Faculty Bibliography

An approach toward (-)-enterocin, an antibiotic isolated from Streptomyces hygroscopicus, is described. Its compact, heavily oxidized protoadamantane core represents a daunting challenge for an efficient synthesis. Convergent assembly of its 2-oxabicyclo[3.3.1]nonane core with a cuprate-mediated Barbier reaction is disclosed. Its functionalization to a suitable substrate for a biomimetic aldol to close the final ring of the natural product is evaluated.

Optogenetics and photopharmacology are powerful approaches to investigating biochemical systems. While the former is based on genetically encoded photoreceptors that utilize abundant chromophores, the latter relies on synthetic photoswitches that are either freely diffusible or covalently attached to specific bioconjugation sites, which are often native or engineered cysteines. The identification of suitable cysteine sites and appropriate linkers for attachment is generally a lengthy and cumbersome process. Herein, we describe an in silico screening approach that is designed to propose a small number of optimal combinations. By applying this computational approach to human carbonic anhydrase and a set of three photochromic tethered ligands, the number of potential site-ligand combinations was narrowed from over 750 down to 6, which we then evaluated experimentally. Two of these six combinations resulted in light-responsive human Carbonic Anhydrases (LihCAs), which were characterized with enzymatic activity assays, mass spectrometry, and X-ray crystallography. Our study also provides insights into the reactivity of cysteines toward maleimides and the hydrolytic stability of the adducts obtained.

A concise route to the azatricyclo[6.2.1.0^4,11]undecane core of (-)-dendrobine and (-)-mubironine C is described wherein an unstabilized azomethine ylide cycloaddition provides the complete carbon framework of the natural products. The cyclization precursor is made in short order from ( R)-carvone through an unconventional high-pressure Ireland-Claisen reaction. Attempts to install a final hydroxyl group through an intramolecular lactonization strategy and the observation of an unexpected and highly complex enal-ene product are also reported.

Divergolide I (1) is a naphthoquinone ansamycin that exhibits broad antibacterial activity. Its tetracyclic ring system is believed to be biosynthetically assembled via ring contraction of a macrocyclic precursor (proto-divergolide) that is both a macrolactone and a macrolactam. We here report a convergent and enantioselective synthesis that delivers the target molecule in less than 20 linear steps. Our work establishes the absolute configuration of divergolide I, confirms its relative configuration, and demonstrates that the biomimetic cyclization of a proto-divergolide can be surprisingly selective.

Patterns formed by reaction and diffusion are the foundation for many phenomena in biology. However, the experimental study of reaction-diffusion (R-D) systems has so far been dominated by chemical oscillators, for which many tools are available. In this work, we developed a photoswitch for the Min system of Escherichia coli, a versatile biological in vitro R-D system consisting of the antagonistic proteins MinD and MinE. A MinE-derived peptide of 19 amino acids was covalently modified with a photoisomerizable crosslinker based on azobenzene to externally control peptide-mediated depletion of MinD from the membrane. In addition to providing an on-off switch for pattern formation, we achieve frequency-locked resonance with a precise 2D spatial memory, thus allowing new insights into Min protein action on the membrane. Taken together, we provide a tool to study phenomena in pattern formation using biological agents.

F1 Fo -ATP synthase is one of the best studied macromolecular machines in nature. It can be inhibited by a range of small molecules, which include the polyphenols, resveratrol and piceatannol. Here, we introduce Photoswitchable Inhibitors of ATP Synthase, termed PIAS, which were synthetically derived from these polyphenols. They can be used to reversibly control the enzymatic activity of purified yeast Yarrowia lipolyticaATP synthase by light. Our experiments indicate that the PIAS bind to the same site in the ATP synthase F1 complex as the polyphenols in their trans form, but they do not bind in their cis form. The PIAS could be useful tools for the optical precision control of ATP synthase in a variety of biochemical and biotechnological applications.

Family A G protein-coupled receptors (GPCRs) control diverse biological processes and are of great clinical relevance. Their archetype rhodopsin becomes naturally light sensitive by binding covalently to the photoswitchable tethered ligand (PTL) retinal. Other GPCRs, however, neither bind covalently to ligands nor are light sensitive. We sought to impart the logic of rhodopsin to light-insensitive Family A GPCRs in order to enable their remote control in a receptor-specific, cell-type-specific, and spatiotemporally precise manner. Dopamine receptors (DARs) are of particular interest for their roles in motor coordination, appetitive, and aversive behavior, as well as neuropsychiatric disorders such as Parkinson's disease, schizophrenia, mood disorders, and addiction. Using an azobenzene derivative of the well-known DAR ligand 2-(N-phenethyl-N-propyl)amino-5-hydroxytetralin (PPHT), we were able to rapidly, reversibly, and selectively block dopamine D1 and D2 receptors (D1R and D2R) when the PTL was conjugated to an engineered cysteine near the dopamine binding site. Depending on the site of tethering, the ligand behaved as either a photoswitchable tethered neutral antagonist or inverse agonist. Our results indicate that DARs can be chemically engineered for selective remote control by light and provide a template for precision control of Family A GPCRs.

The cannabinoid receptor 1 (CB1) is an inhibitory G protein-coupled receptor abundantly expressed in the central nervous system. It has rich pharmacology and largely accounts for the recreational use of cannabis. We describe efficient asymmetric syntheses of four photoswitchable Δ9-tetrahydrocannabinol derivatives (azo-THCs) from a central building block 3-Br-THC. Using electrophysiology and a FRET-based cAMP assay, two compounds are identified as potent CB1 agonists that change their effect upon illumination. As such, azo-THCs enable CB1-mediated optical control of inwardly rectifying potassium channels, as well as adenylyl cyclase.

Fatty acids activate GPR40 and K⁺channels to modulate β-cell function. Herein, we describe the design and synthesis ofFAAzo-10, a light-controllable GPR40 agonist based on Gw-9508.FAAzo-10is a potent GPR40 agonist in thetrans-configuration and can be inactivated on isomerization tociswith UV-A light. Irradiation with blue light reverses this effect, allowingFAAzo-10activity to be cycled ON and OFF with a high degree of spatiotemporal precision. In dissociated primary mouse β-cells,FAAzo-10also inactivates voltage-activated and ATP-sensitive K⁺channels, and allows us to control glucose-stimulated Ca²⁺oscillations in whole islets with light. As such,FAAzo-10is a useful tool to study the complex effects, with high specificity, which FA-derivatives such as Gw-9508 exert at multiple targets in mouse β-cells.

Crocagin A (1) combines an attractive molecular structure with an unusual biosynthesis and bioactivity. An efficient synthesis of crocagin A is presented that hinges on an early formation of the heterotricyclic core, an electrophilic amination, and the stereoselective hydrogenation of a tetrasubstituted double bond. This synthesis confirms the absolute configuration of crocagin A and provides access to the natural product and derivatives thereof for further biological testing.