Host−[2]Rotaxanes as Cellular Transport Agents

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Abstract
Host−[2]rotaxanes, containing a diarginine-derivatized dibenzo-24-crown-8 (DB24C8) ether as the ring and a cyclophane pocket or an aromatic cleft as one blocking group, are cell transport agents. These hosts strongly associate with a variety of amino acids, dipeptides, and fluorophores in water (1 mM phosphate buffer, pH 7.0), DMSO, and a 75/25 (v/v) buffer to DMSO solution. All peptidic guests in all solvent systems have association constants (KA's) in the range of 1 × 104 to 5 × 104 M-1, whereas the KA range for the fluorophores is 1 × 104 to 9 × 105 M-1. Association constants for the cyclophane itself, cyclophane 3, are smaller. These values are in the 1 × 103 to 5 × 103 M-1 range, which shows that the rotaxane architecture is advantageous for guest binding. Cyclophane−[2]rotaxane 1 efficiently transports fluorescein and a fluorescein-protein kinase C (PKC) inhibitor into eukaryotic COS-7 cells, including the nucleus. Interestingly, cleft−[2]rotaxane 2 does not transport fluorescein as efficiently, even though the results from the fluorescence assays show that both [2]rotaxanes bind fluorescein with the same ability.

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