Chemiluminescence quenching of pteroic acid-N-sulfonyl-acridinium-9-carboxamide conjugates by folate binding protein.

N(10)-Trifluoroacetylpteroic acid was conjugated to chemiluminescent N-sulfonylacridinium-9-carboxamide labels at the N(10) or 9-position carboxamide. Upon binding to folate binding protein the light output of the N(10) derivative (9) was quenched up to 62% upon triggering with basic peroxide, while the 9-position carboxamide conjugate (7) was quenched only 12%. The utility of this effect was demonstrated in a model homogeneous chemiluminescent assay for folic acid.