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Bio-inspired cyclopeptidic heterodimers built on [beta]-sheet-like hydrogen-bonding networks and bearing photoactive and electroactive chromophores on the outer surface have been prepared. Different cross-strand pairwise relationships between the side chains of the cyclic [alpha],[gamma]-peptides afford the heterodimers as three nonequivalent dimeric species. Steady-state and time-resolved spectroscopies clearly show an electron transfer process from [PI]-extended tetrathiafulvalene, covalently attached to one of the cyclopeptides, to photoexcited [60]fullerene, located on the complementary cyclopeptide. The charge-separated state was stabilized for up to 1 [mu]s before recombining and repopulating the ground state. Our current example shows that cyclopeptidic templates can be successfully used to form light-harvesting/lightconverting hybrid ensembles with a distinctive organization of donor and acceptor units able to act as efficient artificial photosystems. cyclic peptide nanotubes | fullerenes | self-assembly

Efficient total syntheses of the marine hydrocarbon polyacetylenes callyberynes (A-C) are achieved using highly convergent routes, which involved metal-catalyzed cross-coupling reactions to sp centers as the key steps. The convergent approaches to the three polyacetylenes rely on bond disconnections at the end of central sp centers and employ transition-metal-catalyzed alkynylation reactions (sp-sp, sp(super 2)-sp, or sp(super 3)- sp).

The synthesis of several benzo[b]-, benzo[c]-, and dibenzo[b,g]fluorenones is achieved by the thermal cyclization of 1-[2-(arylethynyl)phenyl]-3-trimethylsilypropynones. The introduction of substituents with the right electronic and steric properties on the aryl rings can cause the ratio of the two isomers to vary between 100.0 and 0:100.

This correspondence addresses the problem of channel estimation and symbol detection in wireless direct-sequence code-division multiple-access (DS-CDMA) communication systems. We introduce a novel multiuser demodulation scheme that proceeds in two steps. First, the multiaccess channel parameters are estimated according to a suitable modification of the maximum-likelihood (ML) criterion using the expectation maximization (EM) algorithm. Subsequently, this estimate and other useful side information are employed to perform ML detection of the transmitted symbols with the Viterbi algorithm. Our main contribution is the development of a novel stochastic ML method for channel estimation that takes advantage of all the available statistical information referred to the transmitted signals and channel noise. Additionally, it can incorporate the knowledge of a fraction of the transmitted symbols; hence, the term semiblind. Computer simulation results are presented that show how close-to-optimum performance is achieved in time-dispersive fading channels using remarkably short training sequences. Index Terms--Channel estimation, code-division multiple access (CDMA), expectation maximization (EM) algorithm, maximum likelihood, multiuser detection, semiblind receivers.

The opening of the bridging ether of 8-oxabicyclo[3,2.1]oct-6-ene systems fused to a five-membered carbocycle is accomplished by choosing the five-membered ring witth a double bond conjugated to the oxabicycle. Data indicate that the double bond either mediates a 1,6-addition reaction or stabilizes the carbanion.

The regioselective synthesis of isoquino(1,2-b)(3)benzazepines or homoprotoberberines using 11-membered stilbene lactams as key intermediates has been undertaken. The lactams were prepared by the intramolecular addition of an aryl radical to a trimethylsilylacetylene. The homoprotoberberines are formed when the amide of both lactams is reduced to an amide functionality and results in a regioselective (7,6)-transannular cyclization.

One of the challenges of modern organic synthesis is coming up with high efficiency in terms of maximized target-relevant molecular complexity and minimal synthetic steps. One option is the manipulation of the rich oxygenation pattern of the cycloadducts, which suggest an immediate entry to cis-2,5-disubstituted tetrahydrofurans by oxidative cleavage of the carbocycle. The results showed that the rich oxygenation and conformational rigidity of the oxabicyclic (5C + 2C) pyrone-alkene adducts offers rich unique opportunities for speeding up the synthesis of tetrahydrofurans.

Fused 6,7,5-tricarboxylic compounds have been synthesized by one-pot coupling of an intramolecular thermal (5C + 2C) pyrone-alkene cycloaddition to a (4C + 2C) Diels-Alder reaction. The compounds consist of a 1,4-oxa-bridge in the seven-membered carbocycle and undergoes transformation involving the net formation of four carbon-carbon bonds. Three new cycles and at least five new stereocenters are also formed during the transformation. Deoxygenated and aromatized products can be formed by opening the oxa-bridge through reaction of the adducts with samarium diiodide and trimethylsilyl triflate.

Silylated stilbene lactams were synthesized by intramolecular addition of an aryl radical to a trimethylsilylacetylene and subsequently converted into protoberberines via dimethyldioxirane epoxidation and acid-catalyzed cyclization of the epoxysilane with HCl. The nonsilylated trans- and cis-stilbene analogues were treated with dimethyldioxirane to produce 13-hydroxytetrahydroprotoberbirines and 13a-hydroxy-13-ketotetrahydroprotoberberines as the major compounds.

The unnecessary length dependent local minima in the autoregressive channels of finite-length constant modulus algorithm (CMA) equalizers can be removed by modifying the CMA cost function. The approach takes advantage of the fact that the equalizer output in autoregressive channels is associated with a delayed input at the length dependent local minima. This correlation is nonzero in the undesired equilibria points and disappears in the desired ones. The validity of the method was demonstrated through a stability analysis of the modified CMA cost function for a first-order autoregressive noiseless channel and a two-tap equalizer.

Vitamin D3 becomes 1alpha,25-dihydroxyvitamin D3 (calcitriol, 1alpha,25-(OH)sub2-Dsub3) in the liver and the kidney. Calcitriol can inhibit the multiplication of malignant cells and suppresses tumor growth, and has been used in the treatement of several diseases. There is increasing interest in developing new vitamin D analogs with strong cell differentiation and weak calcemic effects. Two short, practical synthetic routes to 1alpha-25-dihydroxyvitamin D2 and analogs modified at C24 have been developed.

There has been much research aimed at developing nontoxic vitamin D derivatives to be used in the treatement of hyperproliferative diseases, although there is a need for more practical and flexible approaches. A new approach based on the conjugated triene system of vitamin D and applied to the synthesis of 3-deoxy-1alpha- and 1beta hydroxyvitamin D3 is described. The method has potential for the synthesis of thermally labile derivatives.

A novel method for the synthesis of annelated 3- and 3,3''-substituted bipyridines and terpyridines was developed based on the utilization of Co(I) complexes as catalysts for the formation of the pyridine nuclei. The synthetic process was characterized by the CpCo(CO)2-catalyzed cocyclization of 5-hexanenitrile and unsubstituted 2-ethynylpyridine. The irradiation of the intermediate product led to the formation of a mixture of 2,2'-bipyridine and its 3,2'-bipyridine isomer.

A new method for separating instantaneous linear mixtures of signals is proposed. The technique is based on the constant modulus criterion and uses a linear memoryless multiple input multiple output system. It is particularly suitable for multiuser communications since it requires only statistical signal independence to perform separation and also because adaptation is performed with a convergent stochastic gradient algorithm.

3-Hydroxy-pyridone in 58% yield was produced by the reaction of methylamine and allyl thioether which was derived from the addition of chloropyrone with allylmercaptan and triethylamine. The pyridone that was derived from the chemical reaction was utilized to develope a second pyridone product. The pyridone did not undergo thermal pyrone-alkene cycloaddition due to its aromatic characteristics. Cycloadditions with 4-unsubstituted oxydopyridinium ylides exhibited chemical reactions with high regioselectivity.

The alkaloid (+/-)-clavizepine was prepared from dibenzopyranazepine in nine steps in 17% overall yield. 2,3-Dihydroxybenzaldehyde formed aldehyde after benzylation. Treatment of the aldehyde with 1,3-propanedithiol produced a phenolic dithioketal, which gave a coupled product after -nBuLi treatment and alkylation. Ullman reaction produced a complex mixture of products that formed alkenes by reduction with Raney nickel. Debenzylation of the hydroxylated alkenes gave a phenolic compound which afforded a cyclic compound after treatment with acetic acid. Catalytic hydrogenation of the cyclic compound, reductive cleavage and N-methylation, in that order, gave the amine resembling the structure of (+/-)-clavizepine.

The synthesis and characterization of antitumor lycorines are described. The scheme involves an intramolecular Diels-Alder reaction between an alpha-pyrone and an alkyne, and subsequent loss of carbon dioxide in a retro Diels-Alder reaction. The method has been applied to prepare benzophenanthridine alkaloids via the cycloaddition reactions of alpha-pyrones with benzyne.

Intramolecular Diels-Alder reactions between the aryne and azadiene derivatives result in the formation of lycorine alkaloids. Aryne-azadiene can be obtained by base-activated dehydrohalogenation of an haloarene and enolization of an amide. Alterations in the nature or position of the substituents provide different products due to change in regioselectivity. Cyclization involves a two-step ionic mechanism initiated by nucleophilic attack on the benzyne by the nitrogen atom followed by intramolecular addition of the phenyl carbanion to the promoted benzene ring.

The generation of spectral lines by cyclostationary signals passing through certain nonlinear transformations provides the basis for a new method of adaptive beamforming. A novel optimization objective is used to determine the coefficients of the beamformer. The optimization objective involves minimization of the mean square error between array output after the nonlinearity and a complex exponential. By this method, any signal that produces a spectral line at the frequency of the reference complex exponential will be optimally extracted. The beamformer also eliminates the radiocommunication channel's distortion.

Pyrrolinediones were reacted with two benzyne molecules to produce 4-phenylisoquinolones. Subsequentreaction of the bromopyrrolinedione produced the bromoadduct, phenylated adductand a minor unexpected compound. Results showed a more complex mechanism than those previously cited. New mechanisms for the reaction are suggested. Variation in the R2 groups resulted in corresponding variations in the reactionmechanisms.

N-(phenylfluorenyl)-2-amino-1-indanones were synthesized from cyclization of bromophenylalanine oxazolidinones by lithium-bromine exchange followed by intramolecular acylation of the aryllithium intermediate. A nitrogen-protecting group 9-phenylfluoren-9-yl was used to preserve the integrity of the chiral center by preventing deprotonation of the alpha-carbon.

An improved synthetic route to 1alpha,25-dihydroxyvitamin D2 involves the nucleophilic attack of stannylacetylene on a pregnyl dioxanone, obtained from a dinorcholanol and (3R)-3-hydroxybutyric acid. The attack cleaves the ketone's dioxo-ring and installs the acetylene. Conversion of the resulting alcohol into a ketone and construction of the triene by cross-coupling with a cyclohexenylinyne leads to the target 1alpha,25-dihydroxyvitamin D2.

Aunique synthetic route to C-25 analogues of 1alpha,25-dihydroxyvitamin D3 involves the ultrasound induced conjugate addition of an iodo triflate to electron-deficient olefins under aqueous conditions. The triflate is prepared in three steps from the Inhoffen-Lythgoe diol. The vinyl triflate adducts of the zinc-copper induced sonochemical step then undergo a dienyne convergent process to yield the various C-25 derivatives of 1alpha,25-(OH)2-D3.

Reaction of pyrrolinediones with arynes yields oxoprotoberberines. With the use of chlorine or bromine as protecting groups for the pyrrolinediones, 2, 3-dimethoxy-8-oxyprotoberberine, norketoyobirine and decarbomethoxydehydrogambirtannine were synthesized. 13-bromo-8- oxyprotoberberine was likewise prepared by hydrogenolysis.

Intermolecular benzyne cycloaddition (IBC) is a convergent, regioselective, flexible approach to the synthesis of benzophenanthridines. The process involves the use of pyrrolinediones as aza diene equivalents in the cycloaddition reactions with arynes. The use of IBC in the synthesis of 2,3,8,9- and 2,3,7,8-tetrasubstituted alkaloids leads to the preparation of nitidine, avicine and chelerythrine.

Ashort, simple and efficient synthesis of benzophenathridine alkaloids is described. The process involves a convergent Diels-Alder reaction between a tricyclic alpha-pyrone obtained from phthalimide and arynes derived from the aprotic diazotization of anthranilic acids. It is applied to the synthesis of antineoplastic benzophenanthridines such as nitidine, which is prepared from 4,5-dioxyanthranilic acid.

The preparation of 1-(OPPh2)ethenyl-2-(Me)-5-(OTBS)-cyclohexane and of its enantiomer provides the A-ring fragment for the convergent syntheses of dihydrotachysterol2 (DHT2), its 25-hydroxy analogue (25-OH-DHT2), 10(R),19-dihydro-(5E)-3-epivitamin D2 and the latter's 19-dihydroxy analogue. The cyclohexane is obtained in 32% yield from the Ganem reaction of (+)- and (-)-carvone followed by a seven-step process involving a stereo-directing ozonolysis. From the A-ring fragment, DHT2 is prepared in 74% yield and 25-OH-DHT2 in 84% yield. The enantiomer produces the two epivitamins D2 in 70% and 80% yields.

Trans-hydrindanol and trans-hydrindanone served as precursors in the synthesis of the CD and side-chain fragments of vitamin D metabolites and analogues. An enedione and a tosylate compound provided the starting materials for the corresponding syntheses of the hydrindanol and the hydrindanone. The key procedure in the hydrindanol synthesis involved Wilkinson catalyst-mediated hydrogenation of the hydrindenol intermediates which led to the formation of the desired trans-product in 65% yield. Both hydrindanol and hydrindanone compounds produced the diol form of the CD fragment in 81% and 80% yields, respectively.

A new high-yielding synthetic route to phthalides involves a Parham-type ring formation with the use of a carbamate as an internal electrophilic trap. The addition (at -95 degrees C) of tert-butyllithium to o-bromocarbamates in a tetrahydrofuran solution causes a metal-halogen interchange, yielding the ortho-lithiated intermediates which are trapped on their side chain. The synthetic technique also leads to lactones that may be used as precursors to aristocularine alkaloids.

Isoindolobenzazepine alkaloids are biogenetically linked to proterberines and are often classified as alkaloids of the isoquinoline type. As a class, they belong to the aporhoedane series obtained from Berberidacea from Chile. One good example of this alkaloid type is lennoxamine, whose synthesis can be approached in several ways such as vinyl azide chemistry, enamide photochemistry and electrophilic alkylation. Two new approaches for the synthesis of lennoxamine through radical cyclization are presented.

A modified version of the classical preparation of phenanthrenes was developed by using UV irradiation of stilbenes in the presence of an oxidant. The modification protocol involves the irradiation, in the presence of base, of stilbenes possessing a sulfonyl group linked to the central double bond and could be successfully applied for the synthesis of diverse phenanthrenes and phenanthrenoids.

Several studies are conducted to explain the formation, as well as the characterization of the single self-assembling [alpha],[gamma]-peptide nanotubes. The mechanisms associated with the [alpha],[gamma]-peptide nanotube templating of one-dimensional parallel fullerene arrangements are also discussed.

A photocyclization of tosylstilbenes in the presence of base is used as a key reaction for preparing the CC-1065 analogue.

The design and synthesis of an efficient and selective cyclic A fluorescent sensor is described. The design is refined to increase the affinity constant for cyclin A and also improve the energy transfer efficiency in order to enable the detection of endogenous levels of cyclin in cell lysates.

''Formal'' and standard ruthenium(II)-catalyzed [2+2+2] cycloaddition of 1,6-diynes to alkenes have produced bicyclic 1,3-cyclohexadienes. Density functional theory calculations have shown bicyclic and tricyclic 1,3-cyclohexadienes to be the major products.

A ruthenium-catalyzed tandem cyclization-decarbonylation is developed whereby 7-unsubstituted 1,6-diynes have given exo-alkylidenecyclopentanes. The starting point of this process might be the formation of a Ru-vinylidene complex.

The feasibility of a new type of palladium-catalyzed [4 + 3] intramolecular cycloaddition reaction is examined. This new cycloaddition has allowed the synthesis of appealing, stereochemically rich 5,7-fused bicyclic systems from dienylidenecyclopropanes.

The design and characterization of a novel multicomponent network of pyrene and dapoxyl-derivatives [alpha],[gamma]-cyclic peptides that display controlled fluorescent signal output is described. The network system might be particularly relevant for the development of new biosensor systems specifically tailored for studying networks involving homo- and heterodimerization processes.

A versatile method, which was developed for the preparation of C[alpha]-([omega]-arylalkynyl)glycines by means of Sonogashira-type reactions in mixtures of water with an organic solvent is presented. This new method is considered to be widely applicable to the assembly of modified peptides that are of pharmacological interest, and could be exploited for the manufacture of metal ion sensors, or could adopt predefined conformations upon complexation with metals.

A new, efficient Ru-catalyzed cyclization of terminal alkynes to cycloalkenes is described. Under appropriate catalytic conditions, cycloisomerization to conjugated aldehydes and new possibilities of C-C formation catalyzed by transition metal vinylidenes might be observed.

A new cascade reaction involving a Ru-catalyzed addition of alkenes to 1,6-[diynes.sup.6] followed by a thermal 6[e.sup.-]pi electrocyclization, is described. The results suggest that Ru-catalyzes addition of cyclic alkenes to 1,6-diynes to give (Z)-hexatrienes followed by thermal 6e(super -)pi electrocyclization to afford bicyclic cyclohexadienes.

A new strategy by which complex polycyclic steroid-like systems could be constructed on the steroid CD framework, by a combination of ring-closing metathesis (RCM) and Herck cyclization is described. The method is exemplified by its application to the stereoselective synthesis of 6-8-6 fused carbocyclic systems that mimic the putative transition structure of the isomerization of previtamin D3 to vitamin D3.

The first stereoselective total syntheses of the bioactive marine polyacetylenes (--)-siphonodiol and (--)-tetrahydrosiphonodiol were achieved using highly convergent approaches based on optimized Cadiot-Chodkiewicz and sequential Sonogashira cross-coupling reactions. It was envisioned that both metabolites could be constructed from the di-cis-dibromodienes following a common strategy that would imply stereoselective sequential sp(super 2)--sp cross-coulping reactions.

The first [3C + 2C] cycloaddition process catalyzed by a ruthenium complex constituting a novel nonmetathetic application of the Grubbs carbene complex is reported. The desired cycloadduct to the reaction was obtained in 11% and 35% yields respectively.

The thermal cycloadditions of 6-acetoxy-3-pyranones and 3-silyloxy-4-pyrones with tethered alkenyl sulfoxides is examined by using computational DFT. It confirms that the high level of diastereofacial selectivity obtained is due to the preference of the alkenesulfinyl group to adopt a well-defined conformation in the transition state of the reaction.

Pyridines can be efficiently synthesized by Ru(II)-catalyzed [2 +2 + 2] cycloaddition of 1,6-diynes to alpha, omega-dinitriles or electron-deficient nitriles. The reaction with asymmetric electron-deficient alkynes provides 2,3,6-trisubstituted pyridines in good yield.

Research has been conducted on polyhydroxycyclohexanes. The authors describe the strategy developed for the synthesis of these and related compounds whcih has been carried out via quinic acid derived lactone.

Research has been conducted on dehydro Diels-Alder reactions. The study of the cyclic allene intermediate evolution carried out via theoretical and experimental investigation of these dehydro Diels-Alder reactions in order to examine intramolecular, ionic and radical intermolecular cycloaromatization processes is presented.

Benzyne and substituted derivatives can be efficiently cyclotrimerized to the corresponding triphenylenes by palladium(0) catalysts while the extension of this reaction to polycyclic arynes provides straightforward access to complex polycyclic aromatic hydrocarbons (PAHs).