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1. Catalytic β-Functionalization of Carbonyl Compounds Enabled by α,β-Desaturation

   https://doi.org/10.1021/acscatal.0c01519  

   Wang, Chengpeng; Dong, Guangbin (June 2020, ACS Catalysis)

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2. Amine-Promoted β-Elimination of a β-Aryloxy Aldehyde for Fluorogenic Chemodosimeters

   https://doi.org/10.1021/Jo200947e  

   Leslie, Amanda K.; Li, Dandan; Koide, Kazunori (August 2011, The Journal of Organic Chemistry)

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3. Time-resolved β-lactam cleavage by L1 metallo-β-lactamase

   https://doi.org/10.1038/s41467-022-35029-3  

   Wilamowski, M.; Sherrell, D. A.; Kim, Y.; Lavens, A.; Henning, R. W.; Lazarski, K.; Shigemoto, A.; Endres, M.; Maltseva, N.; Babnigg, G.; et al (December 2022, Nature Communications)

   Abstract Serial x-ray crystallography can uncover binding events, and subsequent chemical conversions occurring during enzymatic reaction. Here, we reveal the structure, binding and cleavage of moxalactam antibiotic bound to L1 metallo-β-lactamase (MBL) from Stenotrophomonas maltophilia . Using time-resolved serial synchrotron crystallography, we show the time course of β-lactam hydrolysis and determine ten snapshots (20, 40, 60, 80, 100, 150, 300, 500, 2000 and 4000 ms) at 2.20 Å resolution. The reaction is initiated by laser pulse releasing Zn 2+ ions from a UV-labile photocage. Two metal ions bind to the active site, followed by binding of moxalactam and the intact β-lactam ring is observed for 100 ms after photolysis. Cleavage of β-lactam is detected at 150 ms and the ligand is significantly displaced. The reaction product adjusts its conformation reaching steady state at 2000 ms corresponding to the relaxed state of the enzyme. Only small changes are observed in the positions of Zn 2+ ions and the active site residues. Mechanistic details captured here can be generalized to other MBLs. 

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4. Confinement directed Photoreactivity of β-Enaminones

   https://doi.org/10.1016/j.jphotochem.2023.115175  

   Khadka, Dipendra; Kannadi Valloli, Lakshmy; Ramamurthy, V.; Sivaguru, J. (January 2024, Journal of Photochemistry and Photobiology A: Chemistry)
5. β-Trioxopyrrocorphins: pyrrocorphins of graded aromaticity

   https://doi.org/10.1039/D1SC03403K  

   Chaudhri, Nivedita; Guberman-Pfeffer, Matthew J.; Li, Ruoshi; Zeller, Matthias; Brückner, Christian (September 2021, Chemical Science)

   Octaethyltrioxopyrrocorphins unexpectedly show macrocycle-aromatic properties, even though they contain the macrocyclic π-system of the non-aromatic pyrrocorphins (hexahydroporphyrins). Two of the four possible triketone regioisomers were first reported in 1969 by one-pot oxidation of octaethylporphyrin but remained essentially unexplored since. We detail here the targeted preparation of the remaining two triketone isomers and the optical and NMR spectroscopic properties of all isomers. All four regioisomers possess unique electronic properties, including broadly varying degrees of diatropicity that were experimentally determined using 1 H NMR spectroscopy and computationally verified. Structural patterns modulating the aromaticity were recognized. These differences highlight the regioisomerically differentiated influences of the three β-oxo-functionalities. We also present the solid state structure of the two most common isomers (in their free base form or as zinc complexes), allowing further conclusions to be made about the resonance structures present in these triketones. Remarkably, also, the halochromic properties of the triketones differ sharply from those of regular (hydro)porphyrins, providing further support for the proposed 16-membered, 18 π-electron aromatic ring-current. The work conceptually expands the understanding of tris-modified hydroporphyrinoid analogues and the factors that enable and control porphyrinoid aromaticity. 

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