ABSTRACT
Muscarinic M3 receptor antagonists and inverse agonists displaying high affinity and subtype selectivity over the antitarget M2 are valuable pharmacological tools and may enable improved treatment of chronic obstructive pulmonary disease (COPD), asthma, or urinary incontinence. On the basis of known M3 antagonists comprising a piperidine or quinuclidine unit attached to a biphenyl carbamate, 5-fluoro substitution was responsible for M3 subtype selectivity over M2, while 3'-chloro substitution substantially increased affinity through a σ-hole interaction. Resultantly, two piperidinyl- and two quinuclidinium-substituted biphenyl carbamates OFH243 (13n), OFH244 (13m), OFH3911 (14n), and OFH3912 (14m) were discovered, which display two-digit picomolar affinities with Ki values from 0.069 to 0.084 nM, as well as high selectivity over the M2 subtype (46- to 68-fold). While weak inverse agonistic properties were determined for the biphenyl carbamates 13m and 13n, neutral antagonism was observed for 14m and 14n and tiotropium under identical assay conditions.
Subject(s)
Aminobiphenyl Compounds/chemistry , Drug Inverse Agonism , Halogens/chemistry , Muscarinic Agonists/chemistry , Muscarinic Antagonists/chemistry , Receptor, Muscarinic M3/agonists , Receptor, Muscarinic M3/antagonists & inhibitors , Aminobiphenyl Compounds/pharmacology , Animals , Caco-2 Cells , HEK293 Cells , Halogens/pharmacology , Humans , Male , Molecular Docking Simulation/methods , Muscarinic Agonists/metabolism , Muscarinic Agonists/pharmacology , Muscarinic Antagonists/pharmacology , Protein Binding/physiology , Protein Structure, Secondary , Rats , Rats, Sprague-Dawley , Receptor, Muscarinic M3/metabolismABSTRACT
Aryl radicals generated in the aqueous phase of biphasic mixtures have-regardless of a comparably low polarity- a strong preference to react with aromatic substrates in the aqueous phase and not to undergo phase-transfer into a lipophilic phase, independent from the presence of a surfactant. These results represent an important prerequisite toward future studies in biological systems, which typically consist of various compartments of either hydrophilic or lipophilic character.
ABSTRACT
Visible-light photoreductive coupling of 2-arylallyl bromides in the presence of the photocatalyst Ru(bpy)3(PF6)2, a Hantzsch ester, and i-Pr2NEt gives 2,5-diaryl-1,5-dienes in high yield. This method avoids the use of stoichiometric metal reductants and is compatible with the presence of halogen, alkyl, electron-donating, and electron-withdrawing substituents on the aromatic ring.
Subject(s)
Alkadienes/chemical synthesis , Allyl Compounds/chemistry , Bromides/chemistry , Organometallic Compounds/chemistry , Alkadienes/chemistry , Catalysis , Light , Molecular Structure , Oxidation-Reduction , Photochemical ProcessesABSTRACT
The coupling of tertiary carbon radicals with alkene acceptors is an underdeveloped strategy for uniting complex carbon fragments and forming new quaternary carbons. The scope and limitations of a new approach for generating nucleophilic tertiary radicals from tertiary alcohols and utilizing these intermediates in fragment coupling reactions is described. In this method, the tertiary alcohol is first acylated to give the tert-alkyl N-phthalimidoyl oxalate, which in the presence of visible-light, catalytic Ru(bpy)3(PF6)2, and a reductant fragments to form the corresponding tertiary carbon radical. In addition to reductive coupling with alkenes, substitution reactions of tertiary radicals with allylic and vinylic halides is described. A mechanism for the generation of tertiary carbon radicals from tert-alkyl N-phthalimidoyl oxalates is proposed that is based on earlier pioneering investigations of Okada and Barton. Deuterium labeling and competition experiments reveal that the reductive radical coupling of tert-alkyl N-phthalimidoyl oxalates with electron-deficient alkenes is terminated by hydrogen-atom transfer.
Subject(s)
Carbon/chemistry , Onium Compounds/chemical synthesis , Oxalates/chemistry , Phthalimides/chemistry , Catalysis , Ethyl Chloride/analogs & derivatives , Ethyl Chloride/chemistry , Imidazoles/chemistry , Light , Molecular Structure , Onium Compounds/chemistry , Photochemical Processes , Pyrroles/chemistryABSTRACT
Tertiary carbon radicals have notable utility for uniting complex carbon fragments with concomitant formation of new quaternary carbons. This article explores the scope, limitations, and certain mechanistic aspects of Okada's method for forming tertiary carbon radicals from N-(acyloxy)phthalimides by visible-light photocatalysis. Optimized conditions for generating tertiary radicals from N-(acyloxy)phthalimide derivatives of tertiary carboxylic acids by visible-light irradiation in the presence of 1 mol % of commercially available Ru(bpy)3(PF6)2, diethyl 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate (8), and i-Pr2NEt and their coupling in dichloromethane at room temperature with alkene acceptors were developed. Four representative tertiary N-(acyloxy)phthalimides and 15 alkene radical acceptors were examined. Both reductive couplings with electron-deficient alkenes and radical substitution reactions with allylic and vinylic bromides and chlorides were examined with many such reactions occurring in good yield using only a slight excess (typically 1.5 equiv) of the alkene. In general, the yields of these photocatalytic reactions were higher than the analogous transformations of the corresponding N-phthalimidoyl oxalates. Deuterium labeling and competition experiments reveal that the reductive radical coupling of tertiary N-(acyloxy)phthalimides with electron-deficient alkenes can be terminated by both hydrogen-atom transfer and single-electron reduction followed by protonation, and that this mechanistic duality is controlled by the presence or absence of i-Pr2NEt.
Subject(s)
Carbon/chemistry , Carboxylic Acids/chemistry , Coordination Complexes/chemistry , Onium Compounds/chemistry , Phthalimides/chemical synthesis , Pyridines/chemistry , Ruthenium/chemistry , Alkenes/chemistry , Catalysis , Light , Molecular Structure , Oxidation-Reduction , Photochemical Processes , Phthalimides/chemistryABSTRACT
The reactivity of phenyldiazenes was studied intensively in the late 1960s, but not much is known about their behavior under acidic conditions. Based on the formation of phenyldiazenes from phenylazocarboxylates, we herein describe how reactions of phenyldiazenes can be directed into ionic or radical pathways. Cycloaddition reactions with furans leading to pyridazinium salts represent the first examples for the direct trapping of phenyldiazenes with conservation of the N=N moiety.
ABSTRACT
Simply aqueous sodium hydroxide is sufficient to exclude ionic side reactions and to prepare 2-aminobiphenyls from aryl diazotates and anilines through a new variant of the Gomberg-Bachmann reaction (see scheme). The metal-free reaction under basic conditions allows to exploit the highly radical-stabilizing effect of the aniline's free amino function for the first time, which leads to a so far unreached regioselectivity.
Subject(s)
Aminobiphenyl Compounds/chemical synthesis , Aniline Compounds/chemistry , Azo Compounds/chemistry , Aminobiphenyl Compounds/chemistry , Molecular StructureABSTRACT
This review summarizes recent advances in the field of aryl radical chemistry. In particular, modern developments of the well-known Meerwein, Pschorr, and Gomberg-Bachmann reactions are presented along with new applications in natural product syntheses. Among the methods for the generation of aryl radicals, tin hydrides play a predominant role, but more and more attractive and promising alternatives are beginning to emerge.
Subject(s)
Free Radicals/chemistry , Hydrocarbons, Aromatic/chemistry , Organometallic Compounds/chemistry , Tin/chemistry , CatalysisABSTRACT
A small library of Fmoc-protected 3-arylated tyrosines was created by radical arylation. The new building blocks were successfully applied in the synthesis of two novel neurotensin receptor ligands. Both isomers showed high affinity for the human NTS2 receptor with K(i) values in the nanomolar range. Interestingly, subtype selectivity strongly depends on the configuration of the peptide in position 11. Isomer (11R)-3 displayed an excellent preference for NTS2 compared to NTS1.
Subject(s)
Neurotensin/chemical synthesis , Neurotensin/metabolism , Receptors, Neurotensin/metabolism , Tyrosine/chemistry , Amino Acid Sequence , Animals , CHO Cells , Cricetinae , Cricetulus , Fluorenes/chemistry , Free Radicals/chemistry , Humans , Ligands , Neurotensin/chemistry , Stereoisomerism , Substrate SpecificityABSTRACT
Radical arylations of para-substituted phenols and phenyl ethers proceeded with good regioselectivity at the ortho position with respect to the hydroxy or alkoxy group. The reactions were conducted with arenediazonium salts as the aryl radical source, titanium(III) chloride as the reductant, and diluted hydrochloric acid as the solvent. Substituted biaryls were obtained from hydroxy- and alkoxy-substituted benzylamines, phenethylamines, and aromatic amino acids. The methodology described offers a fast, efficient, and cost-effective new access to diversely functionalized biphenyl alcohols and ethers. Free phenolic hydroxy groups, aromatic and aliphatic amines, as well as amino acid substructures, are well tolerated. Two examples for the applicability of the methodology are the partial synthesis of a beta-secretase inhibitor and the synthesis of a calcium-channel modulator.
