Biosynthesis of novel 7,8-dihydroxyflavone glycoside derivatives and in silico study of their effects on BACE1 inhibition

7,8-Dihydroxyflavone (7,8-DHF) has been conjugated with glucose moiety to produce glucoside derivatives. Three analogues of 7,8-DHF (7-O-β-d-glucosyl-8-hydroxyflavone, 7-hydroxy-8-O-β-d-glucosyl flavone, and 7,8-di-O-β-d-glucosylflavone) have been successfully produced from in vitro reaction using glycosyltransferase of Bacillus licheniformis. Production of these 7,8-DHF derivatives were shifted to cheaper and easier approach in this study by using engineered Escherichia coli BL21 (DE3) ΔpgiΔzwfΔushA cells in which the flow of glucose-6-phospahte toward glycolysis and pentose phosphate pathway and hydrolysis of UDP-α-d-glucose were blocked while directing the carbon flux toward UDP-α-d-glucose by overexpressing UDP-α-d-glucose pathway genes. Supplementation of 300 μM of 7,8-DHF to the culture resulted in production of 171 μM of 7-O-β-d-glucosyl-8-hydroxyflavone, 68 μM of 7-hydroxy-8-O-β-d-glucoxyflavone, and 55 μM of 7,8-di-O-β-d-glucoxyflavone in laboratory-scale 3-L fermentor, representing 98% bioconversion of initially fed substrate to respective glucoside derivatives within 48 H. These products were characterized by high-performance liquid chromatography-photodiode array (HPLC-PDA), HPLC-PDA-quadruple time of flight-electron spray ionization mass spectrometry, and nuclear magnetic resonance analyses. These newly synthesized derivatives were found to be able to interact with amino acids of active site of human β-site amyloid precursor protein cleaving β-site amyloid precursor protein cleaving enzyme 1 (BACE1) β-secretase enzyme in in silico studies, thus displaying possible application in cure of Alzheimer's disease.