Jake R. Zimmerman

Tin-free radical reactions under minimal solvent conditions for the synthesis of substituted chromones and coumarins

An alkyltin-free radical methodology carried out under minimal solvent conditions is presented. This free radical addition process allows for the preparation of a variety of substrates, including substituted chromones and coumarins. This method is high yielding, conducted at ambient temperature and, in nearly all instances, classical purification techniques such as chromatography are not needed.

The Synthesis of a New Class of Highly Fluorescent Chromones via an Inverse-Demand Hetero-Diels-Alder Reaction.

A new class of fluorophores has been developed utilizing an inverse-demand hetero-Diels-Alder reaction with silyl enol ethers and substituted 3-formylchromones. These compounds yield blue to green fluorescence with quantum yields up to 73%. They also exhibit good potential for use as fluorescent probes in biological systems, as they are cell membrane permeable with low cytotoxicity.

Diastereoselective tin-free tandem radical additions to 3-formylchromones.

A tin-free tandem radical addition methodology onto 3-formylchromones is presented. This radical process yields functionalized chromone structures via two carbon-carbon bond-forming steps. These products contain up to three contiguous stereocenters with good to excellent drs and yields.

Coumarin-based Fluorescent Probes for Selectively Targeting and Imaging the Endoplasmic Reticulum in Mammalian Cells

Developing improved fluorescent probes for imaging the endoplasmic reticulum (ER) is necessary for structure‐activity studies of this dynamic organelle. Two coumarin‐based compounds with sulfonamide side groups were synthesized and characterized as ER‐targeting probes. Their selectivity to target the ER in HeLa and GM07373 mammalian cells was shown with co‐localization experiments using commercially available probes that localize in the ER, mitochondria, or lysozymes. The hydrophobicity of the coumarin‐based probes was comparable to known probes that partition into the ER membrane. Their cytotoxicity in mammalian cells was low with IC50 values that range from 205 to 252 μm. The fluorescent quantum yields of the coumarin‐based probes when excited with 400 nm light were 0.60, and they have a much narrower emission spectrum (from 435 to 525 nm in methanol) than that of the only commercially available ER probe that is exited with 400 nm light (ER‐Tracker™ Blue‐White DPX). Thus, the coumarin‐based probes are more useful for multicolor imaging with yellow and red emitting fluorophores. In addition to the above benefits, ER labeling was achieved with the coumarin‐based probes in both live cells and fixed cells, revealing their versatility for a wide range of cellular imaging applications.