Isolation and characterization of side-products formed through ∆2-isomerization in the synthesis of cefpodoxime proxetil

In the synthesis of cephalosporin antibiotics, esterified in 4-position, the ∆2-isomerization is a well-known side reaction proceeding under basic conditions. In this work, we investigated the ∆2-isomerization of the esterified cefpodoxime proxetil. Due to the R-configuration and S-configuration of the stereogenic center in the side chain in 4-position, there are two starting materials being diastereomeric to each other. Furthermore, an additional stereogenic center is formed in the isomerization step, thus leading to four possible products. To the best of our knowledge, in this work for the first time the ∆2-isomerization of the two isolated diastereomers of AMCA proxetil, a precursor of cefpodoxime proxetil, as a starting material is reported. It has been shown, that each diastereomer only reacts to one of the two possible ∆2-diastereomers. The synthesis, isolation and characterization of (R)-diastereomers as well as (S)-diastereomers of ∆2-AMCA proxetil and cefpodoxime proxetil, respectively, are presented.

An improved method for preparation of cefpodoxime proxetil

Cefpodoxime proxetil, a third-generation cephalosporin for oral administration, was synthesized by a method based on the following sequence of reactions: acylation of 7-aminocephalosporanic acid (7-ACA) with S-benzothiazol-2-yl(2-amino-4-thiazolyl)(methoxyimino)thioacetate (MAEM), chloroacetylation of the cefotaxime formed with chloroacetyl chloride, esterification of the acid function with 1-iodoethyl isopropyl carbonate and final cleavage of chloroacetamide protective group by treatment with thiourea in N,N-dimethylacetamide. The developed procedure allows us to obtain better yields of cefpodoxime proxetil and to eliminate the final purification step by column chromatography, necessary during the synthesis of this antibiotic by the previously reported methods.

AS-924, a novel orally active bifunctional prodrug of ceftizoxime. Synthesis and relationship between physicochemical properties and oral absorption

Ceftizoxime (CZX), a parenteral cephalosporin, has potent and broad antibacterial activity. To improve its oral absorption, we synthesized a series of monofunctional and bifunctional prodrugs of CZX. In rabbits, urinary recovery after oral administration of CZX was improved by esterification of the carboxyl group at the C-4 position with various lipophilic moieties (monofunctional prodrugs), and was further increased by introduction of a hydrophilic L-alanine to the amino group on the thiazole ring at the C-7 position (bifunctional prodrugs). Least-squares analysis showed good parabolic correlations between log P and urinary recovery for monofunctional and bifunctional prodrugs, respectively. AS-924, a bifunctional prodrug with a pivaloyloxymethyl and L-alanyl moiety had the best balance of lipophilicity and water-solubility for oral absorption among the prodrugs synthesized.

AS-924, a novel bifunctional prodrug of ceftizoxime

To improve the oral absorption of ceftizoxime (CZX), 7beta-[(Z)-2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]- 3-cephem-4- carboxylic acid, we synthesized and evaluated a novel series of bifunctional prodrugs, in which L-alanine was introduced into the aminothiazole-oxime moiety at the C-7 position of the various lipophilic esters of CZX. Among these prodrugs, pivaloyloxymethyl 7beta-[(Z)-2-(2-(S)-alanylaminothiazol-4-yl)-2-methoxyiminoa cetamido]-3-cephem-4-carboxylate hydrochloride (ceftizoxime alapivoxil, AS-924) was well absorbed after oral administration in experimental animals and showed potent therapeutic effects in mice infected with gram-positive and gram-negative bacteria.