Application of multicomponent reactions to antimalarial drug discovery. Part 2: New antiplasmodial and antitrypanosomal 4-aminoquinoline gamma- and delta-lactams via a 'catch and release' protocol

A parallel synthesis of a new series of 4-aminoquinoline gamma- and delta-lactams synthesized via the Ugi 3-component 4-centre multicomponent reaction is described. The basicity of the quinoline nitrogen was exploited in the purification of compounds via a 'catch and release' protocol. Yields ranging from 60% to 77% and purities as high as 96% were obtained. Compound 29, the most active against a chloroquine-resistant W2 strain of Plasmodium falciparum with an IC(50) of 0.096 microM, also inhibited recombinant falcipain-2 in vitro (IC(50)= 17.6 microM). Compound 17 inhibited the growth of Trypanosoma brucei with an ED(50) of 1.44 microM whilst exhibiting a favourable therapeutic index of 409 against a human KB cell line.     

6-Acyl-4-aryl/alkyl-5,7-dihydroxycoumarins as anti-inflammatory agents

A series of coumarin derivatives were synthesized in two steps from phloroglucinol. The anti-inflammatory activities of these derivatives were evaluated by means of inhibiting NO production in LPS-induced RAW 264.7 cells. Derivatives 3, 8, 10, 11, and 13 exhibited low micromolar levels of anti-inflammatory activities, and these derivatives also protected DNA against hydroxyl radical attack. Coumarin derivative 8 was the most potent derivative among those tested herein against NO production in LPS-induced RAW 264.7 cells with an IC(50) value of 7.6 microM, and it effectively reduced the hydroxyl radical production by 50% at 100 microM in the electron spin resonance study.     

Synthesis and biological evaluation of novel 5(H)-phenanthridin-6-ones, 5(H)-phenanthridin-6-one diketo acid, and polycyclic aromatic diketo acid analogs as new HIV-1 integrase inhibitors

A new series of phenanthridinone derivatives, and diketo acid analogs, as well as related phenanthrene and anthracene diketo acids have been synthesized and evaluated as HIV integrase (IN) inhibitors. Several new beta-diketo acid analogs with the phenanthridinone scaffold replaced by phenanthrene, anthracene or pyrene exhibited the highest IN inhibitory potency. There is a general selectivity against the integrase strand transfer step. The most potent IN was 2,4-dioxo-4-phenanthren-9-yl-butyric acid (27f) with an IC(50) of 0.38microM against integrase strand transfer. The phenanthrene diketo acids 27d-f were more potent (IC(50)=2.7-0.38microM) than the corresponding phenanthridinone diketo acid 16 (IC(50)=65microM), suggesting that the polar amide bridge in the phenanthridinone system decreases inhibitory activity relative to the more lipophilic phenanthrene system. This might have to do with the possible binding of the aryl group of the compounds binding to a lipophilic pocket at the integrase active site as suggested by the docking simulations. Molecular modeling also suggested that effectiveness of chelation of the active site Mg(2+) contributes to IN inhibitory potency. Finally, some of the potent compounds inhibited HIV-1 replication in human peripheral blood mononuclear cells (PBMC) with EC(50) down to 8microM for phenanthrene-3-(2,4-dioxo)butyric acid (27d), with a selectivity index of 10 against PBMCs.     

Synthesis and antienteroviral activity of a series of novel, oxime ether-containing pyridyl imidazolidinones

A series of novel, oxime ether-containing pyridyl imidazolidinones were synthesized and their antiviral activity was evaluated in a plaque reduction assay. It is very interesting that this class of compounds is specific for human enteroviruses, in particular, enterovirus 71 (EV71). Some derivatives strongly inhibited enterovirus replication with activities higher or comparable to those of the reference compounds such as A1 and A2. Preliminary SAR studies revealed that the chain length of the alkyl linker and the alkyl substituent at the oxime ether group largely influenced the in vitro anti-EV71 activity of this new class of potent antiviral agents. Among this series of compounds synthesized, the pyridyl imidazolidinone with an ethyl oxime ether group located at the para position of the phenoxyl ring (8b) was identified as the most potent enterovirus 71 inhibitor (IC50=0.001 microM) with no apparent cytotoxic effect toward RD (rhabdomyosarcoma) cell lines (CC50>25 microM). Furthermore, this compound has been shown broad-spectrum activity against most of the serotypes of enteroviruses tested in the nanomolar range.     

Discovery and synthesis of a potent sulfonamide ET(B) selective antagonist

The synthesis and structure activity relationships of a series of sulfonamide endothelin antagonists are described. In the course of our modification studies, we discovered ET(B) selective antagonists. The most potent compound 15f displays IC50 values of 1.7 microM and 0.002 microM to ET(A) and ET(B) receptors, respectively.     

Nitrogen-containing flavonoid analogues as CDK1/cyclin B inhibitors: synthesis, SAR analysis, and biological activity

A series of nitrogen-containing flavonoid analogues were designed and synthesized by Mannich reaction, and screened for the inhibitory activities of cyclin-dependent kinases using a FRET-based biochemical assay method. The results showed that C-8 nitrogen-containing baicalein analogues 3a-3f exhibited potent CDK1/Cyclin B inhibitory activities. 5,6,7-Trihydroxy-8-(dimethylaminomethyl)-2-phenyl-4H-chromen-4-one 3a, 5,6,7-trihydroxy-8-(pyrrolid inylmethyl)-2-phenyl-4H-chromen-4-one 3b, and 5,6,7-trihydroxy-8-(piperidinylmethyl)-2-phenyl-4H-chromen-4-one 3c (IC(50) 1.05-1.28 microM) were about sixfold more potent than baicalein 2 (IC(50) 6.53 microM). 5,6,7-Trihydroxy-8-(morpholinomethyl)-2-phenyl-4H-chromen-4-one 3d, 5,6,7-trihydroxy-8-(thiomorpholinomethy)-2-phenyl-4H-chrom en-4-one 3e, and 5,6,7-trihydroxy-8-(4-methylpiperazinylmethyl)-2-phenyl-4H-chromen-4-one 3f (IC(50) 0.27-0.38 microM) were about 20-fold more potent than baicalein, and were at the same level as flavopiridol (IC(50) 0.33 microM).     

Isothiazole dioxides: synthesis and inhibition of Trypanosoma brucei protein farnesyltransferase

A series of isothiazole dioxides was synthesized and evaluated as inhibitors of protein farnesyltransferase from the parasite that causes African sleeping sickness (Trypanosoma brucei). The most potent compound in the series inhibited the parasite enzyme with an IC(50) of 2 microM and blocked the growth of the bloodstream parasite in vitro with an ED(50) of 10 microM. The same compound inhibited rat protein farnesyltransferase and protein geranylgeranyltransferase type I only at much higher concentration.     

Synthesis, cytotoxicity, and anti-inflammatory evaluation of 2-(furan-2-yl)-4-(phenoxy)quinoline derivatives. Part 4

A number of 2-(furan-2-yl)-4-phenoxyquinoline derivatives have been synthesized and evaluated for anti-inflammatory evaluation. 4-[(2-Furan-2-yl)quinolin-4-yloxy]benzaldehyde (8), with an IC(50) value of 5.0 microM against beta-glucuronidase release, was more potent than its tricyclic furo[2,3-b]quinoline isomer 3a (>30 microM), its 4'-COMe counterpart 7 (7.5 microM), and its oxime derivative 13a (11.4 microM) and methyloxime derivative 13b (>30 microM). For the inhibition of lysozyme release, however, oxime derivative 12a (8.9 microM) and methyloxime derivative 12b (10.4 microM) are more potent than their ketone precursor 7 and their respective tricyclic furo[2,3-b]quinoline counterparts 4a and 4b. Among them, 4-[4-[(2-furan-2-yl)-quinolin-4-yloxy]phenyl]but-3-en-2-one (10) is the most active against lysozyme release with an IC(50) value of 4.6 microM, while 8 is the most active against beta-glucuronidase release with an IC(50) value of 5.0 microM. (E)-1-[3-[(2-Furan-2-yl)quinolin-4-yloxy]phenyl] ethanone oxime (11a) is capable of inhibiting both lysozyme and beta-glucuronidase release with IC(50) values of 7.1 and 9.5 microM, respectively. For the inhibition of TNF-alpha formation, 1-[3-[(2-furan-2-yl)quinolin-4-yloxy]phenyl]ethanone (6) is the most potent with an IC(50) value of 2.3 microM which is more potent than genistein (9.1 microM). For the inhibitory activity of fMLP-induced superoxide anion generation, 11a (2.7 microM), 11b (2.8 microM), and 13b (2.2 microM) are three of the most active. None of above compounds exhibited significant cytotoxicity.     

Design, synthesis and anti-plasmodial evaluation in vitro of new 4-aminoquinoline isatin derivatives

A new class of 4-aminoquinoline derivatives based on the natural product isatin scaffold were designed and synthesized for biological evaluation against three strains of the malaria parasite Plasmodium falciparum. These derivatives showed anti-plasmodial IC(50) values in the ranges of 1.3-0.079 and 2.0-0.050muM against a chloroquine-sensitive (D10) and two resistant (K1 and W2) strains of P. falciparum, respectively. In order to determine potential targets for this class of compounds in P. falciparum, selected compounds were also tested against the parasitic cysteine protease falcipain-2. In terms of further development of this class of isatin derivatives, two of the compounds based on a flexible alkyl chain linker and a thiosemicarbazone moiety warrant further investigation as potential anti-plasmodial leads. These two derivatives showed good in vitro activity against K1 and W2 with IC(50) values of 51 and 54nM, respectively, while retaining potency against the D10 strain with IC(50) values of 79 and 95nM, respectively. Generally speaking, the inhibitory potency of all compounds in the series against the parasites did not strongly correlate with inhibitory potency against falcipain-2 for selected compounds tested, which at best was weak to moderate, suggesting other mechanisms of inhibition may also be involved or compounds may be selectively taken up by Plasmodium falciparum.     

N-substituted 4-(4-carboxyphenoxy)benzamides. Synthesis and evaluation as inhibitors of steroid-5alpha-reductase type 1 and 2

In search of non-steroidal inhibitors of human prostatic 5alpha-reductase, we recently described N-substituted 4'-biphenyl-4-carboxylic acids. Here, we report the optimisation of this series of compounds by increasing the conformational flexibility using an ether linker between the steroidal A-C ring mimetics. Ten new compounds were synthesised and tested against human and rat isozymes 1 and 2. The substances showed a broad range of activity from 36% inhibition at a concentration of 10 microM to an IC50 value of 60 nM for compounds 22 and 29 respectively. The most potent compound 26 showed an IC50 value improved by a factor of 5 from 1.9 microM to 0.38 microM in comparison with the parent biphenyl compound 15.     

The design, synthesis and biological evaluation of 7-alkoxy-4-heteroarylamino-3-cyanoquinolines as dual inhibitors of c-Src and iNOS

Because both c-Src and iNOS are key regulatory enzymes in tumorigenesis, a new series of 4-heterocycle amine-3-quinolinecarbonitriles as potent dual inhibitors of both enzymes were designed, synthesized and evaluated as multiple targets agents in cancer therapy. All compounds were evaluated by two related enzyme inhibition assays and an anti-proliferation assay in vitro. The results showed that most compounds inhibited c-Src and iNOS well. The best compound 8 inhibited both enzymes with the IC(50) values of 34.8 nM and 26.7 microM. Several compounds also showed moderate anti-proliferation at 10 microM against colon and liver cancer cell lines.     

Design, synthesis, and QSAR studies of novel lysine derives as amino-peptidase N/CD13 inhibitors

A series of novel l-lysine derivatives were designed, synthesized, and assayed for their inhibitory activities on amino-peptidase N (APN)/CD13 and matrix metalloproteinase-2 (MMP-2). The preliminary biological test showed that most of the compounds displayed a high inhibitory activity against MMP-2 and a low activity against APN except compound B6 which exhibited good potency (IC(50)=13.2microM) similar with APN inhibitor Bestatin (IC(50)=15.5microM), and could be used as lead compound in the future.     

Organic phenyl arsonic acid compounds with potent antileukemic activity

A series of 12 organic arsonic acid compounds has been synthesized and evaluated against human B-lineage (NALM-6) and T-lineage (MOLT-3) acute lymphoblastic leukemia (ALL) cell lines. The lead compounds 2-trichloromethyl-4-[4'-(4"-phenylazo)phenylarsonic acid]aminoquinazoline (compound 19, PHI-P518; IC(50)=1.1+/-0.5 microM against NALM-6 and 2.0+/-0.8 microM against MOLT-3) and 2-methylthio-4-(2'-phenylarsonic acid)aminopyrimidine (compound 15, PHI-P381; IC(50)=1.5+/-0.3 microM against NALM-6 and 2.3+/-0.5 microM against MOLT-3) exhibited potent antileukemic activity at low micromolar concentrations.     

Synthesis and evaluation of isatins and thiosemicarbazone derivatives against cruzain, falcipain-2 and rhodesain

While commercial isatins were practically inactive against the target proteases, thiosemicarbazone derivatives were found to be active. The most active compound from the series displayed an inhibitory IC(50) value of 1 microM against rhodesain. One thiosemicarbazone was found to be active against all three proteases with inhibitory IC(50) values of 10 microM or less. A combination of N-benzylation and appropriate substitution on the aromatic portion of the isatin scaffold was generally found to be beneficial especially against cruzain for ketone inhibitors.     

4-Alkoxy-2,6-diaminopyrimidine derivatives: inhibitors of cyclin dependent kinases 1 and 2

The cyclin dependent kinase (cdk) inhibitor NU6027, 4-cyclohexylmethoxy-5-nitroso-pyrimidine-2,6-diamine (IC(50) vs cdk1/cyclinB1=2.9+/-0.1 microM and IC(50) vs cdk2/cyclinA3=2.2+/-0.6 microM), was used as the basis for the design of a series of 4-alkoxy-2,6-diamino-5-nitrosopyrimidine derivatives. The synthesis and evaluation of 21 compounds as potential inhibitors of cyclin-dependent kinases 1 and 2 is described and the structure-activity relationships relating to NU6027 have been probed. Simple alkoxy- or cycloalkoxy-groups at the O(4)-position were tolerated, with the 4-(2-methylbutoxy)-derivative (IC(50) vs cdk1/cyclinB1=12+/-2 microM and cdk2/cyclinA3=13+/-4 microM) retaining significant activity. Substitutions at the N(6) position were not tolerated. Replacement of the 5-nitroso substituent with ketone, oxime and semicarbazone groups essentially abolished activity. However, the derivative bearing an isosteric 5-formyl group, 2,6-diamino-4-cyclohexylmethoxy-pyrimidine-5-carbaldehyde, showed modest activity (IC(50) vs cdk1/cyclinB1=35+/-3 microM and cdk2/cyclinA3=43+/-3 microM). The X-ray crystal structure of the 5-formyl compound bound to cdk2 has been determined to 2.3A resolution. The intramolecular H-bond deduced from the structure with NU6027 bound to cdk2 is not evident in the structure with the corresponding formyl compound. Thus the parent compound, 4-cyclohexylmethoxy-5-nitrosopyrimidine-2,6-diamine (NU6027), remains the optimal basis for future structure-activity studies for cyclin-dependent kinase inhibitors in this series.     

Structure-activity relationship of aza-steroids as PI-PLC inhibitors

A number of aza-steroids were synthesized as potent phosphatidylinositol phospholipase C (PI-PLC) inhibitors. The epimeric mixtures 22,25-diazacholesterol (8a) and 3beta-hydroxy-22,25-diazacholestane (8b) were among the most active of these inhibitors, with IC(50) values of 7.4 and 7.5 microM, respectively. The 20alpha epimer, 8a2 (IC(50)=0.64 microM), whose stereochemistry at C-20 coincides with that of cholesterol, was found 50 times more potent than the 20beta epimer, 8a1 (IC(50)=32.2 microM). In diaza-estrone derivatives, the 3-methoxy group on the aromatic A-ring of 23 exhibited moderate PI-PLC inhibitory activity (IC(50)=19.7 microM), while compound with a free hydroxyl group (21) was inactive. However, in diaza-pregnane derivatives, epimers with a 3-hydroxyl group (8a, IC(50)=7.4 microM) exhibited more potent PI-PLC inhibitory activity than their counterparts with 3-methoxyl group on the non-aromatic A-ring (26, IC(50)=17.4 microM). We have illustrated in our previous publication that 3-hydroxyl-6-aza steroids are potent PI-PLC inhibitors.(3) However, simultaneous presence of the 6-aza and 22,25-diaza moieties in one molecule as in 13, led to loss of activity. Epimeric mixture 8a showed selective growth inhibition effects in the NCI in vitro tumor cell screen with a mean GI(50) value (MG-MID) of 5.75 microM for 54 tumors.     

Structure-activity study of L-amino acid-based N-type calcium channel blockers

Synthesis and structure-activity relationship (SAR) study of L-amino acid-based N-type calcium channel blockers are described. The compounds synthesized were evaluated for inhibitory activity against both N-type and L-type calcium channels focusing on selectivity to reduce cardiovascular side effects due to blocking of L-type calcium channels. In the course of screening of our compound library, N-(t-butoxycarbonyl)-L-aspartic acid derivative 1a was identified as an initial lead compound for a new series of N-type calcium channel blockers, which inhibited calcium influx into IMR-32 human neuroblastoma cells with an IC(50) of 3.4 microM. Compound 1a also exhibited blockade of N-type calcium channel current in electrophysiological experiment using IMR-32 cells (34% inhibition at 10 microM, n=3). As a consequence of conversion of amino acid residue of 1a, compound 12a, that include N-(t-butoxycarbonyl)-L-cysteine, was found to be a potent N-type calcium channel blocker with an IC(50) of 0.61 microM. Thus, L-cysteine was selected as a potential structural motif for further modification. Optimization of C- and N-terminals of L-cysteine using S-cyclohexylmethyl-L-cysteine as a central scaffold led to potent and selective N-type calcium channel blocker 21f, which showed improved inhibitory potency (IC(50) 0.12 microM) and 12-fold selectivity for N-type calcium channels over L-type channels.     

6-aryl-2,4-dioxo-5-hexenoic acids, novel integrase inhibitors active against HIV-1 multiplication in cell-based assays

A series of 6-aryl-2,4-dioxo-5-hexenoic acids, were synthesized and tested against HIV-1 in cell-based assays and against recombinant HIV-1 integrase (rIN) in enzyme assays. Compound 8a showed potent antiretroviral activity (EC(50)=1.5 microM) and significant inhibition against rIN (strand transfer: IC(50)=7.9 microM; 3'-processing: IC(50)=7.0 microM). A preliminary molecular modeling study was carried out to compare the spatial conformation of 8a with those of L-731988 (4) and 5CITEP (7) in the IN core.     

Design, synthesis, inhibitory activity, and SAR studies of pyrrolidine derivatives as neuraminidase inhibitors

A series of pyrrolidine derivatives were synthesized and evaluated for their ability to inhibit neuraminidase (NA) of influenza A virus (H3N2). All compounds were synthesized in good yields starting from commercially 4-hydroxy-L-proline using a suitable synthetic strategy. These compounds showed potent inhibitory activity against influenza A neuraminidase. Within this series, five compounds, 6e, 9c, 9e, 9f, and 10e, have good potency (IC(50)=1.56-2.71 microM) which are compared to that the NA inhibitor Oseltamivir (IC(50)=1.06 microM), and could be used as lead compoundS in the future.     

N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea and N'-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-chloropyridyl)]-thiourea as potent inhibitors of multidrug-resistant human immunodeficiency virus-1.

We have replaced the pyridyl ring of trovirdine with an alicyclic cyclohexenyl, adamantyl or cis-myrtanyl ring. Only the cyclohexenyl-containing thiourea compound N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]- thiourea (HI-346) (as well as its chlorine-substituted derivative N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-chloropyridyl)]- thiourea/HI-445) showed RT inhibitory activity. HI-346 and HI-445 effectively inhibited recombinant RT with better IC50 values than other anti-HIV agents tested. The ranking order of efficacy in cell-free RT inhibition assays was: HI-346 (IC50 = 0.4 microM) > HI-445 (IC50 = 0.5 microM) > trovirdine (IC50 = 0.8 microM) > MKC-442 (IC5 = 0.8 microM) = delavirdine (IC50 = 1.5 microM) > nevirapine (IC50 = 23 microM). In accord with this data, both compounds inhibited the replication of the drug-sensitive HIV-1 strain HTLV(IIIB) with better IC50 values than other anti-HIV agents tested. The ranking order of efficacy in cellular HIV-1 inhibition assays was: HI-445 = HI-346 (IC50 = 3 nM) > MKC-442 (IC50 = 4 nM) = AZT (IC50 = 4 nM) > trovirdine (IC50 = 7 nM) > delavirdine (IC50 = 9 nM) > nevirapine (IC50 = 34 nM). Surprisingly, the lead compounds HI-346 and HI-445 were 3-times more effective against the multidrug resistant HIV-1 strain RT-MDR with a V106A mutation (as well as additional mutations involving the RT residues 74V,41L, and 215Y) than they were against HTLV(IIIB) with wild-type RT. HI-346 and HI-445 were 20-times more potent than trovirdine, 200-times more potent than AZT, 300-times more potent than MKC-442, 400-times more potent than delavirdine, and 5000-times more potent than nevirapine against the multidrug resistant HIV-1 strain RT-MDR. HI-445 was also tested against the RT Y181C mutant A17 strain of HIV-1 and found to be >7-fold more effective than trovirdine and >1,400-fold more effective than nevirapine or delavirdine. Similarly, both HI-346 and HI-445 were more effective than trovirdine, nevirapine, and delavirdine against the problematic NNI-resistant HIV-1 strain A17-variant with both Y181C and K103N mutations in RT, although their activity was markedly reduced against this strain. Neither compound exhibited significant cytotoxicity at effective concentrations (CC50 >100 microM). These findings establish the lead compounds HI-346 and HI-445 as potent inhibitors of drug-sensitive as well as multidrug-resistant stains of HIV-1.