Fluorescent enzymatic substrate having the structure (I) is new. Fluorescent enzymatic substrate having the structure of formula (S 1>-B 0>(I 1>) n-F 1>) (I) is new. S 1>saccharide skeleton constituted of a saccharide unit comprising monosaccharides, oligosaccharides having 2-9 saccharide and polysaccharide units having at least 10 saccharide units B 0>self-divisible spacer arm having one or more sub-units, where the arm is fixed in an anomeric position 1 of the saccharide unit, anomeric bond position is indifferent in position alpha or beta , and the appropriate sub units of spacer arm in (I) represents a linear or branched hydrocarbon chain optionally substituted, saturated, interrupted and/or terminated by one or more heteroatoms of N, O and S, and/or one or more groups comprising 1-4 carbon alkyl radicals, 1-4 carbon alkoxy, aryl or by one or more functions of ether, ester, amide, carbonyl, carbamate, urea, thiourea or disulfur F 1>fluorophore group carried by the spacer arm I 1>inhibitor group of the fluorescence F 1>, the Group I is a lateral substituent of at least one sub-unit spacer arm and n : 1 or 2. Provided that no covalent bond links the fluorophore group with inhibitor group directly. An independent claim is included for diagnostic reagent comprising a solution constituted of water or a mixture of water and an organic solvent, where the solution contains at least one enzymatic substrate (I).La présente invention est relative à des substrats enzymatiques fluorescents de nature saccharidique comportant un bras espaceur auto-sécable fonctionnalisé par un fluorophore F et par au moins un inhibiteur de la fluorescence de F, à leur utilisation à titre de réactif fluorescent pour la détection dune activité enzymatique in vitro ou pour la préparation dun réactif de diagnostic destiné à limagerie fonctionnelle in vivo.
