Aza-crowns

Leigh D A, Moody A E, Wade F A, King T A, West D and Bahra G S 1995 Second harmonic generation from Langmuir-Blodgett films of fullerene-aza-crown ethers and their potassium ion complexes Langmuir 11 2334-6... 

Early work on the use of chiral phase-transfer catalysis in asymmetric Darzens reactions was conducted independently by the groups of Wynberg [38] and Co-lonna [39], but the observed asymmetric induction was low. More recently Toke s group has used catalytic chiral aza crown ethers in Darzens reactions [40-42], but again only low to moderate enantioselectivities resulted. 

One approach, pursued by two groups in particular, is to use model nucleobases that feature an additional metal-ion binding group. Gokel and co-workers have used this strategy with aza-crown derivatives (50,51). X-ray crystallography of 6is-(3-(l-thyminyl)propyl)-4,13-diaza-18-crown-6, 4, reveals the Na+ is coordinated by T-02 [Na-0 distances 2.488 and 2.468 Al (51). Aza-crown derivatives with multiple base substi-... 

In a different approach three different structurally defined aza-crown ethers were treated with 10 different metal salts in a spatially addressable format in a 96-well microtiter plate, producing 40 catalysts, which were tested in the hydrolysis of /xnitrophenol esters.32 A plate reader was used to assess catalyst activity. A cobalt complex turned out to be the best catalyst. Higher diversity is potentially possible, but this would require an efficient synthetic strategy. This research was extended to include lanthanide-based catalysts in the hydrolysis of phospho-esters of DNA.33... 

Other high molecular weight amines to have been successfully used for adduct purification include the aza-crown macrocycles Me4-14-ane-N4 and Me6-18-ane-N6.48 These reversibly form adducts with indium and gallium alkyls, such as [(Et3Ga)4(Me6-18-ane-N6)], [(Et3Ga)6(Me6-18-ane-N6)], [(Pr13Ga)4(Me6-18-ane-N6)], and [(Pr13Ga)4(Me4-14-ane-N4)].49 Formation of... 

The cation affinity of aza-crown ethers depends on the type of substituent attached to the nitrogen. Wester and Vogtle (1978) have determined the cation binding constants for substituted [2.2]-cryptands 138] and [89]—191 ] in... 

Pond SJK, Tsutsumi O, Rumi M et al (2004) Metal-ion sensing lluorophores with large two-photon absorption cross sections aza-crown ether substituted donor-acceptor-donor distyryl benzenes. J Am Chem Soc 126 9291-9306... 

Table 4 Electrochemical data and group I metal cation dependence of ferrocene amide aza crown ethers and model analogues.

When protonation of a probe leads to dramatic effects on the electronic absorption and emission as described above, one can expect that cations other than protons might be capable of inducing similar effects if these ions can be made to bind to the basic atom of the probe molecule. A simple but effective method to do so exists in the formal replacement of the amino substituents ofchromophores by aza crowns. In the resulting chromoionophores the amine nitrogens possess simultaneously an electron-donor... 

Chirality derived from the readily accessible a-amino acids has been incorporated into the side chains of aza and diaza macrocyclic polyethers. A number of procedures suitable for peptide synthesis have proved (178) to be unsuitable for acylating the relatively unreactive secondary amine groups of aza crown ethers. Eventually, it was discovered that mixed anhydrides of diphenylphos-phinic acid and alkoxycarbonyl-L-alanine derivatives do yield amides, which can be reduced to the corresponding amines, e.g., l-172. By contrast, the corresponding bisamides of diaza-15-crown-S derivatives could not be reduced and so an alternative approach, involving the use of chiral A-chloroacetamido alcohols derived from a-amino acids, has been employed (178) in the synthesis of chiral receptors, such as ll-173 to ll-175, based on this constitution. 

Syntheses of N-alkyl aza crown ethers have been based on a modified protocol previously investigated for similar compounds [5,55,56]. The reaction used for S5mthesizing recyclable monoaza crown ethers in this study is illustrated in Scheme 10.1 [57]. Eight monoaza crown ethers were successfully synthesized... 

The cation-binding capabilities of monoaza-substituted crown ethers are extremely pH sensitive [58]. At low pH, the aza crown will be protonated, and... 

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