Macrocyclic amide receptors

Introduction of another ruthenium bipyridine moiety or bridging metallocene (ferrocene, cobaltocenium) results in sensors that specifically bind chloride anions (Figure 16.15). The structural modification of the amide receptor results in a decease in cavity dimensions and significant rigidity of the macrocycle. Therefore it cannot accommodate hydrogen phosphate anions, but only much smaller CF [45, 46]. 

Pyrrole-substituted a,co-diamines 517 varying in length and number of heteroatoms between the amine functionalities were obtained from the corresponding acid and appropriate diamine under standard amide-forming conditions in yields of 18-70%. The amines 517 were reacted with l,l -ferrocenedimethanol 518 under pseudo high-dilution conditions to form 7 r 7-ferrocenes 519, the macrocyclic anion receptors, in 20-35% yields (Equation 122) <2001JOM(637)343>. 

Macrocyclic amides as anion receptors based on directed hydrogen-bonding interactions 03CCR(240)101. 

The macrocyclic amide linked cobalticinium receptor (18) has recently been prepared (Scheme 3) and its crystal structure elucidated (Figure 3). 

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. 

Enantioselective anion sensing is included in a number of reviews covering much broader subjects, namely receptors of anions in general [2-8] and chro-mophoric sensors of anions [9,10]. There are also more specialized reviews dealing with receptors for anions based on macrocyclic polyamines [11], amides [12],... 

In the last two decades, chiral receptors containing amidic functions were designed almost exclusively for binding protected amino acids [49-57], oligopeptides [54,58], and lactic [59], tartaric [60,61] or camphoric acid derivatives [62]. Usually, chiral building blocks such as spirobifluorene [49, 60], binaphthalene [51,57],or amino acid chains containing macrocycles [52-56,58] were employed. An interesting receptor was synthesized via connection of the calix[4]arene moiety with an aza-crown derivative [61]. 

Fig. 12 Colorimetric sensor receptors, a For fluoride, b Amide macrocycle which can detect fluoride, acetate or H2PO4 the moiety in bold lies above the plane of the rest of the molecule...

The general poor solubility of these macrocyclic polycobalticinium systems coupled with their lability to ester hydrolysis has very recently led us to a new synthetic strategy which utilizes the stable amide linkage to construct novel acyclic cobalticinium anion receptors (132). 

A novel Os and Ru bis(bipyridyl) containing an amide macrocyclic receptor has been shown to detect the presence of anions by both electrochemical and optical methodologies. Photophysical studies have clearly shown that the rate constants of the energy transfer process responsible for the quenching of the luminescent ruthenium excited state significantly decreases in the presence of chloride ions. ... 

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