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An efficient synthesis of the mucin core-2 analogue 1a was accomplished using N-p-nitrobenzyloxycarbonyl(PNZ)-protected trichloroacetimidate 4 as a novel glycosyl donor.
The reaction of AlH(3).NMe(3) with RCN proceeds with the evolution of trimethylamine and affords (HAINCH(2)R)(6) (R = Ph (1), p-MeC(6)H(4) (2), p-CF(3)C(6)H(4) (3)). Compounds 1 and 3 are characterized by single-crystal structural analysis. Compound 1 reacts with Me(3)SiBr as well as with PhC[triple bond]CH to give (XAINCH(2)Ph)(6) (X = Br (4), PhC[triple bond]C (5)). Structural data and other characterization data of compounds 4 and 5 show that all the hydridic hydrogen atoms in 1 have been replaced by bromine atoms and PhC[triple bond]C groups, respectively. Compounds 1-5 are potential precursors for the preparation of aluminum nitride. Crystals of 1 are rhombohedral, space group R3 macro, with a = 15.7457(13) A, b = 15.7457(13) A, c = 14.949(2) A, V = 3209.8(5) A(3), and Z = 3. Crystals of 3.(3)/(4)C(7)H(8) are triclinic, space group P1 macro, with a = 17.527(11) A, b = 18.894(12) A, c = 19.246(15) A, alpha = 96.11(7) degrees, beta = 102.23(4) degrees, gamma = 106.79(3) degrees, V = 5867(7) A(3), and Z = 4. Compound 4 crystallizes in the monoclinic space group P2(1)/c, with a = 14.175(4) A, b = 16.678(5) A, c = 10.731(3) A, beta = 106.82(2) degrees, V = 2428.6(11) A(3), and Z = 2. Compound 5. C(7)H(8) crystallizes in the monoclinic space group C2/c, with a = 25.842(5) A, b = 15.443(3) A, c = 20.699(4) A, beta = 105.88(3) degrees, V = 7945(3) A(3), and Z = 4.
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Macrocyclic receptors having extreme thermo-oxidative stability, and which bind a wide range of electron-donor substrates via pi-stacking donor-acceptor interactions, are accessible by cycloimidization of an amine-functionalized aryl ether-sulfone with pyromellitic dianhydride or 1,4,5,8-naphthalenetetracarboxylic dianhydride. The potential of these receptors in supramolecular chemistry is illustrated, for example, by the spontaneous self-assembly and crystallization of a five-component [3]pseudorotaxane from a solution of its constituents.
The complexes (RPh[NPN]Ta)2(mu-H)4 (RPh[NPN] = RP(CH2SiMe2NPh)2) activate molecular nitrogen to give (RPh[NPN]Ta)2(mu-eta1-eta2-N2)(mu-H)2; however, addition of hydrazine to (CyPh[NPN]Ta)2(mu-H)4 promotes cleavage of the N-N bond and N-H activation to give the bridging bisimide complex (CyPh[NPN]Ta)2(mu-H)2(mu-NH)2. Substitution of the phosphine substituent from cyclohexyl to phenyl allows for characterization of (PhPh[NPN]Ta)2(mu-H)2(mu-NH)2 crystallographically. Addition of the substituted hydrazine Me2NNH2 results in formation of a mono(nitride) complex, (RPh[NPN]Ta)2(mu-H)3(mu-N). The N-N bond has again been cleaved, but the second nitrogen atom has been functionalized and ejected as Me2NH.
Reaction of [RGa(NMe(2))(2)](2), where R = Me, Et, Bu, and Hx, with ammonia at 150 degrees C in an autoclave produced insoluble white powders formulated as oligomers of [RGaNH](n). The analogous reaction between NH(3) and MeGa[N(SiMe(3))(2)](2) at low temperature (<25 degrees C) formed an isolable intermediate, [MeGa(mu-NH(2))N(SiMe(3))(2)](2), that was characterized using single-crystal X-ray diffraction. Infrared spectroscopy and X-ray diffraction of the oligomers were consistent with a rodlike structure comprised of six-membered, [RGaNH](3) rings stacked perpendicular to the long axis of the rod. The method of synthesis, formula, and diffraction results suggested a structural similarity between the alkyl, [RGaNH](n)(), and the previously reported hydride, [HGaNH](n). The structural and electronic properties of rods having the general formula H(3)[(HXYH)(3)](n)H(3) (XY = GaN, GeC; n = 1-9) were investigated using density functional theory. Atomic electronegativity differences between the group 13/15 and 14/14 systems were found to play important roles in the geometrical structures of the two rods and also caused significant differences in the electronic structures. Energetically, it was found to be increasingly favorable to add additional cyclotrigallazane rings to the GaN rods, while for the GeC rods, there was a roughly constant energy cost associated with each additional ring. The electric dipole moments of the GaN rods increased substantially with length; in the GeC rods, charge separation occurred to a much smaller extent and had a polarization opposite to that found in GaN. In addition, increased dipole moments correlated with smaller electronic excitation energies, as predicted by time-dependent density functional theory. All of the powders exhibited luminescence in the visible spectrum at room temperature. Structure observed in the photoluminescence spectra of [HGaNH](n) and [MeGaNH](n) was interpreted as arising from rods of different length.
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A series of dihydro-1H-pyrrolizine-3,5(2H,6H)-diones were synthesized and evaluated for their ability to reverse electroconvulsive shock (ECS) induced amnesia in mice. Among the structure-activity relationships explored were the effects of ring size, the presence of heteroatoms (sulfur) in the ring system, and the introduction of alkyl substituents. The optimal ring size for the bicyclic system was 5.5 with dihydro-1H-pyrrolizine-3,5(2H,6H)-dione (3), although some activity was present in the corresponding 5.6 [hexahydro-3,5-indolizinedione (7)] and 6.6 [tetrahydro-2H-quinolizine-4,6(3H,7H)-dione (9)] analogues. Replacement of the C-1 carbon atom in compound 3 with a sulfur [dihydropyrrolo[2,1-b]thiazole-3,5(2H,6H)-dione (10)] abolished activity, and the introduction of methyl groups resulted in poorer biological profiles except when the substitution was made at the 7a position [dihydro-7a-methyl-1H-pyrrolizine-3,5(2H,6H)-dione (4)]. In several instances, hydrolysis of the parent bicyclic compound was carried out to furnish the corresponding lactam acids, which were further derivatized. Several exhibited interesting activity, especially the 5-oxo-2-pyrrolidinepropanoic acid derivatives such as 5-oxo-2-pyrrolidinepropanoic acid (12), 5-oxo-2-pyrrolidinepropanoic acid phenylmethyl ester (17), 5-oxo-2-pyrrolidinepropanoic acid (3-chlorophenyl)methyl ester (20), N-4-pyridyl-5-oxo-2-pyrrolidinepropanoic acid amide (25), and N-(2,6-dimethylphenyl)-5-oxo-2-pyrrolidinepropanoic acid amide (27). Compound 3 (CI-911; rolziracetam) was also observed to improve performance on a delayed-response task in aged rhesus monkeys and was selected for evaluation in cognitively impaired human subjects on the basis of its biological profile and a wide margin of safety in animals.
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An evaluation of simple Lewis acids revealed that N-malonylimidates undergo catalyzed [3+2] cycloaddition reactions with aldehydes, imines, and activated olefins to form oxazolines, imidazolines, and pyrrolines, respectively. Reactions proceed optimally at ambient temperature with the addition of 5 mol % of MgCl(2) in CH(3)CN. Experiments aimed at elucidation of the reactive intermediate undergoing cycloaddition suggest that the Lewis acid promotes a 1,2-prototropic shift to give a metal-coordinated azomethine ylide, rather than ionization and proton transfer to give a nitrile ylide.
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[reaction: see text] The intramolecular Diels-Alder reaction of N-acylvinylimidates provides an efficient entry into cis-fused perhydroisoquinoline ring systems. This is demonstrated by the preparation of isoquinoline 2, an intermediate, which has been previously transformed to reserpine.
The pursuit of a clean and healthy environment has stimulated much effort in the development of technologies for the utilization of hydrogen-based energy. A critical issue is the need for practical systems for hydrogen storage, a problem that remains unresolved after several decades of exploration. In this context, the possibility of storing hydrogen in advanced carbon materials has generated considerable interest. But confirmation and a mechanistic understanding of the hydrogen-storage capabilities of these materials still require much work. Our previously published work on hydrogen uptake by alkali-doped carbon nanotubes cannot be reproduced by others. It was realized by us and also demonstrated by Pinkerton et al. that most of the weight gain was due to moisture, which the alkali oxide picked up from the atmosphere. Here we describe a different material system, lithium nitride, which shows potential as a hydrogen storage medium. Lithium nitride is usually employed as an electrode, or as a starting material for the synthesis of binary or ternary nitrides. Using a variety of techniques, we demonstrate that this compound can also reversibly take up large amounts of hydrogen. Although the temperature required to release the hydrogen at usable pressures is too high for practical application of the present material, we suggest that more investigations are needed, as the metal-N-H system could prove to be a promising route to reversible hydrogen storage.