Palladium-catalyzed synthesis of heterocycles and highly functionalized polycyclics

Palladium catalyzes the regio- and stereoselective annulation of allenes by vinylic halides bearing tertiary alcohol and p-toluenesulfonamide groups to produce a variety of 5- and 6-membered ring heterocycles containing a 1,3-diene moiety. In addition, the palladium-catalyzed reaction of N-(2-iodo-2-alkenyl)-p-toluenesulfonamides with diphenylacetylene or 4,4-dimethyl-2-pentyne affords pyrolidine derivatives containing a 1,3-diene moiety, or unexpected 2-alkenyl substituted [alpha],[beta]-unsaturated aldehydes. These synthetically useful intermediates are difficult to prepare or inaccessible by other existing methodology;A number of 3,4,6-tri- and 3,4,5,6-tetrasubstituted [alpha]-pyrones have been prepared in good yields by the reaction of vinylic iodides or triflates bearing ester functionality with internal alkynes in the presence of a palladium catalyst. The methodology provides an especially simple, convenient, and regioselective route to [alpha]-pyrones containing aryl, silyl, tert,-alkyl and other hindered groups. This methodology is important due to the fact that [alpha]-pyrones occur as structural subunits in numerous natural products that exhibit a wide range of biological activity, and very recently, low molecular weight [alpha]-pyrones have been shown to be potent HIV-1 protease inhibitors;2,5-Cyclohexadienyl-substituted aryl and vinylic iodides have been reacted with carbon nucleophiles (diethyl malonate, 2-methyl-1,3-cyclohexanedione), nitrogen nucleophiles (morpholine, potassium phthalimide, N-benzyl tosylamide, di-tert,-butyl iminodicarboxylate, lithium azide and anilines), a sulfur nucleophile (sodium benzenesulfinate), and oxygen nucleophiles (lithium acetate and phenols) in the presence of a palladium catalyst to afford products of cyclization and subsequent cross-coupling in good to excellent yields. In most cases, this process is highly diastereoselective and the products are formed as single diastereoisomers. The structures of the representative compounds have been determined by 1H NMR, 13C NMR, COSY, HMQC, and NOESY spectroscopy. This methodology has potential applications in natural product synthesis, and may provide quick access to a library of compounds with different skeletons and functionality

Pairwise Comparison and Distance Measure of Hesitant Fuzzy Linguistic Term Sets

A hesitant fuzzy linguistic term set (HFLTS), allowing experts using several possible linguistic terms to assess a qualitative linguistic variable, is very useful to express people’s hesitancy in practical decision-making problems. Up to now, a little research has been done on the comparison and distance measure of HFLTSs. In this paper, we present a comparison method for HFLTSs based on pairwise comparisons of each linguistic term in the two HFLTSs. Then, a distance measure method based on the pairwise comparison matrix of HFLTSs is proposed, and we prove that this distance is equal to the distance of the average values of HFLTSs, which makes the distance measure much more simple. Finally, the pairwise comparison and distance measure methods are utilized to develop two multicriteria decision-making approaches under hesitant fuzzy linguistic environments. The results analysis shows that our methods in this paper are more reasonable

Perspectives on studies on soil carbon stocks and the carbon sequestration potential of China

Peer reviewedPostprin

A novel HIV-1 restriction factor that is biologically distinct from APOBEC3 cytidine deaminases in a human T cell line CEM.NKR

<p>Abstract</p> <p>Background</p> <p>Isolation of novel retroviral restriction factors will open new avenues for anti-HIV/AIDS treatment. Although HIV-1 replication is restricted by APOBEC3G/APOBEC3F, TRIM5α, and CD317, none defend HIV-1 infection under natural conditions. Previously, we demonstrated a host factor from the human T cell line CEM.NKR that potently restricted wild-type HIV-1 replication. Interestingly, this restriction resembled the APOBEC3G/APOBEC3F pattern in that viral replication was inhibited from the second round of replication cycle at a post-entry step.</p> <p>Results</p> <p>Here, we further characterized this factor and found it distinguishable from the known anti-HIV APOBEC3 proteins. Although CEM.NKR cells expressed both APOBEC3G and APOBEC3F, their levels were at least 10 or 4-fold lower than those in H9 cells, and importantly, Vif effectively neutralized their activity. Among eight subclones isolated from CEM.NKR cells, one was relatively permissive, four were semi-permissive, and three were completely non-permissive for HIV-1 replication. When the levels of APOBEC3 expression were determined, all these clones retained similar low levels of APOBEC3DE, APOBEC3F, APOBEC3G and APOBEC3H expression, and no APOBEC3B expression was detected. Since the <it>vif </it>from SIVmac can effectively neutralize APOBEC3B and APOBEC3H, recombinant HIV-1 expressing this SIV gene were created. However, these viruses still failed to replicate in CEM.NKR cells. We also confirmed that HIV-1 restriction in CEM.NKR was not due to a loss of calnexin expression.</p> <p>Conclusion</p> <p>Taken together, these results not only demonstrate that all these aforementioned anti-HIV APOBEC3 proteins do not contribute to this HIV-1 restriction, but also shed light on a novel and potent HIV-1 inhibitor in CEM.NKR cells.</p

Effect of Nb Additive on the Dynamic Compression Property of a Zr-Ta Alloy

In this paper, Ta50-Zr50 and Ta45-Zr45-Nb10 alloys were compounded by casting. Quasi-static and dynamic compression tests were applied for both alloys, and also the role of Nb additive on the mechanical property of Zr-Ta alloy, was studied. The microstructure characterization demonstrated that both alloys had relative homogeneous structure with micro-laminate structure inside grains. The Nb additives increased the strength of the alloy by various strain rates, while the ductility of the alloys was decreased. The various parameters of constitutive equations for both alloys were obtained by fitting data. The constitutive equations are applied in theoretical models, the simulation software helps to predict the strength of alloy through various strain rates

Navigating the depths: a stratification-aware coarse-to-fine received signal strength-based localization for internet of underwater things

Underwater wireless sensor networks (UWSNs) are the primary enabling technology for the Internet of underwater things (IoUT), with which all underwater objects can interact and communicate. In UWSNs, localization is vital for military or civilized applications since data collected without location are meaningless. However, accurate localization using acoustic signals in UWSNs is challenging, especially for received signal strength (RSS)-based techniques. The adverse effect of hybrid loss (path and absorption loss) and stratified propagation may severely impact localization accuracy. Even though some schemes have been proposed in the literature, the accuracy is unsatisfactory. To this end, this study proposes a coarse-to-fine localization method (CFLM). The problem is reformed into an alternating nonnegative constrained least squares (ANCLS) framework, where a constrained ellipse adjustment (CEA) using block principal pivoting is proposed to obtain the coarse estimation. A refined step using a Taylor series expansion is then further presented, in which a corrected solution is acquired by iteration. Additionally, this study derives the Cramér-Rao lower bound (CRLB) to evaluate the proposed method. Simulation results show that the proposed CFLM improves the localization accuracy by up to 66 percent compared with weighted least squares (WLS), privacy-preserving localization (PPSL), two-step linearization localization approach (TLLA), particle swarm optimization-based (PSO) localization, and differential evolution-based (DE) localization under different scenarios