Search for: All records

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field. 

Abstract Biocatalytic processes are highly selective and specific. However, their utility is limited by the comparatively narrow scope of enzyme‐catalysed transformations. To expand product scope, we are developing biocompatible processes that combine biocatalytic reactions with chemo‐catalysis in single‐flask processes. Here, we show that a chemocatalysed Pictet‐Spengler annulation can be interfaced with biocatalysed alcohol oxidation. This two‐step, one‐pot cascade reaction converts tyramine and aliphatic alcohols to tetrahydroisoquinoline alkaloids in aqueous buffer at mild pH. Tryptamine derivatives are also efficiently converted to tryptolines. Optimization of stoichiometry, pH, reaction time, and whole‐cell catalyst deliver the tetrahydroisouinolines and tryptolines in >90 % and >40 % isolated yield, respectively, with excellent regioselectivity. 

Dinitroalkanes are powerful synthetic building blocks because of the versatility of the 1,3-dinitro motif. Here, we show that dinitroalkanes can be synthesized from aliphatic aldehydes in a three-step cascade reaction catalysed by phosphate buffer and the amino acid lysine. We further show that this methodology can be expanded to limited alcohol substrates (1-butanol and 1-pentanol) with the inclusion of a biocatalysed alcohol oxidation. Simultaneous addition of all reagents gives a maximal yield of 52% of 3-(nitromethyl)hexane, derived from 1-butanol and nitromethane, whereas staggering the introduction of the amino acid catalyst and nitromethane substrate boosts the yield to 71% of 3-(nitromethyl)hexane with near-quantitative consumption of the n-butyraldehyde intermediate. Taken together, this work presents a mild synthetic method that couples multi-step catalytic cascades generate 1,3-dinitroalkanes.