A platform for the rapid synthesis of molecular glues (Rapid-Glue) under miniaturized conditions for direct biological screening

Molecular glues, functioning via inducing degradation of the target protein while having similar molecular weight as traditional small molecule drugs, are emerging as a promising modality for the development of therapeutic agents. However, the development of molecular glues is limited by the lack of general principles and systematic methods. Not surprisingly, most molecular glues have been identified serendipitously or through phenotypic screening of large libraries. However, the preparation of large and diverse molecular glue libraries is not an easy task and requires extensive resources. We previously developed platforms for rapid synthesis of proteolysis targeting chimeras (PROTACs) that can be used directly for biological screening with minimal resources. Herein, we report a platform of rapid synthesis of molecular glues (Rapid-Glue) via a micromolar scale coupling reaction between hydrazide motif on the E3 ligase ligands and commercially available aldehydes with diverse structures. A pilot library of 1520 compounds is generated under miniaturized conditions in a high throughput manner without any further manipulation including purification after the synthesis. Through this platform, we identified two highly selective GSPT1 molecular glues through direct screening in cell-based assays. Three additional analogues were prepared from readily available starting materials by replacing the hydrolytic labile acylhydrazone linker with a more stable amide linker based on the two hits. All three analogues showed significant GSPT1 degradation activity and two of them possess comparable activity to the corresponding hit. The feasibility of our strategy is thus verified. Further studies by increasing the diversity and size of the library followed by appropriate assays will likely yield distinct molecular glues targeting novel neo-substrates.