Versatile Synthesis of Chlorophylls and Bacteriochlorophylls for Fundamental Studies in Photosynthesis

With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Jonathan S. Lindsey of North Carolina State University will study how to synthesize the chief pigments that carry out photosynthesis. Those pigments are the well-known chlorophylls that give plants their characteristic green color, and the lesser-known bacteriochlorophylls of selected bacteria. The studies will develop methods for creating Nature’s molecules for photosynthesis. The reason for carrying out this work is that the ability to create these molecules, and variants thereof, will allow examination of deep questions concerning their basic chemistry and to probe aspects of the conversion of light into chemical energy. The broader impacts of the proposed activity will include the professional development of high school science teachers to improve teaching of photosynthesis (via a chlorophyll-based experiment) in schools and to inspire high school students to STEM, and the expanded deployment to middle schools of a previously developed chlorophyll experiment. The lack of synthetic methods for preparing (bacterio)chlorophylls and analogues constitutes an intellectual and technical deficit in the photosynthetic sciences. The Lindsey lab aims to fill this gap by developing robust methods for synthesis of such valuable macrocycles. A casual observer may consider the synthesis of chlorophyll to be a finished story – and this couldn't be more wrong. In fact, no small-molecule synthetic starting material has ever been converted to a chlorophyll by chemical synthesis, and there are no reports of any attempts to synthesize bacteriochlorophylls. The proposed work will build on the first example of the total synthesis of a photosynthetic tetrapyrrole, wherein the requisite stereochemical features are installed with simple early precursors via established asymmetric methods. Objectives to be met are to further streamline a recently developed synthetic route; explore a step-down dehydrogenation approach that provides access from bacteriochlorins to chlorins and porphyrins; examine late-stage derivatization approaches to install critical peripheral functional groups; and in so doing demonstrate access to a handful of representative members of photosynthetic tetrapyrroles. Six collaborations using synthetic (bacterio)chlorophylls will be undertaken with labs in the US, Germany, and Japan. Every effort will be made to use practical methods that are broadly accessible. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.