Synthesis of CpFe(CO)(L) complexes of hydantoin anions (Cp = eta(5)-C5H5, L = CO, PPh3), and the use of the 5,5-diphenylhydantoin anion complexes as tracers in the nonisotopic immunoassay CMIA of this antiepileptic drug

As part of our ongoing development of the CMIA nonisotopic immunoassay meth od, in which the tracers are metal carbonyl complexes and detection is by F ourier transform infrared spectroscopy, we examined the potential use as tr acers of the complexes CpFe(CO)(2)(5,5-diphenylhydantoin) 2d and CpFe(Co)(P Ph3)(5,5-diphenylhydantoin) 3. The present study involved the synthesis of a series of hydantoin complexes (2a-2d), in particular that of the derivati ve of 5,5-diphenylhydantoin 2d. The structure of 2d was confirmed by X-ray crystallography. The infrared analysis, establishing the position and inten sity of the characteristic metal-carbonyl peaks of complexes 2d and 3 in th e 1850-2200 cm(-1) region, shows that measurement of the absorbance values of these characteristic peaks will permit quantitative analysis in the pico mole range, the norm for routine use in immunoassay and thus suitable for u se as CMIA tracers. Cross-reaction rates of these tracers with anti-DPH spe cific antibodies show that 2d and 3 are both recognized by anti-DPH antibod ies (cross-reaction rates 43 and 20%, respectively). In developing a CMIA o f DPH with these tracers, it was found that 3, with a single, intense band at 1977 cm(-1), had very promising IR characteristics for use in multiassay CMIA, but probably owing to its relatively weak affinity for the antibodie s, it was not possible to develop a CMIA for DPH using this tracer. Complex 2d, however, showed better recognition by the antibodies, and using this c omplex as a tracer, it was possible to develop a particularly sensitive mon oassay of DPH by the CMIA method.