Cell-permeable photoswitchable small molecules, termed optojasps, are introduced to optically control the dynamics of the actin cytoskeleton and cellular functions that depend on it. These light-dependent effectors were designed from the F-actinstabilizing marine depsipeptide jasplakinolide by functionalizing them with azobenzene photoswitches. As demonstrated, optojasps can be employed to control cell viability, cell motility, and cytoskeletal signaling with the high spatial and temporal resolution that light affords. Optojasps can be expected to find applications in diverse areas of cell biological research. They may also provide a template for photopharmacology targeting the ubiquitous actin cytoskeleton with precision control in the micrometer range.

Actin is essential for key processes in all eukaryotic cells. Cellpermeable optojasps provide spatiotemporal control of the actin cytoskeleton, confining toxicity and potentially rendering F-actin druggable by photopharmacology. Here, we report cryo electron microscopy (cryo-EM) structures of both isomeric states of one optojasp bound to actin filaments. The high-resolution structures reveal for the first time the pronounced effects of photoswitching a functionalized azobenzene. By characterizing the optojasp binding site and identifying conformational changes within F-actin that depend on the optojasp isomeric state, we refine determinants for the design of functional F-actin photoswitches. Actin is a key player in eukaryotic cell biology and involved in cellular motility, cytokinesis, intra-cellular cargo transport and endocytosis. [1] The 42 kDa globular protein (G-actin) assembles into polar filaments (F-actin) that form complex and dynamic networks. To fulfill its diverse functions, the conformation and dynamics of actin filaments are clocked by ATP hydrolysis and the subsequent release of phosphate. [2, 3] Furthermore, actin polymerization and the assembly of higher order structures is tightly controlled in space and time by a plethora of actin binding proteins (ABPs). [4] While actin may serve as a potential entry for drug design due to its involvement in many cellular processes, it is also

The natural product jasplakinolide is a widely used tool compound to stabilize F-actin and influence actin dynamics. We have previously introduced photoswitchable jasplakinolides (optojasps) that are activated with violet light and deactivated with blue light. Based on insights from cryo-electron microscopy and structure-activity relationship (SAR) studies, we now developed a new generation of functionally superior optojasps that are better suited for biological investigations. These compounds are procured through chemical total synthesis and feature rationally designed red-shifted azobenzene photoswitches. Our new optojasps can be activated with longer wavelengths in the visible range (e.g. 440-477 nm) and rapidly return to their inactive state through thermal relaxation. This has enabled the reversible control of F-actin dynamics, as shown through live-cell imaging and cell migration, as well as cell proliferation assays. Brief sub-cellular activation with blue-green light resulted in highly localized F-actin clusters that gradually dissolved in the dark. Our light-responsive tools can be useful in diverse fields to study actin dynamics with outstanding spatiotemporal precision.

A base promoted cyclization of the protected N-propargylaminopyridines was shown to be an efficient method for the preparation of imidazo[1,2-a]pyridine derivatives. The reactions were carried out with a small excess of base, at room temperature or slightly above producing the heterocyclic products in moderate to good yields. The stereoelectronic properties of substituents on the pyridine ring were shown to influence the cyclization process.

A library of P-rhodamines was prepared via a new robust sequence that creates the core heterocycle by addition of diaryllithium reagents to esters. The first SAR study for P-rhodamines shows that they are NIR-emissive and highly bright fluorophores.