Subhash Mohan Agarwal

Synthesis and antiamoebic activity of metronidazole thiosemicarbazone analogues

Repeated treatment of Entamoeba histolytica infection with commonly used antiamoebic drugs results in not only increasing the toxicity potential but also leads to the development of clinical resistance. Thus new effective agents with less toxicity against amoebiasis are urgently required. With this view, metronidazole thiosemicarbazone analogues 1-11 were synthesized wherein thioamide moiety was substituted by different cyclic and aromatic amines. These compounds were screened against HM1:IMSS strain of E. histolytica parasite cultured in vitro and the sensitivity of the parasite to the metronidazole thiosemicarbazones was evaluated using the microdilution method. Eight compounds (1-4, 7-9 and 11) were found better inhibitors of E. histolytica growth since IC50 values elicited by these compounds were much lower than metronidazole with compound 4 showing the most promising antiamoebic activity (IC50=0.56 microM). The study suggests the beneficial potential of these leads that need to be further explored in order to discover and develop better and yet safer therapeutic agents for amoebiasis.

Metronidazole thiosalicylate conjugates: synthesis, crystal structure, docking studies and antiamoebic activity.

Metronidazole thiosalicylate conjugates were synthesized and crystallised in order to discover new molecules having better efficacy than therapeutically administered drug metronidazole, used against Entamoeba histolytica. The three compounds (4-6) showed lower IC(50) values than metronidazole on HM1:IMSS strain of E. histolytica and displayed low cytotoxicity on MCF-7 cell line. In order to get an insight into the mechanisms of action of these compounds, a homology model of E. histolytica thioredoxin reductase (EhTHRase) was constructed and molecular docking was performed into the binding pocket to identify the nature of interactions. The docking studies suggest that the improved inhibitory activity of the newly synthesised metronidazole analogues could be due to involvement of the additional hydrophobic interactions in the binding mode. The result of the present study indicates the molecular fragments that play an essential role in improving the antiamoebic activity.

Metronidazole hydrazone conjugates: Design, synthesis, antiamoebic and molecular docking studies

Metronidazole hydrazone conjugates (2-13) were synthesized and screened in vitro for antiamoebic activity against HM1: IMSS strain of Entamoeba histolytica. Six compounds were found to be better inhibitors of E. histolytica than the reference drug metronidazole. These compounds showed greater than 50-60% viability against HeLa cervical cancer cell line after 72 h treatment. Also, molecular docking study was undertaken on E. histolytica thioredoxin reductase (EhTHRase) protein which showed significant binding affinity in the active site. Out of the six actives, some of the compounds showed lipophilic characteristics.

Novel terpene based 1,4,2-dioxazoles: synthesis, characterization, molecular properties and screening against Entamoeba histolytica.

In present investigation a series of 20 dioxazole analogues (1-20) were synthesized, characterized and subjected to molecular properties prediction, anti-amoebic screening and cytotoxicity evaluation. Out of the twenty compounds viz. 3,5-substituted-1,4,2-dioxazoles, six compounds have shown IC(50) values in the range (1.00-1.10 μM) lower than the standard drug metronidazole (IC(50) = 1.45 μM). The toxicological studies of the active compounds on H9c2 rat cardiac myoblasts showed that all compounds were nontoxic. The pKa, and log P values have also been predicted. Compound 8 showed the most promising results based on anti-amoebic evaluation, cytotoxicity studies and physico-chemical properties prediction.

Nucleotide Composition and Amino Acid Usage in AT-Rich Hyperthermophilic Species

Nucleotide composition, codon usage and amino acid content are important molecular signatures that vary in different groups of organisms. AT-rich (or GC poor) hyperthermophiles have relatively been unexplored in these aspects. In this study, we have examined the compositional characteristics of AT rich genomes viz. Methanococcus jannaschii, Sulfolobus solfataricus, Sulfolobus tokodaii and Nanoarcheum equitans by their comparison with four mesophiles having similar genomic GC content. The analysis revealed a significant increase in purine content of ORFs due to increase in guanine content. Moreover, the influence of dinucleotide composition on protein thermostability was found even larger. Accordingly, increased usage of codons that are constituted of dinucleotides RR was observed. Arginine, proline, valine and tyrosine were most abundant amino acids in hyperthermophilic proteomes, and similar bias was seen when dipeptidic composition of proteins was compared. Further amino acid composition analysis of alpha helices indicates an increased usage of E, K, R and decreased usage of N and Q. Summing up, the study suggested that elevated growth temperature im- pose selective constraints at all the three molecular levels- nucleotide composition, codon usage and amino acid content.

Heterocyclic Lead Compounds Against Amebiasis

Amebiasis is a widespread parasitic disease caused by Entamoeba histolytica. This protozoan organism is the third leading parasitic cause of death in the developing world. Nitroimidazole-based drugs such as metronidazole, tinidazole, and ornidazole are the only agents for treating invasive amebiasis, followed by administration with luminal agents. Several side effects in addition to clinical resistance and carcinogenicity to this class of compounds, especially metronidazole, have been observed. Therefore, to combat this neglected protozoan disease it has become essential to discover new leads for the development of novel drugs that are superior or equally effective against E. histolytica but less toxic for humans. Keeping this in mind our group has been making sustained efforts in developing heterocyclic compounds as noble leads because these molecules act as highly functionalized scaffolds. Over a period of a decade hundreds of compounds corresponding to several classes (thiosemicarbazone, metronidazole analogues, azoles, pyrimidines, hydrazones, and triazines) have been synthesized, screened, and evaluated for their antiamoebic activity. In this chapter we discuss the compounds that exhibit new structural scaffolds having antiamoebic activity and elaborate on molecular fragments that play an essential role in improving the activity.

Genomic distribution of genes encoding 68 cytoplasmic ribosomal protein families in rice

Completion of rice genome sequencing has necessitated identification of transcripts encoded by the genome and their corresponding functions. In the present study we have catalogued cytoplasmic ribosomal protein complement of rice genome corresponding to 68 families. Mining TIGR (The Institute for Genomic Research) rice database and unigene sequences available from National Centre for Biotechnology Information (NCBI) produced a non-redundant set of these sequences. This resulted in identification of 209 candidate r-proteins of which 22 have not been reported previously. The number of genes per family ranges from 1 to 8 distributed throughout the genome with maximum occurrence at chromosome 7. Mapping of r-proteins on BAC clones revealed several small clusters of genes. Unigene sequences corresponding to most of the reported r-proteins were identified indicating these genes are being expressed.