Carbapenems and Penems

Abstract

In the period up to 1970 most β‐lactam research was concerned with the penicillin and cephalosporin group of antibiotics. Since that time, however, a wide variety of new mono‐ and bicyclic β‐lactam structures have been described. The carbapenems originated from natural sources; the penem ring and its derivatives are the products of the chemical synthetic approach to new antibiotics. The chemical names are: 7‐oxo‐( R )‐1‐azabicyclo[3.2.0]hept‐2‐ene‐2‐carboxylic acid, C 7 H 7 NO 3 , and 7‐oxo‐( R )‐4‐thia‐1‐azabicyclo[3.2.0]hept‐2‐ene‐2‐carboxylic acid, C 6 H 5 NO 3 S, respectively. Carbapenems include thienamycin (C 11 H 16 N 2 O 4 S), MM 4550 (C 13 H 16 N 2 O 9 S 2 ), MM 13902 (C 13 H 16 N 2 O 8 S 2 ), MM 17880 (C 13 H 18 N 2 O 2 S 2 ), PS‐5 (C 13 H 18 N 2 O 4 S), carpetimycin A (C 14 H 18 N 2 O 6 S), asparenomycin A (C 14 H 16 N 2 O 6 S), and pluracidomycin A (C 9 H 11 NO 10 S 2 ). Only S. cattleya and S. penemfaciens have been reported to give thienamycin. Thienamycin is isolated as a colorless, hygroscopic, zwitterionic solid. Carbapenems are extremely sensitive to many reaction conditions. Many derivatives of the amino, hydroxy, and carboxy group of thienamycin have been prepared primarily to study structure–activity relationships. One consequence of the discovery of the carbapenem natural products has been the development of new synthetic methods. Only chemical synthesis could provide the quantities of N ‐formimidoyl thienamycin (MK 0787) necessary for clinical trials and commercial production. A synthetic approach that involves the [3,4] bond formation using a carbene insertion reaction has been highly successful. A second method makes use of the lactone from acetone dicarboxylate. Thienamycin, the olivanic acids, and the majority of carbapenems are highly active broad‐spectrum antibiotics. Of the natural products, thienamycin is the most potent. Unlike carbapenems, no penems have been found in nature. The penem acid was shown to possess antibacterial activity in spite of its rather limited stability. Penems include SCH 29482 (C 10 H 13 NO 4 S 2 ), SCH 34343 (C 11 H 14 N 2 O 6 S 2 ), FCE 221201 (C 10 H 12 N 2 O 6 S), and others. 6‐Unsubstituted penems exhibit good activity against both gram‐positive and gram‐negative bacteria. Extensive carbapenem and penem antibiotic research has been ongoing since thienamycin was discovered in 1978. However, only the imipenem–cilastatin combination has become a commercial product. Meropenem was expected to be the second carbapenem on the market.