*2.2.1 Fluorescent coumarin maleimides*

*Phytochemicals in Human Health*

Sodium (E)-4-((4-(2-(6,7-

dimethoxycoumarin-3-yl)vinyl)benzoyl) oxy)-2,3,5,6-tetrafluorobenzenesulfonate

**Coumarin Ex/Em** 

**Coumarin Ex/Em** 

Coumarin-6-sulfonyl chloride

2-(benzo[d]thiazol-2-yl)-3-oxo-3Hbenzo[f]chromene-9-sulfonyl chloride

thiazol-2-yl)-7-isothiocyanatocoumarin

*Fluorescent coumarin sulfonyl chlorides used for biomolecule labelling.*

**Coumarin Ex/Em** 

*Fluorescent coumarin isothiocyanate used for biomolecule labelling.*

**Table 3.**

3-(benzo[d]

**Table 4.**

**Table 2.**

**(nm)**

*Fluorescent coumarin 4-sulfotetrafluorophenyl (STP) ester used for biomolecule labelling.*

**(nm)**

**Physicochemical features and biological applications**

**Physicochemical features and biological applications**

nucleotides with strong blue fluorescence. Blue-fluorescent dye, water soluble and pH insensitive with excellent photostability

392/490 Used to label proteins and

and phenols in mild conditions. Fluorescence produced in alkaline solution or in the presence of β-cyclodextrin

changes in bio environments

**Physicochemical features and biological applications**

Selective determination of flu antigen

360/460 Used to label amines, amino acids,

405/435 Biosensor sensitive toward polarity

**Ref.**

**Ref.**

[95, 96]

[99, 100]

[101]

**Ref.**

[102]

**166**

disulfides) is a major competing reaction for the iodoacetamide modifications of thiol compounds [18, 19, 105]. Due to the disinterest on the development of new coumarin iodoacetamides, for the above reasons, only the fluorescent coumarin maleimides will be focused in this section. **Figure 2** represents, in a general schematic diagram, the

**(nm)**

485/535 (conjug.)

thiol-labelling reaction with fluorescent coumarin maleimides.

Maleimides readily react with thiol moieties of biomolecules to form thioether conjugates even under neutral conditions. The thioether bond formed is quite stable and is known to be responsible for the light produced, especially in the solution. Maleimides require conjugation conditions less rigorous than those of iodoacetamides and do not react with histidine and methionine under physiological conditions. Most labelling reactions can be done at room temperature at neutral pH. However, either elevated or reduced pH or temperature may be required for a particular labelling reaction [18, 19, 68]. In **Table 5**, the most important fluorescent coumarin maleimides used for labelling biomolecules are presented, as the corresponding values of maximal excitation (Ex) and emission (Em) wavelengths and their physicochemical features and biological applications.
