Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

Abstract

The asymmetric polymerization of 4′‐isocyanatobenzo‐18‐crown‐6 with the lithium amide of (S)‐(2‐methoxymethyl)pyrrolidine successfully proceeded to afford end‐functionalized poly(4′‐isocyanatobenzo‐18‐crown‐6) with (S)‐(2‐methoxymethyl)pyrrolidine (polymer 2). In the circular dichroism (CD) spectrum of 2, a clear positive Cotton effect was observed in the range of 240–350 nm corresponding to the absorption of the polymer backbone, indicating that 2 partially formed a one‐handed helical structure, which was preserved by the chirality of (S)‐(2‐methoxymethyl)pyrrolidine bonding to the terminal end in 2. In the titration experiments for the CD intensity of 2 in the presence of D‐ and L‐Phe·HClO4 (where Phe is phenylalanine), a small but remarkable difference was observed in the amount of the chiral guest needed for saturation of the CD intensity and in the saturated CD intensity, indicating that the extremely stable, one‐handed helical part should exist in the main chain of 2, which was not inverted even when the unfavorable chiral guest for the predominant helical sense, L‐Phe·HClO4, was added. In addition, helical polymer 2 exhibited a chiral discrimination ability toward racemic guests; that is, the guests were extracted from the aqueous phase into the organic phase with enantiomeric excess. The driving force of the chiral discrimination ability of 2 should certainly be attributed to the one‐handed helical structure in 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 325–334, 2006

Asymmetric Polymerization

“…The optical activity of the polymers was presumably attributed to the helicity of the polymer main chains induced by a chiral initiator residue, which was attached to the end of the chain, rather than to a chiral initiator residue itself. Chiral discrimination of racemic amino acid derivatives using a single -handed helical polyisocyanate bearing a crown ether moiety was reported [282] . A single -handed helicity induction of achiral polyisocyanates by means of chiral acid -base interaction or hostguest complexation has recently been developed [236,283 -286] .…”

A novel type of optically active helical polymers: Synthesis and characterization of poly(α,β‐unsaturated ketone)

“…Polymers with single handed helical sense exhibit potential functions, such as chiral recognition toward racemic compound, liquid crystal formation, and chirally catalytic activity,3–4 and have attracted great attention in the past few years as the single handed helical polymer poly(triphenylmethyl methacrylate) (TrMA) was used as a chiral stationary phase for high‐performance liquid chromatography (HPLC) 3–7. At present, a large amount of polymers which keep a single handed helical conformation in solution have been prepared from aldehydes,8–9 isocyanates,10–13 isocyanides,14–17 styrenes,18–24 acrylamides,25–29 acetylenes,30–33 N ‐Propargylphosphonamidates,34 and so on. More recently, Deng et al35 reported optically active helical poly( N ‐propargylureas) and our group have prepared successfully optically active helical polyether 36–37.…”

Host–guest complexation‐triggered chiroptical change of poly(phenylacetylene)s bearing binaphthocrown ether moieties on the main chain

“…In particular, the helical polymer capable of responding to a specific molecular recognition event has been recently become important based on the increasing demand to develop smart and intelligent polymer inspired by biological macromolecules 6–8. Through a number of sophisticated investigations, the molecular design of the binding sites has been found to be essential for the realization of the desired stimuli‐responsive helicity change 9–38. Thus, the novel and unprecedented molecular design of the interaction site has the significant potential to expand the limit and scope in the field of stimuli‐responsive helical polymers.…”