Postmodification of an Amine-Functionalized Covalent Organic Framework for Enantioselective Adsorption of Tyrosine

Thedevelopment of chiral covalent organic frameworks (COFs) bypostsynthetic modification is challenging due to the common occurrencesof racemization and crystallinity decrement under harsh modificationconditions. Herein, we employ an effective site-selective syntheticstrategy for the fabrication of an amine-functionalized hydrazone-linkedCOF, NH2-Th-Tz COF, by the Schiff-base condensation betweenaminoterephthalohydrazide (NH2-Th) and 4,4 ',4 ''-(1,3,5-triazine-2,4,6-triyl)-tribenzaldehyde(Tz). The resulting NH2-Th-Tz COF with free amine groupson the pore walls provides an appealing platform to install desiredchiral moieties through postsynthetic modification. Three chiral moietiesincluding tartaric acid, camphor-10-sulfonyl chloride, and diacetyl-tartaricanhydride were postsynthetically integrated into NH2-Th-TzCOF by reacting amine groups with acid, acyl chloride, and anhydride,giving rise to a series of chiral COFs with distinctive chiral poresurfaces. Moreover, the crystallinity, porosity, and chirality ofchiral COFs were retained after modification. Remarkably, the chiralCOFs exhibited an exceptional enantioselective adsorption capabilitytoward tyrosine with a maximum enantiomeric excess (ee) value of upto 25.20%. Molecular docking simulations along with experimental resultsunderscored the pivotal role of hydrogen bonds between chiral COFsand tyrosine in enantioselective adsorption. This work highlightsthe potential of site-selective synthesis as an effective tool forthe preparation of highly crystalline and robust amine-decorated COFs,which offer an auspicious platform for the facile synthesis of tailor-madechiral COFs for enantioselective adsorption and beyond.