Highly potent inhibitors of proprotein convertase furin as potential drugs for treatment of infectious diseases

Optimization of our previously described peptidomimetic furin inhibitors was performed and yielded several analogs with a significantly improved activity. The most potent compounds containing an N-terminal 4- or 3-(guanidinomethyl)phenylacetyl residue inhibit furin with K(i) values of 16 and 8 pM, respectively. These analogs inhibit other proprotein convertases, such as PC1/3, PC4, PACE4, and PC5/6, with similar potency, whereas PC2, PC7, and trypsin-like serine proteases are poorly affected. Incubation of selected compounds with Madin-Darby canine kidney cells over a period of 96 h revealed that they exhibit great stability, making them suitable candidates for further studies in cell culture. Two of the most potent derivatives were used to inhibit the hemagglutinin cleavage and viral propagation of a highly pathogenic avian H7N1 influenza virus strain. The treatment with inhibitor 24 (4-(guanidinomethyl)phenylacetyl-Arg-Val-Arg-4-amidinobenzylamide) resulted in significantly delayed virus propagation compared with an inhibitor-free control. The same analog was also effective in inhibiting Shiga toxin activation in HEp-2 cells. This antiviral effect, as well as the protective effect against a bacterial toxin, suggests that inhibitors of furin or furin-like proprotein convertases could represent promising lead structures for future drug development, in particular for the treatment of infectious diseases.     

A bicyclic pentapeptide-based highly potent and selective pan-SIRT1/2/3 inhibitor harboring Nε-thioacetyl-lysine

Past few years have seen an active pursuit of the inhibitors for the deacylation catalyzed by the seven human sirtuins (i.e. SIRT1-7) as valuable chemical biological/pharmacological probes of this enzymatic deacylation and lead compounds for developing novel therapeutics for human diseases. In the current study, we prepared eight monocyclic and one bicyclic analogs of a linear pentapeptide-based potent (sub-μM IC₅₀’s) pan-SIRT1/2/3 inhibitor Zheng laboratory discovered recently that harbors the catalytic mechanism-based SIRT1/2/3 inhibitory warhead N^ε-thioacetyl-lysine at its central position. We found that the bicyclic analog exhibited largely comparable SIRT1/2/3 inhibitory potencies to those of the parent linear pentapeptide, however, the former is proteolytically much more stable than the latter. Moreover, the bicyclic analog displayed very weak inhibition against SIRT5/6/7, was cell permeable, and exhibited an anti-proliferative effect on the human SK-MEL-2 melanoma cells. This bicyclic analog could be a lead for the future development of more potent and still selective pan-SIRT1/2/3 inhibitors whose use in studies on human sirtuin biology, pharmacology, and medicinal chemistry could complement with the use of the potent inhibitors selective for a single human sirtuin.     

Synthesis and LTD4-antagonist activity of desamino-2-nor-leukotriene analogs

A series of desamino-2-nor-leukotriene analogs has been prepared by the reaction of various thiols with several methyl trans-4,5-epoxy-6Z-alkenoates, followed by deprotection. The products were assessed for their ability to antagonize the LTD4-induced contraction of the isolated guinea pig trachea. Several compounds displayed potent leukotriene antagonist activity, i.e., KB values in the sub-micromolar range, while only minimally affecting basal airway tone. The most potent analog, 4-hydroxy-5-(2-carboxyethylthio)-6Z-nonadecenoic acid, antagonized both LTD4- and LTE4-induced contractions of the trachea in an apparently competitive fashion. These agents possess increased potency relative to SK&F 101132, the first leukotriene analog identified as having LT-antagonist activity. Thus, these results demonstrate that deletion of the peptide amino group can produce leukotriene analogs which have minimal intrinsic contractile activity on the isolated guinea pig trachea, yet possess potent leukotriene-antagonistic effects.     

Cyclic tripeptide-based potent human SIRT7 inhibitors

In the current study, two cyclic tripeptides respectively harboring a thiourea-type and a carboxamide-type of catalytic mechanism-based sirtuin inhibitory warheads as the central residue were found to behave as potent (low μM level) inhibitors against the tRNA-activated human SIRT7 deacetylase activity. Despite exhibiting a potent pan-inhibition against the deacylase activities of the five tested human sirtuins (i.e. SIRT1/2/3/6/7), these two compounds represent the first examples of potent SIRT7 inhibitors ever identified thus far, and their identification could facilitate the future development of more potent and selective SIRT7 inhibitors.     

3-[Benzimidazo- and 3-[benzothiadiazoleimidazo-(1,2-c)quinazolin-5-yl]-2H-chromene-2-ones as potent antimicrobial agents

A series of 3-[benzimidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one (6a-6f) and 3-[benzothiadiazole- imidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one derivatives (7a-7f) that incorporate a variety of substituents at the 6- and/or 8-positions of the coumarin moieties have been synthesized utilizing cellulose sulfuric acid as an efficient catalyst under both conventional heating and microwave irradiation procedures. These analogs were evaluated for their antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Streptococcus pyogenes (Gram-positive bacteria), Escherichia Coli, Klebsiella pneumonia, Salmonella typhimurium (Gram-negative bacteria), and Aspergillus niger, Candida albicans, and Aspergillus flavus (Fungi). Two analogs, 6c (a 6,8-dichloro analog, MIC([SA]) = 2.5 μg/mL; MIC([ST]) = 2.5 μg/mL) and 7d (a 6,8-dibromo analog, MIC([ST]) = 2.5 μg/mL) were identified as potent antibacterial agents, and two analogs, 6b (a 6-bromo analog, MIC([AF]) = 10 μg/mL) and 6d (a 6,8-dibromo analog, MIC([AF]) = 15 μg/mL; MIC([CA]) = 15μg/mL), were identified as potent antifungal agents. Based on the MIC data, analogs 6b, 6c, 6d, and 7d were identified as the most potent antimicrobial agents in the series.     

Synthesis and biological evaluation of B-ring modified colchicine and isocolchicine analogs

A series of modified colchicine and isocolchicine analogs (C-7 substituent) were synthesized and evaluated in vitro against a PC3 cancer cell line and for inhibition of microtubule polymerization. The colchicine analogs all displayed strong inhibition of tubulin polymerization, while compounds 6 and 20 also possessed an increased cytotoxic activity as compared to colchicine. More importantly, isocolchicine analogs 7, 15, and 17 showed inhibition of microtubule polymerization with IC(50) values ranging from 58 to 68muM. In addition, 7 displayed strong cytotoxic activity with an IC(50)=93nM which was more potent than colchicine analog 12.     

Tryptamine-based human beta3-adrenergic receptor agonists. Part 3: improved oral bioavailability via modification of the sulfonamide moiety

The continued SAR investigation of tryptamine-based human beta(3)-adrenergic receptor (AR) agonists is reported. Prior efforts resulted in the identification of 2 as a potent beta(3)-AR agonist. Further modification of the left side arylsulfonamide portion in 2 provided compounds with good cell permeability, which have potent agonistic activity for beta(3)-AR. Cinnamylamine analog 16i exhibited an excellent agonistic profile in vitro and good oral bioavailability in rats.     

Structure–activity relationships of N-substituted ligands for the α7 nicotinic acetylcholine receptor

A series of α7 neuronal nicotinic acetylcholine receptor ligands were designed based on a structural combination of a potent, but non-selective ligand, epibatidine, with a selective lead structure, 2. Three series of compounds in which aryl moieties were attached via a linker to different positions on the core structure were studied. A potent and functionally efficacious analog, (3aR,6aS)-2-(6-phenylpyridazin-3-yl)-5-(pyridin-3-ylmethyl)octahydropyrrolo[3,4-c]pyrrole (3a), was identified.     

Design of purine nucleoside phosphorylase inhibitors

Purine nucleoside phosphorylase inhibitors hold promise as specific immunosuppressive, anti-T cell leukemic, and antiuricopoietic agents. The best inhibitors available that are biologically active have Ki values from 10(-6) to 10(-7) M and fall into two categories: noncleavable nucleosides preferably iodinated at the C-5' position and C-8-substituted guanine or acycloguanosines. More potent inhibition is shown by phosphorylated acyclonucleosides that function as multisubstrate analogs, but these compounds are excluded from cells. The X-ray analysis of the human erythrocytic enzyme is beginning to reveal the nature of the active site and to explain the structure-activity relationships that have been established with analog substrates and inhibitors.     

Potent Kv1.3 inhibitors from correolide-modification of the C18 position

Kv1.3, the voltage-gated potassium channel in human T cells, represents a new target for treating immunosuppression and autoimmune diseases. Correolide (1), a pentacyclic natural product, is a potent and selective Kv1.3 channel blocker. Simplification of correolide via removal of its E-ring generates enone 4, whose modification produced a new series of tetracyclic Kv1.3 blockers. The structure-activity relationship for this class of compounds in two functional assays, Rb_Kv and human T cell proliferation, is presented herein. The most potent analog 43 is 15-fold more potent than correolide as inhibitor of human T cell proliferation.     

Inhibition of mammalian xanthine oxidase by folate compounds and amethopterin

We have examined the effects of folate compounds and the folate analog amethopterin (methotrexate) as inhibitors of mammalian xanthine oxidase and have found that they offer potent inhibition of the enzyme. We have compared the inhibitory potency of folic acid and its coenzyme derivative tetrahydrofolic acid to that of allopurinol, a known inhibitor of xanthine oxidase, and have demonstrated that folic acid and tetrahydrofolic acid are severalfold more potent than allopurinol as inhibitors of xanthine oxidase. Comparative inhibition constants calculated were 5.0 X 10(-7) M for folic acid. 1.25 X 10(-6) M for tetrahydrofolic acid, and 4.88 X 10(-6) M for allopurinol. Incubation of xanthine oxidase with folic acid at a concentration of 10(-6) M abolished 94% of the enzymic activity within 1 min of incubation with the enzyme. At the same concentration, allopurinol was almost ineffective as an inhibitor of xanthine oxidase. The substrate xanthine protected the enzyme against total inhibition by folic acid. Reversibility of the enzymic inhibition by folic acid was demonstrated. Folic acid-inactivated enzyme was totally regenerated either by filtration through Sephadex G-200 or by precipitation with ammonium sulfate. 2-Amino-4-hydroxypteridine was a poor substrate for the enzyme but a potent inhibitor for the oxidation of xanthine by the enzyme. The inhibition constant calculated was 1.50 X 10(-6) M. In the presence of an excess of xanthine oxidase, neither folic acid nor tetrahydrofolic acid and allopurinol exhibited any change in intensity of their absorbance or in the wavelength of their maximal absorbance that might have been suggestive of substrate utility. The folate analog amethopterin was also determined a potent inhibitor of mammalian xanthine oxidase. The inhibition constant calculated was 3.0 X 10(-5) M.     

Comparison of DNA binding between the carcinogen 2,6-dinitrotoluene and its noncarcinogenic analog 2,6-diaminotoluene

We used ³²P-postlabelling to compare DNA binding between the potent hepatocarcinogen 2,6-dinitrotoluene and its noncarcinogenic analog 2,6-diaminotoluene. The two compounds were compared to determine whether differences in DNA binding could partly explain the differences in their carcinogenicity. Fischer-344 rats were administered 1.2 mmol/kg of a compound by single i.p. injection and examined for DNA adduct formation in the liver. Four adducts were detected following administration of 2,6-dinitrotoluene, with a total adduct yield of 13.5 adducted nucleotides per 10⁷ nucleotides. Qualitatively identical adducts were also detected after treatment with the derivative 2-amino-6-nitrotoluene. Adduct yields from 2,6-dinitrotoluene were 30 times greater than from 2-amino-6-nitrotoluene. No adducts were observed following treatment with 2,6-diaminotoluene. 2,6-Dinitrotoluene and 2,6-diaminotoluene were also compared for qualitative differences in hepatotoxicity. 2,6-Dinitrotoluene produced extensive hemorrhagic necrosis in the liver, whereas no evidence of hepatocellular necrosis was detected following administration of the latter. The differences between the two compounds in both DNA binding and cytotoxicity were consistent with the differences in their carcinogenicity.     

Convenient synthesis of indeno[1,2-c]isoquinolines as constrained forms of 3-arylisoquinolines and docking study of a topoisomerase I inhibitor into DNA-topoisomerase I complex

11-hydroxyindeno[1,2-c]isoquinolines 12a-c were prepared as constrained forms of 3-arylisoquinolines through an intramolecular cyclization reaction. Among the synthesized compounds, the 11-(i)butoxy analog 15l displayed potent in vitro cytotoxicity against four different tumor cell lines as well as topoisomerase 1 inhibitory activity. A FlexX docking study was performed to explain the topoisomerase 1 activity of 15l.     

Synthesis and antioxidant, cytotoxicity and antimicrobial activities of novel curcumin mimics

Claisen-Schmidt condensation of 3-(1,2,3,6-tetrahydro-1-methylpyridin-4-yl)-2,4,5- trimethoxybenzaldehyde 3 and various aromatic, heterocyclic and alicyclic amides of 3- aminoacetophenone 6(a-s) afforded novel curcumin mimics. All the synthesized compounds were characterized by IR, (1)H NMR, Mass spectroscopy and evaluated for antioxidant, cytotoxicity and antimicrobial activity. Out of the 20 compounds screened, compounds 7i, 7l, 7q, and 7n have shown excellent radical scavenging activity, compounds 7o, 7t, 7f, and 7r have shown significant xanthine oxidase inhibition, and compounds 7a, 7k and 7l were found to be potent inhibitors of selected cancer cell lines. Compounds 7h, 7t, 7l, 7i, and 7e have shown good antibacterial activity, whereas compounds 7j, 7f, 7o, 7h, and 7t exhibited significant antifungal activity.     

Synthesis, stereochemical assignments, and biological activities of homoisoflavonoids

A series of four naturally occurring homoisoflavonoids and eight analogs have been synthesized starting from an appropriately substituted phenol through chroman-4-one, in four steps. The products were assigned as E-isomers based on NMR spectroscopic data. The E-isomers were converted into Z-isomers by photoisomerization. The E- and Z-isomers showed distinct chemical shifts and the differences between (E) and (Z)-homoisoflavonoids in the proton NMR spectra afford a useful method for ascertaining the stereochemistry. The antioxidant activity of homoisoflavonoids was determined by superoxide (NBT) and DPPH free radical scavenging methods. The analog 7-hydroxy-3-[(3,4,5-trihydroxyphenyl)methylene]chroman-4-one displayed excellent activity followed by sappanone A in both the methods and were several times potent than the commercial antioxidants like BHA, BHT, etc. These compounds were evaluated in vitro for their inhibitory activities against 5-lipoxygenase (5-LOX) enzyme. The analog 7-hydroxy-3-[(N,N-dimethylaminophenyl)methylene]chroman-4-one was found to possess potent inhibitory activity and was comparable to that of the standard, nordihydroguiaretic acid. These results suggest that these homoisoflavonoids, with their potent antioxidant and 5-LOX inhibitory activities, may have useful applications as antioxidants and lead compounds for asthma and inflammatory diseases.     

Exploring the active site of phenylethanolamine N-methyltransferase with 1,2,3,4-tetrahydrobenz[h]isoquinoline inhibitors

1,2,3,4-Tetrahydrobenz[h]isoquinoline (THBQ, 11) is a potent, inhibitor of phenylethanolamine N-methyltransferase (PNMT). Docking studies indicated that the enhanced PNMT inhibitory potency of 11 (hPNMT K(i)=0.49microM) versus 1,2,3,4-tetrahydroisoquinoline (5, hPNMT K(i)=5.8microM) was likely due to hydrophobic interactions with Val53, Met258, Val272, and Val269 in the PNMT active site. These studies also suggested that the addition of substituents to the 7-position of 11 that are capable of forming hydrogen bonds to the enzyme could lead to compounds (14-18) having enhanced PNMT inhibitory potency. However, these compounds are in fact less potent at PNMT than 11. Furthermore, 7-bromo-THBQ (19, hPNMT K(i)=0.22mM), which has a lipophilic 7-substituent that cannot hydrogen bond to the enzyme, is twice as potent at PNMT than 11. This once again illustrates the limitations of docking studies for lead optimization.     

Design,Synthesis, and Cytotoxic Activity of 3‐Aryl‐N‐hydroxy‐2‐(sulfonamido)propanamides in HepG2, HT‐1080, KB,and MCF‐7 Cells

A new series of (sulfonamido)propanamides ( 6a1 – 6a13 , 6b1 – 6b15 , 7c1 – 7c5 , 6d1 – 6d5 , 6e1 – 6e6 ) was designed and synthesized. All the synthesized compounds were characterized by NMR and mass spectrometry. The target compounds were evaluated for their in vitro cytotoxic activity against hepatocellular carcinoma (HepG2), fibrosarcoma (HT‐1080), mouth epidermal carcinoma (KB), and breast adenocarcinoma (MCF‐7) cell lines with the sulforhodamine B (SRB) assay, with gemcitabine and mitomycin C as positive controls. Most of these compounds exhibit a more potent cytotoxic effect than the positive control group on various cancer cell lines and the most potent compound, 6a7 , shows the IC₅₀ values of 29.78±0.516 μm , 30.70±0.61 μm , and 64.89±3.09 μm in HepG2, HT‐1080, KB, and MCF‐7 cell lines, respectively. Thus, these compounds with potent cytotoxic activity have potential for development as new chemotherapy agents.     

Synthesis, nicotinic acetylcholine receptor binding, antinociceptive and seizure properties of methyllycaconitine analogs

A series of methyllycaconitine (1a, MLA) analogs was synthesized where the (S)-2-methylsuccinimidobenzoyl group in MLA was replaced with a (R)-2-methyl, 2,2-dimethyl-, 2,3-dimethyl, 2-phenyl-, and 2-cyclohexylsuccinimidobenzoyl (1b-f) group. The analogs 1b-f were evaluated for their inhibition of [(125)I]iodo-MLA binding at rat brain alpha7 nicotinic acetylcholine receptors (nAChR). In order to determine selectivity, MLA and the analogs 1b-f were evaluated for inhibition of binding to rat brain alpha,beta nAChR using [(3)H]epibatidine. At the alpha7 nAChR, MLA showed a K(i) value of 0.87 nM, analogs 1b-e possessed K(i) values of 1.67-2.16 nM, and 1f showed a K(i) value of 26.8 nM. Surprisingly, the analog 1e containing the large phenyl substituent (K(i)=1.67 nM) possessed the highest affinity. None of the compounds possessed appreciable affinity for alpha,beta nAChRs. MLA antagonized nicotine-induced seizures with an AD(50)=2 mg/kg. None of the MLA analogs were as potent as MLA in this assay. MLA and all of the MLA analogs, with the exception of 1b, antagonized nicotine's antinociceptive effects in the tail-flick assay. Compound 1c (K(i)=1.78 nM at alpha7 nAChR) with an AD(50) value of 1.8 mg/kg was 6.7 times more potent than MLA (AD(50)=12 mg/kg) in antagonizing nicotine's antinociceptive effects but was 5-fold less potent than MLA in blocking nicotine-induced seizures. Since MLA has been reported to show neuroprotection against beta-amyloid(1-42), these new analogs which have high alpha7 nAChR affinity and good selectivity relative to alpha,beta nAChRs will be useful biological tools for studying the effects of alpha7 nAChR antagonist and neuroprotection.     

Protective effect of an orally administered, highly potent somatostatin analog (RC-121) against absolute ethanol-induced hemorrhagic erosions of the rat gastric mucosa

The cytoprotective effect of a highly potent somatostatin (SRIF) analog, RC-121 (H-D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2), was examined in the absolute ethanol-induced gastric erosion model in rat. This analog diminished the degree of gastric erosion by 50-55% when administered in i.p. doses of 2 x 10(-10)-10(-8) g/100 g body weight, or in oral doses of 10(-8)-2 x 10(-7) g/100 body weight. The orally active, highly potent SRIF analogs may be useful as therapeutic agents in the treatment of human peptic ulcer.     

Cytotoxic activities and anti-tumor-promoting effects of microbial transformation products of prenylated chalcones from Angelica keiskei

Three prenylated chalcones, 4-hydroxyderricin (1), xanthoangelol (2), and xanthoangelol F (3), isolated from Angelica keiskei, were transformed by the fungus Aspergillus saitoi. These chalcones were converted to flavanones (i.e., 4, 8, and 12), and prenyl-chain-hydrated (i.e., 5, 7, 9-11, and 13) and ring-B-hydroxylated (i.e., 6) chalcones. The structures of three new metabolites, 7, 9, and 13, were established as 2″,3″-dihydro-4,3″-dihydroxyderricin, 6″,7″-dihydro-7″-hydroxyxanthoangelol, and 6″,7″-dihydro-7″-hydroxyxanthoangelol F, respectively. Upon evaluation of cytotoxic activities of compounds 1-13, the metabolite 7 exhibited potent cytotoxicity against HL60 cells, and this cell death was revealed to be mostly due to apoptosis. In addition, compounds 1-4, 7-10, 12, and 13 were examined for their inhibitory effects on the induction of Epstein-Barr virus early antigen (EBV-EA) by 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. All compounds tested showed inhibitory effects against EBV-EA activation with potencies higher than that of β-carotene. Furthermore, the metabolite 13 exhibited inhibitory effect on skin tumor promotion in an in vivo two-stage mouse skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as promoter.