The self-assembly of ligand-metal-ligand sandwich complexes involving a novel quinoxalinecontaining crown ether, 1, was studied by electrospray ionization mass spectrometry (ESI-MS). Donor-acceptor -stacking interactions between the electron-poor quinoxaline group of 1 and electron-rich benzene groups from benzo-or dibenzo-18-crown-6 were found to significantly enhance the formation of mixed-ligand sandwich complexes with a free energy gain of up to 17 kJ/mol relative to sandwich formation involving macrocycles without such aromatic functionalities. The relative intensities of the sandwich complexes were greatest with the alkali metals Na In the present report, we present electrospray ionization mass spectrometry (ESI-MS) results on a novel crown ether which demonstrate that donor-acceptor -stacking interactions can be used to direct the self-assembly of noncovalent macrocycle-metal complexes.For probing metal complexation of macrocyclic systems, ESI-MS has proven to be an invaluable tool. Since ESI© is© capable© of© transferring© even© very© weakly© bound noncovalent complexes to the gas phase, mass spectrometry can be used to qualitatively and quantitatively evaluate the binding selectivities of the hosts or the relative binding constants of the resulting host-guest complexes© [4© -22].©Furthermore,©many©studies©have demonstrated that the results of ESI-MS analysis of these host-guest complexes correlate well with mea- Although binding of the second ligand in a ligandmetal-ligand sandwich complex in solution is typically not as strong as for the first ligand for unsubstituted crown©ethers© [27],©it©is©expected©that©the©addition©of certain functional groups on the macrocycle could enhance the formation of sandwich complexes. An analogous result has been observed for the formation of bis-crown ether-metal complexes studied by ESI-MS [13,© 23,© 28].© For© these© macrocycles,© the© preorganization offered by the covalently linked crown ethers results in very strong metal complexation in which the metal cation is simultaneously coordinated by both crown ethers.Rather than rely on covalently linked structures, such as those used in bis-crown ethers, other chemical interactions must be leveraged to create sandwich complexes which can self-assemble. -Stacking interactions, present in many biological systems and having demonstrated utility in strengthening other types of molecular interactions© [32][33][34][35],© represent© a© novel© means© of© enhanc-

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Alkylation of 2-mercaptopyridine with 1,2-dibromoethane affords a cyclic dihydrothiazolopyridinium salt that can serve as a precursor of 2-aminopyridines. Its reaction with primary or secondary amines, either neat or in DMSO, under mild conditions gives the title compounds.

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The reaction between the tetrahedral cluster Co 2 Rh 2 (CO) 12 (1) and a 2-fold excess of dimethyl acetylenedicarboxylate (dmad) proceeds rapidly at room temperature to give alkyne-substituted clusters Co 3 Rh(CO) 10 -(µ-dmad) (3) and CoRh 3 (CO) 9 (µ-dmad) 3 (4) as the major products in good yield. Cluster 3 was characterized in solution by IR and 1 H NMR spectroscopies and by comparison to an independently prepared sample of 3 from the reaction of dmad with the known tetrahedral cluster Co 3 Rh(CO) 12 (2). Cluster 4 was characterized by IR and NMR ( 1 H and 13 C) spectroscopies and FAB mass spectrometry, and the solid-state structure was established by X-ray diffraction analysis. The structure of CoRh 3 (CO) 9 (µ-dmad) 3 consists of a square planar array of metals where two of the three dmad ligands cap both of the CoRh 3 faces and the remaining dmad ligand bridges one of the Rh-Rh edges. The nine ancillary CO groups are all terminally bound, with one Co(CO) 3 and three Rh(CO) 2 moieties structurally found. The facile cluster fragmentation/metal redistribution observed upon reaction with dmad is briefly discussed relative to other alkyne ligands that react with cluster 1 to furnish the arachno clusters Co 2 Rh 2 (CO) 10 (µ 4 -alkyne).

Neuropathic pain is a maladaptive immune response to peripheral nerve injury that causes a chronic painful condition refractory to most analgesics. Nitric oxide (NO), which is produced by nitric oxide synthases (NOSs), has been implicated as a key factor in the pathogenesis of neuropathic pain. b-Carbolines are a large group of natural and synthetic indole alkaloids, some of which block activation of nuclear factor k-light-chain-enhancer of activated B cells (NF-kB), a predominant transcriptional regulator of NOS expression. Here, we characterize the inhibitory effects of a novel 6-chloro-8-(glycinyl)-amino-b-carboline (8-Gly carb) on NO formation and NF-kB activation in macrophages. 8-Gly carb was significantly more potent than the NOS inhibitor NG-nitro-Larginine methyl ester in inhibiting constitutive and inducible NO formation in primary rat macrophages. 8-Gly carb interfered with NF-kB-mediated gene expression in differentiated THP1-XBlue cells, a human NF-kB reporter macrophage cell line, but only at concentrations severalfold higher than needed to significantly inhibit NO production. 8-Gly carb also had no effect on tumor necrosis factor a (TNFa)-induced phosphorylation of the p38 mitogenactivated protein kinase in differentiated THP1 cells, and did not inhibit lipopolysaccharide-or TNFa-stimulated expression of TNFa and interleukin-1b. These data demonstrate that relative to other carbolines and pharmacologic inhibitors of NOS, 8-Gly carb exhibits a unique pharmacological profile by inhibiting constitutive and inducible NO formation independent of NF-kB activation and cytokine expression. Thus, this novel carboline derivative holds promise as a parent compound, leading to therapeutic agents that prevent the development of neuropathic pain mediated by macrophage-derived NO without interfering with cytokine expression required for neural recovery following peripheral nerve injury.