To improve the oral absorption of meropenem (MEPM), we synthesized and evaluated a series of its double-promoiety prodrugs, in which lipophilic promoieties were introduced into carboxyl and pyrrolidinyl groups. Among these prodrugs, pivaloyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate (4) and 1-ethylpropyloxycarbonyloxymethyl (1R,5S,6S)-2-[(3S,5S)-5-(N,N-dimethylcarbamoyl)-1-(isobutyryloxymethyloxycarbonyl)pyrrolidin-3-ylthio]-6-[(1R)-1-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate (8) were chosen for further evaluation. Compounds 4 and 8 were well absorbed after oral administration to rats and beagles (bioavailability 18.2-38.4%), and expected to show potent therapeutic efficacy in patients infected with various pathogens, such as penicillin-resistant S. pneumoniae and b-lactamase-negative ampicillin-resistant H. influenzae. The Journal of Antibiotics (2011) 64, 233-242; doi:10.1038/ja.2010; published online 12 January 2011Keywords: carbapenem; double-promoiety prodrug; meropenem; single-promoiety prodrug
INTRODUCTIONCarbapenems are the most potent class of b-lactam antibiotics, which have a broad spectrum of potent antibacterial activities against Grampositive and Gram-negative organisms, including P. aeruginosa. 1,2 Carbapenems are stable to hydrolysis by various b-lactamase, and thus, effective against most cephalosporin-resistant microorganisms. [3][4][5] Imipenem, panipenem and meropenem (MEPM) have long been used for serious infectious diseases, including complicated urinary tract infection and complicated respiratory tract infection (Figure 1). 1 Recently, doripenem has been launched as a new potent carbapenem (Figure 1). 6 However, these are all for parenteral use only. Imipenem and panipenem are unstable chemically and to renal dehydropeptidase-I, and are thus used in combination with cilastatin and betamipron, respectively. MEPM and doripenem have a 1b-methyl group, and are stable against chemical degradation and hydrolysis by dehydropeptidase-I, 7-9 and are thus used without cilastatin or betamipron.All these parenteral carbapenems have a carboxyl group at the carbapene C-3 position, which is essential for interaction with a target protein, penicillin-binding protein, 1 and a basic group at the pyrrolidine N-1 position, which promote their invasion through D2 porin into P. aeruginosa, 10 resulting in little oral absorption because of the two ionizable groups. Many attempts to find new orally active carbapenems have been reported, 11,12 in which the basic group at the pyrrolidine N-1 position was eliminated and the carboxyl group was esterified by easily hydrolizable promoiety to increase oral absorption, but most showed very weak antibacterial activity against P. aeruginosa. Recently, tebipenem was developed in Japan and approved as a new orally active carbapenem ( Figure 1). Tebipenem showed potent activity against penicillin-resistant S. pneumoniae, b-lactamase-negat...