Synthesis of a 3′-naphthamido-LacNAc fluorescein conjugate with high selectivity and affinity for galectin-3

Described is the synthesis of a fluorescent LacNAc derivative appended with a 3′-deoxy-3′-naphthamido functionality, 2-(fluorescein-5/6-amido)ethyl 3-deoxy-3-(2-naphthamido)-β-d-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranoside, which confers high affinity (Kd 170 nM) and selectivity for galectin-3 via a stacking interaction with Arg144. Its use as a selective and sensitive galectin-3 probe is demonstrated with fluorescence polarization measurements.