Salmon-Gal 

Salmon-Gal (Red-Gal, 6-Chloro-3-indolyl-β-D-galactopyranoside, CAS 138182-21-5) serves as an alternative chromogenic substrate to X-Gal for detecting β-galactosidase (β-Gal, EC 3.2.1.23) activity in molecular cloning and microbiology, hydrolyzing at the β1-4 glycosidic bond to release 6-chloroindol-3-ol that spontaneously dimerizes and oxidizes into a pink-red to salmon-colored insoluble precipitate, enabling clear visual discrimination of enzyme-positive colonies or plaques. With molecular formula C14H16ClNO6 (MW 329.73 g/mol), this white crystalline compound features β-D-galactopyranose O-linked to the 3-position of 6-chloro-1H-indol-3-ol, offering improved contrast and reduced background compared to the blue X-Gal product in crowded plates or light-colored media, while maintaining equivalent sensitivity for lacZ α-complementation screening in E. coli hosts (JM109, DH5α). Used with IPTG (0.1-1 mM) at 20-100 μg/mL in LB agar, it produces pink-red recombinants (lacZ-) versus non-recombinants (lacZ+), supporting high-throughput blue/white screening orthogonal to GUS/X-GlcA systems, with applications extending to mammalian β-Gal detection in lysosomal storage disorder diagnostics (GM1-gangliosidosis) and functional assays of engineered galactosidases. The single chlorine substitution enhances color purity (λmax ~520-550 nm) and oxidation kinetics over dibromo-dichloro analogs, minimizing diffusion artifacts while providing permanent archival staining visible under daylight without UV excitation.

Appearance

• White to off-white crystalline powder.
• Enzymatic hydrolysis yields pink-red to salmon insoluble precipitate.

Source

• Koenigs-Knorr synthesis: protected β-D-galactopyranosyl halide + 6-chloroindol-3-ol.
• Commercial molecular biology grade (Sigma-Aldrich, Duchefa >98%).

Molecular Weight and Structure

• Formula: C14H16ClNO6; MW 329.73 g/mol.
• (2S,3R,4S,5R,6R)-2-(6-chloro-1H-indol-3-yloxy)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol.

Sugar Specificity

• Selective β-D-galactopyranoside for β-galactosidases (lacZ, lysosomal).
• Negligible cross-reactivity with glucosidases.

Biological Activity

• Chromogenic β-Gal reporter; equivalent sensitivity to X-Gal.
• Non-toxic; pink-red product formation.

Purity and Microbial Contamination

• 98% (HPLC); molecular biology certified.
• Synthetic reagent; non-sterile.

Identity and Quality Control

• ¹H-NMR (anomeric H-1 ~5.2 ppm d, J=7.8 Hz); [α]D ~-50° (c=1, DMF).
• Pink-red hydrolysis product confirmed.

Shelf Life and Storage

• 3 years at 2-8°C dry; soluble in DMSO/DMF.
• Light/moisture protected.

Applications

• Alternative to X-Gal for lacZ blue/white screening.
• β-Galactosidase assays, recombinant selection.

Key Characteristics

• Pink-red color (less background than X-Gal blue).
• Improved contrast in light media; daylight visible.

Citation Links

• https://pubchem.ncbi.nlm.nih.gov/compound/44630036
• https://duchefa-biochemie.com/product/details/number/S1403
• https://pubchem.ncbi.nlm.nih.gov/compound/10336708
• https://www.sigmaaldrich.com/IN/en/product/sigma/res1364c
• https://cymitquimica.com/cas/138182-21-5/
• https://www.chemicalbook.com/ChemicalProductProperty_IN_CB8278753.htm
• https://kd15.krackeler.com/catalog/sigma/SIGMA/RES1364C
• https://cymitquimica.com/products/SR-98551/138182-21-5/
• https://www.chemicalbook.in/product/5-bromo-6-chloro-3-indolyl-beta-d-galactoside-1131648
• https://www.abcam.com/en-us/products/biochemicals/x-gal-chromogenic-beta-galactosidase-substrate-ab144388