Post-synthesis of boric acid–functionalized magnetic covalent organic framework as an affinity probe for the enrichment of N-glycopeptides

A novel type of boric acid–functionalized magnetic covalent organic framework (mCOF) with polyethyleneimine (PEI) as a linker (denoted as mCOF@PEI@B(OH)₂) has been prepared through a post-synthesis strategy, which points out an achievable path for the construction of boronic acid–functionalized COFs. Based on the boric acid chemistry, the obtained core-shell structured mCOF@PEI@B(OH)₂ can selectively isolate glycopeptides through the modified boronic acid groups. The mCOF@PEI@B(OH)₂ exhibits excellent performance with good reusability (ten cycles), low detection limit (0.5 fmol·μL⁻¹), size-exclusion effect, and relatively high loading capacity (80 μg·mg⁻¹), recovery yield (94.9 ± 2.8%), and selectivity (HRP digests:BSA digests = 1:500). Detection is done by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition, 37 endogenous glycopeptides are captured from human saliva with mCOF@PEI@B(OH)₂, providing effective proofs for its capability to capture low-abundance glycopeptides from actual biological samples. Graphical abstract: