Dehydropeptidase

In addition to variable chemical stabiUty the carbapenems are susceptible to P-lactam cleavage by a dehydropeptidase en2yme (DHP-I) located on the bmsh borders of the kidney (53). Clinically, MK 0787 (18) is used with an inhibitor of this en2yme, cil a sta tin [78852-98-9] (MK 0791) (34), 16 26 2 5 dramatic effect not only on the urinary recovery of the drug, but also reduces any nephrotoxic potential (52) (see Enzyme... 

In terms of activity there seems little to prevent some of these compounds finding a place in therapy, especially those such as SCH 29482, SUN 5555, and FCE 25199 which have oral absorption properties. However, as is the case for the carbapenems, some penems ate extensively metabolized by human renal dehydropeptidase-1 enzyme (144). Although no penem has received approval for clinical use as of this writing, expectations ate high that future research and development will change that. 

Thienamycin (Fig. 5.5E) is a broad-spectrum /3-lactam antibiotic with high /3-lactamase resistance. Unfortunately, it is chemically unstable, although the TV-formimidoyl derivative, imipenem, overcomes this defect. Imipenem (Fig. 5.5E) is stable to most/3-lactamases but it readily hydrolysed by kidney dehydropeptidase and is administered with a dehydropeptidase inhibitor, cilastatin. Meropenem, which has yet to be marketed, is more stable than imipenem to this enzyme and may thus be administered without cilastatin. Its chemical structure is depicted in Fig. 5.5F. 

By screening 53 Rhodococcus and Pseudomonas strains, an NHase-amidase biocatalyst system was identified for the production of the 2,2-dimethylcyclopropane carboxylic acid precursor of the dehydropeptidase inhibitor Cilastatin, which is used to prolong the antibacterial effect of Imipenem. A systematic study of the most selective of these strains, Rhodococcus erythropolis ATCC25 544, revealed that maximal product formation occurs at pH 8.0 but that ee decreased above pH 7.0. In addition, significant enantioselectivity decreases were observed above 20 °C. A survey of organic solvent effects identified methanol (10% v/v) as the... 

The modified Hantzsch condensation of nitroacetone, 2,l,3-benzoxadiazol-4-carboxaldehyde 253, and ( S,ZR)-Z-(3,5-dinitrophenylcarbonylamino)-2-methoxycarbonyl-l-methylethyl 3-aminocrotonate afforded a mixture of the two diastereomers that differ in configuration (S or R) at the C-4 position of the 1,4-DHP ring (DHP - dehydropeptidase) (Equation 49) <2004JME254>. 

The first carbapenem released for clinical use was imipenem (5.46), a compound with relatively high resistance to microbial /3-lactamases. The addition of the (iminomethyl)amino side chain renders imipenem chemically more stable than thienamycin. But, like thienamycin, imipenem is also easily hydrolyzed by renal dehydropeptidase I, producing a mixture of /3-lactam ring-opened 1-pyrrolidine epimers at C(3) [161], The renal metabolism of imipenem can be minimized by co-administration of cilastatin (5.53), a competitive inhibitor of DHP-I [15 6] [162],... 

Like carbapenems, several penems have also been found to be susceptible to renal dehydropeptidase degradation [165-167], 6-Substituted methyl-idene-penems 5.56 are very potent broad-spectrum inhibitors of bacterial /3-lactamase, with the inhibitory activity residing predominantly in the (5R)-enantiomers. As a rule, the (5S)-enantiomers are less stable than the (5R)-enantiomers toward DHP-I [168],... 

H. Kropp, J. G. Sundelof, R. Hajdu, F. M. Kahan, Metabolism of Thienamycin and Related Carbapenem Antibiotics by the Renal Dipeptidase, Dehydropeptidase I , Antimi-crob. Agents Chemother. 1982, 22, 62-70. 

M. Hikida, M. Yoshida, S. Mitsuhashi, Comparative Stability of Carbapenem and Pe-nem Antibiotics to Renal Dehydropeptidase-1 , Arzneim.-Forsch. 1993, 43, 71-73. 

This enzyme [EC 3.5.1.14] (also referred to as histozyme, hippuricase, benzamidase, dehydropeptidase II, amino-acylase I, and acylase I) catalyzes the hydrolysis of an A-acyl-L-amino acid to yield a fatty acid anion and an L-amino acid. The enzyme has a wide specificity for the amino acid derivative. It will also catalyze the hydrolysis of dehydropeptides. 

There are many dipeptidases [EC 3.4.13.x]. Cytosol nonspecific dipeptidase [EC 3.4.13.18] (also referred to as peptidase A, glycylglycine dipeptidase, glycylleucine dipeptidase, and A -)3-alanylarginine dipeptidase) catalyzes the hydrolysis of dipeptides. Membrane dipeptidase [EC 3.1.13.19] (also known as microsomal dipeptidase, renal dipeptidase, and dehydropeptidase I) is a zinc-dependent enzyme (a member of the peptidase family M19) that also catalyzes the hydrolysis of dipeptides. 

Pharmacology This product is a formulation of imipenem, a thienamycin antibiotic, and cilastatin sodium, the inhibitor of the renal dipeptidase, dehydropeptidase-1, which is responsible for the extensive metabolism of imipenem when it is administered alone. Cilastatin prevents the metabolism of imipenem, increasing urinary recovery and decreasing possible renal toxicity. The bactericidal activity of imipenem results from the inhibition of cell-wall synthesis, related to binding to penicillin-binding proteins (PBP). 

Imipenem-cilastatin is only available for intramuscular or intravenous administration because oral bioavailability is poor. The enzyme, dehydropeptidase 1, present in renal tubules, converts imipenem to an inactive metabolite. To decrease metabolic clearance, imipenem is combined with cilastatin, an inhibitor of dehydropeptidase I. Additional pharmacokinetic information appears in Table 45.2. 

Meropenem (Merrem) is another carbapenem antibiotic with a broad spectrum of activity comparable to that of imipenem. A methyl group attached at the one-position on the five-member ring confers stability to dehydropeptidase 1. Consequently, meropenem does not require administration with cilastatin. When compared in human trials, imipenem-cilastatin and meropenem achieve similar clinical outcomes in patients with serious intraabdominal and soft tissue infections. Both imipenem-cilastatin and meropenem are used to treat infections caused by highly resistant Klebsiella pneumoniae producing ESBLs.The major cUnicaUy relevant distinction between imipenem-cilastatin and meropenem... 

Mechanism of Action A fixed-combination carbapenem. Imipenem penetrates the bacterial cell membrane and binds to penicillin-binding proteins, inhibiting cell wall synthesis. Cilastatin competitively inhibits the enzyme dehydropeptidase, preventing renal metabolism of imipenem. Therapeutic Effect Produces bacterial cell death. Pharmacokinetics Readily absorbed after IM administration. Protein binding 13%-21%. Widely distributed. Metabolized in the kidneys. Primarilyexcreted in urine. Removed by hemodialysis. Half-life 1 hr (increased in impaired renal function). 

IV administration renal clearance (half-life 1 h), dosed every 6-8 h, cilastatin added to prevent hydrolysis by renal dehydropeptidase Toxicity Seizures especially in renal failure or with high doses (> 2 g/d)... 

Meropenem, doripenem Intravenous, similar activity to imipenem stable to renal dehydropeptidase, lower incidence of seizures... 

Bicyclic-P-lactams Antibacterial and highly stable to porcine renal dehydropeptidase-I (DHP-I)... 

In humans, imipenem was foimd to be metabolized by an enzyme in the kidney, renal dehydropeptidase-I, which acts as a P-lactamase. Since the enzyme appears to serve no essential role in human metabolism, scientists were able to develop a synthetic competitive inhibitor, cilastatin, which they then used with imipenem to produce the combination drug, primaxin (Tienam). Primaxin was introduced into medical practice in 1985. 

Of the many derivatives prepared, BRL 42715 (31) was the compound with the best overall activity and stability. The enzyme, renal dehydropeptidase I (RDHP) is known to be a major cause of metabolic inactivation of carbapenems, such as imipenem, and penems. Whereas the ethylidene derivative (90c) showed substantial degradation of the biologically active (5R)-enantiomer in the presence of human kidney homogenate, BRL 42715 proved particularly stable, with 68% surviving after I hour s exposure to human kidney [90,91], In addition, BRL 42715 was only moderately bound (68%) to human serum. 

Thienamycin and its derivatives are exciting new antibiotics. Then-clinical use is limited, however, by their susceptibility to the kidney enzyme dehydropeptidase I. Reversible inhibition of this enzyme is provided by cilastatin [11]. The preparation of the S-cyclopropane portion [10] of cilastatin is achieved (16) by decomposition of ethyl diazoacetate in isobutylene [9] in the presence of the chiral copper catalyst R-7644. The product [10] is obtained in 92% e.e. and then further processed to cilastatin. Cilastatin is now marketed in combination with the thienamycin derivative imipenem as a very-broad-spectnim antibiotic. 

In the last 25 years, various natural carbapenems have been discovered (1). However, their potential is limited by chemical instability. Imipenem (N-formimidoylthienamycin), the first carbapenem in use, is therefore a stabilized synthetic compound. To overcome a second difficulty, namely inactivation by a kidney dehydropeptidase, imipenem has to be combined with cilastatin, a competitive inhibitor of that enzyme. Meropenem has better stability in the presence of renal dehydropeptidase I (2). The... 

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