Preparation of 1-acyloxyethyl esters of 7-(2-(2-aminothiazol-4-yl)acetamido)-3-(((1-(2-dimethylaminoethyl)-1H-tetrazol-5-yl)thio)methyl)ceph-3-em-4-carboxylic acid (cefotiam) and their oral absorption in mice.

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Abstract
In a separate study on the orally active acyloxymethyl esters (1) of 7-[2-(2-aminothiazol-4-yl)acetamido]-3-[[[1-(2-dimethylaminoethyl)-1H-tetrazol-5-yl]thio]methyl]ceph-3-em-4-carboxylic acid (cefotiam, CTM), we have shown, by quantitative structure-oral bioavailability (BA) relation analysis, that the R2 group in the acyl group R2CO must have both an adequate lipophilicity (HANSCH''s lipophilic parameter, .pi.) and steric hindrance (TAFT''S Es value). However, to satisfy these requirements, a complex alkyl group R2 must be employed, the ester of which is difficult to synthesize and has unique metabolic fate. In this study, we selected and prepared the 1-acyloxethyl esters (2) of CTM instead of 1 to avoid R2 groups that are too complicated. We found that the esters (2) gave improved oral BAs over 1: the 1-(3-methylvaleryloxy)ethyl ester (2h) showed the highest peak plasma CTM level (Cmax) comparable to that obtained after subcutaneous injection of CTM. The 1-(cyclohexylacetoxy)ethyl ester (2t), the 1-(2-ethylbutyryloxy)ethyl ester (2j), and 2h showed BAs near 100%. For these esters (2), good correlations were also observed among the .pi., the Es values of R2, and the log Cmax and log BA in the analysis of the quantitative structure-oral bioavailability relation; an ester having an alkyl group as R2 with .pi. valur of 3.07 or 3.08 and a Es value of -1.04 or -1.29 gave the highest Cmax or BA, respectively. As expected, the optimal .pi. values are almost the same as those obtained with 1 but the optimal Es values are larger (Es = -2.07). Thus, it has been confirmed by preparing 1-acyloxyethyl esters (2) of CTM that the oral bioavailability of CTM can further be improved without preparing acyloxymethyl esters (1) with a complicated acyl group.