The application of proton coupled electron transfer (PCET) processes in organic synthesis has opened the door to new radical intermediates for synthesis such as alkyl radicals in remote positions to a ketone. Herein, we present the addition of these remote alkyl radicals to electron deficient double bonds under photoorganocatalyzed and very mild conditions. The method is not only applicable to diactivated double bonds, but monoactivated ones are also accessible using more stabilized alkyl radicals, and alkyl chains of any length can be introduced. The final products can be easily converted into more complex structures via a one‐pot process, and the activating functional groups were transformed in the more versatile methyl esters. Mechanistic investigations support a mechanistic proposal based on a PCET process.
A novel quadruplex ligand based on 1,10-phenanthroline and incorporating two guanyl hydrazone functionalities, PhenQE8, is reported herein. Synthetic access was gained in a two-step procedure with an overall yield of 61%. X-ray diffraction studies revealed that PhenQE8 can adopt an extended conformation that may be optimal to favor recognition of quadruplex DNA. DNA interactions with polymorphic G-quadruplex telomeric structures were studied by different techniques, such as Fluorescence resonance energy transfer (FRET) DNA melting assays, circular dichroism and equilibrium dialysis. Our results reveal that the novel ligand PhenQE8 can efficiently recognize the hybrid quadruplex structures of the human telomeric DNA, with high binding affinity and quadruplex/duplex selectivity. Moreover, the compound shows significant cytotoxic activity against a selected panel of cultured tumor cells (PC-3, HeLa and MCF-7), whereas its cytotoxicity is considerably lower in healthy human cells (HFF-1 and RPWE-1).
The reactions of the chlorosilyl-substituted cyclopentadienyl niobium compound [Nb(η 5 -C 5 H 4 SiMe 2 Cl)Cl 4 ] (1) with 1 equiv. of 2-methoxyethylamine, 3-methoxypropylamine, and allylamine in toluene specifically afford the corresponding amine adducts [Nb(η 5 -C 5 H 4 SiMe 2 Cl){NH 2 (CH 2 ) n OMe}Cl 4 ] (n = 2, 2; 3, 3) and [Nb(η 5 -C 5 H 4 SiMe 2 Cl)(NH 2 CH 2 CH=CH 2 )Cl 4 ] (4). In contrast, a similar reaction with 1,2-phenylenediamine proceeds with the aminolysis of a Nb-Cl bond and the formation of the amido-amine compound [Nb(η 5 -C 5 H 4 SiMe 2 Cl)(NHC 6 H 4 -2-κNH 2 )Cl 3 ] (5). When such reactions are performed in the presence of 2 equiv. of an additional base, they progress through [a]
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