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Catalytic Asymmetric Michael Addition of 1,3-Dicarbonyls to Nitroalkenes
Published in Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera, Catalytic Asymmetric Reactions of Conjugated Nitroalkenes, 2020
Irishi N. N. Namboothiri, Meeta Bhati, Madhu Ganesh, Basavaprabhu Hosamani, Thekke V. Baiju, Shimi Manchery, Kalisankar Bera
The Wang group reported binaphthyl-derived bifunctional amine-thiourea C3 catalyzed Michael addition of 1,3-diketone 2 to nitroalkenes 1a.3 As low as 1 mol% of catalyst C3 was sufficient to promote the reaction and provided the Michael adducts 3 in high yields and enantioselectivities (Scheme 1.2). The Michael adducts 3 were further utilized for the synthesis of substituted-α-amino acids. The Bolm group synthesized ephedrine- and pseudoephedrine-derived bifunctional tertiary amine-thiourea catalysts and investigated their catalytic properties for the Michael addition of 1,3-diketone 2 to nitroalkenes 1a (Scheme 1.2).4 Among those catalysts, C4 provided the products 3 in excellent yields and enantioselectivities up to 94% ee. Song and co-workers described an asymmetric Michael addition of acetylacetone 2 to nitroalkenes 1a by employing chiral bifunctional L-thiazoline-thiourea derivative C5 (Scheme 1.2).5 In the proposed mechanism, nitroalkene 1a gets activated by the thiourea moiety of catalyst C5 through H-bonding interactions, whereas the tertiary N-atom of catalyst C5 deprotonates the acidic proton of 1,3-diketone 2 forming a ternary complex. In addition, the synergistic steric effects of the chiral motif of the catalyst C5 increased the stereocontrol of this reaction, offering products 3 exclusively with (S)-configuration.
UVC- and UVC/H2O2-Driven nonribosomal peptide antibiotics degradation: application to zinc bacitracin as a complex emerging contaminant
Published in Journal of Environmental Science and Health, Part A, 2020
Patrícia Metolina, Felipe Rebello Lourenço, Antonio Carlos Silva Costa Teixeira
In fact, the biosynthesis of bacitracin by certain strains of Bacillus licheniformis and Bacillus subtilis results in a mixture of peptide congeners with identical structure, except for specific amino acids situated in defined positions (Figure 1). More than 50 components have been therefore distinguished in bacitracin mixtures.[3] The therapeutic importance is associated with bacitracin A, B1, B2, and B3, which represent more than 96% of the antimicrobial activity of commercial bacitracin products,[4] with bacitracin A being the major congener and exhibiting the highest antimicrobial activity. Conversely, bacitracin F is the oxidation product of bacitracin A and is microbiologically inactive, besides being nephrotoxic.[2,4] The difference between these two congeners is the presence of the ketothiazole moiety in bacitracin F instead of an amino-thiazoline (Figure 1). The thiazoline ring was pointed out as the main responsible for the antimicrobial activity of the drug.[5] Further conversions between the congeners of the bacitracin mixture include the oxidation of the microbiologically active components Bc B1, B2, and B3 into inactive Bc F, H1, H2 and H3 (Figure 1).[4,6]