An unusual occurrence on attempted purine C-8 electrophilic fluorination of 5'-noraristeromycin

Conversion of a AuI Fluorido Complex into an N-Fluoroamido Derivative: N-F versus Au-N Reactivity

The Au^I complex [Au{N(F)SO₂ Ph}(SPhos)] (SPhos=dicyclohexyl(2',6'-dimethoxy[1,1'-biphenyl]-2-yl)phosphane) (2) bearing a fluoroamido ligand has been synthesized by reaction of the fluorido complex [Au(F)(SPhos)] (1) with NFSI (NFSI=N-fluorobenzenesulfonimide). A reaction with CO resulted in an unprecedented insertion into the N-F bond at 2. With the carbene precursor N₂ CH(CO₂ Et) N-F bond cleavage gave the Au-F bond insertion product [Au{CHF(CO₂ C₂ H₅ )}(SPhos)] (7). The presence of CNtBu led to Au-N cleavage at 2 and concomitant amide formation to give the cationic complex [Au(CNtBu)(SPhos)][N(F)SO₂ Ph)] (5), which reacted further to give FtBu as well as the cyanido complex [Au(CN)(SPhos)] (6). These results led to the development of a process for the amination of electrophilic organic substrates by transfer of the fluoroamido group NF(SO₂ Ph)^- .

Multi-faceted reactivity of N-fluorobenzenesulfonimide (NFSI) under mechanochemical conditions: fluorination, fluorodemethylation, sulfonylation, and amidation reactions

In the search for versatile reagents compatible with mechanochemical techniques, in this work we studied the reactivity of N-fluorobenzenesulfonimide (NFSI) by ball milling. We corroborated that, by mechanochemistry, NFSI can engage in a variety of reactions such as fluorinations, fluorodemethylations, sulfonylations, and amidations. In comparison to the protocols reported in solution, the mechanochemical reactions were accomplished in the absence of solvents, in short reaction times, and in yields comparable to or higher than their solvent-based counterparts.

Metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide via cleavage of S-N bonds: expeditious synthesis of diarylsulfones

A novel metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide (NFSI) toward the synthesis of diarylsulfones has been developed. The reaction represents a rare example of sulfonylation reaction using NFSI as an efficient sulfonyl donor and the first example of acid-mediated sulfonylation of unactivated arenes with NFSI via selective cleavage of S-N bonds. This protocol provides a concise approach for the construction of pharmaceutically and biologically important diarylsulfones. Applications in the functionalization of natural products (e.g., β-estradiol) and in the synthesis of a key intermediate to an inhibitor of farnesyl-protein transferase, as well as in the gram-scale synthesis of the EPAC2 antagonist, are demonstrated.

Selective synthesis of sulfoxides and sulfones via controllable oxidation of sulfides with N-fluorobenzenesulfonimide

A practical and mild method for the switchable synthesis of sulfoxides or sulfones via selective oxidation of sulfides using cheap N-fluorobenzenesulfonimide (NFSI) as the oxidant has been developed. These highly chemoselective transformations were simply achieved by varying the NFSI loading with H₂O as the green solvent and oxygen source without any additives. The good functional group tolerance makes the strategy valuable.

Copper-Catalyzed Functionalization of Benzylic C-H Bonds with N-Fluorobenzenesulfonimide: Switch from C-N to C-F Bond Formation Promoted by a Redox Buffer and Brønsted Base

A copper catalyst in combination with N-fluorobenzenesulfonimide (NFSI) has been reported to functionalize benzylic C-H bonds to the corresponding benzylic sulfonimides via C-N coupling. Here, we reported a closely related Cu-catalyzed method with NFSI that instead leads to C-F coupling. This switch in selectivity arises from changes to the reaction conditions (Cu/ligand ratio, temperature, addition of base) and further benefits from inclusion of MeB(OH)2 in the reaction. MeB(OH)2 is shown to serve as a "redox buffer" in the reaction, responsible for rescuing inactive Cu(II) for continued promotion of fluorination reactivity.

A Convenient Late-Stage Fluorination of Pyridylic C-H Bonds with N-Fluorobenzenesulfonimide

Pyridine features prominently in pharmaceuticals and drug leads, and methods to selectively manipulate pyridine basicity or metabolic stability are highly sought after. A robust, metal-free direct fluorination of unactivated pyridylic C-H bonds was developed. This convenient reaction shows high functional-group tolerance and offers complimentary selectivity to existing C-H fluorination strategies. Importantly, this late-stage pyridylic C-H fluorination provides opportunities to rationally modulate the basicity, lipophilicity, and metabolic stability of alkylpyridine drugs.

Iron-Catalyzed, Fluoroamide-Directed C-H Fluorination

This communication describes a mild, amide-directed fluorination of benzylic, allylic, and unactivated C-H bonds mediated by iron. Upon exposure to a catalytic amount of iron(II) triflate (Fe(OTf)₂), N-fluoro-2-methylbenzamides undergo chemoselective fluorine transfer to provide the corresponding fluorides in high yield. The reaction demonstrates broad substrate scope and functional group tolerance without the use of any noble metal additives. Mechanistic and computational experiments suggest that the reaction proceeds through short-lived radical intermediates with F-transfer mediated directly by iron.

OxaD: A Versatile Indolic Nitrone Synthase from the Marine-Derived Fungus Penicillium oxalicum F30

Indole alkaloids are a diverse class of natural products known for their wide range of biological activities and complex chemical structures. Rarely observed in this class are indolic nitrones, such as avrainvillamide and waikialoid, which possess potent bioactivities. Herein the oxa gene cluster from the marine-derived fungus Penicillium oxalicum F30 is described along with the characterization of OxaD, a flavin-dependent oxidase that generates roquefortine L, a nitrone-bearing intermediate in the biosynthesis of oxaline. Nitrone functionality in roquefortine L was confirmed by spectroscopic methods and 1,3-dipolar cycloaddition with methyl acrylate. OxaD is a versatile biocatalyst that converts an array of semisynthetic roquefortine C derivatives bearing indoline systems to their respective nitrones. This work describes the first implementation of a nitrone synthase as a biocatalyst and establishes a novel platform for late-stage diversification of a range of complex natural products.

9H-purine scaffold reveals induced-fit pocket plasticity of the BRD9 bromodomain

The 2-amine-9H-purine scaffold was identified as a weak bromodomain template and was developed via iterative structure based design into a potent nanomolar ligand for the bromodomain of human BRD9 with small residual micromolar affinity toward the bromodomain of BRD4. Binding of the lead compound 11 to the bromodomain of BRD9 results in an unprecedented rearrangement of residues forming the acetyllysine recognition site, affecting plasticity of the protein in an induced-fit pocket. The compound does not exhibit any cytotoxic effect in HEK293 cells and displaces the BRD9 bromodomain from chromatin in bioluminescence proximity assays without affecting the BRD4/histone complex. The 2-amine-9H-purine scaffold represents a novel template that can be further modified to yield highly potent and selective tool compounds to interrogate the biological role of BRD9 in diverse cellular systems.

Fluorinated 1-phenyl-1H-tetrazol-5-yl sulfone derivatives as general reagents for fluoroalkylidene synthesis

Julia-Kocienski olefination reagents 1-fluoropropyl, (cyclopropyl)fluoromethyl, 1-fluoro-2-methyl-2-propenyl, and 1-fluoro-5-hexenyl 1-phenyl-1H-tetrazol-5-yl (PT) sulfones were prepared by metalation followed by electrophilic fluorination. Although metalation-fluorination of n-propyl, 5-hexenyl, and (cyclopropyl)methyl PT-sulfones proceeded under homogeneous conditions, fluorination of 2-methyl-2-propenyl PT-sulfone required heterogeneous fluorination conditions. Condensation reactions of fluoro PT-sulfones with aldehydes resulted in fluoroalkylidenes in high yields. Screening of olefination conditions showed that stereoselectivity depended on reagent and carbonyl structure and can in many cases be tuned either toward E- or Z-selectivity. For example, LHMDS-mediated condensations of 1-fluoropropyl PT-sulfone in the presence of MgBr(2) x OEt(2) were Z-selective with electron-rich aromatic aldehydes, a hindered aromatic aldehyde, and cinnamaldehyde. Low-temperature KHMDS-mediated condensations were E-selective with electron-rich and electron-deficient aromatic aldehydes and Z-selective with n-octanal. Dialkyl, aryl alkyl, and diaryl ketones reacted as well to give fluoro olefin products in 71-99% yields.