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Elucidating the Anomalous Binding Enhancement of Isoquinoline Boronic Acid for Sialic Acid Under Acidic Conditions: Expanding Biorecognition Beyond Vicinal Diols
Author(s) -
Wellington Nadine,
Macklai Sabrina,
BritzMcKibbin Philip
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201904442
Subject(s) - boronic acid , chemistry , vicinal , sialic acid , moiety , isoquinoline , sulfonic acid , fluorescence , stereochemistry , organic chemistry , combinatorial chemistry , biochemistry , physics , quantum mechanics
A zwitterionic heterocyclic boronic acid based on 4‐isoquinolineboronic acid (IQBA) exhibits the highest reported binding affinity for sialic acid or N ‐acetylneuraminic acid (Neu5Ac, K= 5390±190 m −1 ) through the formation of a cyclic boronate ester complex under acidic conditions (pH 3). This anomalous pH‐dependent binding enhancement does not occur with common neutral saccharides (e.g., glucose, fructose, sorbitiol), because it is mediated via selective complexation to a α‐hydroxycarboxylate moiety forming a stable ion pair and ternary complex with Neu5Ac in phosphate buffer. IQBA expands biorecognition beyond classical vicinal diols under neutral or alkaline buffer conditions, which enables the direct analysis of Neu5Ac by native fluorescence with sub‐micromolar detection limits.