4-Piperidines and 3-pyrrolidines as dual serotonin and noradrenaline reuptake inhibitors: Design, synthesis and structure–activity relationships

Ligand Effects in Carboxylic Ester- and Aldehyde-Assisted β-C-H Activation in Regiodivergent and Enantioselective Cycloisomerization-Hydroalkenylation and Cycloisomerization-Hydroarylation, and [2 + 2 + 2]-Cycloadditions of 1,6-Enynes

Herein, we report room temperature, atom-economic protocols for high regio- and enantioselective tandem cycloisomerization-hydroarylation and cycloisomerization-hydroalkenylation of 1,6-enynes leading to vicinal carba-functionalized pyrrolidines, tetrahydrofurans, and cyclopentanes. The latter steps in these processes involve carbonyl-coordination-assisted ortho-C-H activation of aromatic aldehydes and esters, and, a similar, yet rarely seen, β-C-H activation in the case of the acrylates. Synthetically useful enantioselective versions of such reactions are rare and are limited to the C2-H activation of indoles and pyrroles. A similar reaction is also observed with N-vinylphthalimide, which also has a carbonyl group suitable for C-H activation. A dibenzooxaphosphole ligand, (2S,2S',3S,3S')-MeO-BIBOP was uniquely identified as crucial to achieving the challenging regio- and enantioselectivity. This methodology gives access to substituted five-membered carbo- and heterocyclic compounds in good yields and excellent enantioselectivities under a low catalyst loading. A primary KIE of 3.5 is observed in an intermolecular competition experiment with methyl benzoate and d5-methyl benzoate, which indicates that the C-H cleavage is the turnover-limiting step of this process. Unlike the acrylates, which undergoes exclusive hydroalkenylation, a β, γ-unsaturated ester, methyl but-3-enoate, undergoes the highly enantioselective cycloisomerization-coupling sequence with a 1,6-enyne giving either a [2 + 2 + 2]-cycloaddition with (S, S)-BDPP or hydroalkenylation with (2S,2'S,3S,3'S)-MeO-BIBOP depending on the ligand employed. The (E)-configuration of the newly formed double bond at the terminal alkynyl carbon (of the starting enyne) in the hydroalkenylation product of β,γ-unsaturated ester suggests a more classical migratory insertion-β-hydride elimination route for the formation of this product.

Mild Condition for the Deoxygenation of α-Heteroaryl-Substituted Methanol Derivatives

A mild condition via PPh₃/I₂/imidazole for the deoxygenation of substituted methanol derivatives has been identified. This metal-free process was found to proceed well on secondary or tertiary alcohols substituted with one or two heteroaryl groups, and it tolerates acid-sensitive heterocycles. This condition works for methanol derivatives substituted with 2-pyridyl, 4-pyridyl, or other heterocyclic groups, allowing the negative charge formed during the reaction to resonate to a nitrogen atom. Methanol derivatives substituted with 3-pyridyl or heterocyclic groups that do not allow the negative charge formed during the reaction to resonate to a nitrogen atom will not undergo deoxygenation under this condition.

Mechanistic insight into the acid-catalyzed isomerization of biomass-derived polysubstituted pyrrolidines: an experimental and DFT study

The mechanism of the acid-catalyzed isomerization of polysubstituted pyrrolidines was unravelled by a combination of experimental, spectroscopic and computational studies.

Synthesis of Enantiomeric Polyhydroxyalkylpyrrolidines from 1,3-Dipolar Cycloadducts. Evaluation as Inhibitors of a β-Galactofuranosidase

Enantiomeric 2,3,4-tris(hydroxyalkyl)-5-phenylpyrrolidines have been synthesized from the major cycloadducts obtained by the 1,3-dipolar cycloaddition of sugar enones with azomethine ylides derived from natural amino acids. Reduction of the ketone carbonyl group of the cycloadducts, which possess a basic structure of bicyclic 6-(menthyloxy)hexahydropyrano[4,3-c]pyrrol-7(6H)one, afforded a number of pyrrolidine-based bicyclic systems. A sequence of reactions, which involved hydrolysis of the menthyloxy substituent, reduction, N-protection, and degradative oxidation, afforded varied pyrrolidine structures having diverse configurations and patterns of substitution; in particular, polyhydroxylated derivatives have been obtained. The unprotected products were isolated as pyrrolidinium trifluoroacetates. Because of the furanose-like nature of the target trihydroxyalkyl pyrrolidines, these molecules have been evaluated as inhibitors of the β-galactofuranosidase from Penicillium fellutanum. The compounds showed practically no inhibitory activity for concentration of pyrrolidines in the range of 0.1-1.6 mM.

Indium(iii)-catalyzed tandem synthesis of 2-alkynyl-3,3-dichloropyrrolidines and their conversion to 3-chloropyrroles

A convenient route to 2-alkynyl-3,3-dichloropyrrolidines was described by addition of terminal acetylenes to 2,2,4-trichloroaldimines using In(OTf)₃ as a catalyst. In the presence of a base these pyrrolidines were transformed into 3-chloropyrroles.

The Challenges of Multi-Target Lead Optimization

During multi-target lead optimization, medicinal chemists must address three principal challenges. First, the various desired activities must be adequately balanced and the activity profile of any active metabolites must also be considered. Second, undesired activities associated with side effects need to be removed. Third, a pharmacokinetic profile appropriate for the desired route of administration, usually oral, must be obtained. Given the extent of these challenges, the need for a high quality lead compound is paramount.