Indoxyl glycosides are useful chromogenic substrates for the detection of glycosidase activity; hydrolysis of the glycosidic bond releases a free indoxyl moiety that can oxidatively dimerize to produce insoluble indigo-type dyes. A classic and ubiquitous example of an indoxyl glycoside is 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside, commonly called as X-gal. This analog of lactose can be cleaved by β-galactosidase enzyme to produce insoluble intensely blue product 5,5'-dibromo-4,4'-dichloro-indigo upon hydrolysis. Several methods to generate these indoxyl glycoside bearing pyranose sugars have been reported in the past. Our group is specifically interested in septanose containing indoxyl glycosides. Septanoses are the synthetic analogs of pyranoses with one extra carbon atom added to the ring. The synthesis of indoxyl glycosides bearing septanose sugars are made via combination of an individually synthesized donor and acceptor using a glycosylation reaction. Our key intermediates, per-<i>O</i>-acetyl septanoses, are generated using benzyl protected pyranose lactols via a five-step process. These sugars are converted to their anomeric bromides and then transformed to the indoxyl glycosides via a phase transfer glycosylations. We report the synthesis of the septanosides and preliminary hydrolysis experiments with Streptomyces β-glucosidase Bgl.

X-Sept: Synthesis of indoxyl septanosides as chromogenic glycosidase substrates

254th National Meeting (2017)

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