Simple Reduction of Heteroaromatic Esters to Alcohols Using a Sodium Borohydride–Methanol System

Some heteroaromatic esters were reduced to the corresponding alcohols by using a sodium borohydride–methanol system. The reduction was completed within 0.15–2.0 h in refluxing THF. The alcohol products were isolated after aqueous workup in moderate to excellent yield (48–97%).     

Synthesis of Some Selectively N-Protected (1S,2S)-p-Nitrophenylserinol–Based Diamino-1,3-dioxanes and Tripodands

The unconventional methodology for the non-epimerizable cycloacetalization of optically active (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diol (p-nitrophenylserinol) (condensed H₂SO₄ 96% as solvent and catalyst, i.e., sulfuric transacetalization) producing (2R,4S,5S) diamino-1,3-dioxanes was enlarged by the use of N-protected forms of 2,2-dimethoxyethylamine (DMEA, aminoacetaldehyde dimethylacetal). Conversely, N-protected derivatives of p-nitrophenylserinol were successfully cyclocondensed with DMEA in the same sulfuric conditions. N-Functionalization of DMEA upon treatment with trimesic acid trichloride and cyanuric chloride yielded the corresponding triple amide and melamine, respectively. Their adapted sulfuric transacetalization in triplicate in reaction with arylserinols (aryl: phenyl, p-nitrophenyl) afforded a new series of optically active tripodands.     

Bioactive meroditerpenes and indole alkaloids from the soil fungus Neosartorya fischeri (KUFC 6344), and the marine-derived fungi Neosartorya laciniosa (KUFC 7896) and Neosartorya tsunodae (KUFC 9213)

Two new metabolites including a new aszonalenin analogue (1c) and a new meroditerpene (3) were isolated, together with aszonalenin (1a), acetylaszonalenin (1b), 13-oxofumitremorgin B (2), aszonapyrone A (4b) and helvolic acid, from the culture of the soil fungus Neosartorya fischeri (KUFC 6344). While the ethyl acetate extract of the culture of the diseased coral-derived fungus Neosartorya laciniosa (KUFC 7896) furnished aszonapyrone B (4a), aszonapyrone A (4b), tryptoquivaline L and 3′-(4-oxoquinazolin-3-yl) spiro[1H-indole-3,5′-oxolane]-2,2′-dione, the ethyl acetate extract of the culture of the marine sponge-associated fungus Neosartorya tsunodae (KUFC 9213) yielded a new analogue of chevalone C (5) and helvolic acid. The structures of the new compounds were established based on 1D and 2D NMR spectral analysis as well as HR-ESIMS. Compounds 1a–c, 2, 3, 4a, 4b and 5 were evaluated for their in vitro growth inhibitory activity on the MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer) and A375-C5 (melanoma) cell lines by the protein binding dye SRB method.     

A fast parallel clustering algorithm for molecular simulation trajectories

We implemented a GPU‐powered parallel k‐centers algorithm to perform clustering on the conformations of molecular dynamics (MD) simulations. The algorithm is up to two orders of magnitude faster than the CPU implementation. We tested our algorithm on four protein MD simulation datasets ranging from the small Alanine Dipeptide to a 370‐residue Maltose Binding Protein (MBP). It is capable of grouping 250,000 conformations of the MBP into 4000 clusters within 40 seconds. To achieve this, we effectively parallelized the code on the GPU and utilize the triangle inequality of metric spaces. Furthermore, the algorithm's running time is linear with respect to the number of cluster centers. In addition, we found the triangle inequality to be less effective in higher dimensions and provide a mathematical rationale. Finally, using Alanine Dipeptide as an example, we show a strong correlation between cluster populations resulting from the k‐centers algorithm and the underlying density. © 2012 Wiley Periodicals, Inc.     

用Lewis酸或Brnsted酸催化剂和N2汽提法使木糖脱水为糠醛（英文）

The activity of Lewis (Nb2O5) and Br nsted (Amberlyst 70) acid catalysts for the cyclodehydration of xylose to furfural was studied. The nature of the acidity resulted in significant changes in the reaction mechanism. Lewis acid sites promote the formation of xylulose, while Br nsted acid sites are required to further dehydrate the sugar to furfural. Amberlyst 70 in water/toluene at 175 ℃ showed lower activity but gave a higher furfural yield. Using N2 as the stripping agent considerably improved the furfural yield and product purity in the stripped stream. Catalyst stability was also studied.     

Harnessing the Flexibility of Peptidic Scaffolds to Control their Copper(II)‐Coordination Properties: A Potentiometric and Spectroscopic Study

Designing small peptides that are capable of binding Cu²⁺ ions mainly through the side‐chain functionalities is a hard task because the amide nitrogen atoms strongly compete for Cu²⁺ ion coordination. However, the design of such peptides is important for obtaining biomimetic small systems of metalloenyzmes as well as for the development of artificial systems. With this in mind, a cyclic decapeptide, C‐Asp, which contained three His residues and one Asp residue, and its linear derivative, O‐Asp, were synthesized. The C‐Asp peptide has two Pro? Gly β‐turn‐inducer units and, as a result of cyclization, and as shown by CD spectroscopy, its backbone is constrained into a more defined conformation than O‐Asp, which is linear and contains a single Pro? Gly unit. A detailed potentiometric, mass spectrometric, and spectroscopic study (UV/Vis, CD, and EPR spectroscopy) showed that at a 1:1 Cu²⁺/peptide ratio, both peptides formed a major [CuHL]²⁺ species in the pH range 5.0–7.5 (C‐Asp) and 5.5–7.0 (O‐Asp). The corrected stability constants of the protonated species (log K*_CuH(O?Asp)=9.28 and log K*_CuH(C?Asp)=10.79) indicate that the cyclic peptide binds Cu²⁺ ions with higher affinity. In addition, the calculated value of K_eff shows that this higher affinity for Cu²⁺ ions prevails at all pH values, not only for a 1:1 ratio but even for a 2:1 ratio. The spectroscopic data of both [CuHL]²⁺ species are consistent with the exclusive coordination of Cu²⁺ ions by the side‐chain functionalities of the three His residues and the Asp residue in a square‐planar or square‐pyramidal geometry. Nonetheless, although these data show that, upon metal coordination, both peptides adopt a similar fold, the larger conformational constraints that are present in the cyclic scaffold results in different behaviour for both [CuHL]²⁺ species. CD and NMR analysis revealed the formation of a more rigid structure and a slower Cu²⁺‐exchange rate for [CuH(C‐Asp)]²⁺ compared to [CuH(O‐Asp]²⁺. This detailed comparative study shows that cyclization has a remarkable effect on the Cu²⁺‐coordination properties of the C‐Asp peptide, which binds Cu²⁺ ions with higher affinity at all pH values, stabilizes the [CuHL]²⁺ species in a wider pH range, and has a slower Cu²⁺‐exchange rate compared to O‐Asp.     

Synthesis of Densely Functionalised 5‐Halogen‐1,3‐oxazin‐2‐ones by Halogen‐Mediated Regioselective Cyclisation of N‐Cbz‐Protected Propargylic Amines: A Combined Experimental and Theoretical Study

A very efficient synthesis of 5‐halogen‐1,3‐oxazin‐2‐ones has been accomplished by the halocyclisation reaction of chiral nonracemic N‐carbobenzyloxy (N‐Cbz)‐protected propargylic amines by using I₂, Br₂ and Cl₂ as electrophile sources. The nature of the halogen influences the reaction time and yield. However, in all cases the reaction is totally regioselective taking place through a 6‐endo‐dig process regardless of the nature of the halogen and of the substituents in the starting material. To rationalise the experimental results, theoretical studies at the B3LYP/6‐311G* level have been performed.     

Surface‐Mediated Synthesis of Dimeric Rhodium Catalysts on MgO: Tracking Changes in the Nuclearity and Ligand Environment of the Catalytically Active Sites by X‐ray Absorption and Infrared Spectroscopies

The preparation of dinuclear rhodium clusters and their use as catalysts is challenging because these clusters are unstable, evolving readily into species with higher nuclearities. We now present a novel synthetic route to generate rhodium dimers on the surface of MgO by a stoichiometrically simple surface‐mediated reaction involving [Rh(C₂H₄)₂] species and H₂. X‐ray absorption and IR spectra were used to characterize the changes in the nuclearity of the essentially molecular surface species as they formed, including the ligands on the rhodium and the metal‐support interactions. The support plays a key role in stabilizing the dinuclear rhodium species, allowing the incorporation of small ligands (ethyl, hydride, and/or CO) and enabling a characterization of the catalytic performance of the supported species for the hydrogenation of ethylene as a function of the metal nuclearity and ligand environment. A change in the nuclearity from one to two Rh atoms leads to a 58‐fold increase in the catalytic activity for ethylene hydrogenation, a reaction involving unsaturated, but stable, dimeric rhodium species.