We
report herein versatile, transition metal-free and additive-free
(hetero)aryl–aryl coupling reactions promoted by the oxidative
electrocoupling of unsymmetrical tetra(hetero)arylborates (TABs) prepared
from ligand-exchange reactions on potassium trifluoroarylborates.
Exploiting the power of electrochemical oxidations, this method complements
the existing organoboron toolbox. We demonstrate the broad scope,
scalability, and robustness of this unconventional catalyst-free transformation,
leading to functionalized biaryls and ultimately furnishing drug-like
small molecules, as well as late stage derivatization of natural compounds.
In addition, the observed selectivity of the oxidative coupling reaction
is related to the electronic structure of the TABs through quantum-chemical
calculations and experimental investigations.
Spurred on by the recent emerging interest from the chemical community for unsaturated four-membered heterocycles, an unprecedented approach to nitrogen-containing four-membered rings has been designed. 3,4-Disubstituted 2-azetines were synthesized from commercially available substrates, allowing for a straightforward access to a new library of chiral functionalized azetidines and amino alcohols. This original approach was applied to efficiently prepare functionalized azobenzenes, an emerging class of molecules with a large potential in photopharmacology.
α‐Galactosylceramides are glycosphingolipids that show promise in cancer immunotherapy. After presentation by CD1d, they activate natural killer T cells (NKT), which results in the production of a variety of pro‐inflammatory and immunomodulatory cytokines. Herein, we report the synthesis and biological evaluation of photochromic derivatives of KRN‐7000, the activity of which can be modulated with light. Based on established structure–activity relationships, we designed photoswitchable analogues of this glycolipid that control the production of pro‐inflammatory cytokines, such as IFN‐γ. The azobenzene derivative α‐GalACer‐4 proved to be more potent than KRN‐7000 itself when activated with 370 nm light. Photolipids of this type could improve our mechanistic understanding of cytokine production and could open new directions in photoimmunotherapy.
Bearing in mind the often insufficient metabolic stability of carbohydrate antigens, which impairs both the bioavailability and immunogenicity of a given hapten, the development of chemically modified analogs with improved antigenicity is an important step towards effective glycoconjugate vaccines. Recently, strategic glycan fluorination has become an interesting approach to this, and several examples of fluorinated carbohydrate antigens that show better metabolic stabilities and comparable or even enhanced immunogenicities have been reported to date. In this paper, we present a small library of fluorinated trisaccharides based on a privileged motif from the lipophosphoglycan capping structure of Leishmania donovani, a protozoan parasite responsible for fatal visceral leishmaniasis. These epitope analogs were synthesized by a sequential [1+1+1] glycosylation strategy. An amine linker is present at the reducing end to allow conjugation and enable future applications in immunological studies for the development of diagnostic tools and vaccines.
Conventional methods carrying out C(sp
2
)−C(sp
2
) bond formations are typically mediated by transition‐metal‐based catalysts. Herein, we conceptualize a complementary avenue to access such bonds by exploiting the potential of electrochemistry in combination with organoboron chemistry. We demonstrate a transition metal catalyst‐free electrocoupling between (hetero)aryls and alkenes through readily available alkenyl‐tri(hetero)aryl borate salts (ATBs) in a stereoconvergent fashion. This unprecedented transformation was investigated theoretically and experimentally and led to a library of functionalized alkenes. The concept was then carried further and applied to the synthesis of the natural product pinosylvin and the derivatization of the steroidal dehydroepiandrosterone (DHEA) scaffold.
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