Mutualistic Synthesis from Orthogonal Dynamic Covalent Reactions

Mutualisms are interactions that benefit all species involved. It has been widely investigated in neighbouring subjects, such as biology, ecology, sociology, and economics. However, such a reciprocal relationship in synthetic chemical systems has rarely been studied. Here, we demonstrate a mutualistic synthesis where byproducts from two orthogonal chemical reactions aid each other's production. Disulfide exchange and hydrazone exchange were chosen to generate two dynamic combinatorial libraries. A minor tetrameric macrocycle from the active disulfide library was quantitatively amplified in the presence of the hydrazone library. This incorporation also turned on the previously inert hydrazone reaction, producing a linear species that formed a "handcuffs" catenane with the disulfide tetramer. These findings not only lend robust support to the hypothesis of "RNA-peptide coevolution" for the origin of life but also broaden the scope of synthetic chemistry, highlighting the untapped potential of minor products from different reactions. Additionally, the co-self-assembly of these mutualistic entities to form supramolecular structures opens new avenues for future development of composite nanosystems with synergistic properties.

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Template Assisted One-Pot Synthesis of [2], Linear [3], and Radial [4]Catenane via Click Reaction

Design and synthesis of higher order catenane are unexpectedly complex and involve precise cooperation among the precursors overcoming competing and opposing interactions. We achieved synthesis of [2], linear [3], radial [4] in a one-pot reaction by consecutive ring closing through click reactions. This synthesis gave three isolable products due to two, four, and six-click reactions between suitable coupling partners. Yields of the isolate templated-catenane decrease from lower to higher-ordered catenane (40 %, 12 %, and 4 %), probably due to the bite angle as well as the flexibility of the reacting partners. Removal of templating cobalt(III) ion leads to the formation of fully organic [2], linear [3], and radial [4]catenane. These synthesized catenanes were purified by column chromatography and characterized by 1H-NMR, 13C-NMR, and ESI-MS spectroscopy. The synthesized catenanes have free binding sites suitable for post-functionalization and may be used for the synthesis of higher-ordered catenane.

Catenane and Rotaxane Synthesis from Cucurbit[6]uril-Mediated Azide-Alkyne Cycloaddition

The chemistry of mechanically interlocked molecules (MIMs) such as catenane and rotaxane is full of new opportunities for the presence of a mechanical bond, and the efficient synthesis of these molecules is therefore of fundamental importance in realizing their unique properties and functions. While many different types of preorganizing interactions and covalent bond formation strategies have been exploited in MIMs synthesis, the use of cucurbit[6]uril (CB[6]) in simultaneously templating macrocycle interlocking and catalyzing the covalent formation of the interlocked components is particularly advantageous in accessing high-order catenanes and rotaxanes. In this review, catenane and rotaxane obtained from CB[6]-catalyzed azide-alkyne cycloaddition will be discussed, with special emphasis on the synthetic strategies employed for obtaining complex [n]rotaxanes and [n]catenanes, as well as their properties and functions.

Distinctive features and challenges in catenane chemistry

From being an aesthetic molecular object to a building block for the construction of molecular machines, catenanes and related mechanically interlocked molecules (MIMs) continue to attract immense interest in many research areas. Catenane chemistry is closely tied to that of rotaxanes and knots, and involves concepts like mechanical bonds, chemical topology and co-conformation that are unique to these molecules. Yet, because of their different topological structures and mechanical bond properties, there are some fundamental differences between the chemistry of catenanes and that of rotaxanes and knots although the boundary is sometimes blurred. Clearly distinguishing these differences, in aspects of bonding, structure, synthesis and properties, between catenanes and other MIMs is therefore of fundamental importance to understand their chemistry and explore the new opportunities from mechanical bonds.

Macrocycle Dynamics in a Branched [8]Catenane Controlled by Three Different Stimuli in Three Different Regions

A branched [8]catenane from an efficient one-pot synthesis (72 % HPLC yield, 59 % isolated yield) featuring the simultaneous use of three kinds of templates and cucurbit[6]uril-mediated azide-alkyne cycloaddition (CBAAC) for ring-closing is reported. Design and assembly of the [8]catenane precursors are unexpectedly complex that can involve cooperating, competing and non-influencing interactions. Due to the branched structure, dynamics of the [8]catenane can be modulated in different extent by rigidifying/loosening the mechanical bonds at different regions by using solvent polarity, acid-base and metal ions as the stimuli. This work not only highlights the importance of understanding the delicate interplay of the weak and non-obvious supramolecular interactions in the synthesis of high-order [n]catenane, but also demonstrates a complex control of dynamics and flexibility for exploiting [n]catenanes applications.

Synthesis, structure elucidation and functionalization of sulfonamide [2]catenanes

A pyrene-functionalized [2]catenane with switchable optical output was constructed through a novel sulfonamide [2]catenane synthesized by a self-templation approach.