- Dimeric carbamoylguanidine-type histamine H2 receptor ligands: A new class of potent and selective agonists
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The bioisosteric replacement of the acylguanidine moieties in dimeric histamine H2 receptor (H2R) agonists by carbamoylguanidine groups resulted in compounds with retained potencies and intrinsic activities, but considerably improved
- Kagermeier, Nicole,Werner, Kristin,Keller, Max,Baumeister, Paul,Bernhardt, Günther,Seifert, Roland,Buschauer, Armin
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- Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding
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A series of mono- and bi-functional compounds 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepared to study the mode of aggregation of these compounds in the bulk and in solution. Compounds 2-7 exhibit thermotropic liquid crystalline properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (Dho) phase of 2a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bi-functional compounds form cyclic dimers at millimolar concentrations, and these dimers exist in equilibrium with linear species above a critical concentration, which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. Circular dichroism measurements in chloroform did not show a Cotton effect. Dodecane solutions of compounds 3, 4b, and 7b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was observed in mixtures of 7a and 7b, but not in mixtures of 4a and 4b, indicating that 7a and 7b form mixed polymeric aggregates with a helical architecture in dodecane solution, whereas 4a and 4b do not. The Cotton effect is lost upon increasing the temperature. Half of the helicity is lost at 25°C for 3 and at 60°C for 4b, suggesting that 3, bearing the shorter spacer, forms less stable columns than 4b. Compound 7b loses half of its helicity at 45°C. Compounds 2b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effects.
- Hirschberg, J. H. K. Ky,Koevoets, Rolf A.,Sijbesma, Rint P.,Meijer
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p. 4222 - 4231
(2007/10/03)
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- Preparation of isocyanates using a silver salt promoted rearrangement
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The present invention relates to a process for producing isocyanates which comprises reacting an N-halogenated amide with an organic base in an essentially water-free modified Hofmann reaction using a soluble silver salt promoter in the presence of an organic solvent. Also disclosed is a process for producing a carbamate which comprises reacting an N-halogenated amide with an organic base in an essentially water-free modified Hofmann reaction using a soluble silver salt promoter in the presence of an alcohol solvent.
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- Novel difunctional compounds as latent diisocyanates
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N,N'-bis(trialkylamino)alkanediimides are useful as intermediates for forming latent isocyanates which in turn are useful for curing polymers containing active hydrogen, and as reactants in the production of polyurethane resins. The difunctional N,N'-bis(trialkylamino)alkanediimides are prepared by reacting a dicarboxylic acid dihydrazide with an alkyl halide to quaternize the dihydrazide and then neutralizing the resulting salt with an appropriate base in either aqueous or alcohol medium.
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