Replacement of the phosphorodiester linkages of RNA with guanidinium linkages: the solid-phase synthesis of ribonucleic guanidine

[reaction: see text] Replacement of the negatively charged phosphodiester linkages of RNA with positively charged guanidinium linkages provides the polycationic ribonucleic guanidine (RNG). RNG is anticipated to bind strongly to target DNA/RNA through the specific interactions of nucleobases and the attractive electrostatic interactions of backbones. Preparation of building blocks and the solid-phase synthesis of RNG are reported. Both trimeric and pentameric uridyl RNG have been synthesized.     

Density functional calculation of the electronegativity and other related properties of atoms and ions of the principal groups of the periodic table

The relation between the electronegativityχ of an atom or an ion (χ=??E(Z,N)/?N) and its finite difference (Mulliken like) counterpart has been studied for the elements of the groups IA to VIIA of the Periodic Table, using an approximate Density Functional Theory. Only the valence electrons are taken into account and the effect of the ionic core is simulated by a simple empty core pseudopotential. The first derivative ?χ/6N of the electronegativity has also been computed. The interest inχ and?χ/?N is illustrated by a simple model for the transfer of electronic charge in a molecule. Molecular electronegativities are then computed.     

Palladium-catalyzed C-O bond formation: direct synthesis of phenols and aryl/alkyl ethers from activated aryl halides

A simple and efficient palladium-catalyzed carbon-oxygen bond formation is reported. The palladium-tri-tert-butylphosphine complex was found to be effective in converting haloarenes to corresponding substituted phenols. This methodology offers a direct transformation of aryl halides to phenols, as well as the straightforward application to generate a wide variety of diaryl or alkyl/aryl ethers.     

Thermal and autoxidation reactions of poly-3-methylenecyclobutene and poly-1-methyl-3-methylenecyclobutene

The thermal ring-opening reactions, autoxidation and hydrogenation of polymethy-lenecyclobutene (PMCB) and poly-1-methyl-3-methylenecyclobutene (PMMCB), were investigated. Both polymers were prepared by cationic polymerization and consisted almost entirely of 1,5-repeating units containing cyclobutene rings in the polymer backbone. Both polymers showed well behaved exothermic processes at elevated temperatures which apparently resulted in crosslinking. These processes were investigated by differential scanning calorimetry and interpreted to involve thermal ring-opening reactions. Autoxidation occurred very rapidly in PMCB but much more slowly in PMMCB as predicted by Bolland's rules. Attempts to hydrogenate the cyclobutene rings in both polymers resulted in the occurrence of hydrogenolysis in PMCB and little or no reaction with PMMCB for a Pd-catalyzed reaction and partial hydrogenation of the latter for a diimide reaction.     

Versatile solid-phase synthesis of secondary amines from alcohols. Development of an N-Boc-(o-nitrobenzene)sulfonamide linker

The development of a versatile amine releasing linker based on the modified o-nitrobenzene sulfonamide protective group is described. This new N-Boc-o-nitrobenzenesulfonamide (Boc-ONBS) linker enables the elaboration on resin of primary and secondary amines by sequential substitution of the sulfonamide moiety using the Mitsunobu reaction. A 16-member array of secondary and Boc protected primary amines was then prepared using this linker.     

Transferable atom equivalent multicentered multipole expansion method

The transferability of atomic and functional group properties is an implicit concept in chemistry. The work presented here describes the use of Transferable Atom Equivalents (TAE) to represent molecular electrostatic potential fields through the use of integrated atomic multipole moments that are associated with each TAE atom type used in the reconstruction. TAE molecular surface distributions of electrostatic potentials are compared with analytical ab initio and empirical (Gasteiger) partial charge reference models for several conformations of test peptides. Surface electrostatic potential distributions computed using TAE multipole representations were found to converge at the octopole level, with incremental improvement observed when hexadecapoles were included. Molecular electrostatic potential fields that were produced using the TAE method were observed to be responsive to conformational changes and to compare well with ab initio reference distributions. Generation of TAE atom types and their associated multipoles does not involve fitting to sample electrostatic potential fields, but rather utilizes integrated AIM atomic electron density distributions within representative chemical environments. The RECON program was used for TAE reconstruction. RECON is capable of processing 5,000 drug-sized molecules or 25 proteins per minute per 1.7 GHz P4 Linux processor.     

Extended Koopmans' theorem ionization potentials for beryllium atom shake-up transitions

The ionization potentials were calculated for Be using the extended Koopmans' theorem (EKT ) using several full configuration interaction (CI ) and multiconfigurational-self-consistent-field (MCSCF ) wave functions as reference wave functions. The wave functions used account for 89.7–96.7% of the correlation energy. Comparisons are made with experimental values and with δCI values calculated as the difference in energy obtained from CI wave functions for Be and Be⁺. The best EKT IP differed from the δCI value by 0.0003 eV for the lowest IP and by 0.0006 eV for ionization into the lowest ²P state of Be⁺. A calculation of ionization into the second ²P state of Be⁺ requires diffuse orbitals that are unimportant in the wave function for the ground state of Be. This results in small natural orbital occupation numbers for natural orbitals needed in the EKT calculation. © 1994 John Wiley & Sons, Inc.     

A study of nuclear prenylation of 2,4-dihydroxy phenyl benzyl ketone: Syntheses of linear and angular 6″,6″-dimethyl pyrano-isoflavones,and their 2-methyl and 2-phenyl analogues

2,4-Dihydroxyphenyl benzyl ketone (I) condenses with 2-methyl but-3-en-2-ol in the presence of boron trifluoride etherate to afford a mixture of 3-C-, 5-C- and 3,5-di C C-prenyl derivatives separable by chromatography. The above mixture without the 5-C-prenyl but with the 4-O-prenyl derivative results when ketone I is treated with prenyl bromide in the presence of methanolic potash. 3-C-(III a) and 5-C-(IV) prenyl derivatives undergo ready oxidative cyclization with DDQ to yield the corresponding pyrano derivatives VIII and XII respectively which form good starting materials for various isoflavone condensations. Thus both linear and angular 6″,6″-dimethyl pyrano-isoflavones and their 2-methyl and 2-phenyl analogues have been synthesized.     

Über die gemeinsame Umsetzung von α-Mercaptoketonen mit Oxoverbindungen und α-Aminocarbonsäureestern

Zusammenfassung Bei der Umsetzung von -Mercaptoketonen mitSchiffschen Basen aus Glykokolläthylester und Oxoverbindungen (Aldehyden, Cyclohexanon) bzw. bei der gemeinsamen Einwirkung derSchiffschen Base-Komponenten Glykokolläthylester und Oxoverbindungen auf -Mercaptoketone entstehen in glatter Reaktion ⁴-Thiazolin-3-yl-essigsäureäthylester.Als cyclische Enamine lassen sich diese ⁴-Thiazoline mit Ameisensäure zu den entsprechenden beständigen Thiazolidinyl-3-essigsäureäthylestern hydrieren.Die ⁴-Thiazolin-3-yl-essigsäureäthylester, die in 2-Stellung monosubstituiert sind, erleiden beim Erhitzen auf etwa 150° Thermolyse, wobei es unter Abspaltung von Essigsäureäthylester zur Bildung von Thiazolen kommt.

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-Mercapto ketones react with aldehydes (or cyclohexanone) and esters of -amino acids (or their hydrochlorides) or with theSchiff bases formed by these compounds to form esters of ⁴-thiazolin-3-ylacetic acids. These esters can be hydrogenated with formic acid to the corresponding thiazolidines.Esters of ⁴-thiazolinylacetic acids which have a H atom in position 2, can be pyrolysed by heating at about 150° to form the corresponding thiazoles and alkyl acetate. These reactions are illustrated for the case of 2-mercaptopentan-3-on as -mercapto ketone, glycinethylester as amine component and various aldehydes or cyclohexanone as oxo compound.

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60. Mitt.:F. Asinger, W. Schäfer, H. Kersten undA. Saus, Mh. Chem.98, 1841 (1967).

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Teil der DiplomarbeitC. Dudeck, Techn. Hochschule Aachen, 1967.     

PHOTOREACTION OF BENZ(A)PYRENE IN SOLUTIONS CONTAINING POLYMER

Abstract— An unusual photo-reaction of benz(a)pyrene has been investigated by measuring prompt and delayed fluorescence spectra. The proposed mechanism involves adsorption of triplet benz(a)pyrene by the polymer and its reaction to give substitution products. Further work is in progress with pyrene, which also undergoes photo-reaction in the presence of polymer.