A benzisothiazolone class of potent, selective mechanism-based inhibitors of human leukocyte elastase

Crystal structure of 2-(4-(2-(4-(2-fluorophenyl)piperazin-1-yl)ethyl)benzyl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide, C26H26FN3O3S – a saccharin dervative

C26H26F1N3O3S1, triclinic, P1̅ (no. 2), a = 7.0252(14) Å, b = 9.3017(19) Å, c = 19.388(4) Å, α = 97.80(3)°, β = 97.77(3)°, γ = 106.84(3)°, V = 1180.9(5) Å3, Z = 2, R gt(F) = 0.0729, wR ref(F 2) = 0.1854, T = 296.15 K.

Synthesis and Antitumor Activity of Novel Arylpiperazine Derivatives Containing the Saccharin Moiety

Prostate cancer is a major public health problem worldwide. For the development of potential anti-prostate cancer agents, a series of novel arylpiperazine derivatives containing the saccharin moiety based on previous studies was designed, synthesized, and evaluated in prostate (PC-3, LNCaP, and DU145) cancer cell lines for their anticancer activities. The majority of the compounds exhibited excellent selective activity for the tested cancer cells. Compounds 4 and 12 exhibited strong cytotoxic activities against DU145 cells (half maximal inhibitory concentration (IC₅₀) < 2 μM). The structure–activity relationship (SAR) of these arylpiperazine derivatives was also discussed based on the obtained experimental data. This work provides a potential lead compound for anticancer agent development focusing on prostate cancer therapy.

2015 Philip S. Portoghese Medicinal Chemistry Lectureship. Curing Hepatitis C Virus Infection with Direct-Acting Antiviral Agents: The Arc of a Medicinal Chemistry Triumph

The development of direct-acting antiviral agents that can cure a chronic hepatitis C virus (HCV) infection after 8-12 weeks of daily, well-tolerated therapy has revolutionized the treatment of this insidious disease. In this article, three of Bristol-Myers Squibb's HCV programs are summarized, each of which produced a clinical candidate: the NS3 protease inhibitor asunaprevir (64), marketed as Sunvepra, the NS5A replication complex inhibitor daclatasvir (117), marketed as Daklinza, and the allosteric NS5B polymerase inhibitor beclabuvir (142), which is in late stage clinical studies. A clinical study with 64 and 117 established for the first time that a chronic HCV infection could be cured by treatment with direct-acting antiviral agents alone in the absence of interferon. The development of small molecule HCV therapeutics, designed by medicinal chemists, has been hailed as "the arc of a medical triumph" but may equally well be described as "the arc of a medicinal chemistry triumph".

2,4,5-Triphenylisothiazol-3(2H)-one 1,1-dioxides as inhibitors of human leukocyte elastase

A series of substituted 2,4,5-triphenylisothiazol-3(2H)-one 1,1-dioxides 9 was synthesized and investigated as inhibitors of human leukocyte elastase (HLE). All compounds were found to inhibit HLE in a time-dependent manner and most of them exhibited kobs/[I] values > 300M(-1)s(-1). The most potent 3-oxosultam of this series was 91 (kobs/[I] = 2440 M(-1)s(-1)). Kinetic investigations performed with 9g and different substrate concentrations did not allow to clearly distinguish between a competitive or noncompetitive mode of inhibition. A more complex interaction is supported by the failure of a linear dependency of kobs values on the inhibitor concentration.

Acylating agents as enzyme inhibitors and understanding their reactivity for drug design

A series of bicyclic trans-fused gamma-lactones and gamma-lactams have been previously described for the inhibition of human neutrophil elastase and as possible development candidates. During the discovery program, it had been assumed that their acylating power was due in part to the inherent strain energy in the bicyclic structure that was released upon ring opening. This is now shown not to be the case, and in fact, these compounds are no more reactive than simple but analogous gamma-lactams and gamma-lactones. The strain energy is not released in the transition state for alkaline hydrolysis or alcoholysis because the reaction proceeds with rate-limiting formation of the tetrahedral intermediate. A reactivity index of k(OH) is proposed as a simple guide to determine the usefulness of a potential inhibitor as an enzyme acylating agent.

Potent inhibition of serine proteases by heterocyclic sulfide derivatives of 1,2,5-thiadiazolidin-3-one 1,1 dioxide

The existence of subtle differences in the Sn' subsites of closely-related (chymo)trypsin-like serine proteases, and the fact that the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold docks to the active site of (chymo)trypsin-like enzymes in a substrate-like fashion, suggested that the introduction of recognition elements that can potentially interact with the Sn' subsites of these proteases might provide an effective means for optimizing enzyme potency and selectivity. Accordingly, a series of heterocyclic sulfide derivatives based on the 1,2,5-thiadiazolidin-3-one 1,1 dioxide scaffold (I) was synthesized and the inhibitory activity and selectivity of these compounds toward human leukocyte elastase (HLE), proteinase 3 (PR 3) and cathepsin G (Cat G) were then determined. Compounds with P1 = isobutyl were found to be potent, time-dependent inhibitors of HLE and, to a lesser extent PR 3, while those with P1 = benzyl inactivated Cat G rapidly and irreversibly. This study has demonstrated that 1,2,5-thiadiazolidin-3-one 1,1 dioxide-based heterocyclic sulfides are effective inhibitors of (chymo)trypsin-like serine proteases.

2-(diethylamino)thieno1,3ŏxazin-4-ones as stable inhibitors of human leukocyte elastase

A series of 2-(diethylamino)thieno1,3ŏxazin-4-ones was synthesized and evaluated in vitro for inhibitory activity toward human leukocyte elastase (HLE). The Gewald thiophene synthesis was utilized to obtain several ethyl 2-aminothiophene-3-carboxylates. These precursors were subjected to a five-step route to obtain thieno2,3-d1,3ŏxazin-4-ones bearing various substituents at positions 5 and 6. Both thieno2,3-d and thieno3,2-d fused oxazin-4-ones possess extraordinary chemical stability, which was expressed as rate constants of the alkaline hydrolysis. The kinetic parameters of the HLE inhibition were determined. The most potent compound, 2-(diethylamino)-4H-1benzothieno2,3-d1,3ŏxazin-4-one, exhibited a K(i) value of 5.8 nM. 2-(Diethylamino)thieno1, 3ŏxazin-4-ones act as acyl-enzyme inhibitors of HLE, similar to the inhibition of serine proteases by 4H-3,1-benzoxazin-4-ones. The isosteric benzene-thiophene replacement accounts for an enhanced stability of the acyl-enzyme intermediates.

1,2-Benzisothiazol-3-one 1,1-dioxide inhibitors of human mast cell tryptase

A library of compounds were prepared by reacting 2-(bromomethyl)-1, 2-benzisothiazol-3(2H)-one 1,1-dioxide (5) with commercially available carboxylic acids in the presence of potassium carbonate or a tertiary amine base. From this library, (1,1-dioxido-3-oxo-1, 2-benzisothiazol-2(3H)-yl)methyl N-[(phenylmethoxy)carbonyl]-beta-alanate (7b) emerged as a potent inhibitor of human mast cell tryptase (IC50 = 0.85 microM). Extension of the side chain of 7b by two carbons gave (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 5-[[(phenylmethoxy)carbonyl]amino]pentanoate (7d) which was an 8-fold more potent inhibitor (IC50 = 0.1 microM). Further modification of this series produced benzoic acid derivative (1, 1-dioxido-3-oxo-1,2-benzisothiazol-2(3H)-yl)methyl 4-[[(phenylmethoxy)carbonyl]amino]benzoate (7n) which is the most potent inhibitor identified in this series (IC50 = 0.064 microM). These compounds exhibit time-dependent inhibition consistent with mechanism-based inhibition. For 7b, the initial enzyme velocity is not a saturable function of the inhibitor concentration and the initial Ki could not be determined (Ki > 10 microM). The steady-state rate constant, Ki, was determined to be 396 nM. On the other hand, compounds 7d and 7n are time-dependent inhibitors with a saturable initial complex. From these studies, an initial rate constant, Ki, for 7d and 7n was found to be 345 and 465 nM, respectively. The steady-state inhibition constants, Ki, for 7d and 7n were calculated to be 60 and 52 nM, respectively. Compound 7n is a 13-fold more potent inhibitor than 7b, and these kinetic studies indicate that the increase in inhibitory activity is due to an increase in initial affinity toward the enzyme and not an increase in chemical reactivity. These inhibitors generally show high selectivity for tryptase, being 40-fold weaker inhibitors of elastase, being 100-fold weaker against trypsin, and showing no inhibition against thrombin. These compounds are not inhibitors of thrombin, plasmin t-PA, urokinase, and factor Xa (IC50 > 33 microM). In the delayed-type hypersensitivity (DTH) mouse model, a model of skin inflammation, a 5% solution of 7d reduced edema by 69% compared to control animals.

Novel natural product 5,5-trans-lactone inhibitors of human alpha-thrombin: mechanism of action and structural studies

High-throughput screening of methanolic extracts from the leaves of the plant Lantana camara identified potent inhibitors of human alpha-thrombin, which were shown to be 5,5-trans-fused cyclic lactone euphane triterpenes [O'Neill et al. (1998) J. Nat. Prod. (submitted for publication)]. Proflavin displacement studies showed the inhibitors to bind at the active site of alpha-thrombin and alpha-chymotrypsin. Kinetic analysis of alpha-thrombin showed tight-binding reversible competitive inhibition by both compounds, named GR133487 and GR133686, with respective kon values at pH 8.4 of 1.7 x 10(6) s-1 M-1 and 4.6 x 10(6) s-1 M-1. Electrospray ionization mass spectrometry of thrombin/inhibitor complexes showed the tight-bound species to be covalently attached, suggesting acyl-enzyme formation by reaction of the active-site Ser195 with the trans-lactone carbonyl. X-ray crystal structures of alpha-thrombin/GR133686 (3.0 A resolution) and alpha-thrombin/GR133487 (2.2 A resolution) complexes showed continuous electron density between Ser195 and the ring-opened lactone carbonyl, demonstrating acyl-enzyme formation. Turnover of inhibitor by alpha-thrombin was negligible and mass spectrometry of isolated complexes showed that reversal of inhibition occurs by reformation of the trans-lactone from the acyl-enzyme. The catalytic triad appears undisrupted and the inhibitor carbonyl occupies the oxyanion hole, suggesting the observed lack of turnover is due to exclusion of water for deacylation. The acyl-enzyme inhibitor hydroxyl is properly positioned for nucleophilic attack on the ester carbonyl and therefore relactonization; furthermore, the higher resolution structure of alpha-thrombin/GR133487 shows this hydroxyl to be effectively superimposable with the recently proposed deacylating water for peptide substrate hydrolysis [Wilmouth, R. C., et al. (1997) Nat. Struct.Biol. 4, 456-462], suggesting the alpha-thrombin/GR133487 complex may be a good model for this reaction.

Novel thieno[2,3-d][1,3]oxazin-4-ones as inhibitors of human leukocyte elastase

A series of thieno[2,3-d][1,3]oxazin-4-ones was synthesized and evaluated in vitro for inhibitory activity toward human leukocyte elastase. New synthetic routes to 2-alkoxy-, 2-alkylthio-, and 2-sec-amino-substituted derivatives are reported. This study demonstrates the versatility of 2-aminothiophenes prepared by Gewald reaction as a synthetic entry to serine protease-inhibiting, fused 1,3-oxazin-4-ones. Introduction of ethoxy, n-propoxy, and ethylthio groups at C-2 delivered the most potent inhibitors of this series with Ki values lower than 11 nM. Kinetic studies and product analyses revealed the formation of acyl-enzymes as a result of the attack of the active site serine at the carbon C-4 and subsequent deacylation. This mode of action is similar to the inhibition of serine proteases by 4H-3,1-benzoxazin-4-ones. Replacement of the benzene ring in benzoxazinones by a (substituted) thiophene led to improved hydrolytic stability and retained inhibitory potency.

Phthalimidomethyl as a drug pro-moiety. Probing its reactivity

Phthalimidomethyl derivatives 1, encompassing a wide range of leaving group abilities, are rapidly hydrolysed to the corresponding phthalamic acid via rate-determining attack at the phthalimide carbonyl group.

Recent advances in antiviral research: identification of inhibitors of the herpesvirus proteases

Major advances have been reported in the last two years regarding the molecular biology and structural properties of the herpesvirus proteases. X-ray diffraction studies have enabled several groups to solve the structure of the human cytomegalovirus protease. Fluorescence-based substrate assays have also been recently reported. These substrates exhibit sufficient kinetic and sensitivity properties to enable high-throughput screening efforts dedicated toward the discovery of protease inhibitors. Three classes of inhibitors have been reported recently: nonpeptidic aryl trifluoromethylketones; alternate substrate inhibitors (benzoxazinones/azalactones); and thiol-modifying inhibitors. The thiol-modifying class offers a unique opportunity to discover inhibitors specific to the human cytomegalovirus protease, as this protease requires reduced cysteine residues for its enzymatic activity.

Design, synthesis, and in vitro inhibitory activity toward human leukocyte elastase, cathepsin G, and proteinase 3 of saccharin-derived sulfones and congeners

The inhibitory activity toward human leukocyte elastase (HLE), cathepsin G (Cat G), and proteinase 3 (PR 3) of a series of saccharin derivatives having a sulfinate leaving group was investigated. The results of this study revealed that (a) inhibitory activity is dependent on the nature and pKa of the leaving group, and (b) the synthesized saccharin derivatives exhibit selective inhibition toward HLE and PR 3, with low or no activity toward cathepsin G. The results of exploratory biochemical, HPLC and high-field 13C NMR studies are also described.