Showing papers on "Amide published in 1972"
TL;DR: In this article, the carboxy-group of a series of substituted N-methylmaleamic acids is shown to be remarkably sensitive to the pattern of substitution on the carbon-carbon double bond.
Abstract: The efficiency of intramolecular catalysis of amide hydrolysis by the carboxy-group of a series of substituted N-methylmaleamic acids is remarkably sensitive to the pattern of substitution on the carbon–carbon double bond. A single alkyl group increases the rate of hydrolysis by a factor which increases with its size. A second alkyl substituent has a disproportionately larger effect, which is sharply reduced when the two groups are joined together in a ring. The rates of hydrolysis of a series of dialkyl-N-methylmaleamic acids range over more than ten powers of ten, and the ‘effective concentration’ of the carboxy-group of the most reactive compound studied is greater than 1010M. This amide, dimethyl-N-n-propylmaleamic acid, is converted into the more stable dimethylmaleic anhydride with a half-life of less than 1s at 39 °C below pH 3. The mechanism of catalysis, and the factors responsible for this extremely high reactivity, are discussed.
154 citations
101 citations
TL;DR: Five purposes for which the dicarboxylic anhydrides have been utilized are discussed in the chapter, which include protein dissociation, protein hybridization, mapping of lysine peptides, peptide sequencing, lysines side-chain reactivity and function, and introduction of new functional groups.
Abstract: Publisher Summary This chapter discusses acylation with dicarboxylic acid anhydrides. Succinic and maleic anhydride, or analogs of these two compounds, is utilized in a variety of protein modification studies. During the course of the reaction most of the anhydride is hydrolyzed. The dicarboxylic acid side product may be separated from the modified protein by dialysis, by passage through a column of anion exchange resin (for example, Amberlite IRA-400 in the chloride form), or by gel exclusion chromatography (for example, with Sephadex G-25). The stability of the half amide adduct depends on the anhydride used in the reaction. Five purposes for which the dicarboxylic anhydrides have been utilized are discussed in the chapter, which include protein dissociation, protein hybridization, mapping of lysine peptides, peptide sequencing, lysine side-chain reactivity and function, and introduction of new functional groups. The relatively high specificity of succinic and maleic anhydride for primary amino groups suggests that these reagents may be useful for studying the reactivities of lysine side chains and for elucidating the roles these residues may play in the biological activities of proteins.
88 citations
TL;DR: Half-lives of 17 aminoacyl-tRNAs have been determined in three solvent systems according to the positive or negative induction (+I and −I effects) of substituents on the α-CH responsible for stabilization or labilization of the ester group.
79 citations
TL;DR: The results with N,N-dimethylacetamide suggest that a hydrogen bond between a tyrosyl hydroxy group and a carbonyl oxygen of the peptide backbone may be one mechanism for producing a large red shift in proteins.
64 citations
TL;DR: High‐molecular‐weight poly‐L‐alanine dissolved in hexafluoroisopropanol exhibits infrared, ultraviolet, circular dichroism, and optical rotatory dispersion spectra which are unique and unlike any other previously reported polypeptide spectra.
Abstract: High-molecular-weight poly-L-alanine dissolved in hexafluoroisopropanol exhibits infrared, ultraviolet, circular dichroism, and optical rotatory dispersion spectra which are unique and unlike any other previously reported polypeptide spectra. Strong evidence that a helical conformation is present is shown by the high degree of hypochromism in the 187mμ absorption peak and by the positions of the amide infrared bands. The CD and ORD spectra are also similar to those of α-helical polypeptides, though important qualitative and qualitative differences are observed. To explain the novel spectra, which are not mixtures of the spectra of previously reported polypeptide conformations, a new α-helix-like conformation is proposed. The postulated conformation (a doubly hydrogen-bonded helix) is a distorted α-helix in which the peptide carbonyl groups point slightly out from the helix axis and are hydrogen bonded simul taneously both to the NH of the fourth peptide residue to the carboxyl terminal side (as in the classical α-helix), as well as to a solvent molecule's hydroxyl hydrogen.
63 citations
TL;DR: The Raman spectra of the double helical complexes of poly C–poly G and poly I–poly C at neutral pH are presented and compared with the spectraOf the constituent homopolymers.
Abstract: The Raman spectra of the double helical complexes of poly C–poly G and poly I–poly C at neutral pH are presented and compared with the spectra of the constituent homopolymers.
When a completely double-helical structure is formed in solution a strong sharp band at 810–814 cm−1 appears which has previously been shown to be due to the A-type conformation of the sugar–phosphate backbone chain. By taking the ratio of the intensity of the 810–814 cm−1 band to the intensity of the 1090–1100 cm−1 phosphate vibration, one can obtain an estimate of the fraction of the backbone chain in the A-type conformation for both double-stranded helices and self-stacked single chains. This type of information can apparently only be obtained by Raman spectroscopy.
In addition, other significant changes in Raman intensities and frequencies have been observed and tabulated: (1) the Raman intensity of certain of the ring vibrations of guanine and hypoxanthine bases decrease as these bases become increasingly stacked (Raman hypochromism), (2) the Raman band at 1464 cm−1 in poly I is asigned to the amide II band of the cis-amide group of the hypoxanthine base. It shifts in frequency upon base pairing to 1484 cm−1, thus permitting the determination of the fraction of I–C pairs formed.
57 citations
54 citations
TL;DR: Gross amide hydrogendeuterium exchange kinetics in 2H2O indicates that these four amides have a highly diminished interaction with the solvent, as in the Schwyzer model for cyclohexapeptides.
47 citations
TL;DR: In this paper, the crystal and molecular structure of diaquobis(picolinato)cobalt(II) dihydrate has been determined from three-dimensional MoKα X-ray collected by the multiple-film Weissenberg method.
Abstract: The formation constants of the following have been measured with a polarographic method: binary copper(II) complexes of pyridine-2-carboxamide (picolinamide) and pyridine-2-carboxylic acid (picolinic acid), a ternary copper(II) complex of picolinic acid and imidazole, and a binary copper(I)-imidazole complex. The larger formation constant for picolinic acid over picolinamide is ascribed to the greater chelating ability of a carboxylate group over an amide carbonyl oxygen. The crystal and molecular structure of diaquobis(picolinato)cobalt(II) dihydrate, [Co(H2O)2(pc)2].2H2O, has been determined from three-dimensional MoKα X-ray collected by the multiple-film Weissenberg method. The unit cell dimensions are: a=9.89 ± 0.02 A, b=5.17 ± 0.01 A, c=17.50 ± 0.06 A, β=123.8 ± 0.4°. The space group is P21/c, and the calculated density is 1.67 g cm−3 with two formula weights per cell. The measured density is 1.67 g cm−3. The structure was solved by the Patterson method and refined by a least-squares method....
44 citations
TL;DR: The finding of internal hydrogen bonding, together with the assignment of the environment of one peptide bond, places major constraints on the number of allowable conformations of this linear polypeptide hormone.
Abstract: Automated tritium-hydrogen exchange measurements have been made on the linear octapeptide Val5-angiotensin II amide. All six amide hydrogens of the peptide backbone are observable, and are resolved into three classes according to their exchange rates. The rate of exchange of the slowest class, t1/2 of 300 min at 0°C (pH 2.5), is compared with that of hydrogens that exchange abnormally slowly in other peptides. It is concluded that these slow hydrogens in angiotensin II are involved in secondary structure with either one or both forming stable, intramolecular hydrogen bonds. This finding demonstrates that linear peptides may have hydrogen-bonded conformations in aqueous solutions. Analysis of the pH dependence of the rate of exchange indicates that one peptide amide hydrogen, namely that of the Asn1-Arg2 peptide bond, is not involved in hydrogen bonding and is freely accessible to the solvent. Thus, the finding of internal hydrogen bonding, together with the assignment of the environment of one peptide bond, places major constraints on the number of allowable conformations of this linear polypeptide hormone.
TL;DR: Theoretical and experimental studies suggest that lithium ion binds strongly to the carbonyl group in amides and the consequent changes in the molecular geometry of the amide are verified by changes in infrared spectra and increased barrier heights to rotation as discussed by the authors.
TL;DR: In this article, the reaction of carboxylic acid amide dihalides with phosphorous acid was studied and it was shown that the trihalides plus water can be used in lieu of phosphorous acids in the reaction with carboxyl acid amides.
Abstract: Durch Umsetzung von Carbonsaureamiddihalogeniden oder Carbonsaureamidhydrohalogeniden mit phosphoriger Saure bzw. von Carbonsaureamiden mit Phosphortrihalogenid/Wasser entstehen die 1-Aminoalkan-1, 1-diphosphonsauren 1, 2 oder 3. Aus Formamid bildet sich je nach Reaktionsbedingung entweder Aminomethandiphosphonsaure (la) oder 2-Oxo-2-hydroxy-5-amino-1,4,2-oxazaphospholidin-3-phosphonsaure (5).
1-Aminoalkane-1,1-diphosphonic acids 1, 2 or 3 are formed in the reaction of carboxylic acid amide dihalides or carboxylic acid amide hydrohalogenides with phosphorous acid. Phosphorus trihalides plus water may be used in lieu of phosphorous acid in the reaction with carboxylic acid amides. With formamide either aminomethanediphosphonic acid (1a) or 2-oxo-2-hydroxy-5-amino-1,4,2-oxazaphospholidine-3-phosphonic acid (5) are obtained depending on the reaction conditions.
TL;DR: In this article, an experimental study of proton, deuteron, and nitrogen resonance of dimethylformamide and deuterated DMF has been made in oriented nematic liquid crystals of polyglutamic acid.
Abstract: An experimental study of proton, deuteron, and nitrogen resonance of dimethylformamide and deuterated DMF has been made in oriented nematic liquid crystals of poly‐L‐glutamic acid. The solvents used were various mixtures of DMF and H2O or D2O. From the proton spectra the complete order matrices were determined for each solvent system. From consistency between the solvent systems the angle HCN of the amide could be determined and was found to be 107± 1°. From the observed quadrupole splittings of all deuterium nuclei and of nitrogen in (deuterated) DMF in three solvent systems, all elements of the quadrupole coupling tensors of these nuclei were obtained. The quadrupole coupling constants and asymmetry factors found were: for the amide deuteron 197 kHz, 0.13; for the methyl deuterons trans to the amide oxygen 46 kHz, 0.19 and for those cis to the amide oxygen 64 kHz, 0.06 (averaged over methyl rotation); for the nitrogen 3.3 MHz, 0.4. Deuteron quadrupole splitting of solvent water was also observed, while ...
01 Jan 1972
TL;DR: A detailed knowledge of the orientation of the carbonyl groups of the acyl moieties in the acetyl-en enzyme and the indoleacryloyl-enzyme has led to a clearer understanding of the stereochemistry of the deacylation mechanism.
Abstract: The reaction of p-nitrophenyl cyanate with chymotrypsinogen A and chymotrypsin A has been studied to determine the potential of this reagent in the field of enzyme modifications. These experiments have shown that p-nitrophenyl [14C]cyanate can react at specific loci on the enzyme under mild conditions. These conditions can be controlled in such a manner as to virtually eliminate nonspecific side reactions. p-Nitrophenyl [14C]cyanate reacts differently with the various species of chymotrypsin A. The reagent reacts simultaneously at two sites in chymotrypsin Aπ and Aδ, the active-site Ser-195 and the amino terminal of Cys-1, to give a dicarbamylated product. However, in chymotrypsin Aα, the reagent reacts principally at Ser-195 giving at first a monocarbamylated product. This difference in behavior has been shown to be due to a difference in the reactivity of the amino terminal of Cys-1 in the various enzyme species. Crystals of monocarbamyl-chymotrypsin Aα were readily obtained in a form isomorphous with native and tosyl-chymotrypsin Aα. The structure of the carbamyl derivative has been determined from crystallographic studies at 2.5-A resolution. The carbamyl group occupies the same region as the carbonyl group of indoleacryloyl-chymotrypsin Aα and the sulfonyl group of the tosyl derivative. It is stabilized in a single conformation by a hydrogen-bonding network involving a water molecule, the carbonyl oxygen of the carbamyl group, the peptide carbonyl of Phe-41 and the amide nitrogen of Gly-193. Based on information taken from the carbamyl derivative, the structure of acetyl-chymotrypsin Aα has been proposed. A detailed knowledge of the orientation of the carbonyl groups of the acyl moieties in the acetyl-enzyme and the indoleacryloyl-enzyme has led to a clearer understanding of the stereochemistry of the deacylation mechanism.
TL;DR: The p.m.r. spectra of the dimethylamides of D-lysergic acid (3) and D-iso-lysergic acid(4) are reported in this article.
Abstract: The 220 MHz p.m.r. spectra of the dimethylamides of D-lysergic acid (3) and D-iso-lysergic acid (4) are reported. Extensive use of double resonance experiments and the presence of four long-range coupling constants provide an unambiguous assignment for the conformation of 3 in CDCl3. Its D ring is shown to exist in a half-chair form in which the 8-β amide function is pseudo-equatorial. Its epimer essentially exists in the other half-chair form with a pseudo-equatorial 8-α amide function. Data from the p.m.r. spectra of a series of N,N-dialkylamides of these acids are also presented.The spectrum of protonated 3 at 23 °C shows two forms of the 6-NCH3 and 8-CON(CH3)2 groups but only one for the epimer 4.
TL;DR: On the other hand, in this article, the helical poly-(γ-benzyl L-glutamate) in chloroform-trifluoracetic acid was converted into the random coil form, and the 13C spectrum showed an upfield displacement of 3·0 p.p.m.
Abstract: On conversion of the helical poly-(γ-benzyl L-glutamate) in chloroform–trifluoracetic acid into the random coil form, the 13C spectrum shows an upfield displacement of 3·0 p.p.m. for the α carbon and 2·7 p.p.m. for the amide carbon.
TL;DR: The molecular structure of a stereospecific (isotactic) polymerization catalyst of the acetaldehyde-monomer complex, [Me2Al·O·CPh: NPh,MeCHO]2, has been determined on the basis of three-dimensional X-ray data collected photographically.
Abstract: The molecular structure of a stereospecific (isotactic) polymerization catalyst of the acetaldehyde-monomer complex, [Me2Al·O·CPh: NPh,MeCHO]2, has been determined on the basis of three-dimensional X-ray data collected photographically. The crystal belongs to the orthorhombic system (space group Pcca) with four dimer formula units in a cell with the dimensions of: a=15.83(3), b=12.61(1), and c=17.66(1) A. The structure was established by the heavy-atom method and refined by block-diagonal, least-squares procedure. The molecule is dimeric and has a C2-2 symmetry. A monomer molecule, acetaldehyde, is inserted in the Al–N bond of the original polymerization catalyst. The oxygen atom bridges both aluminum atoms, Al–O=1.858(6) and 1.985(6) A. The α-carbon atom of acetaldehyde bonds to the nitrogen atom of the amide moiety, C–N=1.469(12) A. The aluminum atom is penta-co-ordinated and has a trigonal bipyramidal conformation.
TL;DR: In this paper, the effect of changes in the electronic environment of the sp2 hybridised carbene carbon atom bound to the metal in a series of 18 complexes of the type (CO)5MCXY, where M = Cr or W; X = OR or NR1R2, and Y is an organic group, are discussed with the aid of 13C n.m.
Abstract: The effect of changes in the electronic environment of the sp2 hybridised carbene carbon atom bound to the metal in a series of 18 complexes of the type (CO)5MCXY, where M = Cr or W; X = OR or NR1R2, and Y is an organic group, are discussed with the aid of 13C n.m.r. spectroscopy. The chemical shift of the carbene carbon is more strongly influenced by X than by either M or Y. Carbene complexes of the transition metals are better considered as metal-stabilised carbonium ions than as carbonyl (ester or amide) analogues. The resonances of the carbonyl ligands in carbene complexes are compared with those in isonitrile complexes of the type RNCCr(CO)5. Evidence is presented from both 13C and 1H n.m.r. spectra which shows that overall electron release rather than π→p interaction is important in the stabilisation of the carbene carbon by the group Y.
Patent•
13 Dec 1972
TL;DR: In this paper, a gelation inhibitor in the form of a cyclic amide, such as an N-substituted 2-pyridone, or a 2pyrrolidinone monomer or polymer substituted in the 1-position, was proposed.
Abstract: Polymerization of epoxides and mixtures of epoxides with lactones and vinyl compounds, polymerizable through the action of cationic catalysts, is controlled by providing, in association with a radiation-sensitive catalyst precursor, a gelation inhibitor in the form of a cyclic amide, such as an N-substituted 2-pyridone, or a 2-pyrrolidinone monomer or polymer substituted in the 1-position.
TL;DR: In this article, an N-acyl-amino acid n-alkyl amide (N-caproyl-L-valine n-hexyl amides) was synthesized, which fulfills the general requirements for the reversible association between the enantiomers and the asymmetric solvent molecules.
Abstract: TFA-amino acid esters and TFA-dipeptide esters have been employed as optically active stationary phases for the resolution of amino acid enantiomers by gas chromatography. Structural consideration of the hydrogen bonded diastereoisomeric association complex formed during the separation of amino acid enantiomers led to the synthesis of an N-acyl-amino acid n-alkyl amide (N-caproyl-L-valine n-hexyl amide). This amino acid derivative fulfills the general requirements for the reversible association between the enantiomers and the asymmetric solvent molecules. The results obtained show that the amide portion, when in competition with the ester portion of a dipeptide phase, is involved in formation of the diastereoisometric association complex between the enantiomeric solutes and the chiral solvent by hydrogen bonds.
TL;DR: In this paper, the model reactions between phthalic anhydride and o-phenylenediamine were studied under conditions analogous to the polymerization and post-cyclization of dianhydrides with bis(o-diamines) to form polyimidazopyrrolones (Pyrrones).
TL;DR: Some complexes of 2-acetamidothiazole with NiII and CuII have been prepared and three types of co-ordination behaviour distinguished on the basis of their i.r. spectra as discussed by the authors.
Abstract: Some complexes of 2-acetamidothiazole and 2-acetamidobenzothiazole with NiII and CuII have been prepared and three types of co-ordination behaviour distinguished on the basis of their i.r. spectra. The organic ligand donor atoms may be (a) carbonyl oxygen and thiazole nitrogen, (b) amide nitrogen and thiazole nitrogen, or (c) carbonyl oxygen, amide nitrogen, and thiazole nitrogen. Types (b) and (c) are of interest as examples of co-ordination via a non-deprotonated amide nitrogen atom.
TL;DR: In this article, the selectivity of hydrogen-bond formation in chromatographically important, chiral solute-solvent systems have been performed with the aid of 1 H and 13 C nuclear magnetic resonance techniques.
TL;DR: In this paper, an extensive investigation has been made concerning the structure of a series of aqueous amide solutions using nuclear magnetic resonance techniques, and changes in spectral parameters as a function of solution composition and temperature were used to determine the effect of the intrinsic amide molecule structure on the structural structure of water and the solution as a whole.
TL;DR: In this article, a new total synthesis of L(+)-muscarine is described, which was resolved at the α-carbon by stereospecific hydrolysis of the N-acetyl group of the L-isomer with hog kidney acylase I.
Abstract: A new total synthesis of L(+)-muscarine is described. Performic acid oxidation of N-acetylcrotylglycine gave the corresponding 4,5-diol which was resolved at the α-carbon by stereospecific hydrolysis of the N-acetyl group of the L-isomer with hog kidney acylase I. The resulting α-L(+)-aminoacid diol (3; Chart 1) was deaminated with nitrous acid to give 4-hydroxy-5-methyl-2-tetrahydrofuran carboxylic acid with retention of configuration at position 2. Reaction of the corresponding methyl ester with dimethylamine gave two major amide constituents in 65% yield. Reduction of these two N,N-dimethylamides (5a and b) with lithium aluminum hydride followed by quaternization with methyl iodide afforded a pure isomer of L(+)-muscarine (6a) and L(+)-muscarine (6b) in high yields. The biological activity of the latter was the same as that of the natural alkaloid.