| The putative 2:1 Yb3+: pyrocatechol violet (PV) complex developed by Yin et al. as a phosphate sensor was evaluated for detection of pyrophosphate analogues, namely, phosphonocarboxylates and bisphosphonates. Foscarnet (PFA), alpha,alpha-dichloro phosphonoacetate, pamidronate, methylenebisphosphonate, thiophosphonoformic acid (TPFA), zoledronate and alpha-hydroxy methylenebisphosphonate all displaced yellow PV from the blue Yb3+/PV complex in aqueous HEPES buffer at pH 7, analogously to phosphate and ATP. However, the titration curves were sigmoidal, in contrast to the linear titration curves for phosphate and ATP reported by Yin. Reinvestigation of the Yb3+/PV system with phosphate and ATP reveals these analytes also produce non-linear titration curves under Yin's conditions, and that the stoichiometry of the Yb3+/PV complex is actually 1:1. Using suitably revised assay conditions and this corrected stoichiometry, quantitative analyses of ATP, phosphate and PFA were constructed. The minimum detectable concentrations of PFA were < 1 microM at 623 nm and < 2 microM at 443 nm for PFA using 50 microM sensor and a 1 cm path length. The sensitivity of this new assay for PFA is significantly higher than previous UV, electrochemical or other detection methods.;In studies to explore new approaches to improve the bioavailability of foscarnet, C-epsilon-amido-Lys-Aa-OR (1) and P-gamma-ester Ser-OR (2) conjugates of PFA were investigated. The syntheses of five derivatives 1 were studied: PFA-L-Lys-L-Phe-OMe, PFA-L-Lys-L-Phe, PFA-D-Lys-D-Phe, PFA-L-Lys-L-Tyr and PFA-L-Lys-LTrp. Application of Mitsunobu chemistry to Ser ethyl ester and C-Ph O-Me PFA, produced a novel cyclic carbamide in low yield. |
