Side-chain Carbon Atoms Research Articles

On the reaction of derivatives of thiosemicarbacide with bis-imidochlorides of oxalic acid

Arylsubstituted oxalic bis-imidochlorides1 react with thiosemicarbazones of type5 as well as13 to give five-membered-ring heterocycles8,11, and16.13C-NMR spectroscopy, chemical methods and X-ray crystallography have been used to investigate the nature of the structures obtained. The13C-chemical shifts of13 and imidazolidines16 are correlated with Hammett σ p constants and dual substituent parameters to evaluate the transmission of theX substitutent electronic effects via the side-chain iminyl carbon atom into the heterocyclic ring and its neighbouring phenyl groups.

Unambiguous Assignment of the13C NMR Resonances of the Side-Chain Carbon Atoms of Dipropylglyoxal Bis(Amidinohydrazone) by DEPT and Selective Heteronuclear Proton Decoupling Techniques

Abstract The previously unassigned carbon-13 NMR resonances of the side-chain carbon atoms of the enzyme inhibitor dipropylglyoxal bis(amidinohydrazone) (DPGBG) have been unambiguously assigned with the aid of DEPT measurements and experiments involving the selective decoupling of the protons of one of the methylene groups. The chemical shifts of the side-chain carbon atoms of DPGBG decrease in a nearly linear fashion as a function of the position of the atom in the side chain, the terminal methyl groups having the lowest shift value. The carbon-13 shifts are positively correlated with the chemical shifts of the corresponding hydrogen atoms.

Synthesis and stereochemistry of 23,24-dihydrocalysterol: implications for marine sterols of a unified biosynthetic scheme involving protonated cyclopropanes

The partial synthesis of the marine cyclopropyl-sterol dihydrocalysterol (1), which has allowed the confirmation of the originally postulated absolute stereochemistry around the cyclopropane ring, is described. The firm knowledge of this stereochemistry and that of the other marine sterols petrosterol (7), dehydroaplysterol (21), ficisterol (22), nicasterol (8), and hebesterol (23) has allowed us to construct a unified biosynthetic scheme for these sterols of diverse side-chain structure. Our central postulate, that the intermediate in sterol side biomethylation may be described in terms of a protonated cyclopropane species [i.e. protonated dihydrocalysterol (1)], enables us to interrelate the absolute stereochemistries of the above sterols and predict the biosynthetic origin of the side-chain carbon atoms.

The chemistry of pyrrolic compounds. LV. 13C chemical shift data for the isomeric protoporphyrins

The 13C n.m.r, spectra of the 15 isomeric protoporphyrin dimethyl esters have been determined. Measurements were made on the zinc chelate derivatives of the porphyrins in the presence of pyrrolidine and assignments are given for the side chain and methine carbon atoms.

Carbon-13 NMR Spectra of Lignins, 9. Spin-Lattice Relaxation Tines (T) and Determination of Interunit Linkages in Three Hardwood Lignins (Alnus Glutinosa, Corylus Auellanus and Acer Pseuooplatanus)

Abstract The spin–lattice relaxation times (T1) of the twelve most abundant carbon atoms in acetylated milled wood lignin (MWL) from hazelnut (Corylus avellanus) have been determined by the progressive saturation pulse Fourier transform (PSFT) technique. T1 values below 0.5 s have been found for the aliphatic carbon atoms in the C3 side chains, while substituted aromatic, carbonyl and CH3 carbon atoms in methoxy and acetyl groups have T values ranging between 1 and 3 a. From these results a quantitative determination of interunit linkages in lignin may be possible from car-bon-13 spectra with pulse interval times of at least 3 s. Furthermore, the carbon-13 NPIR spectra of three acetylated hardwood It MWLs, from black alder, hazelnut and mountain maple, have been recorded at 90.7 MHz. Five interunit linkages, β-0-4, α, β–bis-0-4, β-1, β-β and β-5, have been traced in each lignin and their frequences qualitatively compared with each other.

Trapping of metabolically generated electrophilic species with cyanide ion: metabolism of methapyrilene.

The popular antihistamine methapyrilene [N,N-dimethyl-N'-(2-pyridyl)-N'-(2-thienylmethyl)-1,2-ethanediamine] recently has been shown to be a potent hepatocarcinogen. Metabolic studies with rabbit liver 100000g microsomal preparations have resulted in the partial characterization of the in vitro metabolic profile of methapyrilene. Evidence for the formation of the N-oxide and the three possible carbinolamines resulting from the NADPH-dependent oxidation of the (dimethylamino)ethyl side chain nitrogen and carbon atoms of methapyrilene is presented. Attempts to trap iminium ion intermediates with electrophilic alkylating potential by coincubating methapyrilene with sodium cyanide have led to the isolation of N-(cyanomethyl)normethapyrilene. The possibility of characterizing the iminium ion intermediate that would result from the oxidative deamination of the dimethylamino moiety was precluded by the chemical instability of the corresponding alpha-cyano amine, which undergoes a spontaneous retro-Michael reaction and hydrolysis to the corresponding amide. The results are discussed in terms of the metabolic activation of methapyrilene to potential alkylating species.

Neighboring group participation by the pyrrole nucleus

Using proton and carbon-13 NMR spectroscopy, the transformation of 2-hydroxyethylpyrroles (5,15) into 2-haloethylpyrroles by treatment with thionyl chloride or carbon tetrabromide/triphenylphosphine is shown to proceed by randomization of the two side-chain carbon atoms. A spirocyclopropylpyrrolium ion (19) is postulated as an intermediate in this unexpected process.

Synthesis of 3‐indolyl(1‐14C)acetic, 3‐indolyl(2‐14C) acetic and 3‐indolyl(1,2‐14C2)acetic acids

AbstractThe synthesis of 3‐indolylacetic acid labelled with 14C in side chain carbon atoms has been effected using (1‐14C)glycolic acid, (1,2‐14C2)glycolic acid and (2‐14C)glycolic acid in an yield of 40‐60%. Some of the parameters that affect the synthesis have been studied and the results are reported in this paper.

N.M.R. spectroscopy and calcium binding of sialic acids: N-glycolylneuraminic acid and periodate-oxidized N-acetylneuraminic acid

N.m.r. spectroscopy ( 1H- and 13C-) of N-glycolylneuraminic acid, and of its interaction product with Ca 2+ at pH 7, indicated that a 1:1 complex is formed, with a formation constant of 193 M −1 [compared to 121 M −1 for N-acetylneuraminic acid ( 1)]. From analysis of electric-field shifts, an approximate position of the Ca 2+ ion in the complex is inferred, with the hydroxyl group of the N-glycolyl group providing the additional binding. Compound 1 was oxidized with sodium periodate, and 13C-n.m.r. spectroscopy was applied in an attempt to identify the aldehyde formed, and to demonstrate that the loss of the glycerol-1-yl side-chain (carbon atoms 8 and 9) decreases its Ca 2+ ion-binding capacity.

Primary structure and chiroptical properties of polydiasteriomers obtained by steroelective polymerization of N-[(S)-sec-butyl] and N-[(R)-sec-butyl-N-methyl-N-(R,S)-thiirane-2-ylmethyl] amine isomers

Stereoisomers of N-( sec-butyl)- N-methyl- N-((R,S)-thiirane 2-ylmethyl) amine ((S)- sec-butyl, optical purity O.P. ∼94% and (R)- sec-butyl, O.P. ∼26%) were polymerized using a chiral initiator system (1:1) ZnEt 2 R(-)3,3- dimethyl-1,2- butanediol (R(-)BMBD) (stereoelective polymerization). In agreement with the homosteric character of this initiator, the configuration of the asymmetric centre located in the heterocycle of the elected diastereoisomer is shown to be R from c.d. spectra of residual monomers, whatever the configuration of the asymmetric centre located in the pendant group. O.r.d. and c.d. spectra of stereoelected polydiastereoisomers are described and compared to those of corresponding polydiastereoisomers bearing racemic main-chain chiral centres. 13C n.m.r. spectra of different polydiastereoisomers are reported. The stereosensitivity to tacticity of the main-chain carbons is poor but some of the side-chain carbon atoms are very sensitive to the presence of two asymmetric centres per repeat unit. The optical purity of main-chain chiral centres is deduced from the split resonance of one of these carbons atoms. It is shown that chiroptical properties of polydiastereoisomers primarily depend on configurations of the two chiral sites without obvious contributions from macromolecular conformations. The 242 nm c.d. band assigned to the n → σ∗ electronic transition of sulphur chromophores is sensitive only to the optical purity of main-chain chiral centres and can be used to evaluate the configurational enrichment due to the stereoelective polymerization.

Studies on petroleum sulphonates: Correlation between their chemical structure and the oil—Water emulsion stability characteristics

AbstractThe average molecular weight distribution, emulsion stability of oil—water emulsion, the chemical structure of the hydrocarbon portions of petroleum sulphonates, and surface active properties have been determined with a view to establishing a correlation between the chemical structure of petroleum sulphonates and their emulsion stability characteristics. It has been found that the emulsion stability of oil—water emulsions imparted by sodium petroleum sulphonates depends on: (i) average molecular weight of sodium petroleum sulphonates; (ii) their molecular weight distribution; (iii) oil—water interfacial tension; (iv) hydrophile—lipophile balance values. The structural parameters which predominantly effect the emulsion stability are the ratio of the percentage distribution of carbon atoms in paraffin side chains to the percentage distribution of carbon atoms, the aromatic rings (CP/CA), the relative proportions of long chain mono‐aromatics and the orientation of the sulphonate group relative to the paraffin alkyl chains in the molecules.

Biosynthesis of (2 E,4 E,6 E)-5-acetoxymethyltetradeca-2,4,6-trienoic acid in Eremophila oppositifolia

Evidence is presented indicating that the triple conjugated branched chain fatty acid from Eremophila oppositifolia R.Br. arises by the acetate-malonate pathway with the side chain carbon atom originating from the S-methyl group of methionine.

The Binding of Flavins by Apoflavodoxins from Peptostreptococcus elsdenii and Azotobacter vinelandii as Studied by Temperature‐Jump Technique

AbstractThe binding of various flavins by apoflavodoxins from P. elsdenii and A. vinelandii has been studied by the temperature‐jump technique using fluorescence detection. P. elsdenii apoflavodoxin interacts only with flavins possessing 5 carbon atoms in the N(10) side chain and a terminal phosphate group. Employing a wide range of concentrations of deoxy‐FMNFlavin = 3,4‐dimethyl‐lO‐substituted isoalloxazine = 3,4‐dimethyl‐ lO‐substituted‐2,3,4,10‐tetrahydro‐benzo[g]‐pteridine‐2,4‐dione; FMN = riboflavin‐5′‐monophosphate. and apoflavodoxin only one relaxation process was observed, indicating a one‐step binding mechanism. With native flavodoxin no relaxation could be observed.The kinetic parameters of the interaction of A. vinelandii apoflavodoxin with various flavin analogs (Structure I) have also been investigated. The interaction between apoflavodoxin and flavin derivatives carrying an ionizable, terminal functional group on the side chain becomes very weak when the number of the side chain carbon atoms is decreased below 4. This observation is interpreted in terms of repulsive forces due to negatively charged amino acid residues located in the flavin side chain binding region of the apoflavodoxin. All complexes studied revealed only one relaxation process. This observation is in contradiction with published results [10]. The published traces are instrumental artifacts.

Higher aliphatic aldehyde polymers, VII: poly(n-decaldehyde)

n-Decaldehyde (DA) was polymerized to crystalline poly(n-decaldehyde) (PDA) of reasonable molecular weight in methylcyclohexane (MCH) solvent with lithiumtert-butoxide (LTB) as the initiator under carefully controlled temperature conditions. The polyacetal structure ofPDA was established by IR and PMR spectroscopy as well as by the characteristic degradation of the polymer in the presence of 2,4-dinitrophenylhydrazine.PDA had the dual melting behavior typical of aliphatic polyaldehydes with four or more side chain carbon atoms. The DSC scans of crystallinePDA in the first, or side chain, transition region showed as many as three endothermic peaks between 45 and 65°C. The X-ray diffraction pattern of crystalline PDA was similar to that which had been observed for other polyaldehydes but with a larger unit cell.PDA was extruded at 53°C in a capillary rheometer and gave a filament whose X-ray diffraction pattern indicated medium orientation effects.

Substituent effects on the carbon-13 N.M.R. chemical shifts of side-chain carbons in aromatic systems

Carbon-13 chemical shifts have been measured for the side-chain carbon atoms of a number of meta- and para-disubstituted benzenes. The side chains examined were CN, CF3, Ac, CO2Et, Me, OMe and NMe2. The substituent-induced 13C shifts of these side chains were related to Hammett substituent effects by the Dual Substituent Parameter method and showed a widely varying dependence upon the blend of inductive and resonance effects. The transmission of substituent effects through aromatic systems and the factors that influence 13C shifts are discussed.

13C spin relaxation studies of the basic pancreatic trypsin inhibitor

AbstractThe longitudinal 13C spin relaxation times T1 and the 13C{1H} nuclear Overhauser enhancement were measured in a concentrated aqueous solution of the basic pancreatic trypsin inhibitor. The correlation time for overall rotational motions of the basic pancreatic trypsin inhibitor molecules was found to be τR ≈ 2 × 10−8 s. In connection with previous 1H n.m.r. studies of intramolecular motions of the aromatics, we were particularly interested in the correlation times τG for intramolecular segmental motions of the aromatic rings. The present experiments revealed no manifestation of intramolecular motions of the aromatics, indicating that τG ≫ 2 × 10−8 s for the aromatic ring carbon atoms. On the other hand, rapid segmental motions were evidenced for the peripheral carbon atoms of aliphatic amino acid sidechains. Comparison of the 1H and 13C n.m.r. data on the basic pancreatic trypsin inhibitor indicates that the time scale of high resolution 1H n.m.r. at high fields may in many instances be more appropriate for studies of the molecular dynamics in globular proteins than the time scale of spin relaxation measurements.

The enzymatic synthesis of l-tryptophan analogues

A convenient method for the synthesis of l-tryptophan analogues is described. The method utilizes E. coli tryptophan synthetase, which catalyses the condensation of indole and l-serine to yield l-tryptophan. It is found that several indole analogues will replace indole as substrate for the enzyme to give the corresponding l-tryptophan analogues in good yield. By using [ 14C]serine, analogues can be prepared radioactively labeled in the side-chain carbon atoms.

Biosynthesis of phytoquinones. Homogentisic acid: a precursor of plastoquinones, tocopherols and alpha-tocopherolquinone in higher plants, green algae and blue-green algae.

1. By means of (14)C tracer experiments and isotope competition experiments the roles of d-tyrosine, p-hydroxyphenylpyruvic acid, p-hydroxyphenylacetic acid, phenylacetic acid, homogentisic acid and homoarbutin (2-methylquinol 4-beta-d-glucoside) in the biosynthesis of plastoquinones, tocopherols and alpha-tocopherolquinone by maize shoots was investigated. It was established that d-tyrosine, p-hydroxyphenylpyruvic acid and homogentisic acid can all be utilized for this purpose, whereas p-hydroxyphenylacetic acid, phenylacetic acid and homoarbutin cannot. Studies on the mode of incorporation of d-tyrosine, p-hydroxyphenylpyruvic acid and homogentisic acid showed that their nuclear carbon atoms and the side-chain carbon atom adjacent to the nucleus give rise (as a C(6)-C(1) unit) to the p-benzoquinone rings and nuclear methyl groups (one in each case) of plastoquinone-9 and alpha-tocopherolquinone and the aromatic nuclei and nuclear methyl groups (one in each case) of gamma-tocopherol and alpha-tocopherol. 2. By using [(14)C]-homogentisic acid it has been shown that homogentisic acid is also a precursor of plastoquinone, tocopherols and alpha-tocopherolquinone in the higher plants Lactuca sativa and Rumex sanguineus, the green algae Chlorella pyrenoidosa and Euglena gracilis and the blue-green alga Anacystis nidulans.

BIOSYNTHESIS OF THE PHENYLPROPANOID MOIETY OF CHLORAMPHENICOL.

Cultures of Streptomyces sp. 3022a were grown in the presence of C14-labelled substrates and incorporation of radioactivity into chloramphenicol measured. D-Glucose, labelled in carbons 1 or 2 or uniformly, was an efficient precursor of the p-nitrophenylserinol moiety and of the phenylpropanoid amino acids of the mycelium. The distribution of label in the ring and side-chain carbon atoms of p-nitrophenylserinol and cellular phenylalanine from experiments in which glucose-1-C14, glucose-2-C14, and glycine-2-C14 were fed provided evidence that the two phenylpropanoid systems had a common biosynthetic origin. The results were also consistent with their formation via the shikimic acid – prephenic acid route. Uniformly C14-labelled shikimic acid, though poorly utilized by this organism, was incorporated selectively into both the aromatic portion of chloramphenicol and the aromatic amino acids in the mycelium. L-Phenylalanine-U-C14, L-phenylalanine-carboxyl-C14, L-tyrosine-carboxyl-C14, DL-p-hydroxyphenylserine-2-C14, and acetate-2-C14 were poor precursors of the p-nitrophenylserinol moiety. Since phenylalanine and tyrosine were incorporated into the mycelium the biosynthetic route to the phenylpropanoid portion of chloramphenicol evidently does not pass through either of these amino acids but branches at an earlier step.

ASYMMETRICAL INCORPORATION OF C14 ACETATE INTO BETA-CAROTENE BIOSYNTHESIZED BY PHYCOMYCES BLAKESLEEANUS.

Summaryβ-carotene biosynthesized by Phycomyces blakesleeanus was purified by column chromatography over basic silicic acid. Degradation studies on the ring system of this radioactive β-carotene indicate that the carboxyl carbon of acetate is incorporated into positions 1, 1′, 3, 3′, 5 and 5′ of the ring system whereas the methyl carbon is incorporated into all positions of the ring system. Our studies also indicate that the ring carbons are more radioactive than the side chain carbon atoms.