An improved and operationally simple synthesis of 3-indoxyl-β-D-galactopyranoside (indoxyl-
gal) is disclosed. Indoxyl-gal is a sensitive chromogenic histochemical used for the identification
of β-galactosidase enzymatic activity (lacZ gene). Synthesis of indoxyl-gal is improved to 25% overall
yield in 5 linear steps from affordable starting materials with minimal chromatography. Biological testing
confirmed the detection of β-galactosidase activity in all (100%, 19 strains) coliform bacteria using
membrane filtration and modified MI agar.
Keywords: 3-Indoxyl-β-D-galactopyranoside, β-galactosidase, chromogenic dye, coliform bacteria, histochemistry, indicators.
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