Orally absorbable cephalosporin antibiotics. 3. Preparation of biologically active R-isomer of 7-(3-benzothienylglycylamido)deacetoxycephalosporanic acid

The methyl and isopropyl esters of (RS)-3-benzothienylglycine were resolved with (+)- and (-)-tartaric acid in acetonitrile to give the corresponding R and S salts. The R-salt 4 was hydrolyzed to (R)-3-benzothienylglycine (5). The amino group in 5 was protected with the Boc function and the protected R amino acid 6 coupled with the p-NB ester of 7-ADCA to give the diprotected cephalosporin 7. After removal of the Boc and p-NB groups, the R isomer of 7-(3-benzothienylglycylamido)deacetoxycephalosporanic acid (1) was obtained. The p-NB ester of epimeric cephalosporin 7 was separated by preparative chromatography into R and S isomers. After removal of the protective groups, the S epimer was isolated. The comparison of antibacterial activity of the R and S epimers and the RS mixture of cephalosporin 1 is reported.