Synthesis of Bulky Cellulose Derivatives for Efficient Enantioselective Fluorescent Sensing

Abstract

Four cellulose derivatives bearing benzothienyl or carbazolyl fluorophore pendants were successfully synthesized through carbamoylation followed by Steglich esterification or only esterification process, respectively. The enantioselective fluorescent sensing properties of the obtained derivatives were then evaluated using eight chiral substrates, including chiral aromatic amines and chiral amino alcohol-based drug intermediates. The four bulky host macromolecules exhibited good enantioselective fluorescence response to most of the tested guests with high enantioselectivity and sensitivity. Especially, a high enantiomeric fluorescence difference ratio (ef = 37.16) was achieved on cellulose tris(2-benzothienylformate) (Cel-3) for the α-methylbenzylamine (Q2), an important chiral agricultural drug intermediate. Worthy to be mentioned, an interesting opposite fluorescence response and a dual fluorescence enhancement pattern were also observed on the benzothienyl derivative Cel-3 for the enantiomer pairs of 1-(4-methoxyphenyl) ethylamine (Q3) and phenylglycinol (Q6), a critical intermediate for chiral drug as an antilipemic agent in high demand, respectively. It indicated that the bulky Cel-3 possessed excellent enantioselective fluorescent sensing properties to the chiral aromatic amine and amino alcohols, revealing good potential as efficient chiral fluorescent sensors. It was speculated that a beneficial chiral domain may be constructed by the appropriate arrangement of bulky conjugated benzothienyl or carbazolyl pendants on the phenylcarbamates or esters surrounding the helical backbone of cellulose, which was crucial for the efficient chiral fluorescent sensing performance. The introduction of bulky fluorophore pendants on the cellulose phenylcarbamates or esters presents an efficient strategy to produce effective chiral fluorescent recognition materials.

Graphical Abstract