Access to fluorescent probes via allyl glycosides: the synthesis of a Brucella trisaccharide epitope linked to a coumarin.

Oligosaccharide allyl glycosides are demonstrated to provide a route to fluorescent probes and simple inhibitors. Ethyl 2-O-acetyl-4-azido-3-O-benzoyl-4,6-dideoxy-1-thio-alpha-D-mannopyranosid e (6) was used as glycosyl donor in the preparation of the trisaccharide [alpha-D-Rha p4NFo-(1----2)-]2-alpha-D-Rha p4NFo-O-allyl (16). Thioglycoside 6 was activated with N-iodosuccinimide and triflic acid or by bromine in the glycosylations and the inhibitor 16 was obtained after deprotection by transesterification, reduction of the azido groups with hydrogen sulfide, and N-formylation with ethyl formate. Ozonolysis of the allyl glycoside in 16 and reductive amination with 7-amino-4-methylcoumarin then gave the target fluorescent trisaccharide conjugate.