Synthesis by carbonate aminolysis and chiral recognition ability of cellulose 2,3-bis(3,5-dimethylphenyl carbamate)-6-(α-phenylethyl carbamate) selectors

Abstract

Abstract: Novel chiral selectors based on cellulose 2,3-bis(3,5-dimethylphenyl carbamate)-6-(α-phenylethyl carbamate) were regioselectively synthesized by carbonate aminolysis and isocyanate chemistry. By oxycarbonylation with phenyl chloroformate, carbamoylation with 3,5-dimethylphenyl isocyanate, and subsequent aminolysis of the previously introduced reactive carbonate moiety at C6 with enantiopure (R)-or (S)-α-phenylethylamine, chiral selectors have been obtained, which regioselectively carry two different phenyl carbamate substituents. The cellulose derivatives were comprehensively characterized by ATR-FTIR, solid-state NMR, GPC, and elemental analysis. In parallel, 3-aminopropyl-functionalized silica gel as an inert carrier material for the chiral selectors was prepared and the obtained coated-type chiral stationary phases were characterized by both solid-state 29Si NMR, 13C NMR, and elemental analysis. The enantioseparation performance of the chiral selectors was studied and compared to cellulose tris(3,5-dimethylphenyl carbamate) as a reference. With this protocol in hand, certain shortcomings of conventional approaches towards the regioselective synthesis of polysaccharide-based chiral selectors were overcome, such as the limitation to standard isocyanate reagents, being able to apply now the whole wealth of commercially available (chiral) primary and also secondary alkylamines instead. Graphical abstract: [Figure not available: see fulltext.]