Synthesis, Novel Crystal Structure, andβ-Amyloid Binding Property of Re(I)(tricarbonyl)+EHIDA Analogue

A neutral compound Re(CO) 3 (L) (L: 2-((2-(2,6-diethylphenylamino)-2-oxoethyl)(2-ethoxy-2-oxoethyl)amino)acetic acid, an IDA analogue) has been synthesized and evaluated for in vitro imaging probes of β -amyloid (A β ) aggregates. Results of X-ray measurement of Re(CO) 3 (L) demonstrated that the coordination mode of Re(CO) 3 (L) was different from that of classical Re/Tc(I) (tricarbonyl)-IDA analogues; the structure of Re(CO) 3 (L) was confirmed by means of infrared spectrum, HPLC-UV, TOF MS, and X-ray measurements (Cambridge Crystallographic Data Centre number is 732731): monoclinic P2 1 / c , a = 15.6636 (12) Å, b = 10.9360 (8) Å, c = 27.756 (2) Å, α = 90.000 (0)°, β = 90.783 (5)°, γ = 90.000 (0)°, and Z = 8. The binding affinity for β -amyloid plaques was assessed by in vitro binding assay using preformed synthetic A β (1–40) aggregates. The neutral compound Re(CO) 3 (L) showed binding affinity to A β aggregates at micromolar level by fluorescence spectroscopy, and this work will encourage for further exploration of imaging agents labeled by 99m Tc(CO) 3 + center as probes for β -amyloid plaques in vivo.