An in depth chemical investigation of the major and minor pyrroloiminoquinone metabolites produced by four species of endemic South African Latrunculid sponges, collected from Algoa Bay and the Tsitsikamma Marine Reserve off the south eastern coast of South Africa, yielded eleven new and twelve known pyrroloiminoquinone metabolites. The structures of the new metabolites were determined using standard spectroscopic techniques. Tsitsikamma pedunculata was shown to contain 7,8-dehydro-3-dihydro-discorhabdin C (2.1), 14-bromo-7,8-dehydro-3-dihydro-discorhabdin C (2.2), discorhabdin S (2.3), 14-bromo-1-hydroxy-discorhabdin S (2.4), 1-bromo-2-hydroxy-4-debromo-discorhabdin S (2.5), and 2,4-debromo-3-dihydro-discorhabdin C (2.6), together with the known compounds 14-bromo-discorhabdin C (1.51), 14-bromo-3-dihydro-discorhabdin C (1.52) and 3-dihydro-discorhabdin C. The metabolites from T. pedunculata were characterised by the presence of a reduced C-3 carbonyl and bromination at C-14. Compounds isolated from a second Latrunculid sponge, Latrunculia lorii, ranged from a substituted bicyclic pyrrolecarboxylic acid, makaluvic acid A (1.47), to the simple tricyclic known pyrroloiminoquinones makaluvamine C (1.33) and damirone B (1.20) and the more complex discorhabdin D type metabolites, discorhabdin M (3.2), 1-amino discorhabdin D (3.3), 1-methoxy discorhabdin D (3.4) and 1-alanyl discorhabdin D (3.5). Discorhabdin G* (3.1) was also isolated and characterised. This is the first reported occurrence of the known compounds 1.20, 1.33 and 1.47 in a Latrunculia sponge. Discorhabdin and bis-pyrroloiminoquinone type compounds predominated in Tsitsikamma favus. Three known, tsitsikammamines A (1.71) and B (1.72), 1.52, and five new pyrroloiminoquinones, tsitsikammamine N-oxime (4.1), tsitsikammamine B N-oxime (4.2), 2.1, 2.4 and 2.6, were isolated from this sponge. A fourth Latrunculid sponge (Strongylodesma sp.) yielded three known compounds, discorhabdins A (1.57), D (1.61) and 1.53, and one new pyrroloiminoquinone 3.3. The dual role of these metabolites as cytotoxic agents and pigments resulted in an attempt to relate the photochemical properties of these metabolites to their cytotoxicity. The pyrroloiminoquinone metabolites studied exhibited moderate singlet oxygen quantum yields, while three compounds (1.57, 4.1 and 4.2) were shown to be capable of producing radicals at a wavelength of 532 nm. The possibility of a correlation between the electrochemical properties and anti-cancer (HCT-116) activity of selected pyrroloiminoquinones was explored. A study of the oesophageal and ovarian cytotoxicities of two pyrroloiminoquinones (1.57 and 1.72), together with an investigation into the intercalation and topoisomerase I inhibitory activity of the bis-pyrroloiminoquinones (1.71, 1.72, 4.1 and 4.2), are presented.

Globally, methicillin resistant Staphylococcus aureus (MRSA) has become increasingly difficult to manage in the clinic and new antibiotics are required. The structure activity relationship (SAR) study presented in this thesis forms part of an international collaborative effort to identify potent and selective inhibitors of an MRSA pyruvate kinase (PK) enzyme target. In earlier work the known marine natural product bromodeoxytopsentin (1.6), isolated from a South African marine sponge Topsentia pachastrelloides, exhibited selective and significant inhibition of MRSA PK (IC₅₀ 60 nM). Accordingly bromodeoxytopsentin provided the initial chemical scaffold around which our SAR study was developed. Following a comprehensive introduction, providing the necessary background to the research described in subsequent Chapters, this thesis has been divided into three major parts. Part one (Chapter 2) documents the synthesis of two natural imidazole containing topsentin analogues 1.40, 1.46, five new synthetic analogues 1.58—1.61, 2.104. In the process we developed a new method for the synthesis of topsentin derivatives via selenium dioxide mediated oxidation of N-Boc protected 3-acetylindoles to yield glyoxal intermediates which were subsequently cyclized and deprotected to yield the desired products. Interestingly we were able to demonstrate a delicate relationship between the relative equivalents of selenium dioxide and water used during the oxidation step, careful manipulation of which was required to prevent the uncontrolled formation of side products. Synthetic compounds 1.40, 1.46, 1.58—1.61 were found to be potent inhibitors of MRSA PK (IC₅₀ 238, 2.1, 23, 1.4, 6.3 and 3.2 nM respectively) with 1000-10000 fold selectivity for MRSA PK over four human orthologs. In the second part of this thesis (Chapter 3) we report the successful synthesis of a cohort of previously unknown thiazole containing bisindole topsentin analogues 1.62—1.68 via a Hantzsch thiazole synthesis. Bioassay results revealed that these compounds were only moderate inhibitors of MRSA PK (IC₅₀ 5.1—20 μM) which suggested that inhibitory activity was significantly reduced upon substitution of the central imidazole ring of topsentin type analogues with a thiazole type ring. In addition in Chapter 3 we describe unsuccessful attempts to regiospecifically synthesize oxazole and imidazole topsentin analogues through a similar Hantzsch method. As a consequence of our efforts in this regard we investigated three key reactions in depth, namely the synthesis of 2.2, 3.38, 3.40, 3.41 via α-bromination of 3-acetylindole and the synthesis of indolyl-3-carbonylnitriles 2.13, 3.45—3.47 and α-oxo-1H-indole-3-thioacetamides 3.48—3.51. The investigation of the latter led to the isolation and elucidation of two anomalous N,N-dimethyl-1H-indole-3-carboxamides 3.52 and 3.53. Finally the third part of this thesis (Chapter 4) deals with in silico assessment of the binding of both the imidazole and thiazole containing bisindole alkaloids to the MRSA PK protein which initially guided our SAR studies. In this chapter we reveal that there appears to be no correlation between in silico binding predictions and in vitro MRSA PK inhibitory bioassay data. Superficially it seems that binding energy as determined by the docking program used for these studies correlated with the size of the indole substituents and did not reflect IC₅₀ MRSA PK inhibitory data. Although this led us to computationally explore possible alternative binding sites no clear alternative has been identified.

Algoa Bay Latrunculid sponges are well known for their production of cytotoxic pyrroloiminoquinones with speculation that these secondary metabolites may have a microbial origin. This study describes a thorough investigation into the bacterial community associated with Tsitsikamma favus, Tsitsikamma scurra a newly described Latrunculia sp. and a yellow encrusting sponge associated with T. scurra. Molecular and chemical characterisation were used in conjunction with traditional taxonomy in identification of the sponge specimens. The 28S rRNA and COX1 analysis confirmed the traditional taxonomy with T. favus and T. scurra being very closely related. Chemical analysis revealed that T. favus and T. scurra shared the discorhabdins 2,4-debromo-3-dihydrodiscorhabdin C, 7,8-dehydro-3-dihydrodiscorhabdin C and 14-bromo-1-hydroxy-discorhabdin V in common with each other and Tsitsikamma pedunculata indicating that these pyrroloiminoquinones are common to Tsitsikamma sponges in general. The bacterial community associated with T. favus was explored using 16S rRNA molecular techniques including DGGE, clonal libraries of full length 16S rRNA genes, as well as 454 pyrosequencing. DGGE analysis revealed that the bacterial community associated with T. favus appeared to be highly conserved, which was confirmed by both the clone library and 454 pyrosequencing, with the Betaproteobacteria as the most dominant class. Further exploration into T. favus, as well as T. scurra, Latrunculia sp. and the yellow encrusting sponge indicated that the bacterial populations associated with each of these sponge species were conserved and species specific. OTU analysis to the species level revealed that T. favus and T. scurra shared an abundant Spirochaete species in common while the most abundant species in the Latrunculia sp. and the yellow encrusting sponge belonged to the class Betaproteobacteria. The exclusivity of the tsitsikammamines to T. favus precipitated attempts to culture the T. favus associated bacteria, with a focus on the dominant betaproteobacterium as indicated by the 16S rRNA clone library. Actinobacteria associated with the Algoa Bay sponge specimens were also cultured and the actinobacterial isolates were sent for screening against Mycobacterium aurum with two Kocuria kristinae isolates and a Streptomyces albdioflavus isolate showing good antimycobacterial activity.