Determination of rare-earth elements by the simultaneous gamma-neutron activation analyses using a microtron

The combination of photon and neutron activation provides an effective method of analysis of rare earths and other elements. A mixed -neutron field is obtained with electron-to-gamma /e/ and gamma-to-neutron /n/ converters combined with a lucite moderator. The samples are activated simultaneously. The sensitivities of this method have been compared with neutron activation in a graphite moderator cube using the same microtron. The advantages and shortcomings of the method are discussed.Dedicated to Prof. V.D. Nefedov on the occasion of his 70th birthday     

New bis-spirolabdane-type diterpenoids from Leonurus heterophyllus Sw

Twelve natural bis-spirolabdane-type diterpenoids, including eight new, named leoheteronones A-E, 15-epileoheteronones B, D, and E, and four known leopersin B, 15-epileopersin B, leopersin C, and 15-epileopersin C, together with hispanone and galeopsin were isolated from the aerial parts of the medicinal plant Leonurus heterophyllus SW. (Lamiaceae) grown in Vietnam. Their structures were determined by spectroscopic analyses. The current study emphasized the accumulation of C-15 oxygenated bis-spirolabdane-type diterpenoids of both 13R and 13S configurations in L. heterophyllus.     

Lupane-triterpene carboxylic acids from the leaves of Acanthopanax trifoliatus

Two new lupane-triterpene carboxylic acids, called acantrifoic acid A (1) and acantrifoside C (2) have been isolated from the leaves of Acanthopanax trifoliatus. Based on extensive 1D and 2D NMR spectroscopic data, their chemical structures were determined as 3 alpha-acetoxy-30-hydroxylup-20(29)-ene-23,28-dioic acid and 3 alpha-acetoxy-30-hydroxylup-20(29)-ene-23,28-dioic acid 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester.     

Synthesis of new 14-membered macrolide antibiotics via a novel ring contraction metathesis

[reaction: see text] A novel ring opening ring closing metathesis (ROM-RCM) was demonstrated for cyclic conjugated dienes, effecting the excision of a C(2)H(2) unit and a net ring contraction. Applying the ring contraction metathesis, new 14-membered ring macrolide antibiotics were synthesized in a single step from existing 16-membered ring macrolides. This new class of macrolide antibiotics will provide access to new therapeutics for the treatment of macrolide-resistant bacterial infections.     

Top leads for swine influenza A/H1N1 virus revealed by steered molecular dynamics approach

Since March 2009, the rapid spread of infection during the recent A/H1N1 swine flu pandemic has raised concerns of a far more dangerous outcome should this virus become resistant to current drug therapies. Currently oseltamivir (tamiflu) is intensively used for the treatment of influenza and is reported effective for 2009 A/H1N1 virus. However, as this virus is evolving fast, some drug-resistant strains are emerging. Therefore, it is critical to seek alternative treatments and identify roots of the drug resistance. In this paper, we use the steered molecular dynamics (SMD) approach to estimate the binding affinity of ligands to the glycoprotein neuraminidase. Our idea is based on the hypothesis that the larger is the force needed to unbind a ligand from a receptor the higher its binding affinity. Using all-atom models with Gromos force field 43a1 and explicit water, we have studied the binding ability of 32 ligands to glycoprotein neuraminidase from swine flu virus A/H1N1. The electrostatic interaction is shown to play a more important role in binding affinity than the van der Waals one. We have found that four ligands 141562, 5069, 46080, and 117079 from the NSC set are the most promising candidates to cope with this virus, while peramivir, oseltamivir, and zanamivir are ranked 8, 11, and 20. The observation that these four ligands are better than existing commercial drugs has been also confirmed by our results on the binding free energies obtained by the molecular mechanics-Poisson-Boltzmann surface area (MM-PBSA) method. Our prediction may be useful for the therapeutic application.     

Structure of the human telomere in K+ solution: an intramolecular (3 + 1) G-quadruplex scaffold

We present the intramolecular G-quadruplex structure of human telomeric DNA in physiologically relevant K(+) solution. This G-quadruplex, whose (3 + 1) topology differs from folds reported previously in Na(+) solution and in a K(+)-containing crystal, involves the following: one anti.syn.syn.syn and two syn.anti.anti.anti G-tetrads; one double-chain reversal and two edgewise loops; three G-tracts oriented in one direction and the fourth in the opposite direction. The topological characteristics of this (3 + 1) G-quadruplex scaffold should provide a unique platform for structure-based anticancer drug design targeted to human telomeric DNA.     

Muurolane‐type sesquiterpenes from marine sponge Dysidea cinerea

Seven new muurolane‐type sesquiterpenes, (4R,5R)‐muurol‐1(6),10(14)‐diene‐4,5‐diol (1), (4R,5R)‐muurol‐1(6)‐ene‐4,5‐diol (2), (4R,5R,10R)‐10‐methoxymuurol‐1(6)‐ene‐4,5‐diol (3), (4S)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (4), (4R)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (5), (6S,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (6), and (6R,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (7) were isolated from the marine sponge Dysidea cinerea. Their structures were determined by the combination of spectroscopic and chemical methods, including 1D‐NMR, 2D‐NMR, and CD spectra as well as by comparing the NMR data with those reported in the literature. Copyright © 2013 John Wiley & Sons, Ltd.     

The isomeric ratios in photonuclear reactions of natural strontium induced by bremsstrahlungs in the giant dipole resonance region and by 65 MeV bremsstrahlung

We have determined the isomeric ratio of ^85m,gSr in photonuclear reactions of natural strontium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region as well as the isomeric ratios of ^85m,gSr and ^84m,gRb produced at 65 MeV bremsstrahlung. In GDR region the target was irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The target irradiation with 65 MeV bremsstrahlung was performed at the linear electron accelerator of the Pohang Neutron Facility, Pohang, South Korea. The gamma spectra of the samples irradiated in both cases were measured with spectroscopic systems consisting of 8192 channel analyzer and high-energy resolution (180 keV at gamma ray 1332 keV of ⁶⁰Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.