadduct with thymine residues of double stranded DNA. D-fucofuranose is considered essential for histone H3 interactions. However, the poor water solubility has rendered it difficult to develop gilvocarcin as a drug. We aim to design novel gilvocarcin analogues with improved pharmaceutical properties through chemo-enzymatic synthesis and mutasynthesis. Previous studies have characterized many biosynthetic genes encoding the gilvocarcin biosynthetic skeleton. Despite these previous findings the exact functions of many other key genes are yet to be fully understood. Prior gene inactivation and cross-feeding experiments have revealed that the first isolable tetracyclic aromatic product undergoes a series of steps involving C–C bond cleavage followed by two O-methylations, a penultimate C-glycosylation and final lactone formation in order to fully develop the gilvocarcin structure. To provide a deeper understanding of these complex biochemical transformations, three specific aims were devised: 1) synthesis of the proposed intermediate and in vitro enzyme reactions revealed GilMT and GilM’s roles in gilvocaric biosynthesis; 2) utilizing in vitro studies the enzyme responsible for the C–C bond cleavage and its substrate were determined; 3) a small series of structural analogues of the intermediate from the gilvocarcin pathway was generated via chemical synthesis and fed to the mixture of the enzymes, GilMT and GilM. These reaction mixtures were then analyzed to establish the diversity of substrates tolerated by the enzymes.