Article Dans Une Revue Journal of Organic Chemistry Année : 2023

Allosterically Driven Assembly of a Multisite Cage-Based [2]Semirotaxane

Résumé

The assembly of a [2]semirotaxane from a half-dumbbell endowed with a pyrazine coordination site and a bis-Zn(II) porphyrin cage as a multisite ring is reported. The threading is allosterically driven by the coordination of silver(I) ions to the multiple binding sites of the cage linkers, as shown by NMR studies. Addition of chloride ions destabilizes [2]semirotaxane, leading to its disassembly into its cage and half-dumbbell components.

M astering the synthesis of mechanically interlocked molecules (MIMs) made it possible to explore various properties associated with these molecules of peculiar topologies. 1 In particular, molecular switches based on [2]rotaxanes have gained increasing attention over the past 30 years for their applications in the fields of artificial molecular machines, 2 sensors, 3 catalysis, 4 molecular computing, 5 and materials. 6 The assembly of [2]pseudorotaxanes or [2]rotaxanes by threading a molecular axis through a ring, by slipping the ring over one stopper of the dumbbell, by clipping the ring precursor around a dumbbell, or by using a template to gather the ring and the thread components is promoted by specific interactions between sites located on the ring and on the thread. 1a Once the threaded species formed, a chemical, redox, or light stimulus that acts directly on these sites is thus generally used to set the motion of the ring along or around the axis. In contrast, the allosteric regulation of the threading step or of the ring motion in rotaxanes, using chemical effectors that bind to additional sites, has seldom been investigated. 7 Allostery is nevertheless a widespread mechanism of control of the activity of proteins and enzymes. It allows information to be transferred to a remote site using conformational changes induced by an effector binding to a site distinct from the active site. 8 Therefore, allosterically driven conformational and coconformational changes in MIMs represent a first step toward higher order hierarchical information transmission. 9 Seldom have multiannular rings been considered as the ring component of rotaxanes compared to macrocycles. These 3D hollow structures provide an increased preorganization for a higher stabilization of the threaded species compared to their 2D macrocyclic counter-39 part. Most of them are macrobicycles and cryptand-based 40 structures whereas cages with an additional loop offer possible 41 extra sites to govern allosteric effects. 10 However, additional 42 openings can bring some challenge in directing the thread 43 through the openings. 11 44 Herein, we report the allosteric control of the synthesis of a 45 [2]semirotaxane 1a consisting of a monostoppered axis 46 threaded through a bis-porphyrin cage receptor as the ring 47 component. This cage is endowed with remote and orthogonal 48 1,2,3-triazole binding sites from the porphyrin sites. Binding 49 metal ions to these additional sites triggers the threading of a 50 half-dumbbell stabilized by the coordination of its pyrazine to 51 the Zn(II) porphyrins of the cage. 52 The synthesis of [2]semirotaxane 1 requires two organic 53 f1 components, a covalent cage 2 and a half-dumbbell 3 (Figure 54 f1 1). Cage 2 is a multisite ring consisting of two cofacial Zn(II) 55 porphyrins and of eight peripheral 1,2,3-triazoles located on 56 the four porphyrin connectors. 12 Silver(I) complexation by the 57 triazoles was shown to trigger a large conformational change 58 and an opening of the initial flattened structure, leading to a 59 cage complex Ag 4 •2 with a large cavity. It was thus envisioned 60 that silver(I) as effectors could control the threading of a half-61 dumbbell. The half-dumbbell includes a pyrazine to stabilize

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hal-05593085 , version 1 (15-04-2026)

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Ryan Djemili, Sonia Adrouche, Stéphanie Durot, Valérie Heitz. Allosterically Driven Assembly of a Multisite Cage-Based [2]Semirotaxane. Journal of Organic Chemistry, 2023, 88 (20), pp.14760-14766. ⟨10.1021/acs.joc.3c01381⟩. ⟨hal-05593085⟩

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