Cytosine substituted calix[4]pyrroles: neutral receptors for 5'-guanosine monophosphate

Sessler, Jonathan L., Král, Vladimir, Shishkanova, Tatiana V. and Gale, Philip A. (2002) Cytosine substituted calix[4]pyrroles: neutral receptors for 5'-guanosine monophosphate. Proceedings of the National Academy of Sciences of the United States of America, 99 (8), 4848-4853. (doi:10.1073/pnas.062633799).

Abstract

The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a ?- or meso-pyrrolic position, is described. These systems were tested as nucleotide-selective carriers and as active components of nucleotide-sensing ion-selective electrodes at pH 6.6. Studies of carrier selectivity were made using a Pressman-type model membrane system consisting of an initial pH 6.0 aqueous phase, an intervening dichloromethane barrier containing the calix[4]pyrrole conjugate, and a receiving basic aqueous phase. Good selectivity for the Watson-Crick complementary nucleotide, 5'-guanosine monophosphate (5'-GMP), was seen in the case of the meso-linked conjugate with the relative rates of through-membrane transport being 7.7:4.1:1 for 5'-GMP, 5'-AMP, and 5'-CMP, respectively. By contrast, the ?-substituted conjugate, while showing a selectivity for 5'-GMP that was enhanced relative to unsubstituted calix[4]pyrrole, was found to transport 5'-CMP roughly 4.5 times more quickly than 5'-GMP. Higher selectivities were also found for 5'-CMP when both the ?- and meso-substituted conjugates were incorporated into polyvinyl chloride membranes and tested as ion selective electrodes at pH 6.6, whereas near-equal selectivities were observed for 5'-CMP and 5'-GMP in the case of unsubstituted calix[4]pyrroles. These seemingly disparate results are consistent with a picture wherein the meso-substituted cytosine calix[4]pyrrole conjugate, but not its ?-linked congener, is capable of acting as a ditopic receptor, binding concurrently both the phosphate anion and nucleobase portions of 5'-GMP to the calixpyrrole core and cytosine "tails" of the molecule, respectively, with the effect of this binding being most apparent under the conditions of the transport experiments.

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Contributors

Author: Philip A. Gale

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