Folding Construction of a Pentacyclic Quadruply fused Polymer Topology with Tailored kyklo‐Telechelic Precursors

Abstract

Ap entacyclic quadruply fused polymer topology has been constructed for the first time through alkyne-azide addition (click)a nd olefin metathesis (clip) reactions in conjunction with an electrostatic self-assembly and covalent fixation (ESA-CF) process.T hus,aspiro-type,t andem tetracyclic poly(tetrahydrofuran), poly(THF), precursor having two allyloxy groups at the opposite positions of the four ring units was prepared by the click-linking of one unit of an eightshaped precursor having alkyne groups at the opposite positions with two units of as ingle-cyclic counterpart having an azide and an alkene group at the opposite positions.B oth are obtainable through ESA-CF.T he subsequent metathesis clip-folding of the tetracyclic precursor could affordapentacyclic quadruply fused polymer product, of "shippo" form, in 19 %y ield.The programmed folding of polymer molecules,w hich is widely observed in diverse biopolymer events including DNA packaging and protein 3D structure formation, has also been highlighted in av ariety of cyclic peptides,c yclotides,c onstructing fused multicyclic structures formed through the intramolecular SÀSb ridging with cysteine residues,t obe crucial for their extraordinary stability and bioactivity. [1,2] Notably,inparticular, atopologically intriguing,prototypical non-planar K 3,3 -graph construction, which cannot be embedded in the plane in such away that its edges intersect only at their endpoints,h as recently been identified in cyclotides from diverse origins. [1,3] Thee ffective and programmed folding by synthetic polymers into designated multicyclic forms,o nt he other hand, has been an ongoing challenge in polymer chemistry. [4] We have developed an electrostatic self-assembly and covalent fixation (ESA-CF) method [5] for the programmed polymer folding in which linear, star, and other branched telechelic precursors having cyclic ammonium salt groups carrying plurifunctional carboxylate counteranions were employed to form polymeric self-assemblies as key intermediates.T he three forms of dicyclicc onstructions,t hat is, q (fused), 8( spiro), and manacle (bridged), as well as at refoil (spiro-tricyclic) construction have been effectively produced through the ESA-CF process. [5,6] Ac lass of fused multicyclic polymer topologies,r ather than their spiro and bridged counterparts,a re particularly attracting not only by their relevance to their programmed folding of cyclotides but also from the significanse of topological geometry conjectures [5,7] (Scheme 1). Thus,atetracyclic triply fused macromolecular K 3,3 -graph has been constructed through the ESA-CF method using au niformsize dendritic polymer precursor having six cyclic ammonium salt end groups carrying two units of at rifunctional carboxylate counteranions,a nd subsequent covalent conversion by the ring-opening reaction of cyclic ammonium salt groups at an elevated temperature under dilution.[8]Moreover,atandem alkyne-azide addition (click) and olefin metathesis (clip) reaction in conjunction with the ESA-CF proces...

Radius of Gyration, Mean Span, and Geometric Shrinking Factors of Bridged Polycyclic Ring Polymers

“…Results of g from those calculations conform to our theoretical result of g = 1/ f when N exceeds about 100, as shown in Figure 3 . This also validates our theoretical expression of Equation ( 15) . In Figure 3 , deviations from the long-chain asymptotic results of Equation ( 15) for small N are due to the so-called fi nite chain length effects.…”

“…This also validates our theoretical expression of Equation ( 15) . In Figure 3 , deviations from the long-chain asymptotic results of Equation ( 15) for small N are due to the so-called fi nite chain length effects. For instance, when N is fi nite, the mean square radius of a linear Rouse bead-spring chain deviates from the well-known expression of 〈 S 2 〉 = Nb 2 /6, and the exact result contains a fi nite N correction term [ 44 ]…”

“…In most studies, comparisons are made on the peak retention volume of the cyclic sample to that of the corresponding linear polymer having the same molecular weight. Specifically, the ratio G ≡ M SEC / M true was introduced to represent the volume or size shrinkage of the cyclic polymer relative to its linear analog . Here, M SEC is the apparent molecular weight of the cyclic polymer (often referring to the elution peak) measured in SEC by conventional column calibration using linear polymer standards, and M true is the “true” molecular weight measured by an absolute molecular weight determination technique such as NMR, light scattering, or being deduced from the known molecular weight of the corresponding linear polymer before cyclization.…”

“…Due to their unique topological features distinct from linear or branched chains, such cyclic polymers have gained increasing attention from various fields. For instance, many of them have been synthesized by Tezuka and co‐workers . On the theoretical side, the case of f = 2, i.e., ring‐shaped polymer, has been studied extensively.…”

“…For instance, many of them have been synthesized by Tezuka and coworkers. [13][14][15] On the theoretical side, the case of f = 2, i.e., ring-shaped polymer, has been studied extensively. It is well known that for a phantom Gaussian ring, [ 10,16 ] the g -parameter introduced in Equation ( 1) is 0.5.…”