Synthesis of two trisaccharides related to the triterpenoid saponins isolated from Solanum lycocarpum

Chemical synthesis of two trisaccharides related to the triterpenoid saponins isolated from Solanum lycocarpum from commercially available d-Glc, d-Gal and l-Rha have been achieved by following concise and high-yielding route. The target trisaccharide 1 has been made by following a bis-glycosylation approach that has minimized the protecting group manipulations up to great extent. The trisaccharides have been synthesized in the form of their p-methoxyphenyl (OMP) glycosides to leave the scope for further glycoconjugates formation by the selective removal of the OMP glycoside and trichloroacetimidate chemistry. La(OTf)₃ has been used successfully as the promoter for the NIS mediated activation of thioglycosides.     

A Histidine Aspartate Ionic Lock Gates the Iron Passage in Miniferritins from Mycobacterium smegmatis

Dps (DNA-binding protein from starved cells) are dodecameric assemblies belonging to the ferritin family that can bind DNA, carry out ferroxidation, and store iron in their shells. The ferritin-like trimeric pore harbors the channel for the entry and exit of iron. By representing the structure of Dps as a network we have identified a charge-driven interface formed by a histidine aspartate cluster at the pore interface unique to Mycobacterium smegmatis Dps protein, MsDps2. Site-directed mutagenesis was employed to generate mutants to disrupt the charged interactions. Kinetics of iron uptake/release of the wild type and mutants were compared. Crystal structures were solved at a resolution of 1.8–2.2 Å for the various mutants to compare structural alterations vis à vis the wild type protein. The substitutions at the pore interface resulted in alterations in the side chain conformations leading to an overall weakening of the interface network, especially in cases of substitutions that alter the charge at the pore interface. Contrary to earlier findings where conserved aspartate residues were found crucial for iron release, we propose here that in the case of MsDps2, it is the interplay of negative-positive potentials at the pore that enables proper functioning of the protein. In similar studies in ferritins, negative and positive patches near the iron exit pore were found to be important in iron uptake/release kinetics. The unique ionic cluster in MsDps2 makes it a suitable candidate to act as nano-delivery vehicle, as these gated pores can be manipulated to exhibit conformations allowing for slow or fast rates of iron release.     

Miro1 regulates intercellular mitochondrial transport & enhances mesenchymal stem cell rescue efficacy

There is emerging evidence that stem cells can rejuvenate damaged cells by mitochondrial transfer. Earlier studies show that epithelial mitochondrial dysfunction is critical in asthma pathogenesis. Here we show for the first time that Miro1, a mitochondrial Rho‐GTPase, regulates intercellular mitochondrial movement from mesenchymal stem cells (MSC) to epithelial cells (EC). We demonstrate that overexpression of Miro1 in MSC (MSCmiro^Hi) leads to enhanced mitochondrial transfer and rescue of epithelial injury, while Miro1 knockdown (MSCmiro^Lo) leads to loss of efficacy. Treatment with MSCmiro^Hi was associated with greater therapeutic efficacy, when compared to control MSC, in mouse models of rotenone (Rot) induced airway injury and allergic airway inflammation (AAI). Notably, airway hyperresponsiveness and remodeling were reversed by MSCmiro^Hi in three separate allergen‐induced asthma models. In a human in vitro system, MSCmiro^Hi reversed mitochondrial dysfunction in bronchial epithelial cells treated with pro‐inflammatory supernatant of IL‐13‐induced macrophages. Anti‐inflammatory MSC products like NO, TGF‐β, IL‐10 and PGE2, were unchanged by Miro1 overexpression, excluding non‐specific paracrine effects. In summary, Miro1 overexpression leads to increased stem cell repair.     

Evaluation of common cocklebur Xanthium strumarium leaf extract as post‐harvest grain protectant of black gram against pulse beetle Callosobruchus chinensis (Coleoptera: Bruchidae) and isolation of crude compound

The pulse beetle Callosobruchus chinensis L. is considered the most important stored grain pest of black gram Vigna mungo Hepper in Bangladesh and other tropical and subtropical countries. Bioactive compounds derived from plants can be used to control of the pulse beetle as a potential alternative to synthetic insecticides. Therefore, aqueous extracts of common cocklebur Xanthium strumarium L. leaf was examined for insecticidal properties against C. chinensis. The extracts showed toxicity, repellent properties, inhibited fecundity and adult emergence of the insects, and protected grains. Insect mortality was accounted highest (72.6%) with 4% extract at 4 days after treatment. The beetles showed highest repellency rate (58.0%) with 4% concentration at 1 hour exposure; however insect repellency decreased with time. The beetles exerted the lowest fecundity and grain damage and produced the lowest number of offspring when they were reared on grains treated with 4% extract. The insecticidal compounds present in common cocklebur leaf were extracted in chloroform and ethanol, and isolated by thin layer chromatography (TLC) and spectral studies (¹H‐NMR and IR), which identified the presence of aromatic ester, n‐hexyl salicylate or o‐hydroxy‐n‐hexyl‐benzoate and a long‐chain ketone. Therefore, naturally occurring X. strumarium and its derivatives may be potential components for integrated management of C. chinensis.     

The first total synthesis and biological evaluation of marine natural products ma’edamines A and B

We have developed the first total syntheses of marine natural products ma’edamines A (18) and B (20). Structurally, they contain a pyrazine-2-(1H)-one core and were screened for antiproliferative activity on several cancer cell lines. Out of the six cell lines tested, ma’edamines A and B showed significant cytotoxicity against human colon cancer line COLO 205 (IC₅₀ 7.9 and 10.3 μM, respectively), breast cancer cell line MCF-7 (IC₅₀: 6.9 and 10.5 μM, respectively) and human lung adenocarcinoma cell line A549 (IC₅₀: 12.2 and 15.4 μM, respectively). The apoptotic effect of ma’edamines was confirmed by comet assay. Hence ma’edamines are likely to be useful as leads for development of a new class of anti-cancer agents.     

Peptide models of electrostatic interactions in proteins: NMR studies on two beta-turn tetrapeptides containing Asp-His and Asp-Lys salt bridges

Two model peptides Boc-Asp-Pro-Aib-X-NHMe [X = His (1) and X = Lys (2)] were synthesized to simulate intramolecular electrostatic interactions between ionizable side chains. Conformational analysis by 270-MHz 1H NMR in (CD3)2SO reveals that the backbone secondary structures of these two peptides are stabilized by two strong intramolecular hydrogen bonds, involving the consecutive carboxy-terminal NH groups. 1H NMR chemical shifts were measured in 1, 2, and a protected derivative, Boc-Asp(OBzl)-Pro-Aib-His-NHMe (3). These shifts were also measured for the model compounds Ac-Lys-NHMe, Boc-Asp-NHMe, and Boc-His-NHMe in their different states of ionization. An analysis of the chemical shifts of the ionization-sensitive reporter resonances suggests the formation of a strong intramolecular salt bridge in the lysyl peptide 2 and a bridge of moderate strength in the histidyl peptide 1. A comparison of the temperature dependence of chemical shifts in peptides 1-3 suggests that intramolecular salt bridge formation results in diminished backbone flexibility. The results establish that proximity effects confer far greater stability to intramolecular ion pair interactions vis-a-vis their intermolecular counterparts. The salt bridge interaction in peptide 1 displays a remarkable sensitivity to the dielectric constant of the solvent medium. The results suggest that these peptides are good simulators of the role of salt bridges in the structural dynamics of proteins.     

NIS/H2SO4-Silica: a mild and efficient reagent system for the hydrolysis of thioglycosides

Chemoselective hydrolysis of a variety of thioglycosides in the presence of a wide range of protecting groups has been achieved by using N-iodosuccinimide and H(2)SO(4) immobilized on silica in good to excellent yields.     

Conformational and sequence signatures in beta helix proteins

beta helix proteins are characterized by a repetitive fold, in which the repeating unit is a beta-helical coil formed by three strand segments linked by three loop segments. Using a data set of left- and right-handed beta helix proteins, we have examined conformational features at equivalent positions in successive coils. This has provided insights into the conformational rules that the proteins employ to fold into beta helices. Left-handed beta helices attain their equilateral prism fold by incorporating "corners" with the conformational sequence P(II)-P(II)-alpha(L)-P(II), which imposes sequence restrictions, resulting in the first and third P(II) residues often being G and a small, uncharged residue (V, A, S, T, C), respectively. Right-handed beta helices feature mid-sized loops (4, 5, or 6 residues) of conserved conformation, but not of conserved sequence; they also display an alpha-helical residue at the C-terminal end of L2 loops. Backbone conformational parameters (phi,psi) that permit the formation of continuous, loopless beta helices (Perutz nanotubes) have also been investigated.