In this thesis, synthetic chemistry was used as a tool in the exploration of various aspects of natural products discovered by the natural products research group at the University of Canterbury. Work on the constituent amino acids and connectivity of the pteratides, a potently cytotoxic series of cyclodepsipeptides, had been completed before the beginning of this work (carried out by Miss C. Chen). The elucidation of the stereochemistry of the constituent amino acids was undertaken in this present work. The synthesis of all stereochemical entities of a number of unusual amino acids, which were either not available commercially or were expensive, was carried out, providing reference materials for comparison to the natural products. The synthesis of the diastereoisomers of one of these amino acids, 4-methylproline, was carried out by modification of literature procedures, which led to the development of an improved, concise and stereoselective synthesis. The hydrolysis of the natural products, derivatisation of the resultant hydrolysates, synthetic and commercial reference amino acids and HPLC analysis allowed the full stereochemical assignment of the pteratide series. The total synthesis of spiro-mamakone A, a cytotoxic polyketide isolated by Dr S. van der Sar, was undertaken. The synthesis was not successfully completed due to difficulties in the late-stage formation of a crucial enedione motif. However, very advanced intermediates were successfully synthesised. These synthetic analogues of the natural product were analysed for biological activity, allowing valuable insight into the structure-activity relationship, for example, demonstrating the importance of the enedione moiety to biological activity.

In this thesis, synthetic chemistry was used as a tool in the exploration of various aspects of natural products discovered by the natural products research group at the University of Canterbury. Work on the constituent amino acids and connectivity of the pteratides, a potently cytotoxic series of cyclodepsipeptides, had been completed before the beginning of this work (carried out by Miss C. Chen). The elucidation of the stereochemistry of the constituent amino acids was undertaken in this present work. The synthesis of all stereochemical entities of a number of unusual amino acids, which were either not available commercially or were expensive, was carried out, providing reference materials for comparison to the natural products. The synthesis of the diastereoisomers of one of these amino acids, 4-methylproline, was carried out by modification of literature procedures, which led to the development of an improved, concise and stereoselective synthesis. The hydrolysis of the natural products, derivatisation of the resultant hydrolysates, synthetic and commercial reference amino acids and HPLC analysis allowed the full stereochemical assignment of the pteratide series. The total synthesis of spiro-mamakone A, a cytotoxic polyketide isolated by Dr S. van der Sar, was undertaken. The synthesis was not successfully completed due to difficulties in the late-stage formation of a crucial enedione motif. However, very advanced intermediates were successfully synthesised. These synthetic analogues of the natural product were analysed for biological activity, allowing valuable insight into the structure-activity relationship, for example, demonstrating the importance of the enedione moiety to biological activity.

No description available.

Unambiguous structure assignment of standards is essential for metabolome characterization of infected plants. Complete structure elucidation of eleven natural polyphenols, resveratrol (1), (-)-epicatechin (2), pelargonidin chloride (3), cyanidin chloride (4), cyanin chloride (5), keracyanin chloride (6), caftaric acid (7), quinic acid (8), procyanidin B1 (9), procyanidin B2 (10), and procyanidin C1 (11) by 1H-, 13C, COSY-, TOCSY-, ROESY-, and HMBC-NMR is described. The sinusoidal modulation frequency of 1H-13C-cross-peaks (J-HMBC) was fitted iteratively to sin(πJH,Ctvar) and yielded 2,3J-coupling values for 1H-13C-correlations in the natural polyphenols. Satisfactory fit to standard Karplus-equations was achieved for glycosides directly attached to the aromatic core in cyanin chloride. Molecular dynamics simulation data in vacuum at the AM1-level of theory were shown to approximate the NMR-solution data reasonably well. Analysis of these standards enables the characterization of unknown plant metabolites produced by bacterially stressed Thompson grape plants provided by the USDA. Initial steps for structure elucidation of 72 unknown fractions is discussed. In addition, selective HCl-catalyzed H/D-exchange was observed for aromatic protons H6 and H8 in flavonoid structures containing a 5,7-meta-disubstituted chromelynium core with free OH-groups. The exchange took place readily in compounds 3, 4, and 6, whereas 1, 2, and 5 did not exchange.

No description available.

No description available.

Ministry of Higher Education; Sultanate of Oman / Digital full-text is unavailable. Submitted disc unusable.

This thesis describes the isolation and structure elucidation of secondary metabolites formed in static culture from a number of endophytic Xylariaceous fungi. Four Xylaria endophytes isolated from a palm tree in Thailand were surface cultured on an aqueous malt extract-glucose medium. They all produced cytochalasin D, coriloxin, (S)-mellein and (3R,4R)-4-hydroxymellein as the main secondary metabolites suggesting that the four endophytes could be the same species. The endophytic fungus A116 produced cytochalasin D as the main secondary metabolite. Another non-endophytic fungus B315, produced cytochalasin D, (R)-mellein, a mixture of two isomers of 4-hydroxymellein and phloroglucinol. X.62, an endophytic fungus, produced 19,20-epoxycytochalasin C from the mycelium as the main secondary metabolite. The fungus Engleromyces sinensis produced engleromycin acetate as the main secondary metabolite. Fungus X. polymorpha produced (3E)-4-(3¿-acetyl-2¿,6¿-dihydroxy-5¿-methylphenyl)-2-methoxybut-3-enoic acid. / Ministry of Higher Education; Kingdom of Saudi Arabia.

This thesis describes the isolation and structure elucidation of secondary metabolites from a number of endophytic Xylaria fungi. Six Xylaria endophytes were surface cultured on an aqueous malt extract-glucose medium. The fungus A311R, from a palm tree in Thailand, produced nonane-1,2,3-tricarboxylic acid, which was isolated for the first time as a natural product. Also isolated from the same fungus was spiculisporic acid; the first instance of isolation from a Xylaria fungus. The fungus 6RD12 produced cycloepoxydon, which was isolated for the first time from a Xylaria fungus, and 4,5,6-trihydroxy-3-propyl-3,4,6,7-tetrahydro-l//-isochromen- 8(5//)-one, which is a novel compound. The fungi A217R and A517R produced cytochalasin D, (S)-mellein and (3S,4S)-4-hydroxymellein as main secondary metabolites suggesting that the two fungi are the same species. The fungus X04 (Xylaria cf. juruensis) produced 2-Hydroxy-5-ethoxy-3-methylcyclohexa-2,5-dien- 1,4-dione as a novel compound, coriloxin as the main secondary metabolite in addition to (R)-mellein and a mixture of two stereoisomers of the 4-Hydroxymellein. The fungus 6RD8 produced (S)-Omethylmellein as the main secondary metabolite. l

Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-Diels–Alder reaction of diferrocenyl thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2-diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1 and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide 1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical (cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an increase of the sulphur atom oxidation from −2 in 1 to +2 in 3 causes an anodic shift of the ferrocenyl-based oxidation potentials of about 100 mV. The electrochemical oxidation of 1–3 generates mixed-valent cations 1+–3+. These monooxidised species display low-energy electronic absorption bands between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions. Accordingly, the mixed-valent cations 1+–3+ are classified as weakly coupled class II systems according to Robin and Day. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.