Galactosides

X-gal (also abbreviated BCIG for 5-bromo-4-chloro-3-indolyl-β--galactopyranoside) is an organic compound consisting of galactose linked to a substituted indole. The compound was synthesized by Jerome Horwitz and collaborators in 1964. The formal chemical name is often shortened to less accurate but also less cumbersome phrases such as bromochloroindoxyl galactoside. The X from indoxyl may be the source of the X in the X-gal contraction. X-gal is often used in molecular biology to test for the presence of an enzyme, β-galactosidase, in the place of its usual target, a β-galactoside. It is also

A galactoside is a glycoside containing galactose. The H of the OH group on carbon-1 of galactose is replaced by an organic moiety. thumb|224x224px|Structure of ONPG, an example of a β-galactoside. Depending on whether the glycosidic bond lies "above" or "below" the plane of the galactose molecule, galactosides are classified as α-galactosides or β-galactosides.

'''ortho-Nitrophenyl-β-galactoside (ONPG''') is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity. This compound is normally colorless. However, if β-galactosidase is present, it hydrolyzes the ONPG molecule into galactose and ortho-nitrophenol. The latter compound has a yellow color that can be used to check for enzyme activity by means of a colorimetric assay (at 420 nm wavelength). β-Galactosidase is required for lactose utilization, so the intensity of the color produced can be used as a measure of the enzymatic rate.

Phenyl--galactopyranoside is a substituted galactoside.

Ciceritol is a cyclitol. It is a pinitol digalactoside that can be isolated from seeds of chickpea, lentil and white lupin.