Novel 7-hydroxycoumarin based fluorescent labels

Five new 7-hydroxy-8-(N-alkylaminomethyl)coumarin labels (6a-e) were prepared from 4-(4-carboxybutyl)-7-hydroxycoumarin (4) in 28–48% yield. Compared to 4-methylumbelliferone (4-MU, 1), the new fluorescent labels exhibited higher emission intensity over a broader pH range. Extinction coefficients, quantum yields and pKa values are also reported for these labels.