Nitrogen-containing heteroaromatics are ubiquitous in nature. In addition, 75% of FDA-approved drugs currently on the market are based on these compounds, establishing them and their analogues as a primary source of therapeutic agents in the pharmaceutical industry. The structural complexity exhibited by these nitrogen-based moieties necessitates the development of innovative strategies that demand mastery beyond routine and traditional organic chemistry that most synthetic chemists typically cultivate. The second chapter of this thesis describes the use of novel delayed radical precursors in Mn (OAc)3·2H2O mediated oxidative radical cyclization-fragmentation-dimerization processes from Banilides. The first part presents a sequential oxidative radical cyclization-decarboxylative-dimerization process from β-oxoacids, forming three bonds in a one-pot manner. This approach was successful with a diverse range of 3,3′-bisoxindoles substrates obtained in up to 96% yield. The second part of chapter two details a complementary and closely related sequential one-pot oxidative radical cyclization-deformation-dimerization process from β-oxoanilides, this motion was also applicable to a wide array of 3,3′-bisoxindoles with up to 98% yield. There are no clear-cut distinctions between the decarboxylative and deformylation approaches as they appear to be highly complementary to each other. The chapter concludes with a further demonstration of the utility of this methodology, in the formal synthesis of the calycanthaceae alkaloid, (±)-folicanthine via to the best of our knowledge the shortest linear route. The third chapter of this thesis describes a general extension of the second chapter, which involves an atom-efficient silver-catalysed double decarboxylative strategy for the one-step synthesis of quinolin2-ones. This is achieved via an oxidative radical addition–cyclisation–elimination cascade sequence of oxamic acids to acrylic acids, mediated either thermally or photochemically. The reaction proved to be successful with a wide range of 32 quinolin-2-ones synthesized in of up to 84% yield. The method features an elegant double-disconnection approach, which constructed the quinolin-2-one core through the formal and direct addition of a C(sp2)–H/C(sp2)–H olefin moiety to a phenyl formamide precursor. The theme of the thesis is centred around the synthesis of nitrogen-containing heteroaromatics using facile and efficient protocols that offer catalyst, atom and energy efficiency, while also providing substantial economic advantages. Additionally, the thesis presents systematic and in-depth mechanistic studies on both developed protocols to support and offer compelling evidence for the proposed mechanistic cycles. These studies provide insights into the reaction pathways and help establish a more comprehensive understanding of the radical synthetic pathways.

Temporal variability in nutrient supply has not generally been considered to be a factor controlling macroalgal community structure. Frequent sampling in environments with multiple nitrogen (N) inputs reveals that N supply varies greatly on scales of hours, days and weeks. This thesis describes studies of the adaptations of macroalgae to variability in N supply and the effects of this variability on the species composition of a macroalgal community. A study was made of the efficacy of using N flux (water flow rate X N concentration) to predict the growth rate of Gracilaria tikvahiae (Rhodophyta). The relationship between growth rate and flow rate was affected by concentration and the relationship between growth rate and N concentration was affected by flow rate such that growth was a linear function of N flux. Thus, N flux proved to be a better predictor of growth rate than water flow rate or N concentration taken alone. Increased N flux during a period of high N concentration increased both the maximum photosynthetic rate and photosynthetic rates at low irradiances of G. tikvahiae and Enteromorpha clathrata. Storage of N taken up during N pulses (relatively short episodes of high N availability) as photosynthetic pigment protein complexes would thus allow macroalgae to fix carbon rapidly to supply carbohydrates necessary for growth during N-limitation and for rapid N uptake during the next N pulse. The effects of nutritional history on NH⁺₄ uptake by Ulva lactuca, Gracilaria tikvahiae and Enteromorpha spp. were investigated. Algae grown at low N fluxes or in N-free medium took up NH⁺₄ much more rapidly than algae grown at high N fluxes. Enteromorpha spp. took up NH⁺₄ more rapidly than the other species. Rapid uptake by algae immediately after collection from the field, after growth at low N fluxes or after growth in N-free medium suggests that N-limited or starved algae in the field can take up pulses of N rapidly (in excess of immediate requirements). G. tikvahiae, Enteromorpha spp., and filva lactuca grew in N-free medium at rates similar to those observed at the high and low N fluxes for 14, 10 and 9 days (respectively), indicating that N taken up during periods of high N availability can support growth in the absence of N. Experimental manipulation of the frequency with which N pulses occurred in the field showed that the frequency with which N pulses occur in nature may be important in regulating the species composition and productivity of macroalgal communities.

Improving nitrogen (N) use efficiency is crucial for maximizing growth and yield in rice production. Tools to determine precise midseason N rates as well as knowledge of the effects of starter fertilizer N applications on rice growth and yield are lacking. Field experiments were conducted in 2007 and 2008 at the Delta Research and Extension Center to evaluate canopy reflectance as a means for determining yield and N nutrition at midseason and to assess agronomic effects and N recovery efficiency of starter fertilizer N. Measurable in-season parameters were significantly related to grain yield. Grain yield and measured parameters were related to canopy reflectance. The results of this study support the continued research of canopy reflectance for predicting N nutrition indicators and yield. Minimal growth responses were observed when starter N was applied to seedling rice. Nitrogen recovery increased significantly throughout the growing season; however, less than 20% recovery was obtained.

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