O peroksidnim antimalaricima

Several dicyclohexylidene tetraoxanes were prepared in order to gain a further insight into structure-activity relationship of this kind of antimalarials. The tetraoxanes 2-5, obtained as a cis/trans mixture, showed pronounced antimalarial activity against Plasmodium falciparum chloroquine susceptible D6, chloroquine resistant W2 and multidrug-resistant TM91C235 (Thailand) strains. They have better than or similar activity to the corresponding desmethyl dicyclohexylidene derivatives. Two chimeric endoperoxides with superior antimalarial activity to the natural product ascaridole were also synthesized.U ovom radu prikazana je sinteza nekoliko dicikiloheksilidenskih tetraoksana u cilju sagledavanja odnosa struktura-aktivnost ove vrste antimalarika. Jedinjenja 2-5 dobijena kao (cis,trans)-smese pokazala su izraženu antimalarijsku aktivnost prema D6, W2 i TM91C235 (Thailand) sojevima P. falciparum. Ona imaju bolju ili sličnu aktivnost od odgovarajućih desmetil cikloheksilidenskih derivata. Sintetisana su i dva endoperoksida himerne strukture znatno izraženije aktivnosti od prirodnog proizvoda askaridola.

Stavroulakis M. “Electron transfer-induced dehydrogenation reactions within methyl viologen-supported zeolite Na-Y under non-irradiative conditions” Tetrahedron Lett

Abstract-Methyl viologen-supported zeolite Na-Y is a unique and very efficient medium for carrying out electron transferinduced reactions in the absence of an irradiation source (spontaneously). Several monoterpenes loaded within the supported zeolite are dehydrogenated to p-cymene. The reaction occurs even in the open air with formation of minor amounts of ascaridole depending on the substrate. It is proposed that the radical cations of the monoterpenes are formed by single electron transfer to Na-Y, with methyl viologen acting as a promoter. © 2001 Elsevier Science Ltd. All rights reserved. Radical ion pairs are orders of magnitude longer-lived within the pores and the channels of zeolites 1 than in solution, where rapid back electron transfer takes place. Therefore, the confined interior of zeolites should be an ideal medium to carry out electron transfer reactions of organic compounds. However, this aspect of intrazeolite chemistry, especially for zeolite Na-Y, has attracted little attention. We sought to test the efficiency of this system to carry out intrazeolite photoinduced electron transfer reactions. To our great surprise, MV 2+ -supported zeolite Na-Y is a unique and versatile system for performing electron transfer reactions in the absence of a light source (spontaneously). By adding a hexane solution of each of the monoterpenes 1-5 shown in In a representative example, 5 mg of limonene (3, 99% pure) dissolved in 5 mL of dry hexane was added to 0.5 g of MV 2+ /Na-Y. After 30 min of stirring under argon either in the dark, or under ambient light, 5 ml of moistened THF was added and the slurry was stirred for 2 h and then filtered. Analysis by GC or by GC/MS revealed that limonene was completely consumed; the products were 60% p-cymene 6, 15% terpinolene 4, 10% g-terpinene 2, 10% a-terpinene 1, and approximately 2-4% of alcohols with the molecular formula C 10 H 18 O

Reduction of the Diazo Functionality of α-Diazocarbonyl Compounds into a Methylene Group by NH₃BH₃ or NaBH₄ Catalyzed by Au Nanoparticles

Supported Au nanoparticles on TiO2 (1 mol%) are capable of catalyzing the reduction of the carbene-like diazo functionality of α-diazocarbonyl compounds into a methylene group [C=(N2) → CH2] by NH3BH3 or NaBH4 in methanol as solvent. The Au-catalyzed reduction that occurs within a few minutes at room temperature formally requires one hydride equivalent (B-H) and one proton that originates from the protic solvent. This pathway is in contrast to the Pt/CeO2-catalyzed reaction of α-diazocarbonyl compounds with NH3BH3 in methanol, which leads to the corresponding hydrazones instead. Under our stoichiometric Au-catalyzed reaction conditions, the ketone-type carbonyls remain intact, which is in contrast to the uncatalyzed conditions where they are selectively reduced by the boron hydride reagent. It is proposed that the transformation occurs via the formation of chemisorbed carbenes on Au nanoparticles, having proximally activated the boron hydride reagent. This protocol is the first general example of catalytic transfer hydrogenation of the carbene-like α -ketodiazo functionality

Catalysis by supported gold nanoparticles: Beyond aerobic oxidative processes

Bulk gold, being the most stable among all metals, was for many years considered as an inert catalyst. However, gold particles with size on the scale of nanometers (gold nanoparticles, Au NPs) have been recognized as surprisingly active and extraordinary e¿ective green catalysts, generating a highly popular research topic in the frontier between homogeneous and heterogeneous catalysisStratakis, M.; García Gómez, H. (2012). Catalysis by supported gold nanoparticles: Beyond aerobic oxidative processes. Chemical Reviews. 112(8):4469-4506. doi:10.1021/cr3000785S44694506112

VC-level Flow Control and Shared Buffering in the Telegraphos Switch

ABSTRACT: We present three implementations of a fixed-size-packet switch featuring shared buffering, virtual circuit (VC) flow control, and 3 clock cycle cutthrough latency, for applications in gigabit LAN’s, networks of workstations, multiprocessor networks, and WAN’s. VC-level credit-based flow control is essential in data communications, to offer full throughput utilization while preventing throughput collapse under heavy, bursty, and hot-spot traffic. We describe in detail the implementation of VC flow control-- one of few such implementations in hardware. We present an FPGA-based prototype that was built and is now functional, a standard-cell ASIC CMOS single-chip implementation that is currently under fabrication, and a full-custom layout of the pipelined memory shared buffer, which is also under fabrication inside a test chip. VC flow control costs less than 15 % of the switch area in both the FPGA and the ASIC versions. Full-custom yields 4 times less area and 3 times higher speed for the buffer and crossbar, compared to the semi-custom implementation

Synthesis of Formate Esters and Formamides Using an Au/TiO2-Catalyzed Aerobic Oxidative Coupling of Paraformaldehyde

A simple method for the synthesis of formate esters and formamides is presented based on the Au/TiO2-catalyzed aerobic oxidative coupling between alcohols or amines and formaldehyde. The suitable form of formaldehyde is paraformaldehyde, as cyclic trimeric 1,3,5-trioxane is inactive. The reaction proceeds via the formation of an intermediate hemiacetal or hemiaminal, respectively, followed by the Au nanoparticle-catalyzed aerobic oxidation of the intermediate. Typically, the oxidative coupling between formaldehyde (2 equiv) and amines occurs quantitatively at room temperature within 4 h, and there is no need to add a base as in analogous coupling reactions. The oxidative coupling between formaldehyde (typically 3 equiv) and alcohols is unprecedented and occurs more slowly, yet in good to excellent yields and selectivity. Minor side-products (2–12%) from the acetalization of formaldehyde by the alcohol are also formed. The catalyst is recyclable and can be reused after a simple filtration in five consecutive runs with a small loss of activity

Ligandless Regioselective Hydrosilylation of Allenes Catalyzed by Gold Nanoparticles

The first example of Au-catalyzed hydrosilylation of allenes is presented using recyclable gold nanoparticles as catalyst, without the requirement of any external ligands or additives. The hydrosilane addition takes place on the more substituted double bond of terminal allenes in a highly regioselective manner. The observed regioselectivity/reactivity modes are attributed to steric and electronic factors