Cover Picture: Controlling the Chair Conformation of a Mannopyranose in a Large‐Amplitude [2]Rotaxane Molecular Machine (Chem. Eur. J. 21/2009)

Abstract

A domino effect from one extremity to the other is observed in a large‐amplitude mannosyl [2]rotaxane molecular machine. In their Communication on page 5186 ff., F. Coutrot and E. Busseron describe the efficient preparation of new [2]rotaxane molecular machines containing anilinium and either mono‐ or disubstituted pyridinium amide stations. In the case of the disubstituted pyridinium amide, the macrocycle shuttles from the anilinium to the pyridinium upon deprotonation and causes an impressive flipping of the chair conformation of the glucidic moiety.magnified image

A Cholesterol Containing pH‐Sensitive Bistable [2]Rotaxane

“…Several successful approaches can be found in the literature that employ a permanent cationic function that can act as a medium-strong binding site for an ionophore, such as a crown ether and a secondary amine functionality that can act as a strong binding site for an ionophore in the protonated state but not in its neutral form. [12] Three permanent cationic units have been used most in this context: dialkylated 4,4Ј-bipyridinium ions as pioneered by J. F. Stoddart in the late 1990s [13] and more recently alkylated pyridinium ions as employed by S.-H. Chiu, [14] F. Coutrot, [15] T. Ogoshi, [16] and U. Lüning, [17] or alkylated triazolium ions as used by F. Coutrot, [18] Y. Liu, [19] C.-F. Chen, [20] P. D. Beer, [21] and D. A. Leigh. [22] Among these, the latter one is very appealing because the triazole unit can also act as a key structural element to actually synthesis the rotaxane by means of a copper-catalysed azide-alkyne cycloaddition (CuAAC).…”