Solvent-Controlled Selective Transformation of 2-Bromomethyl-2-methylaziridines to Functionalized Aziridines and Azetidines

Oxa-spirocycles: synthesis, properties and applications

A general approach to a new generation of spirocyclic molecules – oxa-spirocycles – was developed. The key synthetic step was iodocyclization. More than 150 oxa-spirocyclic compounds were prepared. Incorporation of an oxygen atom into the spirocyclic unit dramatically improved water solubility (by up to 40 times) and lowered lipophilicity. More potent oxa-spirocyclic analogues of antihypertensive drug terazosin were synthesized and studied in vivo.

A general practical approach to a new generation of spirocyclic molecules – oxa-spirocycles – is developed.

Synthesis of 3-Aryl-3-Sulfanyl Azetidines by Iron-Catalyzed Thiol Alkylation with N-Cbz Azetidinols

New small-ring derivatives can provide valuable motifs in new chemical space for drug design. 3-Aryl-3-sulfanyl azetidines are synthesized directly from azetidine-3-ols in excellent yield by a mild Fe-catalyzed thiol alkylation. A broad range of thiols and azetidinols bearing electron-donating aromatics are successful, proceeding via an azetidine carbocation. The N-carboxybenzyl group is a requirement for good reactivity and enables the NH-azetidine to be revealed. Further reactions of the azetidine sulfides demonstrate their potential for incorporation in drug discovery programs.

Theoretical insight into the regioselective ring-expansions of bicyclic aziridinium ions

Transient bicyclic aziridinium ions are known to undergo ring-expansion reactions, paving the way to functionalized nitrogen-containing heterocycles. In this study, the regioselectivity observed in the ring-expansion reactions of 1-azoniabicyclo[n.1.0]alkanes was investigated from a computational viewpoint to study the ring-expansion pathways of two bicyclic systems with different ring sizes. Moreover, several nucleophiles leading to different experimental results were investigated. The effect of solvation was taken into account using both explicit and implicit solvent models. This theoretical rationalization provides valuable insight into the observed regioselectivity and may be used as a predictive tool in future studies.

Recent advances in synthetic facets of immensely reactive azetidines

Recent developments in synthetic strategies towards functionalized azetidines along with their versatility as heterocyclic synthons.

Cobalt carbonyl-catalyzed carbonylation of functionalized aziridines to versatile β-lactam building blocks

Aziridine to azetidin-2-one carbonylation as a convenient entry to pyrrolidines,C-fused bi- and tricyclic β-lactams and monocyclic carbapenem analogs.

The effect of backbone flexibility on site-selective modification of macrocycles

The interplay of rotatable backbone torsions determines the ring-opening regioselectivity of electrophilic aziridines in macrocyclic peptide scaffolds.

Access to optically active 3-substituted piperidines by ring expansion of prolinols and derivatives

The ring expansion of prolinols via an aziridinium intermediate gives C3-substituted piperidines in good yields and enantiomeric excess, the substituent at the C3 position being derived from the most reactive nucleophile in the reaction mixture. Depending on the nucleophile, the reaction proceeds under thermodynamic or kinetic control. The regioselectivity of attack of nucleophiles on the aziridinium intermediate depends on the nature of the substituents on the nitrogen atom and the C4 position of the starting prolinols.

Nucleophile-dependent regio- and stereoselective ring opening of 1-azoniabicyclo[3.1.0]hexane tosylate

1-[(1R)-(1-Phenylethyl)]-1-azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2-(3-hydroxypropyl)aziridine upon reaction with p-toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio- and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring-opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways.

Exploration of aziridine- and β-lactam-based hybrids as both bioactive substances and synthetic intermediates in medicinal chemistry

The concept of pharmacophore hybridization is attracting an increasing interest from medicinal chemists. Whereas the main motivation for the application of this methodology relates to the pharmacological advantages associated with hybrid molecules, molecular hybridization can also deliver a synthetic advantage through selective chemical modification of the more reactive entity within hybrid systems. Moreover, if both features are combined, new hybrid structures result displaying both a biological and a synthetic benefit, and elaboration of this methodology might culminate in structural diversity and chemical novelty. In this perspective, a new approach based on hybrid structures combining a biologically interesting yet rather chemically reactive nucleus with a privileged heterocyclic scaffold is discussed by means of β-lactam-purine chimeras useful in antiviral research and aziridine-(iso)quinoline hybrids for antimalarial purposes.