Cyclen

Cyclen
File:4Cyclen.png
IUPAC name 1,4,7,10-tetrazacyclododecane
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	294-90-6
PubChem	64963
ChemSpider	58488
SMILES
InChI
InChI key	QBPPRVHXOZRESW-UHFFFAOYAQ
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	C8H20N4
Molar mass	172.271
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

File:Cyclen Zinc InorgChem 1997 4579 commons.jpg

Crystal structure of a Zn(II) coordinated to a cyclen and an ethanol reported in Inorg. Chem., 1997, 4579-4584.

Cyclen or 1,4,7,10-tetraazacyclododecane is a macrocycle and the aza analogue of the crown ether 12-crown-4. Derivatives of cyclen are larger cyclic polyamines but the repeating unit (ethyleneimine) is always the same. Like crown ethers, cyclen compounds are capable of selectively binding cations. They are used as a ligand in chemistry for instance with chemicals used in MRI contrast agents.

Synthesis

Cyclen compounds can be synthesized by combining two separate parts by nucleophilic displacement. In this procedure the terminal amine groups in diethylene triamine (1) are activated as amine anionic nucleophiles by reaction with tosyl chloride in pyridine to the N-tosyl protective group followed by proton abstraction with sodium ethoxide. The alcohol end groups in diethanolamine (2) are activated as electrophile by converting them into tosyl leaving groups. The two segments are joined in dimethylformamide and unless the reactants are very diluted, ordinary polymerization will take place to long linear chains and not cyclization. In the final step the tosyl groups are removed with sulfuric acid.

Cyclen synthesis through a dilute ring closing reaction[1]

High dilution conditions result in a low reaction rate penalty and this disadvantage is removed in an alternative procedure starting from triethylenetetraamine and dithiooxamide to a bisamidine (also a bis(imidazoline)) followed by reduction and ring expansion with DIBAL.

Cyclen synthesis dithiooxamide method

In one study cyclen is covalently bonded through a propylene molecular spacer to adenine and chelated with zinc diperchlorate. This complex is able to selectively bind uracil and uridine in a 1:2 ratio both through the adenine part and cyclen part of the molecule as evidenced by mass spectroscopy.

Further reading

Suchý, M.; Hudson, R. H. E. (2008). "Synthetic Strategies Toward N-Functionalized Cyclens". Eur. J. Org. Chem. 2008: 4847–4865. doi:10.1002/ejoc.200800636. CS1 maint: Multiple names: authors list (link) de:Cyclen it:Ciclene

nl:Cycleen