Metallo—lactamases

It is worthy of note that a-sulfanyl phosphonic acids, which can now be obtained enantioselectively from corresponding a-hydroxyphosphonates, are analogues of the a-sulfanyl carboxylic acids, which, for some of them, are metallo- -lactamases inhibitors [ 112]. To our knowledge, it does not seem that biological activities of a-sulfanyl phosphonic acids have been examined so far. 

Calculations pertaining to the mechanism of action of metallo-/ -lactamases have been performed for the mono-zinc -lactamase of Bacillus cereus as well as on the binuclear P -lactamase of Bacteroidesfragilis. Molecular-dynamics and quantum-mechanical... 

Recently, analogues of nucleosides [60], natural products Huperzine-A [61] and Hydroartemisinin [62], and inhibitors of metallo-/ -lactamases have been synthesised [63]. With acylsilane electrophiles, the initial adducts undergo Brook rearrangement which is interrupted by -Si bond fission with loss of fluoride anion (Eq. 16), leading to the formation of extremely useful difluoro-enol silanes [64]. Of the various fluoride sources employed, the tetrabutylam-monium triphenyldifluorostannate described by Gingras appears to be particularly effective. The numerous other methods for trifluoromethylation formed the subject of an exhaustive review [65]. More recently, the Olah group described a chlorodifluoromethyl trimethylsilane which is expected to have a rich chemistry [66]. 

Alkyl sulfatases have been found in several lower eukaryotes and prokaryotes, and exhibit no sequence similarity with ASs. The alkyl sulfatases do not have an FGly residue, but bear in the active site a dinuclear Zn " " center, and their sequences are related to those of the metallo-/ -lactamase (MBL) superfamily (Figure 21). Depending on the enzyme and catalytic mechanism the alkyl sulfatases can either cleave the... 

According to their genetic relationship and their biochemical mechanism of action (3-lactamases are divided into enzymes of the serine-protease type containing an active-site serine (molecular class A, C, and D enzymes) and those of the metallo-protease type (molecular class B enzymes), which contain a complex bound zinc ion. 

Antibiotic Resistance. Figure 1 According to Bush, Jacoby and Medeiros [2] four molecular classes of (3-lactamases can be discriminated based upon biochemical and molecular features. Classes 1, 2, and 4 included serine-proteases, while metallo enzymes are included in class 3. The substrate spectrum varies between different subclasses and the corresponding genes can be part of an R-plasmid leading to a wider distribution or are encoded chromosomally in cells of specific species. 

The class B metallo- 3-lactamases have emerged more recently as a clinical problem but they are particularly dangerous since many of them hydrolyse all know (3-lactams, with the exception of monobac-tams. In particular, they hydrolyse the suicide substrates mentioned above, as well as carbapenems that usually escape the activity of all the SXXK enzymes, with the exception of the NMCA group. 

P-Lactamases are enzymes that hydrolyze the P-lactam ring of P-lactamantibiotics (penicillins, cephalosporins, monobactams and carbapenems). They are the most common cause of P-lactam resistance. Most enzymes use a serine residue in the active site that attacks the P-lactam-amid carbonyl group. The covalently formed acylester is then hydrolyzed to reactivate the P-lacta-mase and liberates the inactivated antibiotic. Metallo P-lactamases use Zn(II) bound water for hydrolysis of the P-lactam bond. P-Lactamases constitute a heterogeneous group of enzymes with differences in molecular structures, in substrate preferences and in the genetic localizations of the encoding gene (Table 1). 

Class B Metallo p-lactamases L1 enzyme of S. maltophilia enzyme of Aeromonas spp. CcrA enzyme found in 1-3% of 8. fragilis isolates. All enzymes are carbapenemases IMP, VIM and SPM type carbapenemases... 

Buynak et al. [53] synthesized several 6-(mercaptomethyl) penicillanates (9r and 9s, Table 1) that include both C-6 stereoisomers as well as the sulfide and sulfone oxidation states of the penam thiazolidine sulfur. Selected mercaptomethyl penicillanates inactivated both metallo- and serine /5-lactamases, and displayed synergism with piperacillin against various //-lactamase-producing strains, including metallo-/5-lactamase-producing P. aeruginosa strain. Compound 9r would be capable of bidentate chelation of zinc subsequent to enzymatic hydrolysis of the /5-lactam (Scheme 3). 

Lactamases (EC 3.5.2.6) inactivate /3-lactam antibiotics by hydrolyzing the amide bond (Fig. 5.1, Pathway b). These enzymes are the most important ones in the bacterial defense against /3-lactam antibiotics [15]. On the basis of catalytic mechanism, /3-lactamases can be subdivided into two major groups, namely Zn2+-containing metalloproteins (class B), and active-serine enzymes, which are subdivided into classes A, C, and D based on their amino acid sequences (see Chapt. 2). The metallo-enzymes are produced by only a relatively small number of pathogenic strains, but represent a potential threat for the future. Indeed, they are able to hydrolyze efficiently carbape-nems, which generally escape the activity of the more common serine-/3-lac-tamases [16] [17]. At present, however, most of the resistance of bacteria to /3-lactam antibiotics is due to the activity of serine-/3-lactamases. These enzymes hydrolyze the /3-lactam moiety via an acyl-enzyme intermediate similar to that formed by transpeptidases. The difference in the catalytic pathways of the two enzymes is merely quantitative (Fig. 5.1, Pathways a and b). 

R. Nagano, Y. Adachi, H. Imamura, K. Yamada, T. Hashizume, H. Morishima, Car-bapenem Derivatives as Potential Inhibitors of Various beta-Lactamases, Including Class B Metallo-beta-Lactamases , Antimicrob. Agents Chemother. 1999, 43, 2497-2503. 

N. V. Kaminskaia, B. Spingler, S. J. Lippard, Hydrolysis of /3-Lactam Antibiotics Catalyzed by Dinuclear Zinc(II) Complexes Functional Mimics of Metallo-/3-Lactamases ,. /. Am. Chem. Soc. 2000, 122, 6411-6422. 

Yong D, Toleman MA, Giske CG et al (2009) Characterization of a new metallo-beta-lactamase gene, bla(NDM-l), and a novel erythromycin esterase gene carried on a unique genetic structure in Klebsiella pneumoniae sequence type 14 from India. Antimicrob Agents Chemother 53(12) 5046-5054... 

Scheme 7.3 (a) Anchor fragments equipped with two thiol moieties (F-J). (b) Thiol partner fragments (4-22). (c) DCC ntilizing thiol-disulfide exchange and targeting metallo-P-lactamase (Bell). 

Figure 7.5 Deconvoluted, zero charge state mass spectrum demonstrating a hit from a DCL-targeting metallo-[3-lactamase (Bell). The dominant peak corresponds to anrora A kinase linked to extender 23, which is in turn linked to fragment 24 to give 25 (dynamic hit ). Reprinted from Reference 27, with permission from Elsevier, Copyright (2008).

Selevsek, N. Tholey, A. Heinzle, E. Lienard, B. M. R. Oldham, N. J. Schofield, C. J. Heinz, U. Adolph, H.-W. Frere, J.-M. Studies on ternary metallo-[3-lactamase inhibitor complexes using electrospray ionization mass spectrometry. J. Am. Soc. Mass Spectrom. 2006,17, 1000-10004. 

Felici A, Perilli M, Segatore B, Franceschini N, Setacci D, Oratore A, Stefani S, Galleni M, Amicosante G (1995) Interactions of biapenem with active-site serine and metallo-P-lactamases. Antimicrob Agents Chemother 39 1300-1305. 

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