Publications by authors named "Pinguan Zheng"

Introduction: Biological evaluation of ([(125)I]4), a new single-photon emission computed tomography (SPECT) radioligand for imaging the serotonin transporter (SERT) which displayed improved in vivo kinetics for mapping SERT binding sites in the brain.

Methods: In vitro binding studies of [(125)I]4 were performed with membrane homogenates of LLC-PK1 cells stably transfected and overexpressing one of the monoamine transporter (SERT, DAT or NET) and rat cortical homogenates. Biodistribution and ex vivo autoradiography studies were carried out in rats.

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New ligands for in vivo brain imaging of serotonin transporter (SERT) with single photon emission tomography (SPECT) were prepared and evaluated. An efficient synthesis and radiolabeling of a biphenylthiol, FLIP-IDAM, 4, was accomplished. The affinity of FLIP-IDAM was evaluated by an in vitro inhibitory binding assay using [(125)I]-IDAM as radioligand in rat brain tissue homogenates (K(i) = 0.

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In the search of new probes for in vivo brain imaging of vesicular monoamine transporter type 2 (VMAT2), we have developed an efficient synthesis of a novel series of 3-alkyl-dihydrotetrabenazine (DTBZ) derivatives. The affinity of VMAT2 was evaluated by an in vitro inhibitory binding assay using [(125)I]-iodovinyl-TBZ or [(18)F](+)-FP-DTBZ as radioligands in rat striatal tissue homogenates. New DTBZ derivatives exhibited moderate to good binding affinity to VMAT2.

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Catalytically generated acyl azoliums and their α,β-unsaturated counterparts are thought to be key reactive intermediates in a rapidly growing number of transformations promoted by N-heterocyclic carbene (NHC) catalysts. Acyl azoliums are invoked in the postulated catalytic cycles of nearly all of the new NHC-catalyzed reactions of α-functionalized aldehydes reported since 2004, in which they are generally assumed to possess the reactivity of an activated carboxylic acid, that is, analogous to an activated ester. In NHC-catalyzed processes, they are most often obtained through internal redox reactions of functionalized aldehydes but have also been prepared by oxidations of the Breslow intermediates or additions to ketenes.

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A library of chiral triazolium salts has been prepared by late-state diversification of a triazolium amine salt. By utilizing a primary amine as a functional handle, a single triazolium salt can be transformed into a variety of chiral N-heterocyclic carbene precatalysts. This approach makes the preparation of chiral N-heterocyclic carbenes possible by a single-step modification of a triazolium salt, rather than the usual need for multistep organic synthesis and challenging heterocycle formation for each member of a catalyst library.

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In the presence of a chiral azolium salt (10 mol %), enols and ynals undergo a highly enantioselective annulation reaction to form enantiomerically enriched dihydropyranones via an N-heterocyclic carbene catalyzed variant of the Claisen rearrangement. Unlike other azolium-catalyzed reactions, this process requires no added base to generate the putative NHC-catalyst, and our investigations demonstrate that the counterion of the azolium salt plays a key role in the formation of the catalytically active species. Detailed kinetic studies eliminate a potential 1,4-addition as the mechanistic pathway; the observed rate law and activation parameters are consistent with a Claisen rearrangement as the rate-limiting step.

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Treatment of racemic or enantiomerically pure 2,1-benzothiazines (cyclic sulfoximines) with lithium triethylborohydride results in clean loss of the S-aryl group with complete retention of configuration at sulfur to produce diastereomerically and/or enantiomerically pure cyclic sulfinamides in excellent yield.

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Sulfinamides were synthesized from sulfonyl chlorides using a procedure involving in situ reduction of sulfonyl chlorides. The reaction is broad in scope and easy to perform.

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The reaction of S-2-bromophenyl-S-methylsulfoximine with terminal alkynes in the presence of a palladium catalyst resulted in the formation of both 1,2-benzothiazines and 1,2-benzoisothiazoles. A preference for the former was seen with alkylalkynes, while the latter were preferentially formed with alkynylarenes.

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