One-Pot Aldol Cascade for the Preparation of Isospiropyrans, Flavylium Salts, and bis-Spiropyrans.

We probed tandem aldol condensations of sixteen o-hydroxyacetophenones, carrying electron-withdrawing and -donating groups at positions 4 and 5, using five molar equivalents of SiCl4 in anhydrous ethanol. Substrates carrying electron-withdrawing groups (EWGs) (0 < ∑σ > 0.63) populated the equilibria with isospiropyrans (12-74% yield), while those carrying electron-donating groups (EDGs) (∑σ < -0.31) gave flavylium salts (50-80%) or thermochromic bis-spiropyrans (73%). The results are of interest for developing novel organic materials possessing switchable photochromic and thermochromic characteristics.

Cell-Specific Chemical Delivery Using a Selective Nitroreductase-Nitroaryl Pair.

The utility of small molecules to probe or perturb biological systems is limited by the lack of cell-specificity. "Masking" the activity of small molecules using a general chemical modification and "unmasking" it only within target cells overcomes this limitation. To this end, we have developed a selective enzyme-substrate pair consisting of engineered variants of E. coli nitroreductase (NTR) and a 2-nitro- N-methylimidazolyl (NM) masking group. To discover and optimize this NTR-NM system, we synthesized a series of fluorogenic substrates containing different nitroaromatic masking groups, confirmed their stability in cells, and identified the best substrate for NTR. We then engineered the enzyme for improved activity in mammalian cells, ultimately yielding an enzyme variant (enhanced NTR, or eNTR) that possesses up to 100-fold increased activity over wild-type NTR. These improved NTR enzymes combined with the optimal NM masking group enable rapid, selective unmasking of dyes, indicators, and drugs to genetically defined populations of cells.

Encouraging Science Communication through Deliberative Pedagogy: A Study of a Gene Editing Deliberation in a Nonmajors Biology Course.

Deliberative pedagogy encourages productive science communication and learning through engagement and discussion of socio-scientific issues (SSI). This article examines a two-day deliberation module on gene editing that took place in an introductory nonmajors biology course, furthering research on integrating deliberative discussion into the biology classroom. The results demonstrate the benefits of a single, episodic deliberation in the classroom, which can positively encourage active discussion and critical awareness of connections between biology and real-world issues, thus contributing to the development of scientific citizenship. Additionally, the findings show that gene editing is an apt SSI topic for the deliberative process because it encourages productive communication practices of scientific citizenship, including discussion, perspective taking, questioning, and consideration of different types of evidence when coming to a decision.

Synthesis of high contrast fluorescein-diethers for rapid bench-top sensing of palladium.

A new series of palladium sensors based on fluorescein bis(allyl ether) compounds has been designed. We utilized reduced fluoresceins as key synthetic intermediates. These probes exhibit negligible background fluorescence and rapid reaction with palladium, allowing a concentration of <100 ppt to be detected in minutes using a handheld UV lamp.

Selective esterase-ester pair for targeting small molecules with cellular specificity.

Small molecules are important tools to measure and modulate intracellular signaling pathways. A longstanding limitation for using chemical compounds in complex tissues has been the inability to target bioactive small molecules to a specific cell class. Here, we describe a generalizable esterase-ester pair capable of targeted delivery of small molecules to living cells and tissue with cellular specificity. We used fluorogenic molecules to rapidly identify a small ester masking motif that is stable to endogenous esterases, but is efficiently removed by an exogenous esterase. This strategy allows facile targeting of dyes and drugs in complex biological environments to label specific cell types, illuminate gap junction connectivity, and pharmacologically perturb distinct subsets of cells. We expect this approach to have general utility for the specific delivery of many small molecules to defined cellular populations.

Advances in the chemistry of small molecule fluorescent probes.

Small molecule fluorophores are essential tools for chemical biology. A benefit of synthetic dyes is the ability to employ chemical approaches to control the properties and direct the position of the fluorophore. Applying modern synthetic organic chemistry strategies enables efficient tailoring of the chemical structure to obtain probes for specific biological experiments. Chemistry can also be used to activate fluorophores; new fluorogenic enzyme substrates and photoactivatable compounds with improved properties have been prepared that facilitate advanced imaging experiments with low background fluorescence. Finally, chemical reactions in live cells can be used to direct the spatial distribution of the fluorophore, allowing labeling of defined cellular regions with synthetic dyes.

Stereochemically general approach to adjacent bis(tetrahydrofuran) cores of annonaceous acetogenins.

A series of six 2,5-disubstituted adjacent bis(tetrahydrofuran) stereoisomers with trans/erythro/cis, trans/threo/trans, or cis/threo/cis relative stereochemistry have been synthesized from known dihydroxycyclooctenes via ring opening/cross metathesis and Pd(0)-mediated asymmetric double cycloetherification. The stereochemistry of four of these isomers has been found in the biologically active annonaceous acetogenin natural products. [reaction: see text].