Manipulation of biomacromolecules is ideally achieved through unique and bioorthogonal chemical reactions of genetically encoded, naturally occurring functional groups. The toolkit of methods for site‐specific conjugation is limited by selectivity concerns and a dearth of naturally occurring functional groups with orthogonal reactivity. We report that pyroglutamate amide N−H bonds exhibit bioorthogonal copper‐catalyzed Chan–Lam coupling at pyroglutamate‐histidine dipeptide sequences. The pyroglutamate residue is readily incorporated into proteins of interest by natural enzymatic pathways, allowing specific bioconjugation at a minimalist dipeptide tag.
Autocatalytic photoredox Chan-Lam coupling of free diaryl sulfoximines with arylboronic acids
Abstract N- Arylation of NH -sulfoximines represents an appealing approach to access N- aryl sulfoximines, but has not been successfully applied to NH -diaryl sulfoximines. Herein, a copper-catalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids is described. This neutral and ligand-free coupling is initiated by ambient light-induced copper-catalyzed single-electron reduction of NH -sulfoximines. This electron transfer route circumvents the sacrificial oxidant employed in traditional Chan-Lam coupling reactions, increasing the environmental friendliness of this process. Instead, dihydrogen gas forms as a byproduct of this reaction. Mechanistic investigations also reveal a unique autocatalysis process. The C–N coupling products, N- arylated sulfoximines, serve as ligands along with NH -sulfoximine to bind to the copper species, generating the photocatalyst. DFT calculations reveal that both the NH -sulfoximine substrate and the N -aryl product can ligate the copper accounting for the observed autocatalysis. Two energetically viable stepwise pathways were located wherein the copper facilitates hydrogen atom abstraction from the NH -sulfoximine and the ethanol solvent to produce dihydrogen. The protocol described herein represents an appealing alternative strategy to the classic oxidative Chan-Lam reaction, allowing greater substrate generality as well as the elimination of byproduct formation from oxidants.
more »
« less
- Award ID(s):
- 1902509
- NSF-PAR ID:
- 10256864
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract The formation of aryl‐alkyl ether bonds through cross coupling of alcohols with aryl halides represents a useful strategic departure from classical SN2 methods. Numerous tactics relying on Pd‐, Cu‐, and Ni‐based catalytic systems have emerged over the past several years. Herein we disclose a Ni‐catalyzed electrochemically driven protocol to achieve this useful transformation with a broad substrate scope in an operationally simple way. This electrochemical method does not require strong base, exogenous expensive transition metal catalysts (e.g., Ir, Ru), and can easily be scaled up in either a batch or flow setting. Interestingly, e‐etherification exhibits an enhanced substrate scope over the mechanistically related photochemical variant as it tolerates tertiary amine functional groups in the alcohol nucleophile.
-
more » « less
Abstract The formation of aryl‐alkyl ether bonds through cross coupling of alcohols with aryl halides represents a useful strategic departure from classical SN2 methods. Numerous tactics relying on Pd‐, Cu‐, and Ni‐based catalytic systems have emerged over the past several years. Herein we disclose a Ni‐catalyzed electrochemically driven protocol to achieve this useful transformation with a broad substrate scope in an operationally simple way. This electrochemical method does not require strong base, exogenous expensive transition metal catalysts (e.g., Ir, Ru), and can easily be scaled up in either a batch or flow setting. Interestingly, e‐etherification exhibits an enhanced substrate scope over the mechanistically related photochemical variant as it tolerates tertiary amine functional groups in the alcohol nucleophile.
-
more » « less
Abstract Herein, the synthesis of 1,2,3,4‐tetrasubstituted benzenoid rings, motifs found in pharmaceutical, agrochemical, and natural products, is described.[1]In the past, the regioselective syntheses of such compounds have been a significant challenge. This work reports a method using substituted arynes derived from aryl(Mes)iodonium salts to access a range of densely functionalized 1,2,3,4‐tetrasubstituted benzenoid rings. Significantly, it was found that halide substituents are compatible under these conditions, enabling post‐synthetic elaboration via palladium‐catalyzed coupling. This concise strategy is predicated on two regioselective events: 1)
ortho ‐ deprotonation of aryl(Mes)iodonium salts to generate a substituted aryne intermediate, and 2) regioselective trapping of said arynes, thereby improving previously reported reaction conditions to generate arynes at room temperature and in shorter reaction times. Density functional theory (DFT) computations and linear free energy relationship (LFER) analysis suggest the regioselectivity of deprotonation is influenced by both proximal and distal ring substituents on the aryne precursor. A competition experiment further reveals the role of arene substituents on relative reactivity of aryl(Mes)iodoniums as aryne precursors. -
A Pd-PEPPSI-catalyzed (Pd = Palladium, PEPPSI = pyridine-enhanced precatalyst preparation stabilization and initiation) Suzuki-Miyaura cross-coupling of aryl esters via selective C–O cleavage at room temperature is reported. The developed catalyst system displays broad substrate scope with respect to both components under practical ambient reaction conditions using readily-available, cheap, modular, air- and moisturestable Pd-NHC precatalyst (NHC = N-heterocyclic carbene). The use of water proved crucial for achieving high reactivity in this coupling. The catalyst system represents the mildest conditions for the Suzuki-Miyaura cross-coupling of aryl esters reported to date. The protocol also allowed for achieving TON >1,000 (TON = turnover number) in the Suzuki-Miyaura ester coupling for the first time.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-021-21156-w
