New sulphonamide-peptide hybrid molecules as potential PBP 2a ligands and methicillin resistant Staphylococcus aureus actives

Penicillin binding protein 2a (PbP 2a) expression accounts for the insusceptibility of methicillin-resistant Staphylocuccus aureus (MRSA) to β-lactam antibiotics. Here we employed computational strategies to challenge PbP 2a with series of fifty-five 'ala-ala' and 'ala-pro' sulphonamide-dipeptides. Binding stability of two compounds (labeled: 10i and 10n) with theoretical K_i in nM and µM ranges, for PbP 2a active and allosteric sites respectively, were investigated using molecular dynamics simulations. In addition, the results of the sensitivity of four strains of MRSA for compounds 10i and 10n obtained revealed the compounds at 10 µg/ml caused two isolates (S4 and S10) to revert to being susceptible. Finally, a reliable binding conformations of both compounds in the two binding sites of PbP 2a are described to provide rationale for structure-activity optimization of this series.Communicated by Ramaswamy H. Sarma.

Computational studies reveal potential dolichyl-phosphate N-acetylglucosaminephosphotransferase inhibitors amidst existing drugs

Dolichyl-phosphate N-acetylglucosaminephosphotransferase (dpagt1) inhibition is reported to kill tumor cells whose growth progression requires increased branching of N-linked glycans. Available dpagt1 inhibitors are grossly limited and are faced with problems of heamolytic effect and aqueous solubility thereby necessitating the search for new, safe and effective dpagt1 inhibitors. We employed computational methods to screen a dataset of ∼1300 FDA approved drugs in order to obtain theoretical dpagt1 inhibitors which could be repurposed as chemotherapeutic drugs. Top six better performing drugs, binding affinity for dpagt1 at the range of -17.63 to -20.40 kcal/mol, than the reference ligand (tunicamycin; -14.86 kcal/mol) were obtained at the end of structure-based-pharmacophore- and virtual-screening and 'induced fit' docking calculations. Analysis of their binding poses identified essential pharmacophores involved in target-ligand complexation that could be targeted in chemical modification to develop more effective and safe dpagt1 inhibitors.Communicated by Ramaswamy H. Sarma.

Evaluation of the in vitro trypanocidal activity of methylated flavonoid constituents of Vitex simplicifolia leaves

Background

Trypanosomiasis is a neglected tropical disease with complex clinical manifestations, tedious diagnosis, and difficult treatments. The drugs available for the treatment of this endemic disease are old, expensive, and associated with other problems including safety and drug resistant parasites. Therefore, there is an urgent need for the development of new, effective, cheap, and safe drugs for its treatment. Plants are potentially rich sources of leads for new drugs against trypanosomiasis.

Vitex simplicifolia (Verbenaceae) is used traditionally for the treatment of tooth ache, edema, skin diseases, gout and trypanosomiasis in Nigeria. In a preliminary study, the methanol extract of Vitex simplicifolia was shown to exhibit a pronounced trypanocidal activity against T. b. rhodesiense.

The present study was undertaken to investigate the active component responsible for the acclaimed activity of the leaves of Vitex simplicifolia in the traditional treatment of trypanosomiasis in Nigeria and other African countries. Our investigations aim at assessing the plant as a new source of potential trypanocidal compounds.

Methods

The crude extracts were prepared from the dried leaves using methanol, successive extraction with hexane, dichloromethane, ethylacetate and butanol was also done. The ethylacetate fraction was further fractionated and compounds isolated using preparative chromatographic technique and their structures were elucidated by NMR, mass spectrometry and comparison with literature data. Trypanocidal activities and cytotoxicity, using rat skeletal myoblast (L6) cells were investigated and their selectivity indices were determined.

Results

The chromatographic separations of the methanol extracts gave rise to seven compounds. The isolated compounds 2, 3, 6 and 7 exhibited promising trypanocidal activity with IC₅₀ values ranging from 4.7-12.3 μg/ml and cytotoxicity in the range of 1.58- 46.20 μg/ml. Compound 6, however, showed the most selective trypanocidal activity with a selectivity index of 9.8. This is the first report of trypanocidal activity of flavonoids from this plant genus.

Conclusions

The isolated compounds from Vitex simplicifolia exhibited noteworthy trypanocidal activities and hence may provide a source of new antitrypanosomal agents. These results also support the traditional use of Vitex simplicifolia in the treatment of trypanosomiasis. This is the first report of trypanocidal effect of flavonoids from this plant genus.