Synthesis of α-d-Glcp-(1 → 2)-α-d-Glcp-(1 → 3)-α-d-Glcp-O-(CH2)8COOCH3 for use in the assay of α-glucosidase I activity

The chemical synthesis of α-d-Glcp-(1 → 2)-α-d-Glc p-(1 → 3)-α-d-Glcp-O-(CH2)8COOCH3 (9), a substrate specific for α-glucosidase I, is reported. This enzyme removes the terminal α-d-Glcp unit to produce α-d-Glcp-(1 → 3)-α-d-Glcp-O-(CH2)8COOCH3 (10). This is the first synthetic substrate described for glucosidase I that allows kinetic evaluation of substrates and inhibitors of this enzyme. Tetramethylrhodamine was coupled to 9 through an ethylenediamine linker to produce a brilliant red derivative. Addition of this fluorescent dye did not affect enzyme binding to the substrate, as determined by a comparison of the Km value (1.3 mM). The fluorescent label allows visual detection of 2–3 pmol of product by TLC.