Identification of α-Glucosidase Inhibitors from Ipomoea alba by Affinity-Directed Fractionation-Mass Spectrometry

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Size-exclusion chromatography, in conjunction with electrospray ionization mass spectrometry, exemplifies a screening methodology to identify α-glucosidase inhibitors from natural extracts. This approach could be used to speed the time of targeting active principles from complex matrices, as a substitute for the established in vitro enzymatic assays which depend on spectrophotometric methods where disadvantages including sensitivity to turbidity and substance interferences—extract pigmentation, or absorption in the visible light region of tested samples—represent factors that affect the chromogenic screenings. Gel permeation through a spin size-exclusion column allowed separating high-affinity molecules bounded to α-glucosidase in solution. After acid hydrolysis of the enzyme-ligand complex, electrospray ionization mass spectrometry was used as a direct detector for the ligand. This affinity-directed fractionation was illustrated by using a crude extract, semi-purified fractions, and pure active glycolipids from moon vine seeds, Ipomoea alba L., Convolvulaceae, in addition to acarbose (positive control), which led to the identification of albinosides VI (ESI-MS m/z 991 [M + Na]+) and VII (ESI-MS m/z 975 [M + Na]+), two tracked high-affinity glycolipids, which demonstrated an in vitro inhibitory potential of α-glucosidases from yeast and rat intestine. Molecular docking predicted that these inhibitors bind to the enzyme catalytic site as acarbose.