Detection of neurodegenerative diseases

A compound of formula I:

• P—Ar—R—X-T (I)
• wherein
• P is a residue of formula (a)
• wherein
• each of R1, R2, R3, R4, R5 and R6 is, independently, H or C1-C10alkyl, and
• each of S1 and S2 is, independently, a hydrophilic group of formula —C≡C-L-A wherein L is a single bond, C2-C4alkenylene or linear, branched saturated C2-C20 carbon chain interrupted by 1 to 10 oxygen atoms;
• and A is C1-C4 alkyl, a phosphate group or a sulfonate group;
• Ar is C5-C14arylene or heteroarylene on which —R—X-T is in ortho, meta or para position;
• R is —CO—NH—, —NH—CO—, —CH2—CO—NH— or —CH2—NH—CO—;
• and
• either X is a spacer serving to distance the residue T from the residue P without affecting the fluorescence of P and the biological activity of T, X being covalently bound through —S— to the α side chain of an amino-acid forming part of the residue T;
• and T is a peptidic residue selected from a residue of
• an Aβ peptide,
• QSHYRHISPAQVHHQK,
• RPRTRLHTHRNRHHQK,
• CKFFVLK-NH2
• KKFFVLK-NH2,
• KKFFVLKGK-NH2,
• and
• KKFFVLKGC-NH2
• or a derivative or a structural analog thereof, comprising at least one amino acid with an α side chain;
• or X is a spacer serving to distance the residue T from the residue P without affecting the fluorescence of P and the biological activity of T;
• and T is a group of formula (b)