Nor-Seco-Cucurbiturils

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2008-04-22

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Abstract

With rapid growth in molecular recognition and self-assembly in recent years, α−, β−, and γ-cyclodextrins, as a platform for molecular recognition have been widely applied as molecular containers in water. In particular, cyclodextrins have been extensively used in industrial applications, such as drug delivery, cosmetics, and analytical chemistry (mainly chromatography). We, and others, believe that the cucurbit[n]uril family of molecular containers have the potential to supplant the cyclodextrins as platform of choice for molecular recognition in aqueous solution.

   Even though the one-pot synthesis of CB[n] under strongly acidic aqueous condition can be easily performed on multi-kilogram scale, the separation of the various CB[n] (n = 5, 6, 7, 8, 10) is challenging and time consuming.  This disseration focuses on the mechanism of CB[n] formation with the expectation that would allow the tailor-made synthesis of specific CB[n] and suggest versatile routes to new CB[n]-type compounds that might display exciting new properties like chirality, chiral recognition, and allostery. 



   Herein, the condensation of glycoluril with less than two equivalents of formaldehyde delivers a reaction mixture that contains glycoluril oligomers (dimer, trimer, tetramer, pentamer and hexamer) and CB[n] compounds that lack one or more methylene bridges known as nor-seco-cucurbit[n]urils (ns-CB[n]). We studied the ability of double cavity host bis-ns-CB[10] to undergo size dependent homotropic allostery, (±)-bis-ns-CB[6] to undergo diastereoselective recognition toward amino acids and amino alcohols in water, and the transformation of ns-CB[6] to a CB[6] derivative which contains the folding of long chain alkanediammonium ions in water. A comprehensive mechanistic scheme is proposed that accounts for the observed formation of dimer - hexamer and ns-CB[n]. Overall, the experiments establish that a step-growth cyclo-oligomerization process operates during CB[n] formation.

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