Accessing the disallowed conformations of peptides employing amide-to-imidate modification

Selective modification of the C-terminal amide in peptides to dihydrooxazine (a novel stable imidate isostere) by intramolecular nucleophilic cyclo-O-alkylation of the corresponding N-(3-bromopropyl)amides results in constraining of the C-terminal residue in natively disallowed conformations both in crystals and in solution.     

Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide

Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA's drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag⁺ by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal-responsive sensor based on dipeptide demonstrates its potential utility in the environment field.     

Residual‐based a posteriori error estimator for the mixed finite element approximation of the biharmonic equation

A reliable and efficient residual‐based a posteriori error estimator is derived for the Ciarlet‐Raviart mixed finite element method for the biharmonic equation on polygonal domains. The performance of the estimator is illustrated by numerical experiments. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011     

Synthesis of Barleriaquinones-I & II

Synthesis of two naturally occurring anthraquinones, Barleriaquinone-I (BQ-I) and Barleriaquinone-II (BQ-II) is achieved from commercially available naphthalene-1,5-diol. The anthraquinone core is constructed by utilizing simultaneous Heck and cross coupling reaction as the key step.     

Magnetic Alignment of Polymer Macro‐Nanodiscs Enables Residual‐Dipolar‐Coupling‐Based High‐Resolution Structural Studies by NMR Spectroscopy

Experimentally measured residual dipolar couplings (RDCs) are highly valuable for atomic‐resolution structural and dynamic studies of molecular systems ranging from small molecules to large proteins by solution NMR spectroscopy. Here we demonstrate the first use of magnetic‐alignment behavior of lyotropic liquid‐crystalline polymer macro‐nanodiscs (>20 nm in diameter) as a novel alignment medium for the measurement of RDCs using high‐resolution NMR. The easy preparation of macro‐nanodiscs, their high stability against pH changes and the presence of divalent metal ions, and their high homogeneity make them an efficient tool to investigate a wide range of molecular systems including natural products, proteins, and RNA.     

A straight forward and first total synthesis of Penilumamides B–D

A simple and straight forward first total synthesis of rare lumazine peptides, Penilumamide B, C and D isolated from the marine-derived fungi Aspergillus and Penicillium sp. is described from a common starting material, 1,3-dimethyllumazine-6-carboxylic acid. Penilumamide C was prepared from Penilumamide B by oxidation of the methionine residue to the corresponding sulphone.     

Formation of pH‐Resistant Monodispersed Polymer–Lipid Nanodiscs

Polymer lipid nanodiscs are an invaluable system for structural and functional studies of membrane proteins in their near‐native environment. Despite the recent advances in the development and usage of polymer lipid nanodisc systems, lack of control over size and poor tolerance to pH and divalent metal ions are major limitations for further applications. A facile modification of a low‐molecular‐weight styrene maleic acid copolymer is demonstrated to form monodispersed lipid bilayer nanodiscs that show ultra‐stability towards divalent metal ion concentration over a pH range of 2.5 to 10. The macro‐nanodiscs (>20 nm diameter) show magnetic alignment properties that can be exploited for high‐resolution structural studies of membrane proteins and amyloid proteins using solid‐state NMR techniques. The new polymer, SMA‐QA, nanodisc is a robust membrane mimetic tool that offers significant advantages over currently reported nanodisc systems.     

Stereoselective total synthesis of paecilomycin E and F and its two congeners Cochliomycin C and 6-epi-Cochliomycin C

An efficient and concise approach to the total synthesis of Paecilomycins E (1) and F (2), Cochliomycin C (4) and 6-epi-Cochliomycin C (3) is described. The synthesis involves novel route to the synthesis of Paecilomycin E and F and further conversion to Cochliomycin C and 6-epi-Cochliomycin C. Olefin metathesis and base promoted macro lactonization being the key reactions followed by chlorination to achieve target Cochliomycin C and 6-epi-Cochliomycin C.