A new catalytic manifold that merges photoredox with nickel catalysis in aqueous solution is presented. Specifically, the combination of a highly active, yet air-stable, nickel precatalyst with a new electron-deficient pyridyl carboxamidine ligand was key to the development of a water-compatible nickel catalysis platform, which is a crucial requirement for the preparation of DNA-encoded libraries (DELs). Together with an iridium-based photocatalyst and a powerful light source, this dual catalysis approach enabled the efficient decarboxylative arylation of α-amino acids with DNA-tagged aryl halides. This C(sp 2 )−C(sp 3 ) coupling tolerates a wide variety of functional groups on both the amino acid and the aryl halide substrates. Due to the mild and DNA-compatible reaction conditions, the presented transformation holds great potential for the construction of DELs. This was further evidenced by showing that well plate-compatible LED arrays can serve as competent light sources to facilitate parallel synthesis. Lastly, we demonstrate that this procedure can serve as a blueprint toward the adaptation of other established nickel metallaphotoredox transformations to the idiosyncratic requirements of a DEL.
Influenza viruses are responsible for seasonal epidemics and occasional pandemics which cause significant morbidity and mortality. Despite available vaccines, only partial protection is achieved. Currently, there are two classes of widely approved anti-influenza drugs: M2 ion channel blockers and neuraminidase inhibitors. However, the worldwide spread of drug-resistant influenza strains poses an urgent need for novel antiviral drugs, particularly with a different mechanism of action. Favipiravir (T-705), a broad-spectrum antiviral agent, has shown potent anti-influenza activity in cell-based assays, and its riboside (2) triphosphate inhibited influenza polymerase. In one of our approaches to treat influenza infection, we designed, prepared, and tested a series of C-nucleoside analogues, which have an analogy to 2 and were expected to act by a similar antiviral mechanism as favipiravir. Compound 3c of this report exhibited potent inhibition of influenza virus replication in MDCK cells, and its triphosphate was a substrate of and demonstrated inhibitory activity against influenza A polymerase. Metabolites of 3c are also presented.
Novel ethynyltriazole ribonucleosides were synthesized using a simple and efficient two-step procedure involving Sonogashira coupling and subsequent ammonolysis. Compounds 2f and 3o inhibited hepatitis C virus (HCV) replication efficiently, whereas compound 3f demonstrated potent apoptosis-induced antiproliferative activity against pancreatic cancer MiaPaCa-2 cells both in vitro and in vivo. Most interestingly, the notable selective antiviral and antiproliferative activities were achieved respectively for 2f and 3f by modulating the ribose sugar moiety into deprotected and protected forms while retaining a similar trifluoromethylphenylethynyltriazole as the nucleobase. Preliminary structure-activity relationship study revealed that not only the ribose moiety but also the CF(3) group at the p-position of the phenyl ring and the rigid triple bond functionality contributed critically to the observed antiviral activity of 2f against HCV and antiproliferative activity of 3f against pancreatic cancer. These two compounds constitute therefore promising leads in the search for new antiviral and anticancer candidates.
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