Lactam-based inhibitor

Other Unusual P-Lactam Based Inhibitors. There are a number of other unusual p-lactams reported to have p-lactamase inhibition activity (191—194). In general these compounds are not very potent and are not irreversible inhibitors. Data are also very Umited. 

Beginning in the late 1980s, three -lactamase inhibitors (clavulanic acid, sulbactam, and tazobactam) have been used against serine enzymes, usually in combination with penicillins more susceptible to /1-lactamase hydrolysis. This therapeutic strategy has been effective over two decades. The following section provides a brief overview on various classes of -lactam-based inhibitors. 

Other Unusual fS-Lactam-Based Inhibitors. 1 hcrc arc a number of other unusual /i-laclams reported to have /i-laclainase inhibition activity. 

Lee, C.W, Kang, J.S., Lee, K. et al. (2007) Modification of cap group in d-lactam-based histone deacetylase (HDAC) inhibitors. Bioorganic ei Medicinal Chemistry Letters, 17, 6234-6237. 

Among the many other non-oxicam-type substances discovered are a sultam pro-drug for potential P3-lactam thrombin inhibitors <1998BML3683>. Furthermore, an anti-methicillin-resistant Staphylococcus aureus (anti-MRSA) pharmacophore based on the 1,2-thiazine structure has also been recently disclosed <1999BML673>. Workers at Bristol-Meyers Squibb have synthesized and evaluated sultam hydroxamates as MMP-2 inhibitors <2004JME2981>. Hydroxamate 38 displayed the best selectivity for MMP-2 over the other proteins in this superfamily of peptidases (Figure 27). As noted in Section 8.07.3.1, an X-ray crystal structure of 38 bound to the protein MMP-13 protein has been solved. 

The first (3-lactams LE inhibitors were naturally occurring bicyclic compounds, such as clavams and cephalosporins [338], but more recently, synthetic monocyclic (3-lactams have been developed. Time-dependent inhibitors of enzyme HLE, based on the cephem nucleus, have been reported. A series of cephalosporin tert-butyl esters have been examined, and the activity of these compounds has been found to be very sensitive to the C-7 substituents, the greatest activity being showed by small, a-oriented, and electron-withdrawing groups. Additionally, the oxidation... 

Figure 8 Irreversible inhibitors of proteases. Serine and cysteine proteases can be acylated by aza-peptides, which release an alcohol, but cannot be deacylated due to the relative unreactivity of the (thio) acyl-enzyme intermediate. Reactive carbons, such as the epoxide of E64, can alkylate the thiol of cysteine proteases. Phosphonate inhibitors form covalent bonds with the active site serine of serine proteases. Phosphonates are specific for serine proteases as a result of the rigid and well-defined oxyanion hole of the protease, which can stabilize the resulting negative charge. Mechanism-based inhibitors make two covalent bonds with their target protease. The cephalosporin above inhibits elastase [23]. After an initial acylation event that opens the p-lactam ring, there are a number of isomerization steps that eventually lead to a Michael addition to His57. Therefore, even if the serine is deacylated, the enzyme is completely inactive.

A final group of covalent small-molecule inhibitors of proteases are mechanism-based inhibitors. These inhibitors are enzyme-activated irreversible inhibitors, and they involve a two-hif mechanism that completely inhibits the protease. Some isocoumarins and -lactam derivatives have been shown to be mechanistic inhibitors of serine proteases. A classic example is the inhibition of elastase by several cephalosporin derivatives developed at Merck (Fig. 8). The catalytic serine attacks and opens the -lactam ring of the cephalosporin, which through various isomerization steps, allows for a Michael addition to the active site histidine and the formation of a stable enzyme-inhibitor complex (34). These mechanism-based inhibitors require an initial acylation event to take place before the irreversible inhibitory event. In this way, these small molecules have an analogous mechanism of inhibition to the naturally occurring serpins and a-2-macroglobin, which also act as suicide substrates. 

Acyclic nonpeptide acylating agents Heterocyclic inhibitors/inactivators Lactone and coumarin based inhibitors 4H-3,1 - Benzoxazin-4-ones Saccharin derivatives fi-Lactams... 

The discovery of the naturally occurring, mechanism-based inhibitor clavulanic acid, which causes potent and progressive inactivation of lactamases (Fig. I(M). has created renewed interest in /3-lactam combination therapy. This in-Krest has led to the design and synthesis of additional mechanism-based lactamase inhibitors, such as sulbactam and luobaciam. and the isolation of naturally occurring lactams. such as the thienamycins, which both inhibit /S-lacta-nuses and interact with PBPs. 

The chemistry of P-lactams, p-sultams and P-phospholactams has been compared and the potential of the last two as mechanism based inhibitors of bacterial and mammalian proteases... 

This catalytic mechanism is consistent with data from X-ray crystallography, site-specific mutagenesis, and various biochemical studies. In crystal structures of E. coli TEM-1 )8-lactamase (34) and other related class A )8-lactamases (35—37), the side chains of the conserved residues (Ser-70, Lys-73, Ser-130, and Glu-166) are, together with a water molecule, clustered around the bound substrate (penicillin G). The presence of a methoxy or hydroxymethyl group on the a face of the j8-lactam ring, e.g., in cefoxitin or 6a-(hydroxymethyl)penicillanic acid, results in a displacement of the water (-712), thereby allowing the mechanism-based inhibitors to form rather stable acyl-enzyme intermediates (38). Substitution of either Lys-73 by Arg or of Ser-130 by Ala or Gly impairs the acylation step. Substitution of Glu-166 by Asn or Ala drastically reduces the deacylation step, leading to the accumulation of the acyl-enzyme intermediate (39,40). 

Over 80 years since the discovery of penicillin [1], the (3-lactam motif continues to have a great importance in the pharmaceutical and biochemical sciences [2]. Their historically widespread role as antibacterial agoits has come under increased pressure due to recent discoveries of bacterial strains resistant to current drugs [3]. This challenge, coupled with their use in emerging nonantibacterial therapeutic areas, such as serine protease inhibitors [4], makes the development of novel (3-lactam based scaffolds a valuable endeavor. 

Kang MR, Kang JS, Han SB, Kim JH, Kim DM, Lee K, Lee CW, Lee KH, Lee CH, Han G, Kang JS, Kim HM, Park SK. A novel S-lactam-based histone deacetylase inhibitor, KBH-A42, induces cell cycle arrest and apoptosis in colon cancer cells. Biochem. Pharmacol. 2009 78 486-494. 

Borthwick AD, Weingarten G, Haley TM, Tomaszewski M, Wang W, Hu Z, Bedard J, Jih H, Yuen L, Mansour TS. Design and synthesis of monocyclic 6-lactams as mechanism-based inhibitors of human cytomegalovirus protease. Bioorg. Med. Chem. Lett. 1998 8 365-370. 

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