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Crown Ethers

Crown Ethers

Crown ethers are cyclic polyethers that contain multiple oxygen atoms, usually arranged in a regular pattern. The first crown ether was synthesized by Charles Pederson while working at DuPont in 1967. For this work, Pedersen was co-awarded the 1987 Nobel Prize in Chemistry. Crown ethers are named using the formula x-crown-y, where x is the total number of atoms in the ring and y is the number of ether oxygen atoms. The term 'crown' refers to the crown-like shape that these ether...

Thermal and Photochemical Electrocyclic Reactions: Overview

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

Chair Conformation of Cyclohexane

Chair Conformation of Cyclohexane

The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

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Related Experiment Video

Updated: Sep 12, 2025

Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation

Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation

Published on: August 1, 2018

Crown Ether-Peptide Rotaxanes.

Peng-Lai Wang^1,2, Peng Chen¹, Raorao Yang¹

¹School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, P.R. China.

Angewandte Chemie (International Ed. in English)

|August 6, 2025

Summary

This summary is machine-generated.

We developed a metal-free method to synthesize crown ether-peptide rotaxanes. This technique allows for controlled placement of the crown ether on peptide chains, creating protected and stable mechanically interlocked molecules.

Keywords:

Active template synthesis Lasso peptides Mechanically interlocked molecules Rotaxanes

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Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation

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Synthesis of Information-bearing Peptoids and their Sequence-directed Dynamic Covalent Self-assembly

Synthesis of Information-bearing Peptoids and their Sequence-directed Dynamic Covalent Self-assembly

Published on: February 6, 2020

Area of Science:

Supramolecular Chemistry
Organic Synthesis
Chemical Biology

Background:

Mechanically interlocked molecules (MIMs) offer unique structural and functional properties.
Peptide-based MIMs are of interest for biomimetic applications.
Controlled synthesis of peptide-based MIMs remains a challenge.

Purpose of the Study:

To report the metal-free active template synthesis of crown ether-peptide rotaxanes.
To demonstrate selective synthesis and characterization of positional isomers.
To investigate the conformational and stability effects of macrocycle threading.

Main Methods:

Active template synthesis using a 24-crown-8 macrocycle and glycine residues.
Selective extension of the peptide axle from N- and C-termini.
Structural confirmation via 1H nuclear magnetic resonance spectroscopy and tandem mass spectrometry.

Main Results:

Successfully synthesized three distinct positional isomers of heptapeptide [2]rotaxanes.
Confirmed unique macrocycle placement on the peptide axle.
Observed altered conformations, chemical stabilities, and secondary interactions in rotaxanes compared to linear peptides.
Demonstrated localized protection of peptide residues from enzymatic degradation.

Conclusions:

The developed strategy enables metal-free synthesis of crown ether-peptide rotaxanes.
Positional isomerism influences rotaxane conformation and stability.
Crown ether threading provides localized enzymatic protection, paving the way for new peptide analogs.