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Graduation date: 1994

The synthesis of 2:3-benzo-1,1-dimethyl-1-silacyclo-hex-2-ene has been reported. This compound was prepared by the simultaneous addition of 3-(o-bromophenyl)-propyl bromide and dichlorodimethylsilane to excess magnesium in tetra-hydrofuran. The six-membered ring organosilicon compound was readily brominated by N-bromosuccinimide to give the 4-derivative. Attempts were then made to synthesize the 4-cyano and the 4-carboxylate derivatives from this bromination product. Experimental data are also given for an attempted preparation of 2:3-benzo-4-(2-dimethylaminoethoxy)-1,1-dimethyl-1-silacyclohex-2-ene. / Pharmaceutical Sciences, Faculty of / Graduate

When E- or Z-l-methyl-l-phenyl-2-neopentylsilene was generated by the retro-Diels-Alder vacuum-sealed tube thermolysis of its corresponding anthracene adduct, in the presence of various alkoxysilanes, only one diastereomeric adduct was formed in each case, showing that the reactions are stereospecific. An x-ray crystal structure of the methoxytriphenylsilane adduct of the E-silene confirmed its relative configuration as (R,S) or (S,R). This demonstrated that the addition of alkoxysilanes to silenes is stereospecific and syn. The relative configurations of similar alkoxysilane and alkoxystannane adducts to E- and Z-l-methyl-l-phenyl-2-neopentylsilene were assigned based on a combination of xray structures and *3C NMR data. A strong, nonbonded oxygen-metal interaction is apparent in all of those compounds studied. Treatment of the alkoxystannane adducts with alkyl lithium reagents results in tin-lithium exchange in some cases. The results indicate that the resulting <x-lithio alkoxysilanes are not configurationally stable in either THF or hydrocarbon solvents. The reaction of tert butyl lithium with a-trimethylsilylvinylmethylphenylchlorosilane in hydrocarbon solvents yields E- and Z-l-methyl-l-phenyl-2-neopentyl-2-trimethylsilylsilene. In the absence of any traps these silenes undergo a novel tert butyl lithium catalyzed rearrangement to 2-phenyl-3-trimethylsilyl-5,5-dimethyl-2-silahex-3-ene. These silenes were also trapped as their [4+2] cycloadducts with anthracene. The Z-isomer of the anthracene adduct was separated and its stereochemistry confirmed by an x-ray crystal structure. The anthracene adducts of both E- and Z-l-methyl-1-phenyl-2-neopentyl-2-trimethylsilylsilene undergo a facile, stereospecific decomposition at temperatures as low as 190°C to regenerate their respective silenes, the mildest stereospecific route to a silene yet reported. The E- and Z-silenes react stereospecifically with methanol under vacuum-sealed tube conditions. The stereochemistry of the addition is syn and a common mechanism is proposed for the addition of alcohols and the addition of alkoxysilanes to silenes.

At the end of this thesis, 1H and 13C{ 1H} NMR spectra for all the new compounds and the crystallographic details for the X-ray structure are given as Appendices. / Chapter 1 presents an overview of photodynamic therapy, including its historical development, photophysial and biological mechanisms, and current clinical situation. A brief review of second-generation photosensitizers and the different approaches for targeted photodynamic therapy are also given. / Chapter 2 reports the synthesis and characterization of a silicon(IV) phthalocyanine which is substituted axially with two diamino moieties, together with its di- and tetramethylated derivatives. The non-methylated analogue shows a high photocytotoxicity toward HT29 human colorectal adenocarcinoma and HepG2 human hepatocarcinoma cells with IC50 values down to 0.01 muM. Interestingly, this compound also exhibits a pH-dependent behavior. The fluorescence quantum yield increases by four folds and the singlet oxygen quantum yield increases by three folds in water when the pH decreases from 7.0 to 5.0. The preliminary results suggest that this compound is a promising photosensitizer of which the photodynamic activity can be modulated by changing the pH of the environment. Furthermore, this compound can be used as a near-infrared fluorescence probe for optical imaging of intracellular acidic level. / Chapter 3 reports a novel series of aminophenyl-substituted silicon(IV) phthalocyanines. The aminophenyl moieties in these conjugates can also modulate the photophysical and photosensitizing properties of the phthalocyanine core through changing the pH of the environment. These phthalocyanines exhibit a low photocytotoxicity under physiological conditions (pH 7.4). It is likely that the amino groups, in the free amine form, can quench the singlet excited state of phthalocyanine by a photoinduced electron transfer (PET) mechanism, and reduce the chance of intersystem crossing and the efficiency in generating singlet oxygen. The strong aggregation tendency of these compounds in this pH environment is another major reason for the low photocytotoxicity. When the pH is lower to 6.4-6.9, the amino groups are protonated so that they are no longer electron donors, and the compounds become less aggregated. These changes lead to an increase in photocytotoxicity. The results of this study are reported in this Chapter. / Chapter 4 describes a new series of silicon(IV) phthalocyanines conjugated axially with various polyamine derivatives. Polyamines are naturally occurring compounds which are involved in a number of cell processes including cell proliferation and differentiation. Their biosynthetic activity and polyamine levels in some tumor cells are significantly higher than those in normal cells. Conjugation of polyamine analogues is therefore one of the promising approaches to improve the tumor-targeting property of photosensitizers. This Chapter describes the synthesis, spectroscopic characterization, and photophysical properties of these compounds. Their photodynamic activities toward HT29 and Chinese hamster ovary (CHO) cells have also been studied in detail. Their cellular uptake, subcellular localization, cell death mechanism, and in vivo photocytotoxicity have also been studied. / In Chapter 5, we report a series of silicon(IV) phthalocyanines containing one or two cholesterol unit(s) at the axial position(s), including their synthesis, spectroscopic characterization, photophysical properties, and in vitro photodynamic activities. These cholesterol-containing photosensitizers can form stable conjugates with low-density lipoprotein (LDL), which is the major lipoprotein carrier for cholesterol in human plasma. On the basis that cancer cells generally express significantly more LDL receptors than normal cells, these cholesterol-conjugated phthalocyanines are designed with a view to enhancing their selectivity toward tumor. Unfortunately, conjugation of cholesterol reduces the photodynamic activity of the silicon(IV) phthalocyanines as a result of their higher aggregation tendency. / This thesis reports the synthesis, spectroscopic characterization, and photophysical and biological properties of several series of novel silicon(IV) phthalocyanines which are specially designed as efficient and selective photosensitizers for photodynamic therapy. / Jiang, Xiongjie. / Source: Dissertation Abstracts International, Volume: 72-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references and index. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Thesis (Ph. D.)--Open University. BLDSC no. DXN043595.

Thesis (Ph.D.)--Kent State University, 2008. / Title from PDF t.p. (viewed Dec. 17, 2009). Advisor: Mietek Jaroniec. Keywords: mesoporous, FDU-1, SBA-16, organosilicas, pendant groups, bridging groups, adsorption, isocyanurate, template removal, cage-like structures. Includes bibliographical references (p. 219-238).

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