Synthetic studies on novel benzimidazolopeptides with antimicrobial, cytotoxic and anthelmintic potential

Amino acid- and peptide-conjugated heterocyclic compounds: A comprehensive review of Synthesis Strategies and biological activities

Amino acids and peptides have long been recognized as promising candidates for therapeutic development due to their unique structural properties and high specificity. However, their clinical application is often limited by rapid enzymatic degradation, poor bioavailability, and suboptimal pharmacokinetics. Conjugating these biomolecules with heterocyclic compounds has emerged as a transformative strategy to enhance their stability, bioavailability, and overall therapeutic efficacy. This review highlights significant advancements since 2000 in the synthesis and biological applications of amino acid- and peptide-conjugated heterocyclic compounds These conjugates are categorized based on their nitrogen-, sulfur-, and oxygen-containing heterocyclic cores. Key synthetic methodologies, including amide bond formation, carbon-heteroatom coupling, and carbon-carbon bond formation, are discussed in detail. These conjugates exhibit enhanced pharmacological properties, with notable applications in antimicrobial, anticancer, and anti-inflammatory treatments. Despite these advancements, challenges such as synthetic complexity and potential toxicity remain. Future research should prioritize refining synthetic methodologies and leveraging underexplored heterocycles to unlock broader therapeutic applications. Peptide-heterocycle conjugates represent a promising approach to overcoming persistent challenges in modern drug development.

Conjugation as a Tool in Therapeutics: Role of Amino Acids/Peptides-Bioactive (Including Heterocycles) Hybrid Molecules in Treating Infectious Diseases

Peptide-based drugs are gaining significant momentum in the modern drug discovery, which is witnessed by the approval of new drugs by the FDA in recent years. On the other hand, small molecules-based drugs are an integral part of drug development since the past several decades. Peptide-containing drugs are placed between small molecules and the biologics. Both the peptides as well as the small molecules (mainly heterocycles) pose several drawbacks as therapeutics despite their success in curing many diseases. This gap may be bridged by utilising the so called 'conjugation chemistry', in which both the partners are linked to one another through a stable chemical bond, and the resulting conjugates are found to possess attracting benefits, thus eliminating the stigma associated with the individual partners. Over the past decades, the field of molecular hybridisation has emerged to afford us new and efficient molecular architectures that have shown high promise in medicinal chemistry. Taking advantage of this and also considering our experience in this field, we present herein a review concerning the molecules obtained by the conjugation of peptides (amino acids) to small molecules (heterocycles as well as bioactive compounds). More than 125 examples of the conjugates citing nearly 100 references published during the period 2000 to 2022 having therapeutic applications in curing infectious diseases have been covered.

Synthesis, Anticancer, and Antimicrobial Evaluation of Integerrimide-A

Integerrimide-A (IG-A) is a cyclic heptapeptide that was recently synthesized after being recovered from the latex of the Jatropha integerrima tree. This was achieved by first coupling a tetrapeptide unit (Boc-Gly-L-Leu-L-Leu-L-Leu-OMe) with a tripeptide unit (L-Thr-L-Pro-L-Trp-OMe). The characterization was done by using spectral techniques like FT-IR, 1H-NMR, mass spectrometry, and elemental analysis of the newly synthesized cyclic molecule. Antimicrobial and anticancer properties of IG-A were tested using a biological screening. Gram +ve bacteria (B. subtilis and S. aureus) and Gram -ve bacteria (P. aeruginosa and E. coli) were used in the antibacterial testing. Fungal strains such as C. albicans, A. niger, T. mentagrophytes, and M. audouinii were used to test the antifungal activities. Antimicrobial activity analysis revealed that cyclic peptide—IG-A (8)—has modest antibacterial activity and antifungal activities, when compared with the standard drugs ciprofloxacin and griseofulvin, respectively. Comparable MTT assays were performed on HCT116 (human colon carcinoma) and B16F10 (melanoma cells) cell lines with doxorubicin as the standard drug to determine the cytotoxic activity of the synthesized cyclic peptide. Inhibition of growth of HCT116 and B16F10 cell lines was used to calculate the cytotoxic effect. At a dosage of 120 μg/mL, the cyclopeptide IG-A (8) inhibited cell proliferation by 87.5 and 72.5 percent, respectively. Cyclopeptide IG-A had CTC50 values of 77.65 μM and 68.63 μM against HCT116 and B16F10, respectively. The % growth inhibitions at lesser levels are 72.5 and 50 at 60 μg/mL, respectively. The standard drug inhibited growth by 100 percent with CTC50 values of 48.63 μM and 43.25 μM against HCT116 and B16F10, respectively. From the results, it is concluded that IG-A has considerable antimicrobial and cytotoxic effects. Internucleosomal DNA fragmentation may be the underlying mechanism in HCT116 cells, whereas the suppression of eumelanin synthesis in B16F10 cells is another possibility.

Natural Bridged Bicyclic Peptide Macrobiomolecules from Celosia argentea and Amanita phalloides

Bridged peptide macrobicycles (BPMs) from natural resources belong to types of compounds that are not investigated fully in terms of their formation, pharmacological potential and stereo-chemical properties. This division of biologically active congeners with multiple circular rings, has merits over other varieties of peptide molecules. BPMs form one of the most hopeful grounds for establishment of drugs because of their close resemblance and biocompatibility to proteins, and these bio-actives are debated as feasible realistic tools in diverse biomedical applications. Despite huge potential, poor metabolic stability and cell permeability limit the therapeutic success of macrocyclic peptides. In this review, we have comprehensively explored major bicyclic peptides sourced from plants and mushrooms including βs-leucyl-tryptophano-histidine bridged and tryptophano-cysteine bridged peptide macrobicycles. The unique structural features, structure activity relationship, synthetic routes, bioproperties and therapeutic potential of the natural BPMs are also discussed.

Toward the Synthesis of a Heterocyclic Analogue of Natural Cyclooligopeptide with Improved Bio-Properties

AIMS

The present investigation is targeted toward the synthesis of a novel analogue of a natural peptide of marine origin. <P> Background: Marine sponges are enriched with bioactive secondary metabolites especially circular peptides. Heterocycles are established organic compounds with potential biological value. Taking into consideration the bio-properties of heterocycles and marine sponge-derived natural peptides, an effort was made for the synthesis of a heterocyclic analogue of a natural cyclopeptide. <P> Objective: A heterocyclic analogue of a sponge-derived proline-containing cyclic peptide, rolloamide A, was synthesized by interaction of Boc-protected L-histidinyl-L-prolyl-L-valine and L-prolyl-L-leucyl-L-prolyl-L-isoleucine methyl ester and compared with synthetic rolloamide A with bioactivity against bacteria, fungi, and earthworms. <P> Methods: The synthesis of cycloheptapeptide was accomplished employing the liquid phase method. The larger peptide segment was prepared by interaction of Boc-protected L-prolyl-L-leucine with L-prolyl-L-isoleucine methyl ester. Similarly, the tripeptide unit was synthesized from Boc-protected L-histidinyl-L-proline with L-valine ester. The linear heptapeptide segment (7) was cyclized by utilizing pentafluorophenyl (pfp) ester, and the structure was elucidated by elemental and spectral (IR, 1H/13C NMR, MS) analysis. The peptide was also screened for diverse bioactivities such as antibacterial, antifungal, and potential against earthworms and cytotoxicity. <P> Results: The novel cyclooligopeptide was synthesized with 84% yield by making use of carbodiimides. The synthesized cyclopeptide exhibited significant cytotoxicity against two cell lines. In addition, promising antifungal and antihelmintic properties were observed for newly synthesized heterocyclic peptide derivative (8) against dermatophytes and three earthworm species at 6 µg/mL and 2 mg/mL, respectively. <P> Conclusion: Solution-phase technique employing carbodiimide chemistry established to be promising for synthesizing the cycloheptapeptide derivative (8), and C5H5N was proved a better base for heptapeptide circling, when compared to N-methylmorpholine and triethylamine.

A comprehensive review of chemistry and pharmacological aspects of natural cyanobacterial azoline-based circular and linear oligopeptides

The cyanobacterial oligopeptides are recognized for being highly selective, efficacious and relatively safer compounds with diverse bioactivities. Azoline-based natural compounds consist of heterocycles which are reduced analogues of five-membered heterocyclic azoles. Among other varieties of azoline-based natural compounds, the heteropeptides bearing oxazoline or thiazoline heterocycles possess intrinsic structural properties with captivating pharmacological profiles, representing excellent templates for the design of novel therapeutics. The specificity of heteropeptides has been translated into prominent safety, tolerability, and efficacy profiles in humans. These peptidic congeners serve as ideal intermediary between small molecules and biopharmaceuticals based on their typically low production complexity compared to the protein-based biopharmaceuticals. The distinct bioproperties and unique structures render these heteropeptides one of the most promising lead compounds for drug discovery. The high degree of chemical diversity in cyanobacterial secondary metabolites may constitute a prolific source of new entities leading to the development of new pharmaceuticals. This review focuses on the azoline-based natural oligopeptides with emphasis on distinctive structural features, stereochemical aspects, biological activities, structure activity relationship, synthetic and biosynthetic aspects as well as mode of action of cyanobacteria-derived peptides.

Synthesis and Bioactivity of a Cyclopolypeptide from Caribbean Marine Sponge

Synthesis of a natural proline-rich cyclopolypeptide - rolloamide A was carried out by coupling of tri- and tetrapeptide units Boc-Phe-Pro-Val-OMe and Boc-Pro-Leu-Pro-Ile-OMe after proper deprotection at carboxyl and amino terminals using carbodiimide chemistry in alkaline environment followed by cyclization of linear heptapeptide segment in the presence of base. The structure of synthesized peptide was confirmed by spectral techniques including FTIR, ¹H NMR, ¹³C NMR, MS analyses. Newly synthesized peptide was subjected to biological screening against pathogenic microbes and earthworms. Cyclopeptide 8 possessed promising activity against pathogenic fungi Candida albicans (ZOI: 24 mm, MIC: 6 μg/mL) and Gram-negative bacteria Pseudomonas aeruginosa (ZOI: 27 mm, MIC: 6 μg/mL) and Klebsiella pneumoniae (ZOI: 23 mm, MIC: 12.5 μg/mL), in comparison to reference drugs – griseofulvin (ZOI: 20 mm, MIC: 6 μg/mL) and ciprofloxacin (ZOI: 25 mm, MIC: 6 μg/mL/ZOI: 20 mm, MIC: 12.5 μg/mL). Also, newly synthesized heptacyclopeptide exhibited potent anthelmintic activity against earthworms Megascoplex konkanensis,Pontoscotex corethruses, and Eudrilus species (MPT/MDT ratio – 8.22-16.02/10.06-17.59 min), in comparison to standard drugs - mebendazole (MPT/MDT ratio – 10.52-18.02/12.57-19.49 min) and piperazine citrate (MPT/MDT ratio – 12.38-19.17/13.44-22.17 min).

Natural cyclic polypeptides as vital phytochemical constituents from seeds of selected medicinal plants

Cyclopolypeptides are among the most predominant biomolecules in nature, especially those derived from plant seeds. This category of compounds has gained extraordinary attention due to remarkable variety of structures and valuable biofunctions. These congeners display enormous variation in terms of both structure and function and are the most significant biomolecules due to their widespread bioproperties. The estrogenic activity, immunosuppressive activity, cytotoxicity, vasorelaxant activity, and other properties possessed by cyclic peptides from seeds of plants make these congeners attractive leads for the drug discovery process. The current study covers the important structural features, structure-activity relationship, synthesis methods, and bioproperties of plant seeds-originated bioactive peptides from Vaccaria segetalis, Linum usitatissimum, and Goniothalamus leiocarpus, which may prove vital for the development of novel therapeutics based on a peptide skeleton.

Natural bioeffective cyclooligopeptides from plant seeds of Annona genus

The Annona L. is one of the most significant genus of the Annonaceae family due to its widespread medicinal properties. This genus has a variety of active metabolites, including alkaloids, isoquinolines, peptides, acetogenins, lectins, volatile oils etc. Due to the constitution of cyclopeptides with an expanded spectrum of distinctive bioproperties, this genus is predominantly preferred over other species. The cytotoxicity, vasorelaxant activity, anti-inflammatory and other properties exhibited by cyclooligopeptides from seeds of Annona genus plants make these metabolites attractive leads for the drug discovery process. The present review covers the structural characteristics, structure activity relationship, synthesis strategies, pharmacological properties of plant seeds-originated bioactive peptides from Annona genus, which may be vital for the development of novel therapeutics based on peptide skeleton.

Design, synthesis, anti-tobacco mosaic viral and molecule docking simulations of urea/thiourea derivatives of 2-(piperazine-1-yl)-pyrimidine and 1-(4-Fluoro/4-Chloro phenyl)-piperazine and 1-(4-Chloro phenyl)-piperazine - A study

The objectives of the present work are to design, syhthesize and introduce novel urea/thiourea derivatives of 2-(piperazine-1-yl)-pyrimidine and 1-(4-Fluoro/4-Chloro phenyl)-piperazine molecules as tobacco mosaic virus (TMV) inhibitors. A series of urea/thiourea derivatives containing pyrimidine and piperazine moieties were synthesized, characterized using Fourier-transform infrared (FTIR) mass spectra, nuclear magnetic resonance (NMR) spectroscopy, elemental analysis and evaluated their sustainability using biological experiments. The anti-viral bioassay of the title compounds showed an antiviral activity against TMV. The compounds synthesized, 9j, 6g and 3d, showed highly-potential curative, protective, and inhibitory activities against TMV at 500 mg/mL formulation. All these compounds were allowed to quantum-polarized-ligand (quantum mechanical and molecular mechanical (QM/MM)) docking experiments. The compounds 9j, 6g and 3d structurally exhibited identical higher affinity towards TMV-Helicase and TMV-Coat proteins. The docking interactions proposed had two stage inhibition of TMV virus by binding to coat protein and helicase for inhibition of RNA replication. The long-range molecular dynamics (150 ns) simulations has revealed more consistency by 9j, 6g and 3d. The present study outcomes good binding propensity for active-tunnel of TMV-Hel enzyme, by these thiourea, urea derivatives, 9j, 6g and 3d, to suggest that the designed and synthesized were ideal for proposing as selective novel inhibitors to target for TMV.

Natural Bioactive Thiazole-Based Peptides from Marine Resources: Structural and Pharmacological Aspects

Peptides are distinctive biomacromolecules that demonstrate potential cytotoxicity and diversified bioactivities against a variety of microorganisms including bacteria, mycobacteria, and fungi via their unique mechanisms of action. Among broad-ranging pharmacologically active peptides, natural marine-originated thiazole-based oligopeptides possess peculiar structural features along with a wide spectrum of exceptional and potent bioproperties. Because of their complex nature and size divergence, thiazole-based peptides (TBPs) bestow a pivotal chemical platform in drug discovery processes to generate competent scaffolds for regulating allosteric binding sites and peptide–peptide interactions. The present study dissertates on the natural reservoirs and exclusive structural components of marine-originated TBPs, with a special focus on their most pertinent pharmacological profiles, which may impart vital resources for the development of novel peptide-based therapeutic agents.

First Total Synthesis and Pharmacological Potential of a Plant Based Hexacyclopeptide

A new bioactive proline-rich cyclohexapeptide - diandrine C (6), previously isolated from whole plant of Drymaria diandra (Caryophyllaceae), was synthesized through coupling reactions of tetrapeptide unit Boc-Gly--Pro--Tyr--Trp-OH with dipeptide unit -Pro-Gly-OMe using N,N-diisopropylcarbodiimide (DIPC) as the coupling agent, followed by cyclization of linear hexapeptide unit under alkaline condition. Structure of cyclohexapeptide was confirmed by means of chemical, and spectroscopic analyses and also was screened for its antimicrobial and anthelmintic properties. Bioevaluation results indicated that the newly synthesized hexacyclopeptide exhibited potent antimicrobial activity against Gram-negative bacteria Pseudomonas aeruginosa, Klebsiella pneumoniae and pathogenic Candida albicans at 6 μg/mL. Moderate to good level of antihelmintic activity against three earthworm species Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniae was also observed at concentration of 2 mg/mL.

A Temperature-Driven, Reversible, Helical-Handedness Inversion in Peptaibol Analogues Tuned by the C-Terminal Capping Moiety

Trichogin is a natural peptide endowed with antimicrobial and antitumor activity. A member of the peptaibol family, trichogin possesses a C-terminal amino alcohol. In the past, this moiety was substituted for a methyl ester for synthetic purposes and it was observed that this apparently slight modification caused significant changes in the peptide bioactivity. With the aim of understanding the reasons behind such observations, a detailed spectroscopic study on a number of trichogin analogues has been performed. Herein, data obtained from synchrotron radiation circular dichroism, NMR spectroscopy, and fluorescence spectroscopy in organic solvents at cryogenic temperatures are compared with those independently acquired by means of EPR spectroscopy at 80 K. It is unambiguously revealed that the presence of a reversible, temperature-driven, screw-sense interconversion from a right- to left-handed helix is determined by the C-terminal capping moiety. Data demonstrate, for the first time, the key role of a C-terminal methyl ester in promoting peptide screw-sense inversion.

Toward the Synthesis and Improved Biopotential of an N-methylated Analog of a Proline-Rich Cyclic Tetrapeptide from Marine Bacteria

An N-methylated analog of a marine bacteria-derived natural proline-rich tetracyclopeptide was synthesized by coupling the deprotected dipeptide fragments Boc-l-prolyl-l-N-methylleucine-OH and l-prolyl-l-N-methylphenylalanine-OMe. A coupling reaction was accomplished utilizing N,N'-Dicyclohexylcarbodidimde (DCC) and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC·HCl) as coupling agents and Triethylamine (TEA) or N-methylmorpholine (NMM) as the base in the presence of the racemization suppressing agent. This was followed by the cyclization of the linear tetrapeptide fragment under alkaline conditions. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FTIR (Fourier-transform infrared spectroscopy), ¹H NMR (Nuclear magnetic resonance spectroscopy), 13C NMR, and mass spectrometry. From the bioactivity results, it was clear that the newly synthesized proline-rich tetracyclopeptide exhibited better anthelmintic potential against Megascoplex konkanensis, Pontoscotex corethruses, and Eudrilus eugeniae at a concentration of 2 mg/mL as well as improved antifungal activity against pathogenic dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL, as compared to non-methylated tetracyclopeptide. Moreover, N-methylated tetracyclopeptide displayed significant activity against pathogenic Candida albicans.

Total Synthesis and Pharmacological Investigation of Cordyheptapeptide A

The present investigation reports the synthesis of a phenylalanine-rich N-methylated cyclopeptide, cordyheptapeptide A (8), previously isolated from the insect pathogenic fungus Cordyceps sp. BCC 1788, accomplished through the coupling of N-methylated tetrapeptide and tripeptide fragments followed by cyclization of the linear heptapeptide unit. Structure elucidation of the newly synthesized cyclopolypeptide was performed by means of FT-IR, ¹H-NMR, 13C-NMR, and fast atom bombardment mass spectrometry (FABMS), and screened for its antibacterial, antidermatophytic, and cytotoxic potential. According to the antimicrobial activity results, the newly synthesized N-Methylated cyclopeptide exhibited potent antibacterial activity against Gram-negative bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae and antifungal activity against dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL, in comparison to the reference drugs, gatifloxacin and griseofulvin. In addition, cyclopolypeptide 8 displayed suitable levels of cytotoxicity against Dalton's lymphoma ascites (DLA) and Ehrlich's ascites carcinoma (EAC) cell lines.

Toward the Synthesis and Pharmacological Screening of a Natural Cycloheptapeptide of Plant Origin

The solution-phase synthesis of a proline and glycine-rich plant-derived cyclic heptapeptide, gypsophin E (8), is reported via coupling of a tetrapeptide unit Glycyl-L-leucyl-L-valyl-L-proline-OMe with a tripeptide unit Boc-L-isoleucyl-glycyl-L-proline-OH, followed by cyclization of the linear fragment having seven amino acid units. The structure of the newly synthesized cycloheptapeptide was confirmed by means of chemical and spectroscopic methods. The newly synthesized cyclopolypeptide displayed potent antifungal and anthelmintic activities against the pathogenic yeast Candida albicans, the dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at the 6 μg/mL level, and the earthworms Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at a concentration of 2 mg/mL.

First Total Synthesis and Biological Screening of a Proline-Rich Cyclopeptide from a Caribbean Marine Sponge

A natural heptacyclopeptide, stylissamide G (7), previously isolated from the Bahamian marine sponge Stylissa caribica from the Caribbean Sea, was synthesized via coupling of the tetrapeptide l-phenylalanyl-l-prolyl-l-phenylalanyl-l-proline methyl ester with the tripeptide Boc-l-leucyl-l-isoleucyl-l-proline, followed by cyclization of the linear heptapeptide fragment. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FT-IR, ¹H NMR, ¹³C NMR and mass spectrometry. Results of pharmacological activity studies indicated that the newly synthesized cycloheptapeptide displayed good anthelmintic potential against Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at 2 mg/mL and in addition, potent antifungal activity against pathogenic Candida albicans and dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at a concentration of 6 μg/mL.

Synthesis, electronic properties, antioxidant and antibacterial activity of some new benzimidazoles

Two groups of benzimidazole derivatives were synthesized using as precursors 5(6)-substituted 2-mercapto-benzimidazol-thiols and their antioxidant activity was investigated using TBA-MDA test. In the group of 1,3-disubstituted-benzimidazol-2-imines the highest lipid peroxidation inhibition effect 74.04% (IC₅₀=141.89 μg/mL) revealed ethyl [3-(2-ethoxy-2-oxoethyl)-2-imino-5-benzoyl-2,3-dihydro-1H-benzimdazol-1-yl]acetate 12 while in the group of 2-substituted-1,3-thiazolo[3,2-a]benzimidazolones the highest inhibition effect showed 2-(4-fluorobenzylidene)-7-(phenylcarbonyl)[1,3]thiazolo[3,2-a]benzimidazol-3(2H)-one 17 90.76% (IC₅₀=53.70 μg/mL). In order to estimate the capability of the studied benzimidazoles to act as radical scavengers the structure of the most active derivative within the both subseries was optimized at B3LYP/6-311++G(∗∗) level and the respective bond dissociation enthalpies were calculated. The appropriate models for the HAT and SET-mechanism of the antioxidant activity were proposed. The antibacterial activity of the compounds was evaluated against two Gram-positive bacteria (Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 6538) and three Gram-negative bacteria (Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027 and Salmonella abony NCTC 6017). 1,3-Diphenylpropyl-5-methyl-1,3-dihydro-2H-benzimidazol-2-imine 14 exhibited significant activity against B. subtilis, S. aureus, S. abony and E. coli (with MIC values of 0.125, 0.016, 0.50 and 0.50mg/mL, respectively). The group of thiazolobenzimidazolones did not reveal antibacterial activity against the tested strains.

Synthesis, Crystal Structure, and DFT Calculations of 1,3-Diisobutyl Thiourea

1,3-Diisobutyl thiourea was synthesized and characterized by single crystal X-ray diffraction. It gives a monoclinic (α=γ= 90 andβ  ≠90) structure with the space group P21/c. The unit cell dimensions area= 11.5131 (4) Å,b= 9.2355 (3) Å,c= 11.3093 (5) Å,α= 90°,β= 99.569° (2),γ= 90°,V= 1185.78 (8) Å3, andZ= 4. The crystal packing is stabilized by intermolecular (N–H⋯S) hydrogen bonding in the molecules. The optimized geometry and Mullikan's charges of the said molecule calculated with the help of DFT using B3LYP-6-311G model support the crystal structure.

Synthesis, antimicrobial and antimycobacterial evaluation of [2-(substituted phenyl)-imidazol-1-yl]-pyridin-3-yl-methanones

A series of [2-(substituted phenyl)-imidazol-1-yl]-pyridin-3-yl-methanones (1-11) were synthesized and screened for their antimicrobial and antimycobacterial activities. Further, a series of [2-(substituted phenyl)-benzimidazol-1-yl]-pyridin-3-yl-methanones (12-20) reported in our earlier study was also screened for their antimycobacterial activity. The antimycobacterial activity results indicated that [2-(4-Nitro-phenyl)-imidazol-1-yl]-pyridin-3-yl-methanone (8, minimum inhibitory concentration [MIC] = 3.13 µg) was equipotent as standard drug ciprofloxacin and [2-(4-Nitro-phenyl)-benzimidazol-1-yl]-pyridin-3-yl-methanone (16, MIC = 1.56 µg) was equipotent as standard drug ethambutol. The results of antimicrobial screening demonstrated that 2-[1-(Pyridine-3-carbonyl)-1H-imidazol-2-yl]-benzoic acid (compound 11, MIC = 0.002 µg) was two times more effective than standard drug ciprofloxacin (MIC = 0.004 µg) against tested bacterial strains and [2-(2,5-Dimethyl-phenyl)-imidazol-1-yl]-pyridin-3-yl-methanone (compound 3, MIC = 0.005 µg) was equipotent to the reference compound, fluconazole against tested fungal strains.

4-[1-(Substituted aryl/alkyl carbonyl)-benzoimidazol-2-yl]-benzenesulfonic acids: synthesis, antimicrobial activity, QSAR studies, and antiviral evaluation

A series of 4-[1-(substituted aryl/alkyl carbonyl)-benzoimidazol-2-yl]-benzene sulphonic acids (1-20) was synthesized and evaluated, in vitro, for their antimicrobial activity and the results indicated that compounds 4-[1-(4-Nitrobenzoyl)-1H-benzoimidazol-2-yl]-benzenesulfonic acid (9) and 4-(1-octadec-9-enoyl-1H-benzoimidazol-2-yl)-benzenesulfonic acid (18) were found to be the most active ones. QSAR investigations indicated that the multi-target QSAR model was effective in describing the antimicrobial activity over the one-target QSAR models. Further the mt-QSAR model indicated the importance of the topological parameter, Balaban index (J) followed by the electronic parameter, LUMO and topological parameter, valence second order molecular connectivity index (2χv) in describing the antimicrobial activity of synthesized compounds (1-20).

Synthesis, antimicrobial and antiviral activity of substituted benzimidazoles

In the present study we have synthesized (4-nitrophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanones, (2-bromophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanone analogues (1-14) and evaluated them for their antimicrobial and antiviral potential. The results of antimicrobial screening indicated that none of the synthesized compounds were effective against the tested bacterial strains. Compounds 3, 11, 13 and compounds 5, 11, 12 were found to be active against Aspergillus niger and Candida albicans respectively, and may be further developed as antifungal agents. Furthermore, evaluation against a panel of different viruses pointed out the selective activity of compounds 5 and 6 against vaccinia virus and Coxsackie virus B4.

The Synthesis and Anticancer Activities of Peptide 5-fluorouracil Derivatives

A new series of peptide 5-fluorouracil derivatives was designed and synthesised in order to test in vitro anticancer activities. The results indicated that peptide 5-fluorouracil derivatives possessed anticancer activities against human HL-60 and Bel-7402 cell lines. The structures of the compounds were determined by means of 1H NMR, 13C NMR, IR, mass spectra and elemental analyses.

Synthesis and biological activity of peptide derivatives of iodoquinazolinones/nitroimidazoles

Two substituted quinazolinyl/imidazolyl-salicylic acids 5, 6 were synthesized by the reaction of 6-iodo-2-methylbenzoxazin-4-one/5-nitroimidazole with 5-aminosalicylic acid (5-ASA). Coupling of compounds 5 and 6 with different amino acid ester hydrochlorides, dipeptide and tripeptide methyl esters yielded novel quinazolino/imidazolopeptide derivatives 5a-f and 6a-g. The chemical structures of all newly synthesized compounds were confirmed by means of FT-IR, ¹H- and ¹³C-NMR, MS and elemental analysis. Selected peptide ester derivatives were further hydrolyzed by using lithium hydroxide (LiOH) to afford the corresponding acid derivatives 5b_a-d_a and 6e_a-g_a. All peptide derivatives were assayed for antimicrobial and anthelmintic activities against eight pathogenic microbes and three earthworm species. Among the tested compounds, 5e, 5d, 6e and their hydrolyzed analogs 5d_a and 6e_a exhibited higher antimicrobial activity against Pseudomonas aeruginosa, Klebsiella pneumoniae and Candida albicans, and 5a, 6g and 6g_a displayed better antifungal activity against the dermatophytes Trichophyton mentagrophytes and Microsporum audouinii. Moreover, 6f and its hydrolyzed derivative 6f_a showed good anthelmintic activity against Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at dose of 2 mg mL^–1.