Methyl ketones inhibitor

Rehse PH, Steinmetzer T, Li Y, Konishi Y, Cygler M. Crystal structure of a peptidyl pyridinium methyl ketone inhibitor with thrombin. Biochemistry 1995 34 11537-11544. 

The structures of hepatitis A viral 3C proteinases complexed with tetrapeptidyl-based methyl ketone inhibitors were shown to have an episulfide cation embedded in them. The authors concluded that the mechanism of inactivation of 3G peptidases by methyl ketone inhibitors is different than those operating in serine proteinases or in papain-like cysteine peptidases <2006MI673>. 

Reactions using catecholborane proceed smoothly in toluene (Scheme 16) (40). The utility of catalytic hydroboration of ketones has been demonstrated by the efficient enantioselective synthesis of a series of biologically active compounds (41). Scheme 17 shows some compounds prepared by using this method. Enantioselective reduction of trichloro-methyl ketones is a general route to a-amino acids and a-hydroxy esters it also allows ready synthesis of a precursor to the carbonic anhy-drase inhibitor MK-0417 (42). 

Baeyer-Villiger oxidation has been used to selectively oxidize one of two methyl ketones (to esters) in the final step of a stereoselective synthesis of (—)-acetomycin, an antibiotic with potential anti-leukemia activity (equation 25)135. This reaction was accomplished using MCPBA as oxidant, with an excess of sodium bicarbonate and 5-/er/-bulyl-4-hydroxy-2-melhyl phenyl sulfide as a radical inhibitor. 

It is more interesting that reduction of complex ketones could be dramatically improved by optimization of the reaction temperature. In the case of the phenoxyphenylvinyl methyl ketone (6), a 5-lipoxygenase inhibitor synthesis intermediate, we were able to improve the enantiomeric excess from the 80-85% range up to 96% by selection of the optimal temperature for the reduction. In this case, the temperature range for an acceptable enantiomeric excess is very narrow. Generally, Me-CBS is the best catalyst with borane complexes as reducing agent. 

Pliura DH, Bonaventura BJ, Smith RA et al (1992) Comparative behaviour of calpain and cathepsin B toward peptidyl acyloxymethyl ketones, sulphonium methyl ketones and other potential inhibitors of cysteine proteinases. Biochem J 288(Pt 3) 759-762... 

These simple semi-synthetic procedures have been extensively used in the preparation of new allocolchicinoids for biological screening purposes [11], Recently, these molecules found a new interest when it was shown by scientists at Angiogene Pharmaceuticals that A/-acetylcolchinol phosphate 35, termed ZD6126, is a prodrug of jV-acetylcolchinol 31 which causes the selective destruction of tumour vasculature [74], This compound, obtained semi-synthetically from colchicine, is currently under phase I clinical trials. Another patent from Brandeis University described methyl ketone 36 as a reversible inhibitor of tubulin polymerization (in contrast to colchicine), with 100-fold cytotoxicity compared to colchicine toward a number of cell lines [75]. 

The facile reaction of CAA and BAA with nucleosides and nucleotides is one example of many of the applications of the bifunctional reactivity of halogenated aldehydes and ketones in modification of biomolecules. In an early example of the extensive use of halogenated ketones as protease substrate analogues, l-V-tosylamido-2-phenylethyl chloro-methyl ketone (TPCK) 30 was synthesized as a chymotrypsin substrate analogue. Stoichiometric inhibition was accompanied by loss of one histidine residue as a result of alkylation by the chloromethyl moiety68. A host of similar analogues were subsequently prepared and used as selective enzyme inhibitors, in particular for the identification of amino acid residues located at enzyme active sites69. 

Based on the above discussion it was thought that the trifluoro-methyl ketones would be more polarized and thus create a great electrophilicity on the carbonyl carbon which facilitates -OH attack by the serine residue. Yet there is no carbon-oxygen bond to be cleaved In the ketone moiety, and therefore the enzyme-trifluoromethyl ketone transition state complex does not undergo catalytic conversion. The above rationale seems reasonable as trifluoromethyl ketones were found to be extraordinary selective and potent inhibitors of cholinesterases (56) of JHE from T. ni (57) and of meperidine carboxylesterases from mouse and human livers (58). Since JH homologs are alpha-beta unsaturated esters, a sulfide bond was placed beta to the carbonyl in hopes that it would mimic the 2,3-olefln of JHs and yield more powerful inhibitors (54). This empirical approach was extremely successful since it resulted in compounds that were extremely potent inhibitors of JHEs from different species (51,54,59). 

The simplest member of this family of inhibitors, the methoxy-methyl ketone (Fig. 5.8a), has been studied as a complex with papain [14]. This enzyme-inhibitor complex shows binding of the peptide portion of the inhibitor on the prime side of the active site in a manner similar to that seen for Cbz-Leu-Leu-Leu-aldehyde (Fig. 5.2d) bound to papain. In contrast to the thiohemi-acetal seen with the aldehyde, the carbonyl of the methoxy-methyl ketone (Fig. 5.8a) is quite distant from the active site thiol, with no possibility of covalent interaction. Therefore, this inhibitor meets the criteria for class I inhibition. The n-propyloxy ketone (Fig. 5.8b), which also binds on the prime side of the active site, has the ketone in close proximity to the active site thiol of cathepsin K, as seen in the structure of the inhibitor-enzyme complex [20]. Covalent attachment appears to have followed from... 

Recent work from the Schmidt laboratory utilized dipeptide-based acy-loxy methyl ketones as the warhead [24,25]. Unlike the aforementioned compounds, these dipeptides utilize a different leaving group however, presumably enzyme alkylation occurs in a similar fashion. The most potent inhibitors resulted when an Arg residue was positioned proximal to the warhead [25]. However, the authors suggest that inhibition is a result of reversible, noncompetitive binding. This is supported by a warhead-free analog maintaining inhibitory activity despite lacking the chemical ability to irreversibly alkylate the active site. 

Dechert, A.-M.R., et al. (2010). Modulation of the inhibitor properties of dipeptidyl (acyloxy)methyl ketones toward the CaaX proteases. Bioorg Med Chem 18 6230-6237. 

Fig. 10.5. Notable examples of Rcelp inhibitors. Abbreviations shown refer to At,-tosyl-l-phenylalanine chloromethyl ketone (TPCK), p-hydroxymercnribenzoic acid (pHMB), p-hydroxymercuriphenylsulfonic acid (pHMS), mersalyl acid (MSA), (acyloxy)methyl ketone (AOMK), and National Service Center (NSC).

Hara H, et al. Inhibition of interleukin Ibeta converting enzyme family proteases reduces ischemic and excitotoxic neuronal damage. Proc. Natl. Acad. Sci. U. S. A., 1997 94 2007-2012. Schotte P, et al. Non-specific effects of methyl ketone peptide inhibitors of caspases. FEBS Lett. 1999 442 117-121. 

The peptide aldehyde series demonstrated the potential for carbonyl derivatives to be potent inhibitors of serine proteinases. The 200-fold increase in values which was found in going from an aldehyde (7-1) Table 2.7) to its corresponding methyl ketone (7-2) Table 2.7) [129] implied that the physical properties of the carbonyl group were an important factor in determining the potency of the inhibitor. As a means of increasing both the stability and potency of peptide ketone derivatives Trainor and co-workers [130, 131] and Imperiali and Abeles [132] independently prepared the first peptide trifluoromethyl ketone (TFMK) inhibitors of serine proteinases in... 

The synthesis of the C1-C21 subunit of the protein phosphatase inhibitor tautomycin was accomplished by J.A. Marshall et al. During the last steps of the synthetic sequence, the hydrosilylation of a terminal alkyne afforded a five-membered siloxane that was oxidized by the Fleming-Tamao oxidation. The initially formed end tautomerized to the corresponding methyl ketone. 

A novel synthetic route for the preparation of unsymmetrically substituted benzophenones was developed in the laboratory of C.-M. Andersson utilizing an iron-mediated aromatic substitution as one of the key steps. The power of this method was demonstrated by the formal synthesis of the benzophenone moiety of the protein kinase C inhibitor balanol. In the late stages of the synthesis, it became necessary to convert the aromatic methyl ketone functionality of the highly substituted benzophenone substrate to the corresponding carboxylic acid. Bromine was added to sodium hydroxide solution, and the resulting sodium hypobromite solution was slowly added to the substrate at low temperature. Upon acidification the desired carboxylic acid was obtained in fair yield. 

Table 1.22 Peptidyl methyl and perfluoroalkyl ketone inhibitors of HCMV protease...

In the past ten years, there has been developed a series of enzyme inhibitors that combine the features of an alkylating agent with specificity for the active site of an enzyme, thus permitting alkylation and identification of a group at or near the active center of an enzyme, or a particular enzyme to be specifically inactivated. Thus a l-chloro-4-phenyl-3-p-toluenesulfonamido-2-butanone ( W-p-tolylsulfonylphenylalanine chloro-methyl ketone ) inactivates chymotrypsin (which cleaves a peptide bond adjacent to an aromatic residue), and 7-amino-l-chloro-3-p-toluene-sulfonamido-2-heptanone ( a-iV-p-tolylsulfonyllysine chloromethyl ketone ) inhibits trypsin (which cleaves a peptide bond adjacent to lysine. In both cases, a histidine residue at the active site is alkylated, and neither inhibitor will inhibit the other enzyme at low concentrations. 

ISOPROPENYL METHYL KETONE (814-78-8) Forms explosive mixture with air (flash point 68°F/20°C). Violent reaction with aldehydes, nitric acid, perchloric acid, strong oxidizers. Contact with hydrogen peroxide can form unstable peroxides heat and/or inappropriate level of inhibitor may cause polymerization. 

Halo enol lactones are an example of suicide Inhibitors for serine proteases. These analogues were developed by Katzenellenbogen and coworkers at the University of Illinois (34). On normal catalytic processing by the serine hydroxyl functionality, they give rise to a reactive halo-methyl ketone, which subsequently alkylates a nearby nucleophilic residue on the enzyme (Fig. 5.16). Other suicide Inactivators for the serine proteases have been designed by various researchers (32). 

Nucleoside Triphosphates and Their Analogues. - A review has been given of the most useful methods for the synthesis of nucleoside triphosphates. 5 -Triphosphates of 8-(alkylthio)adenosines have been prepared as inhibitors of nucleoside triphosphate diphosphohydrolase, and the triphosphates 202 and that derived from 2,2 -anhydrouridine have been made as agonists for P2X2-purinoceptors, but they showed lesser potencies than the parent nucleosides. Derivatives of ATP, UTP and CTP have been prepared in which methyl ketone groups are attached via spacers to the base units, in order to permit interaction with fluorescent probes after enzymic incorporation into oligonucleotides. The triphosphate was assembed by Eckstein s procedure, in which a 2, 3 -0-iso-propylidene nucleoside is treated sequentially with salicyl phosphorochloridite, pyrophosphate and an oxidant. ... 

Dudley, Read and Walker [475, 123] have reported a novel rhodium(I)-catalyzed oxidation of 1-olefins. Hexene-1, heptene-1 and octene-1 were converted to the corresponding methyl ketones with dioxygen at ambient temperature and pressure in benzene solutions of the complexes [RhH(CO)(PPh3)3] and [RhCl(PPh3)3]. Methyl ketones are not normally produced in Haber-Weiss initiated radical reactions. Furthermore, radical inhibitors such as hydroquinone or 2,6-di-/-butyl-p-cresol do not retard methyl ketone formation. Since these authors are unable to detect radical chain processes, they suggest that reactions involve co-oxygenation of coordinated PPh3 and olefin at the metal center, equation (283). 

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