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Membered Rings (membered + ring)
Selected AbstractsSynthesis of Interlocked 56-Membered Rings by Dynamic Self-Templating,ANGEWANDTE CHEMIE, Issue 46 2009Mee-Kyung Chung Dr. Selbstverliebte Moleküle: ,Narzisstische" Makrocyclen bilden chirale [2]Catenane mit hoher Komponenten-Diastereoselektivität. Im abgebildeten Beispiel ist ein Ring als Kalottenmodell gezeigt (C,grün, O,rot, N,blau, H,grau), der andere als Stabmodell (orange). [source] Synthesis of Furan-Bridged 10-Membered Rings Through [8 + 2]-Cycloaddition of Dienylfurans and Acetylenic Esters.CHEMINFORM, Issue 37 2005Lei Zhang No abstract is available for this article. [source] Crystal structure of 4'-O-methylalpinumisoflavone at 90KCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006R. Kingsford-Adaboh Abstract 4,-O-Methylalpinumisoflavone crystals which hitherto had been difficult to crystallize for X-ray diffraction analyses have been obtained from a demethylated product of O, O-dimethylalpinumisoflavone. The structural and conformational features of the crystal measured at 90 K are reported and compared with previously reported work of O,O-dimethylalpinumisoflavone and 5-O-methyl-4,-O-(3-methyl-but-2-en-1-yl) alpinumisoflavone. Each of these compounds is characterized by a six membered ring that is further fused to a benzopyrone isoflavone moiety resulting in a tricyclic ring system. This six membered ring shows a half-chair conformation in all the molecules studied, with the ring in the title compound showing the least Cremer-Pople puckering amplitude Q and shorter inter and intramolecular contacts. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Facile Construction of Spirocyclopropanated Bi-, Tri- and Tetracyclic Skeletons by Novel Cascades Involving Intra- and Intermolecular Heck Reactions of 2-Bromo-1,6-enynes and BicyclopropylideneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2005Michael Schelper Abstract Acyclic 2-bromo-1,6-enynes 5 -R, 9 -R and 11 -R with bulky substituents at the acetylenic terminus were co-cyclized with the highly strained bicyclopropylidene (12) under palladium catalysis at 80 °C to give the cross-conjugated tetraenes 13 -R, 18 -R and 19 -R in moderate-to-good yields (34,71%). Only the co-cyclization of 5 -Ph gave rise to an additional product, which was identified as the 11-membered ring 20. At elevated temperatures (120,140 °C) the initially formed tetraenes underwent 6,-electrocyclization to give spiro[cyclopropane-1,4,-bicylo[4.3.0]-1(6),2-dienes] 21 -R, 22 -R and 23 -R. This novel class of spirocyclopropanated oligocycles is also accessible by a one-pot protocol. The highest yields for both the tetraenes and bicyclo[4.3.0]nonadiene and its heteroanalogues were obtained with bulky substituents at the alkyne terminus of the precursors. Heteroatom-containing precursors 9 -R and 11 -R gave lower yields than their all-carbon analogues 5 -R. The acyclic 2-bromo-1,8-dien-6-ynes 28a,b,c upon palladium-catalyzed co-cyclization with bicyclopropylidene (12) at 110 °C gave spirocyclopropanated tricycles 31a,b and 32, respectively, in moderate yields (14, 31 and 32%). These products were formed by two consecutive 6,-electrocyclizations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Reactivity studies of ethyl(Z)- N -(2-amino-1,2-dicyanovinyl) formimidate with carbonyl compounds in the presence of base,JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000M. Joséalves The reaction of ethyl(Z)- N -(2-amino-1,2-dicyanovinyl)formimidate 6 with carbonyl compounds in the presence of triethyl amine occurs with formation of the Schiff s base and intramolecular hydrolysis of the adjacent cyano group to give the alkylideneamino derivatives 8a-f. When the ,-carbon of the ketone has at least one proton, the prolonged contact of 8a-f with triethylamine causes intramolecular cyclization between this carbon and the imidate carbon atom to form a seven membered ring. This is followed by cyclization of the cyano and amido groups, leading to the pyrrolo[4,3- b][1,4]diazepines 9. If a strong base is used the first ring to be formed is the pyrrole ring as evidenced in the reaction of 8a with 1,8-diazabicyclo[5.4.0]undec-7-ene leading to 14. The subsequent addition of methyl amine to the reaction mixture, caused cleavage of the alkylideneamino unit and formation of the amidine function from the imi date (15). The addition of acid to the imidates 8a and 8f led to the diazepine compounds 10a and 10f respectively. A suspension of compound 8e in ethanol and triethylamine evolved to a pyrazinone structure 12 under kinetic conditions (4 hours, room temperature) and to the pyrrolo[4,3- b][1,4]diazepine 9e under thermodynamic conditions (48 hours, room temperature). [source] Conformation-activity relationships of cyclo -constrained µ/, opioid agonists derived from the N -terminal tetrapeptide segment of dermorphin/deltorphinJOURNAL OF PEPTIDE SCIENCE, Issue 8 2008Sylwia Rodziewicz-Motowid Abstract The N -terminal tetrapeptide segments of dermorphin (Tyr,D -Ala,Phe,Gly,Tyr,Pro,Ser,NH2) and deltorphin (Tyr,D -Ala,Phe,Asp/Glu,Val,Val,Gly,NH2) are agonists at the opioid receptors µ and ,, respectively. [D -Arg2, Lys4]-dermorphin-(1,4) amide (Tyr,D -Arg,Phe,Lys,NH2, DALDA) and [Dmt1]DALDA (where Dmt is 2,,6,-dimethyltyrosine) are among the most potent and selective µ-agonists reported to date, both in vitro (having picomolar µ receptor affinity) and in vivo. In this communication, conformation-activity studies of the following four cyclic analogs of DALDA are presented and discussed: the lead peptide S2,S4 -cyclo (Tyr,D -Cys,Phe,Cys,NH2), constrained by means of an S4.2S4.4 disulfide between Cys2 and Cys4; its two cis and transC4.2C4.4 -olefinic dicarba analogs, and the product of saturation of them both. They are potent nonselective or moderately µ-selective opioid agonists in vitro. They have been synthesized and tested earlier [Berezowska I, Chung NN, Lemieux C, Wilkes BC, and Schiller PW, Acta Biochim Polon 53, 2006, 73,76]. We have studied their conformations using NMR and molecular dynamics. With major conformational constraints imposed by the 11-membered ring spanning residues 2,4, they show well defined conformations of this ring, while the exocylic Tyr1 and Phe3 side chains still have significant conformational freedom. The more active and selective µ versus , disulfide and saturated dicarba agonists seem to have in common: (i) their ring structures more flexilble than those of the other two and (ii) their ring structures similar to each other and more diverse than those in the other two. Given this and the small size of the peptides having confirmed bioactivity profiles, there is a chance that their conformations determined in solution approach receptor-bound conformations. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] NMR characterization of new 10-membered-ring macrolactones and dihydrobenzophenazine-5-one, oxidized derivatives of benzo[a]phenazinesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2004Marília O. F. Goulart Abstract Peroxidation of the phenazine of ,-lapachone using m -ClC6H4CO3HCH2Cl2 furnished a macrolactone with a rigid 10-membered ring, and the corresponding N -oxide, along with a dihydrobenzophenazine-5-one. All of the new compounds were fully characterized by spectroscopic methods, with the unambiguous assignment of the hydrogens and carbon NMR signals for the N -oxide, with the aid of 2-D NMR, mainly COSY, HMQC, HSQC and HMBC. For the other two compounds some signals could not be assigned owing to their own intrinsic features. Copyright © 2004 John Wiley & Sons, Ltd. [source] Non-bond crosslinked macroporous thermally reversible hydrogels,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2007Yair Avny Abstract Non-bond crosslinked macroporous thermally reversible hydrogels of poly- N -isopropylacrylamide were obtained by copolymerization with the crosslinking agent cyclic octaethylene glycol fumarate, a 29-membered ring, having a polymerizable double bond; threading of polymer chains into the macrocyclic ring being the cause for the crosslinking. These hydrogels showed a high swelling capacity in water which could be controlled by varying the molar ratio of monomer/crosslinking agent. They rapidly ,collapsed' at 33° and swelled back at low temperatures. Copyright © 2007 John Wiley & Sons, Ltd. [source] catena -Poly[bis{,-dihydrogen [(5-carboxypentylimino)dimethylene]diphosphonato-,2O:O,}cadmium(II)]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Shao-Ming Ying The title compound, [Cd(C8H18NO8P2)2]n, synthesized by hydrothermal methods, exhibits a layered structure in which the CdII ion, occupying a centre of symmetry, is coordinated by six O atoms from four phosphonate ligands. The crosslinkage of CdO6 octahedra by bridging phosphonate ligands results in a cadmium(II) phosphonate layer. Within the layer, there exists a 16-membered ring incorporating four ,Cd,O,P,O, linkages. The uncoordinated carboxyl group of the ligand is oriented so that it penetrates the adjacent layer, taking part in hydrogen bonding to two uncoordinated phosphonate O atoms to form a CO2H/HO2P motif. [source] Macrocyclic Hexaureas: Synthesis, Conformation, and Anion BindingCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2009Denys Meshcheryakov Dr. Abstract Varied flexibility: Cyclic oligoureas are formed by using anions as templates. Linking of six xanthene and/or diphenyl ether fragments by urea groups leads to the formation of five macrocyclic compounds with a 48-membered ring with variable flexibility (see picture). Their interaction with anions shows a strong influence of acetate and chloride ions on the cyclization from four precursor molecules. Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appropriate diisocyanate by using a [5+1] (i.e., "XDXDX+D" for XDXDXD), [4+2] (DDDDDD), or [3+3] (XDDXDD) procedure. Compounds XXXXXX and XXDXXD were prepared from two molecules of the dimeric amine XX and two molecules of the respective monomeric diisocyanate (X or D) in a [2+1+2+1] (or 2×[2+1]) reaction. The (nonoptimized) yields in the cyclization step ranged from 45 to 80,%. The linear precursor diamines or diisocyanates were obtained by analogous condensation reactions by using partial protection with a tert -butoxycarbonyl group. All the macrocyclic compounds and synthetic intermediates were characterized by 1H,NMR and mass spectra. Three different crystal structures were obtained for XDDXDD, which show the molecule in a more or less strongly folded conformation determined by intramolecular hydrogen bonding. The interaction of the hexaureas with selected anions was studied by 1H,NMR spectroscopy and UV absorption spectrophotometry. [source] Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Frank Büttner Dr. Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source] Crystal structure of ,-phenoxo bridged dicopper complex: {N-[(2-hydroxylato-5-methyl)benzyl-(2,-hydroxylato-3,,5,-dimethylbenzyl)]ethyl amine dicopper(II)}CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002S. M. Malathy Sony Abstract The title compound crystallizes in monoclinic space group C2/c with cell parameters a = 21.404(2), b = 13.962(1), c = 17.917(1)Å, , = 124.394(2)°, V = 4418.3(6)Å3, Z = 8, Dcal = 1.193Mg/m3 and T = 293 K. The structure was solved by Patterson method and refined by full-matrix least-squares procedures to final R = 0.0882 using 5253 observed reflections. The tetra coordinated copper atom have a slight distorted square planar geometry with the Cu-Cu distance of 2.987(1)Å. The two six membered rings containing copper atom assume distorted sofa conformation. C-H,, and C-H,O type of intermolecular interactions play a role in stabilizing the crystal packing in addition to van der Waals forces. [source] Macrocyclization of Di-Boc-guanidino-alkylamines Related to Guazatine Components: Discovery and Synthesis of Innovative Macrocyclic AmidinoureasEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2009Daniele Castagnolo Abstract The synthesis of new and innovative macrocyclic amidinoureas from linear di-Boc-guanidino-alkylamines related to guazatine was accomplished. The macrocyclization reaction proceeds under mild conditions affording 11- to 16-membered rings with a new and previously undescribed structure in good yields. Enantiomerically pure macrocyclic amidinoureas were also synthesised. The strict correlation between macrocyclic amidinoureas and the natural productguazatine makes them very actractive also from a biological point of view. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] The Effect of Ring Size on Catenane SynthesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2003Stefan Duda Abstract The synthesis of a [2]catenane with 87-membered rings was improved and extended to [2]catenanes with 63- and 147-membered rings. One of the key features is the carbonate linkage between phenols with tolane substituents in the 2- and 6-positions, which serves as a covalent template for the geometrical arrangement of a macrocycle and a ring precursor. Subsequent cyclization of the threaded ring precursor gives the precatenane as the main product, and this is converted into the catenane by carbonate hydrolysis. As well as the precatenane, its dumbbell shaped isomer is formed in the cyclization step. From the known conformation of the templating carbonate moiety and the strong dependence of the ratio of precatenane and dumbbell on the ring size, the dumbbell's origin is attributed to the conformational flexibility of the large rings and not to geometrical ambiguity of the carbonate moiety. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Bayesian conformational analysis of ring molecules through reversible jump MCMCJOURNAL OF CHEMOMETRICS, Issue 8 2005Kim Nolsøe Abstract In this paper, we address the problem of classifying the conformations of m -membered rings using experimental observations obtained by crystal structure analysis. We formulate a model for the data generation mechanism that consists in a multidimensional mixture model. We perform inference for the proportions and the components in a Bayesian framework, implementing a Markov chain Monte Carlo (MCMC) reversible jump algorithm to obtain samples of the posterior distributions. The method is illustrated on a simulated data set and on real data corresponding to cyclo-octane structures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Synthesis of amidocrownophanes with 27- and 28-membered rings and their molecular recognition toward urea and its derivativesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2005Kazuhisha Hiratani Novel crownophanes with 27- and 28-membered rings having two hydroxyl groups, two amide groups, and aromatic moieties such as naphthalene, pyridine, and phenyl rings were successfully synthesized by a one-step reaction from the corresponding macrocyclic polyethers via "tandem Claisen rearrengement" in moderate yields. They can solubilize urea and its derivatives into chloroform solution, while the corresponding macrocyclic polyethers do not solubilize them. According to NMR studies, crownophanes 1 and 2 interact with urea and its derivatives forming 1:1 complexes. [source] Influence of "Alternative" C-terminal amino acids on the formation of [b3 + 17 + Cat]+ products from metal cationized synthetic tetrapeptides,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2004V. Anbalagan Abstract The aim of this study was to investigate the dissociation patterns, and in particular the relative abundance of [b3 + 17 + Cat]+, for peptides with C-termini designed to allow transfer of the ,OH required to generate the product ion, but not necessarily as the most favored pathway. Working with the hypothesis that formation of a five-membered ring intermediate, including intramolecular nucleophilic attack by a carbonyl oxygen atom, is an important mechanistic step, several model peptides with general sequence AcFGGX were synthesized, metal cationized by electrospray ionization and subjected to collision-induced dissociation (CID). The amino acid at position X was one that either required a larger ring intermediate (,-alanine, ,-aminobutyric acid and ,-amino- n -caproic acid to generate six-, seven- or nine- membered rings, respectively) to transfer ,OH, lacked a structural element required for nucleophilic attack (aminoethanol) or prohibited cyclization because of the inclusion of a rigid ring (p - and m -aminobenzoic acid). For Ag+, Li+ and Na+ cationized peptides, our results show that amino acids requiring the adoption of larger ring intermediates suppressed the formation of [b3 + 17 + Cat]+, while amino acids that prohibit cyclization eliminated the reaction pathway completely. Formation of [b3 , 1 + Cat]+ from the alkali metal cationized versions was not a favorable process upon suppression or elimination of the [b3 + 17 + Cat]+ pathway: the loss of H2O to form [M , H2O + Cat]+ was instead the dominant dissociation reaction observed. Multiple-stage dissociation experiments suggest that [M , H2O + Cat]+ is not [b4 , 1 + Cat]+ arising from the loss of H2O from the C-terminus, but may instead be a species that forms via a mechanism involving the elimination of an oxygen atom from an amide group. Copyright © 2004 John Wiley & Sons, Ltd. [source] Polymorphism in the nitrate salt of the [Mn(acetylacetonate)2(H2O)2]+ ionACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010A. R. Biju The crystallization of [Mn(acac)2(H2O)2]+ from solutions containing excess nitrate leads to the formation of four polymorphs. All polymorphs contain two different types of complex ions, one containing essentially coplanar acac ligands and the other in which the two acac ligands together assume a chair conformation. Molecular modelling using DFT (density-functional theory) calculations shows that the coplanar conformation is the electronically stable one. The hydrogen bonding between the trans -water molecules and the nitrate ion produces a one-dimensional chain of 12-membered rings, which are further organized into a two-dimensional network via a lattice water molecule. Lattice-energy calculations have been carried out to compare the stabilities of the four polymorphs. [source] 12-Membered borophosphate rings in KNi5[P6B6O23(OH)13]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009Olga V. Yakubovich The title compound, potassium pentanickel hexaborophosphate tridecahydroxide, was synthesized under hydrothermal conditions from the NiCl2,K3PO4,B2O3,K2CO3,H2O system. The crystal structure was determined using single-crystal X-ray diffraction at 100,K. The KNi5[P6B6O23(OH)13] phase is cubic. For the three crystallographically distinct Ni centers, two occupy sites with 3 symmetry, while the third Ni and the K atom are located on sites. The structure is built from alternating borate and phosphate tetrahedra forming 12-membered puckered rings with K+ ions at the centers. These rings are arranged as in cubic dense sphere packing. A novel feature of the new crystal structure is the presence of linear trimers of face-sharing [NiO6] octahedra occupying the octahedral interstices of this sphere packing, and of single [NiO6] octahedra in the tetrahedral interstices. All oxygen corners of the Ni octahedra are linked to phosphate or borate tetrahedra of the 12-membered rings to form a mixed anionic framework. [source] Poly[[tetraaquatris(,3 -2,2-dimethylmalonato)dilanthanum(III)] monohydrate]ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009Ming-Lin Guo In the title complex, {[La2(C5H6O4)3(H2O)4]·H2O}n, the La atoms are connected by bridging O atoms from carboxylate groups to build, through centres of inversion, two-dimensional layers parallel to the ac plane containing decanuclear 20-membered rings. The coordinated water molecules are involved in intralayer hydrogen-bond interactions. Adjacent layers are linked via hydrogen bonding to the solvent water molecules. This work represents the first example of a new substituted malonate,lanthanide complex. [source] Poly[,-2-aminopyrazine-,2N1:N4 -,-cyanido-copper(I)]: a three-dimensional network from laboratory powder diffraction dataACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2008Silvina Pagola In the title compound, [Cu(CN)(C4H5N3)]n or [Cu(,-CN)(,-PyzNH2)]n (PyzNH2 is 2-aminopyrazine), the CuI center is tetrahedrally coordinated by two cyanide and two PyzNH2 ligands. The CuI,cyano links give rise to [Cu,CN], chains running along the c axis, which are bridged by bidentate PyzNH2 ligands. The three-dimensional framework can be described as being formed by two interpenetrated three-dimensional honeycomb-like networks, both made of 26-membered rings of composition [Cu6(,-CN)2(,-PyzNH2)4]. [source] A tetrahedrally coordinated cobalt(II) phosphonate with a three-dimensional framework containing two-dimensional channelsACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2007Shu-Juan Fu The structure of poly[caesium(I) [(,4 -ethylenediphosphonato)cobalt(II)]], {Cs[Co(C2H5O6P2)]}n, reveals a three-dimensional polymeric open framework consisting of tetrahedral CoII atoms coordinated by four different ethylenediphosphonate O atoms and intermolecular O,H...O hydrogen bonds. The largest open window is made of corner-sharing CoO4 and PO3C tetrahedra, giving 16-membered rings of dimensions 9.677,(5) × 4.684,(4),Å2. There are two independent ethylenediphosphonate ligands, each lying about an inversion centre. [source] Polymeric hexa-,-nicotinato-tricadmium(II) tetrahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2003Hong-Ji Chen The title polymeric complex, poly[tetraaquatricadmium(II)-hexa-,-nicotinato], [Cd3(C6H4NO2)6(H2O)4]n, exhibits two types of metal centers, i.e. a seven-coordinated Cd atom and a six-coordinated Cd atom located on an inversion center. The seven-coordinated Cd atoms are linked by ,3N:O,O,-nicotinate bridges into one-dimensional chains that are further linked by ,2N,O -nicotinate,Cd2,,2N,O -nicotinate bridges into a two-dimensional network which is parallel to the xy plane and which contains large 24- and 36-membered rings. [source] Macrocyclic Hexaureas: Synthesis, Conformation, and Anion BindingCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2009Denys Meshcheryakov Dr. Abstract Varied flexibility: Cyclic oligoureas are formed by using anions as templates. Linking of six xanthene and/or diphenyl ether fragments by urea groups leads to the formation of five macrocyclic compounds with a 48-membered ring with variable flexibility (see picture). Their interaction with anions shows a strong influence of acetate and chloride ions on the cyclization from four precursor molecules. Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appropriate diisocyanate by using a [5+1] (i.e., "XDXDX+D" for XDXDXD), [4+2] (DDDDDD), or [3+3] (XDDXDD) procedure. Compounds XXXXXX and XXDXXD were prepared from two molecules of the dimeric amine XX and two molecules of the respective monomeric diisocyanate (X or D) in a [2+1+2+1] (or 2×[2+1]) reaction. The (nonoptimized) yields in the cyclization step ranged from 45 to 80,%. The linear precursor diamines or diisocyanates were obtained by analogous condensation reactions by using partial protection with a tert -butoxycarbonyl group. All the macrocyclic compounds and synthetic intermediates were characterized by 1H,NMR and mass spectra. Three different crystal structures were obtained for XDDXDD, which show the molecule in a more or less strongly folded conformation determined by intramolecular hydrogen bonding. The interaction of the hexaureas with selected anions was studied by 1H,NMR spectroscopy and UV absorption spectrophotometry. [source] | |||||||||||||||||||||||||