A High Yielding, One-pot Synthesis of Substituted Ureas from the Corresponding Amines Using Mitsunobu’s Reagent

Summary. A Mitsunobu-based protocol has been developed for the synthesis of symmetrically and unsymmetrically substituted ureas from a variety of primary and secondary amines using gaseous carbon dioxide, in good to excellent yields. This protocol is mild and efficient compared to other reported methods.     

An efficient, one-pot synthesis of trithiocarbonates from the corresponding thiols using the Mitsunobu reagent

A novel Mitsunobu-based protocol has been developed for the synthesis of a variety of symmetrical and unsymmetrical trithiocarbonates from primary, secondary and tertiary thiols using carbon disulfide, in good to excellent yields. This protocol is mild and efficient compared to other reported methods.     

Diacetoxyiodobenzene mediated one-pot synthesis of diverse carboxamides from aldehydes

A novel, one-pot, and highly facile protocol has been devised for an easy access of a series of novel glycosyl carboxamides from aldehydes using diacetoxyiodobenzene in the presence of ionic liquid at ambient temperature.     

Interaction of polyethyleneimine-functionalized ZnO nanoparticles with bovine serum albumin

In biological fluids, nanoparticles are always surrounded by proteins. As the protein is adsorbed on the surface, the extent of adsorption and the effect on the protein conformation and stability are dependent on the chemical nature, shape, and size of the nanoparticle (NP). We have carried out a detailed investigation on the interaction of bovine serum albumin (BSA) with polyethyleneimine-functionalized ZnO nanoparticles (ZnO-PEI). ZnO-PEI was synthesized using a wet chemical method with a core size of ~3-7 nm (from transmission electron microscopy). The interaction of BSA with ZnO-PEI was examined using a combination of calorimetric, spectroscopic, and computational techniques. The binding was studied by ITC (isothermal titration calorimetry), and the result revealed that the complexation is enthalpy-driven, indicating the possible involvement of electrostatic interaction. To investigate the nature of the interaction and the location of the binding site, a detailed domain-wise surface electrostatic potential calculation was performed using adaptive Poisson-Boltzmann software (APBS). The result shows that the protein surface can bind the nanoparticle. On binding ZnO-PEI, the protein gets destabilized to some extent, as displayed by CD (circular dichroism) and FTIR (Fourier transform infrared) spectroscopy. Chemical and thermal denaturation of BSA, when carried out in the presence of ZnO-PEI, also indicated a small perturbation in the protein structure. A comparison of the enthalpy and entropy components of binding with those derived for the interaction of BSA with ZnO nanoparticles explains the effect of hydrophilic cationic species attached on the NP surface. The effect of the NP surface modification on the structure and stability of BSA would find useful applications in nanobiotechnology.     

Microstructural and Compressive Deformation Behavior of Aluminum-Foam-Filled Sections

The present research was performed to study the compressive deformation behavior and the energy absorption quantity of aluminum-foam-filled sections. Empty and foam-filled sections were compressed at different strain rates to ascertain the effect to energy absorption. Results show that plateau stress and energy absorption were enhanced due to increase in strain rate. In the case of Al-foam-filled square section, energy absorption was increased up to 26%. Similarly, the plateau stress of mild steel empty section was also found to be increased. Moreover, the energy absorption capacity of mild steel section was enhanced by 25% due to being filled with Al foam. It was noted that square section always absorbs (25–30% depending upon the strain rate) more energy compared to the round sample.     

Biosynthetic activity of recombinant Escherichia coli-expressed Pichia etchellsii β-glucosidase II

The hydrolysis and biosynthetic reactions of partially purified Pichia etchellsii β-glucosidase II from recombinant Escherichia coli pBG22:JM109 are described. With 167 mmol/L of initial glucose, the products of synthetic reactions, glucobiose and glucotriose, accumulated to 18 and 6 mmol/L, respectively. In transglycosylation reactions with 79 mmol/L of initial cellobiose, glucotriose and glucopentaose were obtained at 4.5 and 2 mmol/L, respectively. The effects of incubation time and substrate concentration were studied on the yield of synthesized oligosaccharides. In a reaction time of 24 h with 468 mmol/L of initial cellobiose, glucotriose and glucopentaose levels of 21.6 and 6.6 mmol/L, respectively, were obtained. The addition of dimethyl sulfoxide (DMSO) further increased the yields of the products by 10%. Detailed kinetic analysis indicated a significant (about twofold) increase in V _max/K _M of synthetic reactions in the presence of DMSO. A study of other disaccharides in transglycosylation reactions indicated biosynthetic activity in the order of sophorose > gentiobiose > cellobiose.     

An Efficient,One-Pot Synthesis of Carbamates from the Corresponding Alcohols Using <Emphasis Type="Italic">Mitsunobu</Emphasis>’s Reagent

Summary. A novel Mitsunobu-based protocol was developed for the synthesis of carbamates from the corresponding alcohols using carbon dioxide and amines in good to excellent yields. This protocol is mild, chemoselective, and efficient compared to other reported methods.     

Insertion of a small peptide of six amino acids into the β7–β8 loop of the p51 subunit of HIV-1 reverse transcriptase perturbs the heterodimer and affects its activities

Background  

HIV-1 RT is a heterodimeric enzyme, comprising of the p66 and p51 subunits. Earlier, we have shown that the β7-β8 loop of p51 is a key structural element for RT dimerization (Pandey et al., Biochemistry 40: 9505, 2001). Deletion or alanine substitution of four amino acid residues of this loop in the p51 subunit severely impaired DNA binding and catalytic activities of the enzyme. To further examine the role of this loop in HIV-1 RT, we have increased its size such that the six amino acids loop sequences are repeated in tandem and examined its impact on the dimerization process and catalytic function of the enzyme.     

Chemopreventive action of xanthone derivatives on photosensitized DNA damage

Photosensitized DNA damage participates in solar-UV carcinogenesis, photogenotoxicity and phototoxicity. A chemoprevention of photosensitized DNA damage is one of the most important methods for the above phototoxic effects. In this study, the chemopreventive action of xanthone (XAN) derivatives (bellidifolin [BEL], gentiacaulein [GEN], norswertianin [NOR] and swerchirin [SWE]) on DNA damage photosensitized by riboflavin was demonstrated using [32P]-5'-end-labeled DNA fragments obtained from genes relevant to human cancer. GEN and NOR effectively inhibited the formation of piperidine-labile products at consecutive G residues by photoexcited riboflavin, whereas BEL and SWE did not show significant inhibition of DNA damage. The four XAN derivatives decrease the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an oxidative product of G, by photoexcited riboflavin. The preventive action for the 8-oxodGuo formation of these XAN derivatives increased in the following order: GEN>NOR>BEL>SWE. A fluorescence spectroscopic study and ab initio molecular orbital calculations suggested that the prevention of DNA photodamage is because of the quenching of the triplet excited state of riboflavin by XAN derivatives through electron transfer. This chemoprevention is based on neither antioxidation nor a physical sunscreen effect; rather, it is based on the quenching of a photosensitizer. In conclusion, XAN derivatives, especially GEN, may act as novel chemopreventive agents by the quenching mechanism of an excited photosensitizer.