α-Glucosidase inhibitory effect of a bioactivity guided fraction GIB-638 from Streptomyces fradiae PWH638

The new N-containing maltooligosaccharides GIB-638 were isolated and purified from the culture filtrate of Streptomyces fradiae PWH638 using the chemoenzymatic method. Its physicochemical properties, liquid chromatographic behaviour and spectroscopic data were similar to the reported compounds acarviostatin I03 with a molecular weight of 969 Da. Its structures were determined by spectroscopic methods, including ESI multistage mass spectrometry and two-dimensional NMR techniques. It was the first time isolated from S. fradiae PWH638 and exhibited effective inhibitory activity against human maltase-glucoamylase. The inhibition constants for GIB-638 against MGAMnt and MGAMct were 47.8, 24.03 μmol, respectively. It also could inhibit the maltose hydrolysis and glucose transfer in the in vitro-everted intestine model. The results from this study could provide the scientific evidence for it to use in the treatment of diabetes in medicine.