Synthesis and evaluation of novel orally active p53–MDM2 interaction inhibitors

We have discovered and reported potent p53–MDM2 interaction inhibitors possessing dihydroimidazothiazole scaffold. Our lead showed strong activity in vitro, but did not exhibit antitumor efficacy in vivo for the low metabolic stability. In order to obtain orally active compounds, we executed further optimization of our lead by the improvement of physicochemical properties. Thus we furnished optimal compounds by introducing an alkyl group onto the pyrrolidine at the C-2 substituent to prevent the metabolism; and modifying the terminal substituent of the proline motif improved solubility. These optimal compounds exhibited good PK profiles and significant antitumor efficacy with oral administration on a xenograft model using MV4-11 cells having wild type p53.     

Investigation of quinazolines as inhibitors of breast cancer resistance protein (ABCG2)

Chemotherapy is one of the major forms of cancer treatment. Unfortunately, tumors are prone to multidrug resistance leading to failure of treatment. Breast cancer resistance protein (BCRP), the second member of ABC transporter subfamily G, has been found to play a major role in drug efflux and hence multidrug resistance. Until now, very few potent and selective BCRP inhibitors like Ko143 have been identified. In the search for more potent and selective BCRP inhibitors, we synthesized and investigated a series of differently substituted quinazoline compounds. Several variations at positions 2, 4, 6 and 7 of the quinazoline scaffold were carried out to develop a structure–activity-relationship analysis for these compounds. It was found that compounds bearing a phenyl substituent at position 2 of the 4-anilinoquinazoline scaffold were most potent. On the aniline ring at position 4 of the quinazoline moiety substituents like NO₂, CN, CF₃ led to very high BCRP inhibition potencies. The most potent compounds were further investigated for their intrinsic cytotoxicity and their ability to reverse the multidrug resistance. Compound 20, an anilinoquinazoline bearing a phenyl ring at position 2 and meta-nitro substitution on the 4-anilino ring, was found to have the highest therapeutic ratio. The most active compounds from each variation were also investigated for their effect on BCRP expression. It was found that compound 20 has no significant effect on BCRP expression, while compound 31 decreased the surface BCRP expression. The only difference in the two compounds was the presence of a 3,4-dimethoxyphenyl ring in compound 31 instead of phenyl substitution at position 2 of the quinazoline moiety. From the study of all target compounds, compound 20 was the most prominent compound having inhibitory potency even higher than Ko143, the most potent BCRP inhibitor known. Compound 20 was also found to be selective towards BCRP with a very high therapeutic ratio.     

1H-pyrrolo[2,3-b]pyridine: A new scaffold for human neutrophil elastase (HNE) inhibitors

Human neutrophil elastase (HNE) is a potent serine protease belonging to the chymotrypsin family. It is an important target for the development of novel and selective inhibitors for the treatment of inflammatory diseases, especially pulmonary pathologies. Here, we report the synthesis and biological evaluation of a new series of HNE inhibitors with a pyrrolo[2,3-b]pyridine scaffold, which is an isomer of our previously reported indazoles, in order to assess how a shift of the nitrogen from position 2 to position 7 influences activity. The majority of new compounds were effective HNE inhibitors and had IC₅₀ values in the micromolar/submicromolar range, with some compounds active in low nanomolar levels. For example, 2a and 2b inhibited HNE with IC₅₀ values of 15 and 14?nM, respectively. Molecular modeling of compounds differing in the position of heteroatom(s) in the bicyclic moiety and in the oxadiazole ring demonstrated that the calculated geometries of enzyme-inhibitor complexes were in agreement with the observed biological activities. Docking experiments showed that orientation of the active pyrrolo[2,3-b]pyridines in the HNE catalytic triad Ser195-His57-Asp102 correlated with effectiveness of the inhibitor interaction with the enzyme. Thus, the pyrrolo[2,3-b]pyridine scaffold represents a novel scaffold for the development of potent HNE inhibitors.     

Optimization beyond AMG 232: Discovery and SAR of sulfonamides on a piperidinone scaffold as potent inhibitors of the MDM2-p53 protein–protein interaction

We recently reported on the discovery of AMG 232, a potent and selective piperidinone inhibitor of the MDM2–p53 interaction. AMG 232 is being evaluated in human clinical trials for cancer. Continued exploration of the N-alkyl substituent of this series, in an effort to optimize interactions with the MDM2 glycine-58 shelf region, led to the discovery of sulfonamides such as compounds 31 and 38 that have similar potency, hepatocyte stability and rat pharmacokinetic properties to AMG 232.     

Discovery of 1-arylpyrrolidone derivatives as potent p53–MDM2 inhibitors based on molecule fusing strategy

Introducing an aryl moiety to our previous pyrrolidone scaffold by molecule fusing strategy afforded two sets of isopropylether–pyrrolidone and α-phenylethylamine–pyrrolidone derivatives. Two novel compounds 8b and 8g of the latter serial showed potent p53–MDM2 inhibitory activities with K_i values of 90 nM which were three-time higher than that of the parent compound. We also confirmed compound 8b can activate p53 proteins in lung cancer A549 cells. The results offered us valuable information for further lead optimization.     

The discovery and optimization of a series of 2-aminobenzoxazole derivatives as ChemR23 inhibitors

A structural class of 2-aminobenzoxazole derivatives possessing biphenyltetrazole was discovered to be potent human ChemR23 inhibitors. We initially tried to improve the potency of compound 1, which was found through in-house screening using the human plasmacytoid dendritic cell (pDC)-like cell line CAL-1. The introduction of a chiral methyl moiety at a benzylic position in a center of compound 1 showed a large impact on the inhibitory activity against calcium signaling of ChemR23 induced by the natural ligand chemerin. As a result of further investigations at the benzylic position, (R)-isomer 6b was found to show a 30-fold increased potency over desmethyl compound 1. In addition, an extensive structure-activity relationship study on the benzoxazole moiety successfully led to a further increase in the potency. The antagonistic effect of the compounds was based on the induction of ChemR23 internalization. In addition, we observed that compound 31, which contained an amide moiety on benzoxazole, inhibited chemotaxis of CAL-1 cells induced by chemerin in vitro. These results suggest that our ChemR23 inhibitors are attractive compounds for the treatment of pDC-related autoimmune diseases, such as systemic lupus erythematosus and psoriasis.     

Synthesis and biological evaluation of esters of 16-formyl-17-methoxy-dehydroepiandrosterone derivatives as inhibitors of 5α-reductase type 2

In this study, we investigated the in vitro effect of 16-formyl-17-methoxy dehydroepiandrosterone derivatives on the activity of 5α-reductase type 2 (5α-R2) obtained from human prostate. The activity of different concentrations of these derivatives was determined for the conversion of labelled testosterone to dihydrotestosterone. The results indicated that an aliphatic ester moiety at the C-3 position of these derivatives increases their in vitro potency as inhibitors of 5α-R2 activity compared to finasteride®, which is considered to be a potent inhibitor of 5α-R2. In this case, the augmentation of the lipophilicity of these dehydroepiandrosterone derivatives increased their potency as inhibitors of 5α-R2. However, the presence of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl rings as the cycloaliphatic ester moiety at C-3 of the formyl methoxy dehydroepiandrosterone scaffold did not inhibit the activity of this enzyme. This may be due to the presence of steric factors between the enzyme and the spatial structure of these derivatives.     

Synthesis and evaluation of novel dimethylpyridazine derivatives as hedgehog signaling pathway inhibitors

We report herein the design and synthesis of a series of structural modified dimethylpyridazine compounds as novel hedgehog signaling pathway inhibitors. The bicyclic phthalazine core and 4-methylamino-piperidine moiety of Taladegib were replaced with dimethylpyridazine and different azacycle building blocks, respectively. The in vitro Gli-luciferase assay results demonstrate that the new scaffold still retained potent inhibitory potency. Piperidin-4-amine moiety was found to be the best linker between pharmacophores dimethylpyridazine and fluorine substituted benzoyl group. Furthermore, the optimization of 1-methyl-1H-pyrazol and 4-fluoro-2-(trifluoromethyl)benzamide by different aliphatic or aromatic rings were also investigated and the SAR were described. Several new derivatives were found to show potent Hh signaling inhibitory activity with nanomolar IC₅₀ values. Among these compounds, compound 11c showed the highest inhibitory potency with an IC₅₀ value of 2.33?nM, which was comparable to the lead compound Taladegib. In vivo efficacy of 11c in a ptch^+/?p53^?/? mouse medulloblastoma allograft model also indicated encouraging results.     

Upregulation of p53 through induction of MDM2 degradation: Amino acid prodrugs of anthraquinone analogs

Previously, we reported a class of MDM2-MDM4 dimerization inhibitors that upregulate p53 and showed potent anticancer activity in animal models. However, water solubility hinders their further development. Herein we describe our effort to develop a prodrug approach that overcomes the solubility problem. The prodrug of BW-AQ-238, a potent anthraquinone analog, was made by esterification of the hydroxyl group with various natural amino acids. Cytotoxicity of these compounds toward Hela and EU-1 cells, their aqueous solubility, and the release kinetics of these prodrugs in buffer and in the presence of hydrolytic enzymes were studied. The results demonstrate that the amino acid prodrug approach significantly improved the water solubility while maintaining the potency of the parent drug.     

Synthesis and proteasome inhibition of lithocholic acid derivatives

A new class of proteasome inhibitors was synthesized using lithocholic acid as a scaffold. Modification at the C-3 position of lithocholic acid with a series of acid acyl groups yielded compounds with a range of potency on proteasome inhibition. Among them, the phenylene diacetic acid hemiester derivative (13) displayed the most potent proteasome inhibition with IC₅₀ = 1.9 μM. Enzyme kinetic analysis indicates that these lithocholic acid derivatives are noncompetitive inhibitors of the proteasome.     

Phenylacetic acid regioisomers possessing a N-difluoromethyl-1,2-dihydropyrid-2-one pharmacophore: Evaluation as dual inhibitors of cyclooxygenases and 5-lipoxygenase with anti-inflammatory activity

A novel class of phenylacetic acid regioisomers possessing a N-difluoromethyl-1,2-dihydropyrid-2-one pharmacophore attached to its C-2, C-3 or C-4 position was designed for evaluation as anti-inflammatory (AI) agents. A number of compounds exhibited a combination of potent in vitro cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitory activities. 2-(1-Difluoromethyl-2-oxo-1,2-dihydropyridin-4-yl)phenylacetic acid (9a) exerted the most potent AI activity among this group of compounds. Molecular modeling studies showed that the N-difluoromethyl-1,2-dihydropyridin-2-one moiety present in 9a inserts into the secondary pocket present in COX-2 to confer COX-2 selectivity, and that the N-difluoromethyl-1,2-dihydropyrid-2-one group (9a) binds close to the region of the 15-LOX enzyme containing catalytic iron (His361, His366). Accordingly, the N-difluoromethyl-1,2-dihyrdopyrid-2-one moiety possesses properties that make it an attractive pharmacophore suitable for the design of dual COX-2/5-LOX inhibitory AI drugs.     

Tetra-substituted imidazoles as a new class of inhibitors of the p53–MDM2 interaction

Capitalizing on crystal structure information obtained from a previous effort in the search for non peptide inhibitors of the p53–MDM2 interaction, we have discovered another new class of compounds able to disrupt this protein–protein interaction, an important target in oncology drug research. The new inhibitors, based on a tetra-substituted imidazole scaffold, have been optimized to low nanomolar potency in a biochemical assay following a structure-guided approach. An appropriate strategy has allowed us to translate the high biochemical potency in significant anti-proliferative activity on a p53-dependent MDM2 amplified cell line.     

Bromine oxidation of 1,2-O-isopropylidene-α-d-Glucofuranose and sucrose

Sucrose and $\text{1,2-O-}\text{isopropylidene-α-}\text{d}\text{-glucofuranose}$ (1) were oxidised with bromine in aqueous solution at pH 7 and room temperature. The resulting keto derivatives were converted into their more-stable O-methyloximes, which were characterised by spectroscopic and chromatographic methods. Oxidation of 1 occurred at C-3 and C-5, with a preference for C-5. In the sucrose derivatives isolated after oxidation, those having a keto group in the glucopyranosyl moiety preponderated. The axial fructofuranosyl aglycon protects position 3 in the glucopyranosyl group and oxidation occurs only at C-2 and C-4. Small amounts of sucrose oxidised at C-3 in the fructofuranosyl moiety were also found.     

Design, synthesis, and biological evaluation of (E)-3-(4-methanesulfonylphenyl)-2-(aryl)acrylic acids as dual inhibitors of cyclooxygenases and lipoxygenases

A group of (E)-3-(4-methanesulfonylphenyl)acrylic acids possessing a substituted-phenyl ring (4-H, 4-Br, 3-Br, 4-F, 4-OH, 4-OMe, 4-OAc, and 4-NHAc) attached to the acrylic acid C-2 position were prepared using a stereospecific Perkin condensation reaction. A related group of compounds having 4- and 3-(4-isopropyloxyphenyl)phenyl, 4- and 3-(2,4-difluorophenyl)phenyl and 4- and 3-(4-methanesulfonylphenyl)phenyl substituents attached to the acrylic acid C-2 position were also synthesized, using a palladium-catalyzed Suzuki cross-coupling reaction, for evaluation as dual cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibitors. (E)-2-(3-Bromophenyl)-3-(4-methanesulfonylphenyl)acrylic acid (9h), and compounds having 4-(4-isopropyloxyphenyl-, 2,4-difluorophenyl-, or 4-methylsulfonylphenyl)phenyl moieties at the acrylic acid C-2 position (11a,b,d), were particularly potent COX-2 inhibitors with a high COX-2 selectivity index (COX-2 IC50 approximately 0.32 microM, SI > 316) similar to the reference drug rofecoxib (COX-2 IC50 = 0.5 microM, SI > 200). Acrylic acid analogs with a C-2 4-hydoxyphenyl (9d, IC50 = 0.56 microM), or 4-acetamidophenyl (9g, IC50 = 0.11 microM), substituent were particularly potent 5-LOX inhibitors that may participate in an additional specific hydrogen-bonding interaction. A number of compounds possessing a C-2 substituted-phenyl moiety (4-Br, 4-F, and 4-OH), or a 4- or 3-(2,4-difluorophenyl)phenyl moiety, showed potent 15-LOX inhibitory activity (IC50 values in the 0.31-0.49 microM range) relative to the reference drug luteolin (IC50 = 3.2 microM). Compounds having a C-2 4-acetylaminophenyl, or 4-(2,4-difluorophenyl)phenyl, moiety exhibited anti-inflammatory activities that were equipotent to aspirin, but less than that of celecoxib. The structure-activity data acquired indicate the acrylic acid moiety constitutes a suitable scaffold (template) to design novel acyclic dual inhibitors of the COX and LOX isozymes.     

Nitric oxide-donating carbonic anhydrase inhibitors for the treatment of open-angle glaucoma

Novel bi-functional compounds with a nitric oxide (NO)-releasing moiety bound to a dorzolamide scaffold were investigated. Several compounds were synthesized and their activity as selective carbonic anhydrase inhibitors (CAI) evaluated in vitro on recombinant hCA type I, II and IV enzyme isoforms where they showed different degrees of potency and selectivity to hCA II. A high resolution X-ray crystal structure for the CA II adduct with 8 confirmed the high affinity of this class of compounds for the enzyme. Compounds 4, 6, and 8 showed highly potent and efficacious NO-mediated properties as assessed by their vascular relaxant effect on methoxamine-precontracted rabbit aortic rings. Finally, compounds 4 and 6 exerted potent intraocular pressure (IOP) lowering effects in vivo in normotensive rabbits thereby anticipating their potential for the treatment of hypertensive glaucoma.     

Oxidation at C-16 enhances butyrylcholinesterase inhibition in lupane triterpenoids

A set of triterpenoids with different grades of oxidation in the lupane skeleton were prepared and evaluated as cholinesterase inhibitors. Allylic oxidation with selenium oxide and Jones’s oxidation were employed to obtain mono-, di- and tri-oxolupanes, starting from calenduladiol (1) and lupeol (3). All the derivatives showed a selective inhibition of butyrylcholinesterase over acetylcholinesterase (BChE vs. AChE). A kinetic study proved that compounds 2 and 9, the more potent inhibitors of the series, act as competitive inhibitors. Molecular modeling was used to understand their interaction with BChE, the role of carbonyl at C-16 and the selectivity towards this enzyme over AChE. These results indicate that oxidation at C-16 of the lupane skeleton is a key transformation in order to improve the cholinesterase inhibition of these compounds.     

Structure-activity relationship study of β-oxidation resistant indole-based 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) receptor antagonists

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is formed from 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by the 5-lipoxygenase (5-LO) pathway under conditions associated with oxidative stress. 5-Oxo-ETE is an important pro-inflammatory mediator, which stimulates the migration of eosinophils via a selective G-protein coupled receptor, known as the OXE receptor (OXE-R). Previously, we designed and synthesized structural mimics of 5-oxo-ETE such as 1 using an indole scaffold. In the present work, we added various substituents at C-3 of this moiety to block potential β-oxidation of the 5-oxo-valerate side chain, and investigated the structure-activity relationships of the resulting novel β-oxidation-resistant antagonists. Cyclopropyl and cyclobutyl substituents were well tolerated in this position, but were less potent as the highly active 3S-methyl compound. It seems likely that 3-alkyl substituents can affect the conformation of the 5-oxovalerate side chain containing the critical keto and carboxyl groups, thereby affecting interaction with the OXE-receptor.     

Design,synthesis, and biological evaluation of 1,9-diheteroarylnona-1,3,6,8-tetraen-5-ones as a new class of anti-prostate cancer agents

In search of more effective chemotherapeutics for the treatment of castration-resistant prostate cancer and inspired by curcumin analogues, twenty five (1E,3E,6E,8E)-1,9-diarylnona-1,3,6,8-tetraen-5-ones bearing two identical terminal heteroaromatic rings have been successfully synthesized through Wittig reaction followed by Horner–Wadsworth–Emmons reaction. Twenty-three of them are new compounds. The WST-1 cell proliferation assay was employed to assess their anti-proliferative effects toward both androgen-sensitive and androgen-insensitive human prostate cancer cell lines. Eighteen out of twenty-five synthesized compounds possess significantly improved potency as compared with curcumin. The optimal compound, 78, is 14- to 23-fold more potent than curcumin in inhibiting prostate cancer cell proliferation. It can be concluded from our data that 1,9-diarylnona-1,3,6,8-tetraen-5-one can serve as a new potential scaffold for the development of anti-prostate cancer agents and that pyridine-4-yls and quinolin-4-yl act as optimal heteroaromatic rings for the enhanced potency of this scaffold. Two of the most potent compounds, 68 and 75, effectively suppress PC-3 cell proliferation by activating cell apoptosis and by arresting cell cycle in the G₀/G₁ phase.     

Design,synthesis, in vitro Evaluation and docking studies on dihydropyrimidine-based urease inhibitors

In our previous report, we have identified 3,4-dihydropyrimidine scaffold as promising class of urease inhibitor in a structure based virtual screen (SBVS) experiment. In present study, we attempted to optimize the scaffold by varying C-5 substituent. The elongation of the C-5 chain was achieved by the reaction of C-5 ester with hydrazine leading to C-5 carbohydrazides which were further used as building blocks for the synthesis of fifteen new compounds having diverse moieties. A significantly higher in vitro urease inhibitory activity with IC₅₀ values in submicromolar range was observed for semithiocarbazide derivatives (4a-c, 0.58–0.79 µM) and isatin Schiff base derivative 5a (0.23 µM). Docking analysis suggests that the synthesized compounds were anchored well in the catalytic site and extending to the entrance of binding pocket and thus restrict the mobility of the flap by interacting with its key amino acid residues. The overall results of urease inhibition have shown that these compounds can be further optimized and developed as lead urease inhibitors.     

Discovery of potent pyrrolidone-based HIV-1 protease inhibitors with enhanced drug-like properties

We have developed efficient syntheses of the HIV-1 protease inhibitor 4 and its analogues, which incorporate the pyrrolidone scaffold 2 as P1-P2 moiety. Evaluation of these analogues in the HIV-1 protease enzyme assay resulted in discovery of potent and more water soluble meta-amino- and meta-hydroxy inhibitors 17b and 19b. The SAR observed in this class of PIs could be rationalized with aid of the X-ray structure of inhibitor 28 co-crystallized with the HIV-1 protease, which suggested that the polar meta- (but not para-) benzyl substituents in P2 could side-step the hydrophobic S2 enzyme active pocket by rotating the P2 moiety around its Cbeta-Cgamma bond. Such reorientation allows to engage the unsubstituted, hydrophobic edge of benzyl moiety in P2 in the requisite P2/S2 hydrophobic interaction, and projects polar meta-substituent into the bound water. It appears that the meta-position can be chemically derivatized without potency loss of thus resulting inhibitors, as evidenced by potent 22-26. We thus identified pyrrolidone 2-based inhibitors exemplified by 17b and 19b, which uniquely accommodate both high enzyme potency and which provide a platform for fine-tuning of drug-like properties in this class of PIs by additional chemical manipulations on the meta-position.