UC Santa Cruz

AbstractCO-binding Bis-Pocket Iron Porphyrins: Towards the Development of a CO Poisoning Antidote By Daniel G. Droege A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry

Carbon monoxide (CO) poisoning results in over 50,000 emergency department visits every year in the US and is one of the most common forms of poisoning worldwide. Oxygen is still the accepted treatment for CO poisoning but, depending on the amount of CO inhaled and the time it takes to receive treatment, O2 treatment may not be enough to prevent death or long-term damage. Despite the great need, there is no established antidote for CO poisoning. The toxicity of CO is derived from its interaction with diverse biological targets, and development of a treatment capable of addressing the myriad of symptoms that arise would be difficult. Instead, if the concentration of CO in the body can be lowered fast enough, the negative short-term and long-term effects of CO poisoning can be avoided. Presented here is the initial phase of the investigation of a novel meso-substituted porphyrin scaffold to discover an antidote for CO poisoning. The Lindsey method was used to generate an aryl meso-substituted porphyrin core. Arylaldehydes featuring a 2,6-substitution pattern permit modulation of the bulk of the CO binding pocket either early in the synthesis or at a later stage via Pd-catalyzed Caryl-Caryl coupling. Optimization of the coupling reaction was undertaken to facilitate derivatization. Installation of four sulfonate groups imparted water solubility at physiological pH and also inhibited membrane permeability. The modular nature of this scaffold allowed for the derivatization of multiple complexes. The solubility, CO binding ability, and oxidative stability of the complexes were investigated using UV-vis spectroscopy, IR spectroscopy, and X-ray crystallography. A preliminary demonstration of efficacy was performed using purified red blood cells (RBCs). A suspension of the cells was treated with sodium dithionite and then sparged with CO, generating carboxyhemoglobin (COHb). The COHb-containing RBCs were then washed with PBS and centrifuged to remove any excess dissolved CO. The COHb-containing RBCs were dosed with one of our iron(II) porphyrin compounds. UV-vis spectroscopy of the suspension confirmed the presence of the CO-bound form of the iron(II) porphyrin and the loss of CO from hemoglobin. Using the knowledge gained from the first set of derivatives of this scaffold, new complexes will be targeted. This work will prove useful in the rapid advancement of novel porphyrin derivatives to uncover a small molecule CO poisoning antidote.