Project Summary/Abstract This proposal summarizes ongoing projects in our laboratory focused on natural product classes that have promising biological activity but are burdened with limitations that have prevented them from reaching their therapeutic potential. These classes are structurally complex and modification of their is challenging by semisynthetic and biosynthetic methods. We aim to develop fully synthetic routes to these classes from simple building blocks, enabling chemical modification to overcome their limitations. These efforts are informed by binding data (X-ray or cryo-EM) for each class. The primary goals of project outlined herein are to 1) expand structure–function relationships for each of these important classes of molecules, and 2) discover potent analogs that are suitable for hit-to-lead optimization or for use as tools to study biological systems. Additionally, development of the synthetic routes themselves is highly innovative, and is often accompanied by development of methods that are broadly applicable in chemistry. These efforts mirror our work on streptogramin and lankacidin antibiotics, which was a primary focus in our Early Stage Investigator MIRA (R35GM128656), and led to structural reassignments and to a potent hit compound with activity against resistant strains in vivo. Much of the biology for this work will be enabled by collaboration. Five of the projects summarized herein focus on the development of novel antibiotics that target the ribosome and membrane proteins. Due to our ongoing work in this area, we have several collaborations in place to evaluate the antimicrobial activity, in vivo efficacy, and target engagement of new analogs. Beyond antibiotics, we propose to synthesize and derivatize classes that target Hsp90, an anticancer target, and eEF1A, an anticancer and antiviral target. Evaluation of these compounds for inhibitory activity, isoform selectivity, and binding will be enabled by new collaborations, expanding the scope of our research. With chemical innovation paired with strong biological investigation, we anticipate that the work outlined herein will lead to exciting discoveries in chemical synthesis and to the discovery of hit compounds for the treatment of bacterial infections, cancer, and SARS-CoV-2.