Development of Amylose- and β-Cyclodextrin-Based Chiral Fluorescent Sensors Bearing Terthienyl Pendants

Abstract

Phenylcarbamate derivatives of amylose and β-cyclodextrin show excellent chiral recognition when used as chiral stationary phases (CSPs) for high-performance liquid chromatography. To open up new possibilities of carbohydrate-based materials, we developed chiral fluorescent sensors based on amylose and β-cyclodextrin (Am-1b and CyD-1b, respectively) by attaching fluorescent π-conjugated units on their side chains. Their recognition abilities toward chiral analytes containing a nitrophenyl unit were evaluated by measuring the enantioselective fluorescence quenching behavior. Both sensors showed the same degree of enantioselective fluorescence response for various aromatic nitro compounds. However, in some cases, their enantioselectivities were different depending on the analytes. The difference in the chiral recognition abilities between Am-1b and CyD-1b seems to be based on the structural difference of their inherent backbones, that is, the one-handed helical structure and cyclic structure, respectively. The study on the resolution ability of the Am-1b-based CSP revealed that the terthienyl-based pendant of Am-1b provides not only a fluorescent functionality but also a different chiral recognition site from that of amylose tris(phenylcarbamate).

Preparation of cellulose derivative bearing bulky 4‐(2‐benzothienyl)phenylcarbamate substituents as chiral stationary phase for enantioseparation

“…This distinct difference in the quenching efficiency between ( R ) ‐Q1 and ( S ) ‐Q1 can be facilely discriminated by the naked eye, as shown in Figure 8A,B, suggesting that a good enantioselective fluorescence response for the 1‐phenylethylamine enantiomers was achieved on Cel ‐ 1 with the bulky substituents. Worthy to be mentioned, the good chiral fluorescence quenching efficiency was realized with a much lower concentration of Cel ‐ 1 (1.0 × 10 −5 M, with respect to the repeating glucose unit) compared with that of the quencher enantiomers (0.375 M for ( R ) ‐Q1 and ( S ) ‐Q1 ), implying that Cel ‐ 1 prepared in this study probably possesses high chiral fluorescence quenching efficiency 24,25 . The combination of the arrangement of bulky π‐conjugated benzothienyl pendants on the phenylcarbamate moieties surrounding the helical backbone and the regular higher order structure of the polymer itself probably played a key role for this high chiral fluorescent recognition ability of Cel ‐ 1 .…”

“…Then, the Suzuki–Miyaura coupling of the obtained tris(4‐bromophenylcarbamate) of cellulose ( Cel‐R ) was performed using 1‐benzothiophen‐2‐ylboronic acid (2.5 equiv. to Cel‐R ) in pyridine and potassium carbonate solution (4 ml) in the presence of PdCl 2 (PPh 3 ) 2 (as catalyst), PPh 3 (as a stabilizer), and CuI (as a reductant) to obtain the novel cellulose derivative bearing bulky 4‐(2‐benzothienyl)phenylcarbamate groups at 2,3,6‐positions according to a previously reported method 24 . The 1 H NMR spectrum of cellulose derivative Cel ‐ 1 with bulky 4‐(2‐benzothienyl)phenylcarbamate substituents is shown in Figure 3, and the characteristic proton peaks of the benzothienyl and phenylcarbamate groups of Cel ‐ 1 are assigned to the spectrum, respectively.…”

“…However, all the above‐mentioned derivatives had been prepared mainly by importing the small groups onto the glucose moiety, and the derivatization of polysaccharides using bulky pendants and the related mechanism had still remained obscure yet. Very recently, Ikai et al reported a new kind of cellulose derivatives bearing some bulky substituents, terthienyl or benzo[1,2‐b:4,5‐b′]dithiophene‐based π‐conjugated pendants with three branched alkyl chains, and a good chiral fluorescent quenching property was observed, providing a new design for polysaccharide derivatives as other chiral functional materials besides CSPs for enantioseparation 24,25 …”

“…Very recently, Ikai et al reported a new kind of cellulose derivatives bearing some bulky substituents, terthienyl or benzo [1,2-b:4,5-b 0 ]dithiophene-based π-conjugated pendants with three branched alkyl chains, and a good chiral fluorescent quenching property was observed, providing a new design for polysaccharide derivatives as other chiral functional materials besides CSPs for enantioseparation. 24,25 To investigate the effect of bulky substituents on the structure and enantioseparation ability of polysaccharide derivatives as well as to seek for the efficient CSP for chiral recognition and other functional potential, in the present study, a novel type of cellulose tris (4-(2-benzothienyl)phenylcarbamate) was readily synthesized through the Suzuki-Miyaura coupling reaction (Figure 1). The chiral recognition ability of the obtained derivative was evaluated as a CSP for HPLC.…”

Triazin bazlı kiral floresans bileşiklerin sentezi ve enantiyomerik tanınma çalışmaları

“…Chiral receptor designing and synthesis for molecular recognition studies of chiral guests such as carboxylic acids, amines, amino alcohols and amino acids have become increasingly an important topic in chiral recognition [1,2]. Since the significance of chiral recognition is inevitable for the biomolecules such as proteins, carbohydrates and nucleic acids that play a vital role in nature and thereby our life, the development of chiral receptors has drawn attention in agrochemical, pharmaceutical, food and fragrance industries to ensure the quality of the end products by eliminating undesired enantiomers with useless/harmful activities [3,4]. Among several techniques proposed for discrimination of enantiomers such as circular dichroism (CD) [5], high-performance liquid chromatography (HPLC) [6], capillary zone electrophoresis (CZE) [6], ultraviolet-visible (UV/Vis) [7,8], fluorescence [9][10][11][12][13] and nuclear magnetic resonance (NMR) [14,15] spectroscopy, the best technique considered for this purpose has been fluorescence spectroscopy due to its easy, rapid, accurate, selective, sensitive, costeffective and high-throughput features [16].…”