Matthew Sparks and Dr. Heidi Vollmer-Snarr, BYU Chemistry Department
Age-related Macular Degeneration (AMD) is the leading cause for blindness among the world’s elderly population1. As the central region of the retina, known as the macula, is damaged and begins to deteriorate, central vision becomes clouded. This vision loss progresses until the affected person becomes completely and permanently blind. To date, AMD is an incurable disease.
The Dr. Vollmer-Snarr Research Group hypothesizes that certain amino-retinal chemical compounds are involved in the initiation and progression of AMD. One of these compounds, A2E is formed when two all-trans-retinal compounds react with an ethanolamine compound. A2E has become an important research topic among those studying this disease. As blue light irradiates A2E in the presence of oxygen, the compound becomes very cytotoxic. This phototoxic property could be responsible for the death of photoreceptor cells necessary in the visual process. Preliminary data from FAB, MS+, HPLC/UV analysis suggests that all-trans-retinal may react with other amines found in the eye to create A2E-similar compounds. One aspect of our research focuses on the discovery and characterization of these novel compounds.
As preliminary data suggested, the biogenic-amines phosphatidylserine and spermidine probably react with all-trans-retinal to form compounds similar to A2E. It is hypothesized that these compounds are involved in the progression of AMD. As I began this research project, I intended to accomplish the separation and characterization of these compounds by the end of February. As our research developed, this deadline was found to be impractical as complications arose and more intermediate steps were introduced.
The reactions to form these compounds are not incredibly difficult to perform. In a biomimetic synthesis, one usually follows a “one-pot reaction” protocol. The reagents are all directly added to a vial and allowed to react over a specified amount of time. The first major complication in my research was the separation of these compounds from the many different by-products that formed simultaneously during the reaction.
The preferred manner of separation and purification is to use column chromatography. The reaction mixture is passed through a column packed with silica gel using different solvents and pressure. Different compounds come off the column at different times and can be separately collected. Unfortunately, the compounds I was working with are incredibly difficult to cleanly separate. They tend to come off the column impure. Due to the impurity, they cannot be accurately characterized. Without characterization, the compounds cannot be identified in the human eye or extracted from the eye’s pigment retinal epithelial (RPE) cells.
This purification problem presented quite an obstacle to my research. At about this time, Dr. Xue began work on a new synthetic pathway to produce an A2E intermediate compound. The end result of this pathway will be an easily separable compound that can be reacted with various amines. Being unable to get a clean characterization of the compounds I was researching, I began helping Dr. Xue with this pathway. I can then use the final compound in my syntheses, which will prove invaluable to my research.
During the Fall 2003 and Winter 2004 Semesters, we tried two separate pathways toward our end-goal compound. I performed many different reactions integral to the completion of the synthesis, including the formation of 2-Hydroxy-4-formylpyridine, 2-Bromo-4-picoline, and 2-Bromo-isonicotinic acid. The first pathway2, based on a paper published in the Journal of American Chemical Society, proved ineffective. On many of the steps, the product yields were too low and could not be substantially improved. After more research, we began a second pathway. I was able to perform six of the intermediate reactions on this pathway during the Winter 2004 and Spring 2004 Semesters.
After spending the Summer 2004 Semester at home in Washington State, I returned in the fall and began working on a third synthetic pathway. The second pathway had also proved itself to be a dead end. Currently, we are working on this third pathway and are on the final steps of its completion. After completion of this pathway, I will begin the synthetic work for the phosphatidyl and spermidine reactions. Using the new A2E-intermediate as a base structure, it should be much easier to create the hypothesized compounds and separate them for characterization. After characterization, I will be able to search for and extract these compounds from human eyes, allowing better understanding of the ocular disease AMD.
- Ambati, J et al., An animal model of age-related macular degeneration in senescent Ccl-2- or Ccr-2-deficient mice, Nature Medicine, 9, 1390-1397, 2003.
- Rex, X.; Sakai, N.; Nakanish, K., Total Synthesis of the Ocular Age Pigment A2-E: A Convergent Pathway, J. Am. Chem. Soc., 119, 3619-3620, 1997.