Phenol is highly reactive toward electrophilic aromatic substitution. By this general approach, many groups can be appended to the ring, via halogenation, acylation, sulfonation, and other processes. Phenol contains the hydroxyl group (–OH), which is a strongly activating ortho/para directing group in aromatic electrophilic substitution (AES). AES gives a mixture of ortho-and para isomers, which must be separated. The strong directing ability of phenol can also result in multiple substitutions on the aromatic ring which could be a major concern in the regiospecific synthesis of phenols. AES and Directed ortho--Metalation (DoM) are the only ways to directly substitute a proton on an aromatic ring and to synthesize regiospecifically substituted phenols. Phenol is a versatile precursor to a large collection of drugs, most notably aspirin, but also many herbicides and pharmaceuticals. AES reactions are useful in regiospecific synthesis as a way of introducing many reactive groups on the benzene ring and also help us to design a suitable method for synthesizing compounds in an efficient manner. Dimethylbenzylamine products are obtained as a result of the reaction of phenols with Eschenmoser’s salt (N,N-Dimethylmethyleneiminium iodide). This approach enables us to prepare regiospecifically ortho substituted phenols by using the AES protocol. We have discovered that Eschenmoser’s salt has the ability in basic medium containing triethylamine (TEA) to remove the proton and bond to the aromatic ring exclusively in ortho position to the –OH substituent. Our research work focused on efforts to render isolated products with minimum impurities, greener and more atom economical by use of limiting reagent in the reactions. For the purpose of evaluation of the obtained compounds and intermediates we use Gas Chromatography (GC), Gas Chromatography coupled with Mass Spectrometry (GC-MS) and Nuclear Magnetic Resonance (NMR). Our future work is to synthesize novel benzoheterocyclic compounds from the ortho-derivatised phenols as well as multi-substituted aromatic compounds. The dimethylamino methyl group can act as a directing group in the ortho-lithiation process; subsequent ortho--metalation and treatment with electrophiles generates 1,2,3- trisubstituted phenolic derivatives. Thus, phenolic precursors can be transformed into numerous derivatives which can be used in the chemical, agricultural and pharmaceutical industries.

Doctor of Philosophy / Department of Chemistry / Duy H. Hua / Our research work is divided into three chapters. In the first chapter, synthesis of substituted phenolic compounds including halogenated di- and trihydroxybenzenes, aminophenols, and substituted di-tert-butylphenols, their redox potential, laccase oxidation, and mosquito anti-larval activities are discussed. The synthesized substituted phenols were found to be the substrates but not the inhibitors of laccase. An inverse correlation between the oxidation potential and the laccase oxidation efficiency of halogenated hydroxybenzenes and aminophenols was established. However, substituted di-tert-butylphenols were found to have anti-larval activities in mosquitoes resulting in the death of the larvae just before reaching pupation. Among the di-tert-butyl phenols studied, water insoluble, 2,4-di-tert-butyl-6-(3-methyl-2-butenyl)phenol (16), 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-2-methylpropanal oxime (14), and 6,8-di-tert-butyl-2,2-dimethyl-3,4-dihydro-2H-chromene (17) caused the mortility of 98%, 93%, and 92% of Anopheles gambiae larvae in the concentration of 182 nM, 3.4 µM, and 3.7 µM, respectively. In particular, compound 16 had similar anti-larval activities as compared to MON-0585, an anti-larval agent reported by Monsanto in the 70’s. In the second chapter, inhibition of protein kinase C (PKC) phosphorylation by substituted quinolines (PQs) is inverstigated. PQ compounds such as N-(3-aminopropyl)-6-methoxy-4-methyl-5-(3-(trifluormethyl)phenoxy)quinolin-8-amine (PQ1), N-(furan-2-ylmethyl)-6-methoxy-4-methyl)-5-(3-(trifluoromethyl)phenoxy)quinolin-8-amine (PQ11), and 6-methoxy-4-methyl-N-(quinolin-4-ylmethyl)-5-(3-(trifluoromethyl)phenoxy)quinolin-8-amine (PQ15) were found to inhibit PKC phosphorylation with IC50 values of 35 nM, 42.3 nM, and 216.3 nM respectively, among which PQ1 and PQ11 were found to be potent PKC inhibitors as comparable to that of staurosporine (IC50 = 33 nM). In chapter three, the tissue distribution of PQ1 and PQ11 in normal C57BL/6J mice and the effect of PQ1 on the normal tissues of mice were investigated. Substituted quinolines, PQ1 and PQ11 were distributed in the tissues in concentrations that were more than 40 folds of their effective dose. PQ1 and PQ11 were also found to penetrate the blood brain barrier and collect in the tissue in significant amounts. The administration of PQ1 and PQ11 had no effect in the normal behavior of the animals indicating no short term adverse effects. PQ1 was found to increase the expression of survivin, an anti-apoptotic factor and decrease the expression of cleaved caspase-3 and caspase-8, pro-apoptotic proteins. These studies suggests that PQ1 might have anti-apoptotic activities in normal cells, in contrast to the role of PQ1 in cancer cells where it has demonstrated to induce apoptosis. The study also indicated that PQ11 was better metabolized from the tissues over time as compared to PQ1.

Doctor of Philosophy / Department of Chemistry / Duy H. Hua / Three research projects were carried out and they are described below. The synthesis of substituted phenolic compounds including halogenated di- and trihydroxybenzenes, aminophenols, and substituted di-tert-butylphenols are described. Redox potentials of the synthesized molecules along with various known laccase substrates were measured, and an inverse relationship between the oxidation potential and the efficiency of oxidation by laccase of halogenated hydroxybenzenes and aminophenols is demonstrated. The synthesized substituted phenols were found to be substrates but not inhibitors of laccase. We discovered a new class of di-tert-butylphenols compounds that inhibits the growth of mosquito larvae at low concentrations. Compound 17, 2,4-di-tert-butyl-6-(3-methyl-2-butenyl) phenol caused greater than 98% mortality of third-instar larvae of Anopheles gambiae in the concentration of 0.18 µM. These compounds do not inhibit laccases. It appears that they affect a new target of the mosquito that is different from those of currently existing pesticides. Two anti-Alzheimer molecules, CP2 and TP70, discovered in our laboratory were studied for their pharmacokinetics and distribution. The distribution of CP2 and TP70 in mouse brain region and various tissues of mice were examined. HPLC analysis revealed that CP2 treatment in primary neurons accumulates in mitochondria fraction. Similarly, the amount of CP2 in the brain tissue from wild type and APP/PS1 mice treated with 25 mg/kg/daily for 2 months also have the highest concentration in the mitochondria fractions in the hippocampus. The results show that CP2 and TP70 can penetrate the blood brain barrier and accumulate in the tissue in significant amounts. Pharmacokinetics and bioavailability of compound TP70 were determined. Area under the curve and bioavailability value F were calculated, and data show that TP70 has a good PK profile and bioavailability. For the preparation of a novel tripeptidyl norovirus 3C-like protease (3CL[superscript]pro) inhibitor, the P3 unnatural amino acid, (S)-3-hydroxyphenylalanine was synthesized. The P3 is designed to increase the polarity with the addition of the alcohol group. After combining the P3 unnatural amino acid with the P1 and P2 to form the novel tripeptidyl compound, a study comparing the relations between the structure and its activity (SAR) will confirm whether prediction is correct in our pursuit for an antiviral therapeutic drug in the form of a protease inhibitor.

The base-catalysed reaction of 4H-pyran-4-one with a range of nucleophiles, namely diethyl malonate, ethyl acetoacetate, nitromethane, acetylacetone and ethyl cyanoacetate, was developed as a reliable, high yielding method for the preparation of para-substituted phenols. The methodology was extended to include the use of the substituted pyranones, maltol, 2,6-dimethyl-4H-pyran-4-one and diethyl chelidonate. Reactions were studied using conventional heating methods and microwave irradiation. Microwave irradiation had definite beneficial effects, with improved yields, reduced reaction times and cleaner reaction profiles. The potential of this methodology was examined for the regioselective placement of ¹³C-atoms into benzene rings using ¹³C-labelled nucleophiles or ¹³C-labelled 4H-pyran-4-ones. [3,5-13C₂]4H-Pyran-4-one and [2,6-13C₂]4H-pyran-4-one were prepared from various ¹³C-labelled versions of triethyl orthoformate and acetone. This methodology was applied to the synthesis of [1,3,5-¹³C₃]gallic acid, via the base-catalysed reaction of [3,5-¹³C₂]4H-pyran-4-one with diethyl [2-¹³C]malonate, followed by subsequent transformations to yield [1,3,5-¹³C₃]gallic acid. The preparation of [2-¹³C]phloroglucinol was carried out via [2-¹³C]resorcinol, with regioselective placement of a single ¹³C-atom into the aromatic ring. This was accomplished from non-aromatic precursors, with the source of the ¹³C-atom being [¹³C]methyl iodide. The key step in this synthesis was the introduction of the third hydroxyl group, which was achieved using a modified iridium-catalysed C-H activation/borylation/oxidation procedure. The scope of an existing C-H activation/borylation reaction was modified and expanded to include a range of protected resorcinol derivatives. A catalyst system was developed which allowed high conversion to the intermediate arylboronic acids, followed by oxidation using aqueous Oxone® to yield the corresponding phenols. Finally, to demonstrate the potential of these new methods for application in the synthesis of isotopically labelled natural products and polyphenols, the syntheses of ¹³C-labelled anthocyanins were studied. A route was developed that could be applied to the synthesis of either cyanidin-3-glucoside or delphinidin-3-glucoside. Only the final coupling/cyclisation step to yield the desired anthocyanin targets remains to be carried out.