Trans Addition of B-X Reagents Across Polarized Triple Bonds and Development of Sphingosine-1-Phosphate Transport Inhibitors

• Main Author: Fritzemeier, Russell Glenn
• Other Authors: Chemistry
• Format: Others
• Published: Virginia Tech 2021
• Subjects: Boron; Hydroboration; Oxaborole; Sphingosine-1-phosphate
• Online Access: http://hdl.handle.net/10919/105043

Organoboron compounds are ubiquitous in organic chemistry. Fundamental transformations utilizing organoboron compounds are a necessary addition to any organic chemist's synthetic toolbox. In addition to their extensive use as synthetic intermediates, organoboron compounds are being increasingly studied for their material and medicinal properties. Excitingly, significant advances have been made over the years towards the synthesis of a wide variety of organoboron substrates. In the case of vinylboronic acids, synthesis primarily occurs through cis addition of boron reagents across triple bonds. However, methods affording trans addition products are scarce. Furthermore, many current methods rely on the use of expensive and toxic transition-metal catalysts. Herein, we describe the development of trans addition of boron reagents across polarized triple bonds to afford novel vinylboronic acids. Emphasis is placed on the transition metal-free nature of the reactions as well as the regio- and stereoselectivity observed in the products. In addition, the synthetic utility of the resulting trans addition products is demonstrated in the synthesis of biologically relevant molecules. We first describe the Brønsted base-mediated trans silaboration of propiolamides in which two functional groups with orthogonal reactivity are simultaneously installed. We then go on to describe an organocatalyzed trans hydroboration of propiolate esters as well as a complementary Brønsted base-mediated trans hydroboration reaction of propiolamides. To conclude this portion, we demonstrate how the products from the previous methods can be used to synthesize difluoroborylacrylamides which possess unique and versatile reactivity. Herein we disclose the first small-molecule inhibitors of the sphingosine-1-phosphate (S1P) transporter spinster homolog 2 (SPNS2). While little is known in regard to the structure and function of SPNS2, previous studies have demonstrated the vital role SPNS2 plays in S1P mediated processes and have identified SPNS2 as a potential clinical target. For example, SPNS2 is critical to S1P-mediated lymphocyte egress from primary lymphoid tissues. Thus, small molecule inhibition of SPNS2 represents a novel therapeutic strategy for the treatment of autoimmune disorders such as multiple sclerosis. In this study, we report the discovery of small molecule inhibitors that display low micromolar activity using a novel yeast-based SPNS2 assay. Inhibitor structure-activity-relationship studies led to the discovery of the imidazole-based amine inhibitor 7.54. Furthermore, administration of 7.54 to mice recapitulates the lymphopenic phenotype observed in previous SPNS2 knockout studies. === Doctor of Philosophy === Boron-containing compounds are important in organic chemistry and are involved in the synthesis of a variety of materials and medicines used in everyday life. As such, the ability to efficiently and sustainably prepare boron-containing compounds has far reaching consequences. Access to an important class of boron-containing compounds known as vinylboronic acids has previously been established; however, product selectivity is often limited to what is referred to as cis addition products. Furthermore, access to the corresponding trans addition products is often limited to processes involving expensive transition metal catalysts that produce environmentally toxic waste. Herein, novel transition metal-free trans addition processes are described for preparing vinylboronic acids. In addition, the application of the resulting products is demonstrated through the synthesis of biologically relevant compounds. Sphingosine-1-phosphate (S1P) is an important signaling lipid that is involved in a variety of physiological processes. Improper balance in the amount of S1P in the body is associated with a variety of disease states such as autoimmunity and cancer. Two drugs that inhibit S1P-mediated processes have been approved by the FDA, fingolimod (Gilenya®) and siponimod (Mayzent®). However, there are drawbacks to targeting the S1P receptor directly, including dose-limiting side effects that are associated with these drugs. Consequently, recent efforts have focused on developing new ways to control the effects of S1P. Herein, we describe the discovery and development of the first reported inhibitors of the S1P transporter, spinster homolog 2 (SPNS2). A library of compounds was synthesized and tested for SPNS2 inhibition. The resulting structure-activity-relationship studies led to the discovery of the imidazole-based propanamine derivative 7.54. Furthermore, we demonstrate the potential of SPNS2 inhibition to control the effects of S1P in mice. These studies provide a foundation for future SPNS2-based drug discovery that will hopefully lead to the development of improved therapies for the treatment of autoimmune disease and cancer.