Urease inhibition by polymer analogs of substrate and thiophosphamides

Inhibition of soybean urease by polymeric substrate analogues, urea and thiourea polydisulfides (PDSU and PDSTU, respectively), or three thiophosphoric acid amides (TPAA), tri-(N-3-hydroxyphenyl)thiophosphamide (1), tri-(N-4,4'-aminodiphenyl)thiophosphamide, and di-oxy-(N-alpha-piridyl)thiophosphamide (3) was studied in aqueous solutions at various pH values. The inhibitory effects of all these substances were reversible and competitive with the lowest inhibition constant Ki 2.8 microM for TPAA-1 at pH 3.85. Above and below this pH value, Ki increased reaching 24 [mu]M at pH 7.2. All test substances inhibited urease comparably with known inhibitors such as thiols (cysteamine, etc.) and hydroxamic acid derivatives, but were less efficient than phosphorodiamidates. Structural features of possible urease inhibitors of higher efficiency were proposed.