Patent ID: 8133695

Claim:
An assay for screening a test compound, wherein said assay is a binding assay using a fluorescent tracer and a source of a hERG K + channel or fragment thereof, comprising: a) incubating an assay sample comprising the fluorescent tracer, the source of the hERG K + channel or fragment thereof, an assay buffer, and a test compound; and b) measuring the amount of the fluorescent tracer bound to the hERG K + channel or fragment thereof in the sample, wherein the fluorescent tracer is a compound of structural formula: or a pharmaceutically acceptable salt thereof, wherein: Ar is a benzo ring; R 1 and R 2 are independently hydrogen or —NHSO 2 CH 3 ; the ring system comprising W, X, and Y 6-membered ring system wherein Y is —O—, W is C═O, —CH 2 —, C═NOH, —NH—, CHNH 2 , ═CH—, or ═N—, and X is —CH 2 — or ═CH—; B is a 6-membered N-containing ring; L is —(CR 4 R 5 ) m -Q—(CR 4 R 5 ) q —NH—[CZ—(CR 4 R 5 ) u -(D) w ] z —, wherein R 4 and R 5 are independently hydrogen or C 1-6 alkyl, Q is a bond, —O—, C═O, CHOH, —NR 5 — or —S(O) n —, Z is ═O or ═S, D is —O—, —S(O) n —, —NR 5 —, or —NR 5 SO 2 —, m and q are independently 1 to about 5, n is 0, 1, or 2, u is 0 to about 7, w is 0 or 1, z is 1 or 2; and R 3 is a fluorescent dye.