Date of Degree

2-2018

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor(s)

Charles Michael Drain

Committee Members

Lynn Francesconi

Akira Kawamura

Maria Tamargo

Subject Categories

Organic Chemicals | Secondary Education

Keywords

Porphyrin, Phthaloyanine, Theranostic, Cancer, PDT

Abstract

Porphyrinoids are robust heterocyclic dyes studied extensively for applications in medicine and as photonic materials because of their tunable photophysical properties, diverse means of modifying the periphery, and the ability to chelate most transition metals. Commercial applications include phthalocyanine dyes in optical discs, porphyrins in photodynamic therapy, and as oxygen sensors. Most applications of these dyes require exocyclic moieties to improve solubility, target disease, modulate photophysical properties, or direct self-organization into architectures with desired photonic properties. The synthesis of the porphyrinoid depends on the desired application, but the de novo synthesis often involves several steps, is time consuming, and results in low isolated yields. Thus, applications of core porphyrinoid platforms that can be rapidly and efficiently modified to evaluate new molecular architectures allows researchers to focus on the design concepts rather than the synthetic methods and opens porphyrinoid chemistry to a broader scientific community. This dissertation focuses on two widely available, commercially viable porphyrinoids as platforms: meso-perfluorophenylporphyrin, and perfluorophthalocyanine. The perfluorophenylporphyrin is readily converted to the chlorin, bacteriochlorin, and isobacteriochlorin. Derivatives of all six of these core platforms can be efficiently and controllably made via mild nucleophilic aromatic substitution (NAS) reactions using primary S, N, and O nucleophiles bearing a wide variety of functional groups. The remaining fluoro groups enhance the photo and oxidative stability of the dyes and can serve as spectroscopic signatures to characterize the compounds or in imaging applications using 19F NMR.

Using simple NAS click-type chemistry, we designed a physical organic chemistry experiment for second-year college students. Students performed NAS reactions on 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin (TPPF20) using three different nucleophiles. Substitution occurs preferentially at the 4-position (para) because it is thermodynamically favored, and the 2- and 6- (ortho) positions are kinetically disfavored because of steric interactions with the porphyrin ring. The activation energy depends heavily on the nucleophile. An open-source software (ImageJ from NIH) was used to quantify relative intensities of spots on a TLC plate obtained from different times and varying temperatures. These data were used to generate Arrhenius plots allowing students to determine relative activation energies for three different primary nucleophiles. The experiment was developed by five undergraduates and evaluated by 40 organic chemistry II students and eight students in a physical chemistry laboratory. Students gained a deeper understanding of the relationships between the NAS mechanism, Arrhenius plots, and activation energy. The experiment is published in the Journal of Chemical Education.

Using the same NAS click-type chemistry on perfluorophthalocyanines (Pc), we developed facile synthetic methods for generating Pc derivatives with near IR absorption. The photophysics of these molecules can be fine-tuned via simple click-type substitution chemistry resulting in a decrease in the HOMO-LUMO gap for each substitution. This leads to a red-shifted absorbance that should be ideal for various biomedical and materials applications. A commercially available, cost effective surfactant, isodecyloxypropyl-1,3-diaminopropane (tomamine®), is appended onto zinc 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyanine (ZnF16Pc). This substitution red-shifts the UV-vis absorbance and helps in solubility. Varying the equivalents of tomamine, we were able to isolate mono, di, tri and tetra-substituted products with UV-visible absorbance, lowest energy Q bands, at ca. 748, 765, 786 and 805 nm respectively. An unexpected discovery showed that addition of a 7-membered ring on the outside of ZnF16Pc induces steric interactions that cause the otherwise planar Pc macrocycle to twist and distort. This distortion results in an unexpectedly large shift in the UV-visible spectral peaks. The resulting peak is also much broader because of flexibility in the macrocycle. These compounds are highly soluble in organic and aqueous solvents and showed high photoacoustic and photothermal conversions for photoacoustic imaging and photothermal therapy of cancers.

To increase the targeting efficiency of dyes, the use of glycosylated compounds is actively pursued as a therapeutic strategy for cancer due to the overexpression of various types of sugar receptors and transporters on most cancer cells. Conjugation of saccharides to photosensitizers such as porphyrins provides a promising strategy to improve the selectivity and cell uptake of the photosensitizers, enhancing the overall photosensitizing efficacy. Most porphyrin-carbohydrate conjugates are linked via the carbon-1 position of the carbohydrate because this is the most synthetically accessible approach. However, carbon-1 galactose derivatives diminish binding since the hydroxyl group in the carbon-1 position of the sugar is a hydrogen bond acceptor in the galectin-1 sugar binding site. We therefore synthesized two isomeric porphyrin-galactose conjugates using click chemistry: one linked via the carbon-1 of the galactose, and one linked via carbon-3. Free base and zinc analogues of both conjugates were synthesized. We assessed the uptake and photodynamic therapeutic (PDT) activity of the two conjugates in both monolayer and spheroidal cell cultures of four different cell lines. For both the monolayer and spheroid models we observe that the uptake of both conjugates is proportional to the protein levels of galectin-1, as measured by fluorescence spectroscopy. Compared to the carbon-1 conjugate, the uptake of the carbon-3 conjugate was greater in cell lines containing high expression of galectin-1. After photodynamic activation, MTT and lactate dehydrogenase assays demonstrated that the conjugates induce phototoxicity in both monolayers and spheroids of cancer cells.

Finally, because of the general need for other metal derivatives of the PcF16 platform other than Cu, Ni, and Zn, we embarked on the synthesis of the free base macrocycle based on both literature reports and our experiences with phthalocyanine synthesis. We found that most of the literature methods have serious drawbacks that arise mostly from the unwanted substitution of the F on the macrocycle (via either reactions with the tetrafluorphthalonitrile or of the product). Thus, we have developed a procedure that minimizes the substitution side reactions and shown that the starting materials are reasonably unreactive to substitution reactions.

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