Diwan S. Rawat

Clinical Status of Anti-Cancer Agents Derived from Marine Sources

The chemical, biological and ecological diversity of the marine ecosystem has contributed immensely in the discovery of extremely potent compounds that have shown potent activities in antitumor, analgesia, antiinflammatory, immunomodulation, allergy, anti-viral etc. The compounds of marine origin are diverse in structural class from simple linear peptides to complex macrocyclic polyethers. The recent advances in the sophisticated instruments for the isolation and characterization of marine natural products and development of high-throughput screening, have substantially increased the rate of discovery of various compounds of biomedical application. Didemnin was the first marine peptide that entered in human clinical trials in US for the treatment of cancer and other compounds such as dolastatin-10, soblidotin, didemnin B, ecteinascidin 743, girolline, aplidine, cryptophycins (also arenastatin A), bryostatin 1, ILX 651, kahalalide F, E7389, discodermolide, ES-285 (spisulosine), HTI-286 (hemiasterlin derivative), squalamine, KRN-7000, vitilevuamide, Laulimalide, Curacin A, diazonamide, peloruside A, eleutherobin, sarcodictyin, thiocoraline, salicylihalimides A, ascididemnin, CGX-1160, CGX-1007dictyodendrins, GTS-21 (aka DMBX), manoalide, IPL-576,092 (aka HMR-4011A) have entered in the clinical trials. This article summarize clinical status and synthetic advances of some of these compounds.

Novel 4-aminoquinoline-pyrimidine based hybrids with improved in vitro and in vivo antimalarial activity.

A class of hybrid molecules consisting of 4-aminoquinoline and pyrimidine were synthesized and tested for antimalarial activity against both chloroquine (CQ)-sensitive (D6) and chloroquine (CQ)-resistant (W2) strains of Plasmodium falciparum through an in vitro assay. Eleven hybrids showed better antimalarial activity against both CQ-sensitive and CQ-resistant strains of P. falciparum in comparison to standard drug CQ. Four molecules were more potent (7-8-fold) than CQ in D6 strain, and eight molecules were found to be 5-25-fold more active against resistant strain (W2). Several compounds did not show any cytotoxicity up to a high concentration (60 μM), others exhibited mild toxicities, but the selective index for the antimalarial activity was very high for most of these hybrids. Two compounds selected for in vivo evaluation have shown excellent activity (po) in a mouse model of Plasmodium berghei without any apparent toxicity. The X-ray crystal structure of one of the compounds was also determined.

Synthesis, antimalarial activity and cytotoxicity of 4-aminoquinoline-triazine conjugates.

A series of 4-aminoquinoline-triazine conjugates with different substitution pattern have been synthesized and evaluated for their in vitro antimalarial activity against chloroquine-sensitive and resistant strains of Plasmodium falciparum. Compounds 16, 19, 28 and 35 exhibited promising antimalarial activity against both strains of P. falciparum. Cytotoxicity of these compounds was tested against three cell lines. Several compounds did not show any cytotoxicity up to a high concentration (48microM), others exhibited mild toxicities but selective index for antimalarial activity was high for most of these conjugates.

Antituberculosis drug research: a critical overview.

The increasing drug resistance of Mycobacterium tuberculosis to the currently used drugs and HIV coinfection has caused alarm in the international scientific community. Subsequently, there is an urgent need for the development of new drug molecules with newer targets and with an alternative mechanism of action. Since the last 50 years, the same long‐duration, multidrug treatment plan is being followed for the treatment of tuberculosis. The objective of this review article is to critically analyze the antitubercular potential of various classes of compounds (quinoline, diamine, quinolone, fluoroquinolone, quinone, nitroimidazole, terpenoid, isonicotinyl, oxazolidinone, pyrimidine, and purine), their possibility to be a future drug candidate, and latest information on the clinical status of some novel antitubercular compounds. Compounds such as moxifloxacin, PA824, and TMC207 are well tolerated and there is no adverse effect shown by them. Moxifloxacin and gatifloxacin shows cross‐resistance to the currently used drugs while no cross‐resistance observed in case of TMC207 and PA824. Some compounds like OPC67683 and PA824 are bactericidal in nature.

Synthesis and antibacterial activity evaluation of metronidazole–triazole conjugates

Synthesis and antibacterial activity of metronidazole-triazole conjugates are reported. Total 21 hybrid compounds have been synthesized with different substitution pattern on the triazole ring in order to study their influence on the antibacterial activity. These compounds demonstrated potent to weak antibacterial activity against Gram-positive, and Gram-negative bacteria. Six compounds have shown equal or better antibacterial activity against Gram-negative strains than the reference compound.

Interaction studies of novel cell selective antimicrobial peptides with model membranes and E. coli ATCC 11775

Cationic antimicrobial peptides (CAMPs) are novel candidates for drug development. Here we describe design of six short and potent CAMPs (SA-1 to SA-6) based on a minimalist template of 12 residues H+HHG+HH+HH+NH2 (where H: hydrophobic amino acid and +: charged hydrophilic amino acid). Designed peptides exhibit good antibacterial activity in micro molar concentration range (1-32 mug/ml) and rapid clearance of Gram-positive and Gram-negative bacterial strains at concentrations higher than MIC. For elucidating mode of action of designed peptides various biophysical studies including CD and Trp fluorescence were performed using model membranes. Further based on activity, selectivity and membrane bound structure; modes of action of Trp rich peptide SA-3 and template based peptide SA-4 were compared. Calcein dye leakage and transmission electron microscopic studies with model membranes exhibited selective membrane active mode of action for peptide SA-3 and SA-4. Extending our work from model membranes to intact E. coli ATCC 11775 in scanning electron micrographs we could visualize different patterns of surface perturbation caused by peptide SA-3 and SA-4. Further at low concentration rapid translocation of FITC-tagged peptide SA-3 into the cytoplasm of E. coli cells without concomitant membrane perturbation indicates involvement of intracellular targeting mechanism as an alternate mode of action as was also evidenced in DNA retardation assay. For peptide SA-4 concentration dependent translocation into the bacterial cytoplasm along with membrane perturbation was observed. Establishment of a non specific membrane lytic mode of action of these peptides makes them suitable candidates for drug development.

Marine Peptides and Related Compounds in Clinical Trial

Advances in the sophisticated instruments for the isolation and characterization of marine natural products, and development in the biological assay systems, have resulted in the discovery of various compounds of biomedical application. Marine natural products have been a source of new leads for the treatment of many deadly diseases such as cancer, acquired immuno-deficiency syndrome (AIDS) etc. The compounds of marine origin are diverse in structural class from simple linear peptides to complex macrocyclic polyethers. Number of marine peptides have been isolated in recent years which exhibit potent biological activities, and many of the compounds showed promising anticancer activity. Didemnin was the first marine peptide that entered in human clinical trials in US for the treatment of cancer, and other anticancer peptides such as kahalalide F, hemiasterlin, dolastatins, cemadotin, soblidotin, didemnins and aplidine have entered in the clinical trials. Clinical status of anticancer marine derived peptides have been discussed and reviewed.

Synthesis of 4‐aminoquinoline‐1,2,3‐triazole and 4‐aminoquinoline‐1,2,3‐triazole‐1,3,5‐triazine Hybrids as Potential Antimalarial Agents

We report herein synthesis of a series of 4‐aminoquinoline‐1,2,3‐triazole and 4‐aminoquinoline‐1,2,3‐triazole‐1,3,5‐triazine hybrids and evaluate their antimalarial activity against D6 and W2 strains of Plasmodium falciparum. To study the structure–activity relationship of substituted 4‐aminoquinoline–based hybrids, 34 structurally diverse compounds were synthesized and tested against D6 and W2 strains of P. falciparum. Some of the compounds have shown promising antimalarial activity without toxicity against Vero cells.

Ionic liquids: a versatile medium for palladium-catalyzed reactions

Um grande numero de reacoes de formacao de ligacoes carbono-carbono (tais como: acoplamentos de Heck, Suzuki, Stille, Negishi e Sonogashira, entre outros) e facilitado pela catalise com compostos de paladio. Neste artigo de revisao, apresentamos uma visao detalhada e compreensiva da literatura sobre a versatilidade do uso de liquidos ionicos em conjunto com paladio em varios tipos de reacoes.

Synthesis and antioxidant activity of thymol and carvacrol based Schiff bases.

Thymol and carvacrol are well known antioxidants found in the extract of the plants of thyme species. The Schiff bases of 2-iso-propyl-5-methyl-phenol (thymol/1a), 2-tert-butyl-5-methyl-phenol (1b) and 5-iso-propyl-2-methyl-phenol (carvacrol/1c) exhibited much better antioxidant activity than thymol and carvacrol in DPPH assay. Ten compounds (4k, 4l, 4r, 5k, 5l, 5q, 5r, 6k, 6l and 6r) showed better or similar activity as compared to the reference compound ascorbic acid. Twenty-four most active compounds were also screened by ABTS method and showed 60-90% inhibition at 5 μg/mL concentration.