Showing papers on "Substituent published in 1982"

Diastereogenic Addition of Crotylmetal Compounds to Aldehydes

Abstract: In an ideal synthesis, the formation of the CC bonds as well as the creation of the chiral centers and of the final functionality would be carried out simultaneously in each step. Accordingly, stereoselective CC bond forming reactions are required. Instead of a pair of diastereomers, a synthesis should yield only one of the two possible diastereomers. Such selectivity is often achieved in the addition of crotylboron, -aluminum, -tin, -titanium, and -chromium compounds to aldehydes. Depending on whether one starts from E- or Z-crotyl compounds, one diastereomeric adduct is formed preferentially. In this case the newly formed CC bond carries a methyl substituent. However, the synthetic goal is often a compound carrying an oxygen function at the site of the new CC bond. Compounds of this type can be obtained through addition of heteroatom-substituted allylboronic acid esters or analogous reagents to aldehydes.

Stabilization of methyl anions by first‐row substituents. The superiority of diffuse function‐augmented basis sets for anion calculations

Abstract: The entire set of methyl anions, XCH 2 - , substituted by first-row substituents, Li, BeH, BH 2 , CH 3 , NH 2 , OH, and F, was examined at various ab initio levels. Diffuse orbital-augmented basis sets, such as 4-31+G and 6-31+G ∗ , are needed to describe the energies of these anions adequately. Estimates of proton affinities are further improved by second-order Moller-Plesset (MP2) electron correlation corrections, but relative energies are less affected. The methyl group in the ethyl anion is destabilizing, the amino substituent is borderline, but all other groups are stabilizing. Very large π effects are exhibited by BH 2 and BeH groups; inductive stabilization by the electronegative F and OH groups is less effective. Lithium also is stabilizing, but the best singlet geometry of CH 2 Li - is not planar. A planar CH 2 Li - triplet with a π 1 configuration may be lower in energy.

Nucleic acid related compounds. 37. Convenient and high-yield syntheses of N-[(2-hydroxyethoxy)methyl] heterocycles as "acyclic nucleoside" analogues

Abstract: Treatment of 1,3-dioxolane with acetyl bromide gave (2-acetoxyethoxy)methyl bromide (2a) in 88% yield. A number of pyrimidines and three chloropurines were trimethylsilylated and coupled with 2a. The respective N-1 and N-9 alkylated products (obtained in 79–89% yields) were deacetylated to give N-[(2-hydroxyethoxy)methyl] heterocycles. The 6-amino or 6-chloro substituent of the 2-amino-6-substituted-purine derivatives was hydrolyzed smoothly with adenosine deaminase to give 9-[(2-hydroxyethoxy)methyl]guanine (acycloguanosine), the potent antiviral agent.

The chemical structure of lipid A. Demonstration of amide-linked 3-acyloxyacyl residues in Salmonella minnesota Re lipopolysaccharide.

Abstract: In Salmonella minnesota lipopolysaccharide the lipid A backbone, a substituted diphosphorylated beta 1,6-linked D-glucosamine disaccharide molecule, carries approximately seven residues of fatty acids: one each of dodecanoic, hexadecanoic, D-3-hydroxytetradecanoic and D-3-O-(tetradecanoyl)-tetradecanoic acid in ester linkage and two of D-3-hydroxytetradecanoic acid in amide linkage. In the present study it is shown that treatment of the lipopolysaccharide with alkali at elevated temperature leads, through a beta-elimination reaction, to the generation of amide-bound delta 2-tetradecanoic acid. This suggested that the 3-hydroxyl group of amide-bound hydroxy fatty acids carried a substituent. To elucidate the nature of the substituent, free Salmonella lipid A was methylated with methyl iodine in the presence of silver salts followed by mild acid hydrolysis, a procedure which is known to cleave amide (and not ester) bonds selectively. In the hydrolysate, by means of combined gas-liquid chromatography/mass spectrometry the methyl esters of 3-O-(dodecanoyl)-tetradecanoic and 3-O-(hexadecanoyl)-tetradecanoic acid were identified. This shows that in lipid A amide-linked 3-hydroxytetradecanoic acid residues are 3-O-acylated by dodecanoic and hexadecanoic acid, respectively. Quantitative analyses suggest that the Salmonella lipid A backbone is substituted by four D-3-hydroxytetradecanoyl residues, two being present as esters and two as amides. The nonhydroxylated fatty acids are not bound directly to the backbone. Rather, they are attached to hydroxyl groups of 3-hydroxytetradecanoyl residues: specifically, tetradecanoic acid substitutes ester-bound and dodecanoic and hexadecanoic acid amide-bound 3-hydroxytetradecanoic acid.

13C NMR spectroscopy of coumarin derivatives

Abstract: The 13C chemical shifts of 209 naturally occurring and synthetic coumarin derivatives are listed and a number of methods for signal assignments are explained. Substituent effects on 13C chemical shifts (SCS) in monosubstituted coumarins and non-additivities of SCS in coumarins with more than one substituent are discussed in detail.

Novel pi systems possessing cyclopropenylidene moiety

Abstract: As one of the most attractive Tr systems cyclopropenylidene metal complexes are prepared and their structure, especially carbene carbon—metal bonding is examined. In the lithium complex, this bonding is substantially ionic, on the other hand, in the transition metal complexes the carbene carbon—metal bond is shown to have double bond character by the ii back donation. The G donating and v accepting powers of cyclopropenylidenes change dramatically with presence or absence of amino substituent. Novel triafulvenes, triafulvalenes and related v system are taken up. The simplest triafulvenes and triafulvenes possessing conjugate Tr systems are synthesized. Triafulvalenes (3—5, 3—7, 3—9 systems) are also prepared. The structural features of these triafulvenes and triafulvalenes are discussed based on the spectral data. The parent compound of "cyclic dicalicene" which have peripheral l6v and central 8v structures is synthesized. The X ray analysis indicates that this novel system has planar (D2h) structure. Its v electron configuration is determined by i-H— and 1-3C—NMR spectra and MINDO/3 investigation.

Process for producing conjugated diene polymer using a solubilized lanthanum carboxylate catalyst

Abstract: A process for producing a conjugated diene polymer, characterized by polymerizing at least one conjugated diene with a catalyst consisting of (A) a reaction product of a Lewis base and a carboxylate of a rare earth element of the lanthanum series represented by Ln(R1 CO2)3 wherein Ln is a rare earth element of the lanthanum series having an atomic number of 57 to 71 and R1 is a hydrocarbon substituent having 1 to 20 carbon atoms, (B) an organic aluminum compound represented by AlR2 R3 R4 wherein R2, R3 and R4, which may be identical or different, represent hydrogen atoms or hydrocarbon substituents having 1 to 8 carbon atoms, excluding the case where all of R2, R3 and R4 are hydrogen atoms at the same time, and (C) an (alkyl)aluminum halide represented by AlXn R5 3-n wherein X is Cl, Br, F or I; R5 is a hydrocarbon substituent having 1 to 8 carbon atoms; and n has a value of 1, 1.5, 2 or 3, or consisting of these (A), (B) and (C) components and (D) a conjugated diene. A polymer obtained by said process has a high cis-1,4-configuration content and is excellent in physical properties of vulcanizate.

Liquid chromatographic separation of aromatic hydrocarbons with chemically bonded (2,4-dinitroanilinopropyl)silica

Abstract: A detailed comparison of alumina and chemically bonded silica-R(NH/sub 2/)/sub 2/ and (2,4-dinitroanilinopropyl)silica (DNAP-silica) for the compound-class (ring-numbered) high-performance liquid chromatographic separation of aromatic hydrocarbons was made with 86 model compounds either expected or known to be present in petroleums, coal liquids, or shale oils. Model compounds ranged from one-ring aromatic hydrocarbons to highly condensed polyaromatic hydrocarbons containing six aromatic rings. The importance of substituent and structure effects on separations was determined by varying the degree of alkyl and naphthenic substitution on the basic ring structures. Determination of the best system was based upon the relative retention strengths, grouping tendencies, and the observed structure and substituent effects. The silica-DNAP and alumina were determined to be more sensitive to molecular structure but less sensitive to substituent effects than the silica-R(NH/sub 2/)/sub 2/. The retention characteristics of all three systems are strongly dependent upon steric effects. On the basis of retention strengths and grouping tendencies, the DNAP-silica is considered superior to alumina and silica-R(NH/sub 2/)/sub 2/.

Muonium-substituted organic free radicals in liquids. Muon-electron hyperfine coupling constants and the selectivity of formation of methyl and fluorine-substituted cyclohexadienyl type radicals

Abstract: Muonium-substituted free radicals are observed by muon spin rotation when positive muons are stopped in liquid methyl, and fluorine-substituted benzenes. From muon precession frequencies in high external magnetic fields the isotropic muon-electron hyperfine coupling, constants A gm are determined. They are typical of cyclohexadienyl-type radicals. The individual assignments are based on deuteration and on substituent effects. Comparison of A gm with A p of the hydrogen analogues reveals isotope effects A μ μ p / A p μ μ of 1.15–1.21. Analysis of signal amplitudes yields substituent effects on the relative rates of Mu addition to inequivalent positions in the arenes. Both CH 3 and F are ortho directing. Addition at CH sites is favored over ipso addition by a factor of ≈ 3.

Further studies on the protection of histidine side chains in peptide synthesis: the use of the π-benzyloxymethyl group

Abstract: Further studies on the use in peptide synthesis of N(π)-phenacyl protection for histidine side chains have shown that whilst this prevents the side chain-induced racemisation which can occur if there is a lone pair of electrons available at the π-nitrogen, there are concomitant drawbacks. As an alternative approach to the racemisation problem, the effect of halogenation of the heterocyclic ring carbons (to diminish the availability of the π-nitrogen lone pair) has been investigated. This gives derivatives which are convenient in both classical and solid-phase applications, the halogen modifying groups being removed at the last stage by catalytic hydrogenolysis over a rhodium catalyst. Racemisation is suppressed as expected, but it is not eliminated completely: direct blockade of the π-nitrogen appears to be indispensable for its complete prohibition. Protection of the π-nitrogen with a benzyloxymethyl group has now been found to be much more satisfactory than the use of the phenacyl group for this purpose. A π-benzyloxymethyl substituent not only prohibits side chain-induced racemisation but also gives derivatives with convenient physical properties which can be incorporated into well established classical and solid-phase strategies without the need for any novel or additional operations or changes in protocol. The protecting group is stable to basic conditions, to trifluoroacetic acid, and to aqueous solutions of carboxylic acids, but is cleaved cleanly and rapidly by hydrogen bromide in trifluoroacetic acid or by catalytic hydrogenolysis. N(α)-t-Butoxycarbonyl-N(π)-benzyloxymethyl-L-histidine has been prepared in good yield by a simple procedure from an easily accessible intermediate and isolated as a crystalline solid; its use has been demonstrated by a number of exercises including a solid-phase synthesis of 5-isoleucine-angiotensin II and a classical synthesis of trihistidine.

1-Acyltriazoles as antiinflammatory agents

Abstract: Certain 1-acyl-3-phenyl-5-alkyltriazoles were synthesized and evaluated for antiinflammatory activity using the mouse active Arthus (MAA) reaction as the test system. Modification of the acyl group, 4-phenyl substituent, and alkyl group led to the selection of the most active member of this series, 1-acetyl-3-(4-chlorophenyl)-5-methyl-1,2,4-triazole (3c), for further evaluation as a novel nonacidic antiinflammatory agent.

Characterization of carboxymethylcellulose: Distribution of substituent groups along the chain†

Abstract: A procedure has been developed for characterizing cellulose ethers on the basis of the distribution of substituent groups along the polymer backbone. This method has been applied to carboxy-methylcellulose. The technique uses cellulase, a cellulose-degrading enzyme. Degradation as a function of time is followed by viscosity and reducing sugar measurements. The combination of these data, along with other analytical results, provides information on the number of unsubstituted anhydroglucose residues and the number and average length of blocks of two or more contiguous unsubstituted residues. The results obtained on a series of carboxymethylcellulose samples indicate that the rate of degradation and the number and length of blocks of unsubstituted residues depends not only on the number of substituent groups, but also on other molecular parameters.

4'-Halo-substituted sucrose derivatives

Abstract: Compounds of the general formula (I) ##STR1## (wherein X represents a halogen atom; R 1 and R 2 respectively represent a combination selected from the group consisting of: a hydroxy group and a hydrogen atom; a halogen atom and a hydrogen atom; and a hydrogen atom and a halogen atom; and R 3 and R 4 , which may be the same or different, each represent a substituent selected from the group consisting of a halogen atom and a hydroxy group; at least one of R 1 , R 2 and R 3 representing a halogen atom) are potent sweeteners obtainable by opening a corresponding 3',4'-lyxoepoxide with a source of halide ions.

Quaternary ammonium group-containing polymers having antimicrobial activity

Abstract: Polymeric quaternary ammonium compounds having recurring vinylbenzyl ammonium units are disclosed. The quaternary ammonium units preferably have 2 alkyl substituents of 1 to 4 carbons and 1 alkyl substituent of 4 to 12 carbons. These materials have antimicrobial properties and are particularly useful for preserving ophthalmic solutions.

Asymmetric dichroic dye molecules having poly(arylazo) linking groups, a bis-substituted aryl thiazyl end group, and another end group

Abstract: A dichroic dyestuff having the formula Q--A--Z wherein: A is a poly(arylazo) linking group wherein the aryl comprises 6 to 10 carbon atoms and has 4,4'-azo linkages; Q is a bis-substituted aryl thiazyl substituent wherein the aryl comprises 6 to 10 carbon atoms; and Z is selected from the group consisting of naphthalene having an alkyl substituted amino in the 4 position, 2,3-dihydro-2,2'-substituted-perimidine and julolidine groups; forms guest-host combinations with nematic liquid crystals. These dichroic dyes have absorption maxima at wavelengths greater than 600 nanometers and transmit less than 50% of incident light having wavelengths between 600 and 700 nanometers. Thus these dyes, when combined with dichroic dyes which have absorption maxima between 400 and 600 nanometers, and nematic liquid crystals, are useful to provide electro-optical displays which change from clear to a neutral black color or vice versa when an electric field is applied to the electro-optical display.

Temperature-dependent acid dissociation constants (K/sub a/,. delta. H/sub a/,. delta. S/sub a/) for a series of nitrogen-substituted hydroxamic acids in aqueous solution

Abstract: The acid dissociation constants (K/sub a/) of a series of eight substituted N-phenylacetohydroxamic acids, CH/sub 3/C(O)N(OH)C/sub 6/H/sub 4/X (X = H,4-CH/sub 3/, 4-Cl, 4-I, 3-I, 3-CN, 4-CN, 4-C(O)CH/sub 3/), have been determined in aqueous solution (I = 2.0) for a range of temperatures. The pK/sub a/ data at 25 /sup 0/C exhibit a small variation with the substituent X in the direction expected according to their Hammett substituent constants (p approx. = 0.1). These small variations in pK/sub a/ values are due to compensating trends in ..delta..H/sub a/ and ..delta..S/sub a/, which show significant variation with substituent. These results are discussed in terms of the substituent's influence on hydroxamate anion-slvent interactions and the relative influence on pK/sub a/ of a substituted phenyl group attached to the C or N end of the hydroxamate moiety.

Alkanol ethoxylate-containing detergent compositions

Abstract: Detergent compositions particularly useful in hard-surface cleaning comprise an alkanol ethoxylate component which consists essentially of a mixture of compounds of the formula R--O--CH2 CH2 O--x H, wherein R is an alkyl group of from 8 to 18 carbon atoms, said alkyl group having a linear carbon chain in at least about 50 percent of the ethoxylate molecules; wherein the --O--CH2 --CH2 --O--x H ether substituent is, in at least 40 percent of the molecules of the mixture, bound to R at a carbon atom which is neither a terminal carbon atom nor a carbon atom adjacent to a terminal carbon atom; and wherein x has an average value for all ethoxylate molecules of the mixture which is in the range from about 3 to 9; said ethoxylate component being further characterized as having a hydrophile-lipophile balance that is between about 10.4 and 12.0; and said composition being further characterized as containing less than about 2 percent by mole, calculated on moles of the mixture of ethoxylate compounds therein, of compounds having a C8 to C18 alkyl group substituted by multiple ether substituents.