X‑α‑L‑Fuc 

X‑α‑L‑Fuc (CAS 171869‑92‑4) is a synthetic α‑L‑fucosidase‑specific chromogenic substrate in which 5‑bromo‑4‑chloro‑3‑indoxyl is linked via an α‑glycosidic bond to L‑fucose. When cleaved by α‑L‑fucosidase (EC 3.2.1.51) or fucosidase‑containing systems, the indoxyl aglycone is released and undergoes rapid aerial oxidation to form a green–blue insoluble indigo‑type dye, providing a clear visual readout of enzyme activity. This substrate is commonly incorporated into selective agar media to screen fucose‑utilizing microbes, as well as in enzyme‑kinetic assays and histochemical staining for α‑L‑fucosidase localization in tissue sections or cell preparations. Compared with other X‑type fucosides, X‑α‑L‑Fuc offers high sensitivity and low background, making it suitable for both qualitative and semi‑quantitative analyses under standard laboratory conditions.

Appearance

• Off‑white to pale yellow crystalline or lyophilized powder.
• Free‑flowing, fine‑particle solid suitable for accurate weighing and dissolution.

Source / synthesis

• Synthetically produced by coupling 5‑bromo‑4‑chloro‑3‑indoxyl with α‑L‑fucose under glycosylation conditions to form the α‑L‑fucopyranoside.
• Commercially manufactured by specialty carbohydrate and enzyme‑substrate suppliers as a high‑purity, research‑use‑only reagent.

Molecular weight and structure

• Molecular formula: C14H15BrClNO5\text{C}_{14}\text{H}_{15}\text{BrClNO}_{5}C14H15BrClNO5.
• Molecular weight: 392.63 g/mol.
• Structure: 5‑bromo‑4‑chloro‑1H‑indol‑3‑yl 6‑deoxy‑α‑L‑galactopyranoside (α‑L‑fucopyranoside of 5‑bromo‑4‑chloro‑3‑indolyl, with an α‑(1→?) glycosidic bond to the 3‑position of the indole ring).

Sugar specificity

• Specifically hydrolyzed by α‑L‑fucosidases (EC 3.2.1.51) and closely related α‑L‑fucoside‑cleaving enzymes.
• Shows minimal cross‑reactivity with other α‑ or β‑glycosidases when used under optimized assay conditions.

Biological activity

• Acts as a chromogenic reporter for α‑L‑fucosidase‑mediated hydrolysis of α‑L‑fucosyl linkages in glycoproteins, glycolipids, and oligosaccharides.
• Enzymatic cleavage releases 5‑bromo‑4‑chloro‑3‑indoxyl, which oxidizes and dimerizes into a green–blue, water‑insoluble pigment, enabling sensitive detection in solution‑based, gel‑based, and solid‑medium assays.

Purity and microbial contamination

• Typically supplied at ≥98–99% purity as determined by HPLC or equivalent analytical methods.
• Certificates of analysis usually confirm low levels of residual solvents, heavy metals, and absence of significant microbial contamination when stored and handled under aseptic conditions.

Identity and quality control

• Identity verified by NMR, HPLC, MS, and elemental analysis, with batch‑specific certificates of analysis provided by major suppliers.
• Quality‑control procedures generally include checks for appearance, solubility, spectral characteristics (UV/Vis), and enzyme‑activity performance in a defined α‑L‑fucosidase assay.

Shelf life and storage

• Shelf life is typically 12–24 months when stored as a dry powder at –20 °C in a tightly sealed container, protected from moisture and light.
• Aqueous working solutions are recommended to be prepared immediately before use or stored frozen for short periods to minimize degradation and nonspecific oxidation of the indoxyl moiety.

Application

• Screening and enumeration of α‑L‑fucosidase‑producing microorganisms on selective agar media.
• Enzyme‑activity assays for recombinant or purified α‑L‑fucosidases in solution or immobilized formats.
• Histochemical or cytochemical localization of α‑L‑fucosidase activity in tissue sections, cells, or fixed samples.

Key characteristics

• High sensitivity and low background due to formation of a green–blue, insoluble dye upon α‑L‑fucosidase hydrolysis.
• Defined α‑L‑fucopyranoside linkage providing selectivity for α‑L‑fucosidases over other glycosidases.
• Crystalline, stable powder with a well‑defined molecular weight and formula, suitable for quantitative enzyme assays and standardized media formulations.

citations 

• ChemImpex – 5‑Bromo‑4‑chloro‑3‑indoxyl‑α‑L‑fucopyranoside (X‑α‑L‑Fuc): https://www.chemimpex.com/products/21002
• Hepattack – X‑α‑L‑Fuc product page: https://www.hepattack.com/en/product03_cid_212_pid_482.html
• ChemSynLab – 5‑Bromo‑4‑chloro‑3‑indolyl α‑L‑fucopyranoside: http://chemsynlab.com/en/product/171869-92-4.html
• ChemicalBook – 5‑Bromo‑4‑chloro‑3‑indoxyl‑α‑L‑fucopyranoside: https://www.chemicalbook.com/ChemicalProductProperty_IN_CB4464161.htm
• ChemicalBook India – 5‑bromo‑4‑chloro‑3‑indoxyl‑α‑L‑fucopyranoside listing: https://www.chemicalbook.com/Manufacturers-india/5-bromo-4-chloro-3-indoxyl-alpha-l-fucopyranoside.htm
• Chembind – 5‑Bromo‑4‑chloro‑3‑indolyl‑α‑L‑fucopyranoside (X‑α‑L‑Fuc) product entry: http://chembind.com/products/enzyme-substrates/cbes004-171869-92-4-5-bromo-4-chloro-3-indolyl-a-lfucopyranoside-x-alpha-l-fuc/
• Chembind catalog (2023) – enzyme‑substrate section with X‑α‑L‑Fuc: http://chembind.com/wp-content/uploads/2023/10/Chembind-catalog-2023-6.pdf
• eChemInfo / eChemi – product page for 5‑Bromo‑4‑chloro‑3‑indolyl‑α‑L‑fucopyranoside: https://www.echemi.com/produce/pr2512021472-5-bromo-4-chloro-3-indolyl-l-fucopyranoside.html
• Next‑SSDS – 5‑Bromo‑4‑chloro‑3‑indoxyl‑α‑L‑fucopyranoside chemical‑data entry: https://nextsds.com/substances/171869-92-4-5-bromo-4-chloro-3-indoxyl-alpha-l-fucopyranoside
• AdventChemBio – product information and COA‑style file for X‑α‑L‑Fuc (for reference to assay and purity protocols): https://www.adventchembio.com/uploads/coa/coa-files/CygVwm15zaoU2AASqyjKsD0jwKQd6tcdwmq4m142.pdf