The
domino C–H/N–H allylation of aryl imidates was
accomplished by a versatile cobalt(III) catalyst. In contrast to a
tandem rhodium/palladium catalysis approach, an operationally simple
cationic cobalt complex proved effective in the step-economical C–H/N–H
functionalization of imidates to directly provide expedient access
to decorated vinyl isoquinolines by kinetically relevant C–H
activation.
The late-stage modification of structurally complex peptides bears great potential for drug discovery, crop protection, and the pharmaceutical industry, among others. Whereas traditional approaches largely rely on prefunctionalizations, C-H activation catalysis has in recent years emerged as an increasingly powerful tool for post-translational peptide modifications in a step-economic manner. Herein, we summarize recent progress in organometallic C-H activation on peptides until June 2018, including position- and chemoselective palladium-, ruthenium-, and manganese-catalyzed processes.
After a brief introduction emphasizing the synthetic relevance of the allylic C–H activation step, evoking the first pioneering stoichiometric studies that sowed the “seeds” of this subject, and analyzing similarities and differences between a “classical” and a “direct” Pd‐catalyzed allylation process, this review outlines some selected examples of palladium‐catalyzed direct allylic functionalization. This old reaction, ignored for many years, is now living a new and exciting era.
Strongly coordinating nitrogen heterocycles, including pyrimidines, oxazolines, pyrazoles, and pyridines, were fully tolerated in cobalt-catalyzed C-H amidations by imidate assistance. Structurally complex quinazolines are thus accessible in a step-economic manner. Our findings also establish the relative powers of directing groups in cobalt(III)-catalyzed C-H functionalization for the first time.
The decarboxylative C-H/C-O functionalization was accomplished by air- and water-tolerant manganese(I) catalysis. The versatile C-H allylation occurred by facile organometallic C-H metalation on indoles, arenes, amino acids and synthetically meaningful aryl ketimines with ample substrate scope and high levels of chemo-, site- and regio-selectivity.
Fully complementary bimetallic catalysis has been identified as an increasingly powerful tool for molecular transformations, which was largely inspired by early examples of sequential catalytic transformations. Thus, energy-efficient one-pot reactions involving different metal catalysts orchestrated in concert constitute an attractive alternative to multi-step protocols, with major recent progress through the elegant ligand design in heterobimetallic catalysis as well as sustainable photo-induced C-H transformations, among others. This review provides a critical assessment of the state of the art in heterobimetallic catalysis for sustainable organic syntheses (SOS), highlighting key advances and representative examples until summer 2017.
A substantial challenge worldwide is emergent drug resistance in malaria parasites against approved drugs, such as chloroquine (CQ). To address these unsolved CQ resistance issues, only rare examples of artemisinin (ART)‐based hybrids have been reported. Moreover, protein targets of such hybrids have not been identified yet, and the reason for the superior efficacy of these hybrids is still not known. Herein, we report the synthesis of novel ART–isoquinoline and ART–quinoline hybrids showing highly improved potencies against CQ‐resistant and multidrug‐resistant P. falciparum strains (EC50 (Dd2) down to 1.0 nm; EC50 (K1) down to 0.78 nm) compared to CQ (EC50 (Dd2)=165.3 nm; EC50 (K1)=302.8 nm) and strongly suppressing parasitemia in experimental malaria. These new compounds are easily accessible by step‐economic C−H activation and copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) click reactions. Through chemical proteomics, putatively hybrid‐binding protein targets of the ART‐quinolines were successfully identified in addition to known targets of quinoline and artemisinin alone, suggesting that the hybrids act through multiple modes of action to overcome resistance.
Bioorthogonal late‐stage diversification of structurally complex peptides has enormous potential for drug discovery and molecular imaging. In recent years, transition‐metal‐catalyzed C−H activation has emerged as an increasingly viable tool for peptide modification. Despite major accomplishments, these strategies largely rely on expensive palladium catalysts. We herein report an unprecedented cobalt(III)‐catalyzed peptide C−H activation, which enables the direct C−H functionalization of structurally complex peptides, and sets the stage for a multicatalytic C−H activation/alkene metathesis/hydrogenation strategy for the assembly of novel cyclic peptides.
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