Studies on orally active cephalosporin esters. V. A prodrug approach for oral delivery of 3-thiazoliomethyl cephalosporin

Oral delivery of 3-thiazoliomethyl cephalosporin 1 was attempted through a prodrug approach by applying thiamine chemistry. The 3-thiazoliomethyl group was modified to a ring-opened structure with no ionic charge, and the 4-carboxyl group was converted to pivaloyloxymethyl ester. Lipophilicity of the resulting derivatives (8-10) was suitable for passive absorption from the intestinal tract, and chemical stability in phosphate buffer solution (pH 6.86) was moderate. When administered orally to mice, these derivatives were mainly transformed to a novel 3-spiro cephalosporin 11, and desired reconversion to the 3-thiazoliomethyl cephalosporin was minor. Isomerization to delta 2-cephalosporin 14 was also observed. These results showed that the derivatives (8-10) tested in this study did not serve as orally active prodrugs of 3-thiazoliomethyl cephalosporin 1.