Insight into Mechanism of Action of Anticancer Benzazoles.

BACKGROUND: Targeting the DNA topoisomerase II enzyme (topo II) is a promising anticancer treatment approach. TopoII controls and modifies the topological states of DNA and plays key roles in DNA replication, transcription, and chromosome segregation. The DNA binding and cleavage domain is one of the active sites of this enzyme. It is known that topoisomerase inhibitors, also known as topoisomerase poisons, bind to the transient enzyme-DNA complex and inhibit the religation of DNA, generating single- and double-stranded breaks that harm the integrity of the genome. This ultimately leads to the accumulation of DNA strand breaks and cell death. METHODS: Our previously synthesized benzazole derivatives were tested for their eukaryotic DNA topoisomerase II inhibitory activity in a cell-free system. Their interactions with the enzyme were studied by carrying out molecular docking studies using and comparing two different docking programs. RESULTS: The results of the docking studies clarified binding modes of these compounds to the topoisomerase II enzyme. CONCLUSION: This study also provides guidelines to design novel and more potent antitumor agents functioning as human topoisomerase II enzyme inhibitors.

Benzoxazines as new human topoisomerase I inhibitors and potential poisons.

BACKGROUND: The numbers of topoisomerase I targeted drugs on the market are very limited although they are used clinically for treatment of solid tumors. Hence, studies about finding new chemical structures which specifically target topoisomerase I are still remarkable. OBJECTIVES: In this present study, we tested previously synthesized 3,4-dihydro-2H-1,4-benzoxazin-3-one derivatives to reveal their human DNA topoisomerase I inhibitory potentials. METHODS: We investigated inhibitory activities of 3,4-dihydro-2H-1,4-benzoxazin-3-one derivatives on human topoisomerase I by relaxation assay to clarify inhibition mechanisms of effective derivatives with EMSA and T4 DNA ligase based intercalation assay. With SAR study, it was tried to find out effective groups in the ring system. RESULTS: While 10 compounds showed catalytic inhibitory activity, 8 compounds were found to be potential topoisomerase poisons. 4 of them also exhibited both activities. 2-hydroxy-3,4-dihydro-2H-1,4-benzoxazin-3-one (BONC-001) was the most effective catalytic inhibitor (IC50:8.34 mM) and ethyl 6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-acetate (BONC-013) was the strongest potential poison (IC50:0.0006 mM). BONC-013 was much more poisonous than camptothecin (IC50:0.034 mM). Intercalation assay showed that BONC-013 was not an intercalator and BONC-001 most probably prevented enzyme-substrate binding in an unknown way. Another important result of this study was that OH group instead of ethoxycarbonylmethyl group at R position of benzoxazine ring was important for hTopo I catalytic inhibition while the attachment of a methyl group of R1 position at R2 position were play a role for increasing of its poisonous effect. CONCLUSION: As a result, we presented new DNA topoisomerase I inhibitors which might serve novel constructs for future anticancer agent designs. Graphical abstract.

The 12th AFMC International Medicinal Chemistry Symposium (AIMECS 2019) in Istanbul, Turkey.

AFMC-AIMECS meetings are internationally organized biannually by the Asian Federation for Medicinal Chemistry (AFMC) and are focused on recent studies in drug discovery and development both in academia and industry. Member organizations of the AFMC are the Pharmaceutical Society of Japan, the Chinese Pharmaceutical Association, the Royal Australian Chemical Institute, the Pharmaceutical Society of Korea, the Korean Chemical Society, the Chemical Society Located in Taipei, the Indonesian Society of Medicinal Chemistry, the Medicinal Chemistry Section of the Israel Chemical Society, and the Computer-Aided Drug Design & Development Society in Turkey. Each time, the symposium is organized within these member countries. The AIMECS 2019 symposium was held in Turkey this year, as Prof. Dr. Esin Aki-Yalcin is the current president of the AFMC (2018-2020); the next AIMECS meeting will be organized in 2021 in Tokyo, Japan. In this report, we discuss key topics at the 12th AFMC International Medicinal Chemistry Symposium - New Avenues for Design and Development of Translational Medicine (AIMECS 2019) held in Istanbul, September 8-11, 2019.

4-Thiazolidinone Derivatives as MMP Inhibitors in Tissue Damage: Synthesis, Biological Evaluation and Docking Studies.

Nine 2-(1,2-benzothiazol-3-yl)-N-(4-oxo-2-phenyl-1,3-thiazolidin-3-yl)propanamides combining a benzisothiazole and 4-thiazolidinone in one framework were designed and synthesized. The aim of the study was to verify their effectiveness to affect the inflammatory/oxidative process in which free oxygen and nitrite (ROS and RNS) radicals, inflammatory mediators, such as nuclear factor κB (NF-κB), and matrix metalloproteinases (MMPs) are involved. Docking studies of all the compounds were performed in order to explore their binding mode at the MMP-9 protein. An appreciable anti-inflammatory/potential wound healing effects of the tested compounds was highlighted. Derivative 23, bearing a 4-carboxyphenyl substituent at C2 of the 4-thiazolidinone ring, exhibited the highest activity, being able to inhibit MMP-9 at nanomolar level(IC50 = 40 nM).

Biological evaluation and pharmacophore modeling of some benzoxazoles and their possible metabolites.

A series of benzoxazole derivatives and some possible primary metabolites were evaluated as anticancer agents. In vitro anti-proliferative activities of the compounds were tested using the SRB assay on cancerous (HeLa) and non-cancerous (L929) cell lines. It was found that 17 of 21 tested compounds had cytotoxic activity on HeLa cells and the cytotoxic activities of the compounds were 15-700 times higher than on L929 cells. We generated two distinct pharmacophore models for the cytotoxic activities of the compounds on HeLa and L929 cells. While active compounds such as camptothecin and X8 fitted the two models generated for both cell lines, selective cytotoxic compounds such as XT3B fitted only the model generated for HeLa cells. Evaluation of the genotoxic activities of the cytotoxic compounds with the alkaline comet assay revealed that compounds X17 and XT3 showed strong genotoxic effects against HeLa cells at low concentrations whereas they had no genotoxic effect on L929 cells. Due to the selective ability for inducing DNA strand breaks only on cancerous cells, the compounds were identified as effective derivatives for anticancer candidates.

Determination of the Apoptotic Effect and Molecular Docking of Benzamide Derivative XT5 in K562 Cells.

BACKGROUND: The tyrosine kinase inhibitor, imatinib, used as a first line treatment in Chronic Myeloid Leukemia (CML) patients, may lead to resistance and failure to therapy. Novel combinations of imatinib with other drugs is a strategy to improve treatment efficiency. OBJECTIVE: In this study, the antileukemic and apoptotic effects of a benzamide derivative XT5 and benzoxazole derivative XT2B and their combination with imatinib were investigated in imatinib-sensitive (K562S) and imatinib-resistant (K562R) CML cells. METHODS: In vitro cytotoxicity was determined by MTT assay. Then, apoptotic effect of XT5 on CML cell lines was tested by Annexin V flow cytometry, caspase activation and RT-PCR. Docking calculation was performed using AutoDock Vina in PyMOL environment using AutoDock/Vina plugin for PyMOL. RESULTS: According to our MTT assay data, XT5 indicated significant antiproliferative effect on cell lines, therefore we investigated apoptotic effects of XT5. Treatment of K562 cell lines with a combination of XT5 and imatinib-XT5 increased cytotoxicity, the Annexin V binding and caspase 3/7 activation. In addition to apoptosis assays, we observed an increase in the expression levels of the pro-apoptotic (BAX, BAD and BIM) genes in XT5 treated K562R and K562S cells. Molecular modelling experiments showed that XT5 showed hydrogenbonding interactions with important amino acids of BCR-ABL kinase receptor; however XT2B did not show any hydrogen bond interaction. CONCLUSION: Our results indicate that XT5 could be a potential candidate to be used as a new anticancer drug and XT5 combination with imatinib as an alternate treatment strategy for overcoming imatinib resistance.

Design and synthesis of 2-substituted-5-(4-trifluoromethylphenyl-sulphonamido)benzoxazole derivatives as human GST P1-1 inhibitors.

The glutathione transferases (GSTs) are a family of widely distributed Phase II detoxification enzymes. GST P1-1 is frequently overexpressed in rat and human tumours. It is suggested that overexpression of hGST P1-1 by human tumor cells may play a role in resistance to cancer chemotherapy. Hence, hGST P1-1 can be a promising target for cancer treatment. In this study, new hGST P1-1 inhibitors, 2-(4-substitutedphenyl/benzyl)-5-(4-trifluoromethylphenylsulphonamido) benzoxazole derivatives (Va-Vk) have been designed and synthesized. Surprisingly, in vitro hGST P1-1 enzyme inhibition studies demonstrated that all of the tested compounds except Vj had better activity than the reference drug EA and it is also correlated with the docking results. Additionally we compared the interactions with hGST P1-1 enzyme of newly synthesized compound Vh (bearing CF3 group) and previously synthesized compound 5f (bearing NO2 group). According to the docking results, compound Vh bound to the hGST P1-1 enzyme with a higher affinity compared to 5f. Therefore, we can consider that these data make a sense and can explain its higher activity. The compounds that obtained from this research could be used as scaffolds in design of new potent hGST P1-1 inhibitors useful in the treatment of the resistance of cancer chemotherapy.

Prediction of retention characteristics of heterocyclic compounds.

The CORAL software ( http://www.insilico.eu/coral ) was used to build up quantitative structure-property relationships (QSPRs) for the retention characteristics of 93 derivatives of three groups of heterocyclic compounds: 2-phenyl-1,3-benzoxazoles, 4-benzylsulfanylpyridines, and benzoxazines. The QSPRs are one-variable models based on the optimal descriptors calculated from the molecular structure represented by simplified molecular input-line entry systems (SMILES). Each symbol (or two undivided symbols) of SMILES is characterized by correlation weight. The optimal descriptor is the sum of the correlation weights. The numerical data on the correlation weights were calculated with the Monte Carlo method by the manner which provides best correlation between endpoint and optimal descriptor for the calibration set. The predictive ability of the model is checked with the validation set (compounds invisible during building up of the model). The approach has been checked with three random splits into the training, calibration, and validation sets: all models have apparent predictive potential. The mechanistic interpretation of the molecular features extracted from SMILES as the promoters of increase or decrease of examined endpoints is suggested.

Synthesis and biological evaluation of 2-substituted-5-(4-nitrophenylsulfonamido)benzoxazoles as human GST P1-1 inhibitors, and description of the binding site features.

Glutathione-S-transferases (GSTs) are enzymes involved in cellular detoxification by catalyzing the nucleophilic attack of glutathione (GSH) on the electrophilic center of numerous of toxic compounds and xenobiotics, including chemotherapeutic drugs. Human GST P1-1, which is known as the most prevalent isoform of the mammalian cytosolic GSTs, is overexpressed in many cancers and contributes to multidrug resistance by directly conjugating to chemotherapeutics. It is suggested that this resistance is related to the high expression of GST P1-1 in cancers, thereby contributing to resistance to chemotherapy. In addition, GSTs exhibit sulfonamidase activity, thereby catalyzing the GSH-mediated hydrolysis of sulfonamide bonds. Such reactions are of interest as potential tumor-directed prodrug activation strategies. Herein we report the design and synthesis of some novel sulfonamide-containing benzoxazoles, which are able to inhibit human GST P1-1. Among the tested compounds, 2-(4-chlorobenzyl)-5-(4-nitrophenylsulfonamido)benzoxazole (5 f) was found as the most active hGST P1-1 inhibitor, with an IC50 value of 10.2 µM, showing potency similar to that of the reference drug ethacrynic acid. Molecular docking studies performed with CDocker revealed that the newly synthesized 2-substituted-5-(4-nitrophenylsulfonamido)benzoxazoles act as catalytic inhibitors of hGST P1-1 by binding to the H-site and generating conjugates with GSH to form S-(4-nitrophenyl)GSH (GS-BN complex) via nucleophilic aromatic substitution reaction. The 4-nitrobenzenesulfonamido moiety at position 5 of the benzoxazole ring is essential for binding to the H-site and for the formation of the GST-mediated GSH conjugate.

Synthesis, biological evaluation and 2D-QSAR analysis of benzoxazoles as antimicrobial agents.

A new series of 5(or 6)-nitro/amino-2-(substituted phenyl/benzyl)benzoxazole derivatives were synthesized and evaluated for antibacterial and antifungal activities against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Candida albicans and their drug-resistant isolate. Microbiological results indicated that the synthesized compounds possessed a broad spectrum of activity against the tested microorganisms at MIC values between > 400 and 12.5 microg/ml. The results against B. subtilis, P. aeruginosa, drug-resistant B. subtilis, drug-resistant E. coli, and C. albicans isolate for these kinds of structures are quite encouraging. The 2D-QSAR analysis of a set of newly and previously synthesized benzoxazoles tested for growth inhibitory activity against B. subtilis ATCC 6633 was performed by using the multivariable regression analysis. The activity contributions for substituent effects of these compounds were determined from the correlation equation for predictions of the lead optimization.

Some benzoxazoles and benzimidazoles as DNA topoisomerase I and II inhibitors.

Some novel fused heterocyclic compounds of 2, 5-disubstituted-benzoxazole and benzimidazole derivatives, which were previously synthesized by our group, were investigated for their inhibitory activity on both eukaryotic DNA topoisomerase I and II in a cell free system. 2-Phenoxymethylbenzimidazole (17), 5-amino-2-(p-fluorophenyl)benzoxazole (3), 5-amino-2-(p-bromophenyl)benzoxazole (5), 5-nitro-2-phenoxymethyl-benzimidazole (18), 2-(p-chlorobenzyl)benzoxazole (10) and 5-amino-2-phenylbenzoxazole (2) were found to be more potent as eukaryotic DNA topoisomerase I poisons than the reference drug camptothecin having IC(50) values of 14.1, 132.3, 134.1, 248, 443.5, and 495 microM, respectively. 5-Chloro-2-(p-methylphenyl)benzoxazole (4), 2-(p-nitrobenzyl)benzoxazole (6) and 5-nitro-2-(p-nitrobenzyl)benzoxazole (8) exhibited significant activity as eukaryotic DNA topoisomerase II inhibitors, having IC(50) values of 22.3, 17.4, 91.41 microM, respectively, showing higher potency than the reference drug etoposide.

Synthesis and biological activity of some new benzoxazoles.

The synthesis and antimicrobial activity of a new series of 5-ethylsulphonyl-2-(substituted-phenyl/substituted-benzyl and/or phenylethyl)benzoxazole derivatives (3a-3t) except 3a, 3g, 3h, 3k [R.S. Pottorf, N.K. Chadha, M. Katkevies, V. Ozola, E. Suna, H. Ghane, T. Regberg, M.R. Player, Tetrahedron Lett. 44 (1) (2003) 175] were described. The in vitro antimicrobial activity of the compounds was determined against some Gram-positive, Gram-negative bacteria, a fungi Candida albicans and their drug-resistant isolates in comparison with standard drugs. Antimicrobial results indicated that the synthesized compounds possessed a broad spectrum of activity with MIC values 250-7.81 microg/ml. While all compounds are less potent than fluconazole against C. albicans, most of them are more potent than fluconazole against C. albicans isolate.

In vitro and ex vivo activity of thioridazine derivatives against Mycobacterium tuberculosis.

Thioridazine (TZ) has previously been shown by us to have in vitro and ex vivo activity against antibiotic-susceptible and multidrug-resistant Mycobacterium tuberculosis (MDRTB). Because current therapy of MDRTB is highly problematic even when all five 'first line of defence' drugs are employed, there is a need for effective antituberculosis drugs. New derivatives of TZ were synthesised and their in vitro activity against a reference strain of M. tuberculosis was evaluated with the aid of the BACTEC 460 system. Derivatives that presented significant activity were evaluated by ex vivo studies and were shown to enhance the killing of intracellular M. tuberculosis.

Synthesis and biological evaluation of new N-(2-hydroxy-4(or 5)-nitro/aminophenyl)benzamides and phenylacetamides as antimicrobial agents.

A new series of N-(2-hydroxy-4(or 5)-nitro/aminophenyl)benzamide and phenylacetamide derivatives (1a-1n, 2a-2n) were synthesized and evaluated for antibacterial and antifungal activities against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, and their drug-resistant isolate. Microbiological results indicated that the compounds possessed a broad spectrum of activity against the tested microorganisms at MIC values between 500 and 1.95 microg/ml. Benzamide derivative 1d exhibited the greatest activity with MIC values of 1.95, 3.9, and 7.8 microg/ml against drug-resistant B. subtilis, B. subtilis, and S. aureus, respectively.

High antineoplastic activity of new heterocyclic compounds in cancer cells with resistance against classical DNA topoisomerase II-targeting drugs.

Twenty previously synthesized fused heterocyclic DNA-topoisomerase II (Topo II)-inhibiting compounds were investigated for their potential efficacy in various human cancer cell lines that were derived from different tumor entities. Moreover, different multidrug-resistant variants of these cancer cell lines with decreased Topo II expression were investigated. In parental, drug-sensitive cells merely the compounds BD3 and G35 showed efficacies, in terms of microM, which were similar to that of the classical Topo II inhibitor etoposide. On the other hand, most of the tested heterocyclic compounds were found more effective in drug-resistant cells than in the parental, drug-sensitive ones, and some of the compounds showed high antineoplastic efficacy in several drug-resistant cell models. Compounds BD13, BD14 and BD16 exhibited high antineoplastic activities against the drug-resistant sublines EPG85-257RNOV and EPG85-257RDB derived from gastric carcinoma, EPP85-181RNOV and EPP85-181RDB derived from pancreatic carcinoma, MCF-7/Adr derived from breast cancer, D79/86RNOV derived from fibrosarcoma, and MeWoETO1 derived from melanoma. Furthermore, compound D23 was found highly efficient in the multidrug-resistant variants HT-29RNOV and HT-29RDB derived from colon carcinoma, and compound D24 exhibited the highest antineoplastic activity among the tested compounds in the drug-resistant subline MDA-MB-231ROV derived from breast cancer. In conclusion, compounds BD 13, BD 14, BD 16, D 23 and D 24 may be useful for the treatment of different multidrug-resistant cancer cells with cross resistance against "classical" Topo II-targeting drugs.

Induction of apoptosis and necrosis by resistance modifiers benzazoles and benzoxazines on tumour cell line mouse lymphoma L5718 Mdr+cells.

Eighteen new fused heterocyclic compounds of benzazoles and benzoxazines were investigated for induction and inhibition of apoptosis on tumor cells (L5718, mouse lymphoma cell line containing the human mdr-1 gene). For evaluation of apoptosis, the cells were stained with FITC-labelled Annexin-V and propidium iodide and the results were analysed by flow cytometry. Nine of these substances were also checked for reversal of multidrug resistance. The reversal of multidrug resistance was determined by measuring the rhodamine-123 accumulation in the cancer cells. Rhodamine-123 shows a green fluorescence and its intracellular concentration correlates well with the inhibition of efflux pump activity. Three of the tested compounds, 5-(p-nitrobenzamido)-2-benzylbenzoxazole (BD-3), 6-methyl-2-(o-chlorophenyl) benzoxazole (A-9) and 5-(p-nitrophenoxyacetamido)-2-phenylbenzoxazole (D-30), showed an increased apoptotic effect on mouse lymphoma cells. Moreover, compounds BD-3, A-9 and 5-(2-thienylcarboxyamido)-2-phenylbenzoxazole (D-24) also amplified the apoptosis effect of 12H-benzo(a)phenothiazines (M-627). However, D-24, alone was not effective. Additionally, 2-(p-nitrobenzyl)benzoxazole (B-11), was also found to increase the apoptotic effect of M-627. On the other hand, 5-(p-nitrophenylacetamido)-2-phenylbenzoxazole (D-7) showed an anti-apoptotic effect. No positive correlation was found between the increased drug accumulation effect and the programmed cell death induced by the compounds studied.

3D-QSAR analysis on benzazole derivatives as eukaryotic topoisomerase II inhibitors by using comparative molecular field analysis method.

Selective topoisomerase II inhibitors have created a great deal of interest in recent years for the design of new antitumoral compounds. 3D-QSAR analysis has been performed on a series of previously synthesized benzoxazole, benzimidazole, and oxazolo(4,5-b)pyridine derivatives, which are screened as eukaryotic topoisomerase II inhibitors, using comparative molecular field analysis (CoMFA) with partial least squares fit to predict the steric and electrostatic molecular field interactions for the activity. The CoMFA study was carried out using a training set of 16 compounds. The predictive ability of the model was assessed using a test set of 7 compounds. The analyzed 3D-QSAR CoMFA model has demonstrated a good fit, having r(2) value of 0.997 and cross-validated coefficient q(2) value as 0.435 for the model. The obtained model reveals that the electronegatively charged substituents such as NO(2) or COOCH(3) group on position R and/or R(1) at the heterocyclic ring system and positively charged atom and/or atom groups located between the benzazole moiety and 2-substituted phenyl ring as a bridge element improve the activity. On the other hand, a bulky substituent, such as methoxy group, attached to the ortho position of 2-phenyl-5-nitro-benzoxazole (1) enhances the activity similar to compound 13, which is both a meta and para substituent of the phenyl group attached to the 2-position of benzimidazole ring system, fit into the favored steric region to improve the activity.

Synthesis and antimicrobial activity of some 5-[2-(morpholin-4-yl)acetamido] and/or 5-[2-(4-substituted piperazin-1-yl)acetamido]-2-(p-substituted phenyl)benzoxazoles.

In this study, a series of twelve novel 5-[2-(morpholin-4-yl)acetamido] and/or 5-[2-(4-substituted pip-erazine-1-yl)acetamido]-2-(p-substituted phenyl]benzoxazole derivatives have been synthesized and their structures were confirmed by IR, (1)H NMR, and mass spectral data. These compounds were prepared by reacting 5-(2-chloroacetamido)-2-(4-p-substituted-phenyl)benzoxazoles, which were obtained by using 5-amino-2-[p-substituted-phenyl]benzoxazoles with chloroacetyl chloride, in the presence of morpholine or 1-substituted piperazines. All synthesized compounds 3-14 were tested by using the method of twofold serial dilution technique for in vitro activities against certain strains of Gram-positive, Gram-negative bacteria as well as the yeasts Candida albicans, Candida krusei, and Candida glabrata in comparison with standard drugs. Microbiological results showed that the newly synthesized compounds possessed a broad spectrum of activity, showing MIC values of 3.12-50 mug/mL against the Candida species.

Synthesis and antimicrobial activity of new 2-[p-substituted-benzyl]-5-[substituted-carbonylamino]benzoxazoles.

A series of 23 new 2-[p-substituted-benzyl]-5-[p-substituted-phenyl/benzyl-carbonylamino]benzoxazole derivatives has been synthesized by reacting 5-amino-2-[p-substituted-benzyl]benzoxazoles with the appropriate carboxylic acid chlorides. The structures of the synthesized compounds were confirmed by IR and (1)H-NMR spectral data. Antimicrobial activities of the compounds were investigated using the twofold serial dilution technique against two gram-positive and two gram-negative bacteria and three Candida species in comparison with standard drugs. Microbiological results indicated that the newly synthesized 2-[p-substituted-benzyl]-5-[p-substituted-phenyl/benzyl-carbonylamino]benzoxazole derivatives (3-25) possessed a broad spectrum of activity, showing MIC values of 6.25-200 microg/mL against the gram-positive and gram-negative microorganisms tested. Moreover, they showed significant antifungal activity with MIC values of 3.12-100 microg/mL against the Candida species tested. Especially, with a MIC value of 3.12 microg/mL, 2-benzyl-5-[p-bromobenzyl-carbonylamino]benzoxazole 9 displayed the same activity against C. glabrata as the standard drug myconazol.

A target site for template-based design of measles virus entry inhibitors.

Measles virus (MV) constitutes a principal cause of worldwide mortality, accounting for almost 1 million deaths annually. Although a live-attenuated vaccine protects against MV, vaccination efficiency of young infants is low because of interference by maternal antibodies. Parental concerns about vaccination safety further contribute to waning herd immunity in developed countries, resulting in recent MV outbreaks. The development of novel antivirals that close the vaccination gap in infants and silence viral outbreaks is thus highly desirable. We previously identified a microdomain in the MV fusion protein (F protein) that is structurally conserved in the paramyxovirus family and constitutes a promising target site for rationally designed antivirals. Here we report the template-based development of a small-molecule MV inhibitor, providing proof-of-concept for our approach. This lead compound specifically inhibits fusion and spread of live MV and MV glycoprotein-induced membrane fusion. The inhibitor induces negligible cytotoxicity and does not interfere with receptor binding or F protein biosynthesis or transport but prevents F protein-induced lipid mixing. Mutations in the postulated target site alter viral sensitivity to inhibition. In silico docking of the compound in this microdomain suggests a binding model that is experimentally corroborated by a structure-activity analysis of the compound and the inhibition profile of mutated F proteins. A second-generation compound designed on the basis of the interaction model shows a 200-fold increase in antiviral activity, creating the basis for novel MV therapeutics. This template-based design approach for MV may be applicable to other clinically relevant members of the paramyxovirus family.