the13C NMR Method Research Articles

The carbon isotopic effect in photolysis of an aqueous solution of cyclopentanol measured by the NMR method

Using the13C NMR method, the manifestation of the carbon isotopic effect on the products of the photolysis of an aqueous solution of cyclopentanone is investigated. A relative enrichment by the isotope13C of the carbonyl (13%) and α-carbon (6%) atoms of initial cyclopentanone and of the carbonyl atom of pent-4-en-1-ale (11%), as well as the depletion of the carbonyl (15%) and methyl (7%) carbon atoms of valeric acid are revealed. The isotopic effect observed is shown to have a magnetic nature.

Synthesis of the N-terminal tripeptide sequence of oxytocin with various protective groups for the cysteine residue

The influence of the nature of the protective groups at the sulfur and nitrogen atoms in the cysteine molecule on the reactivity of this amino acid in the peptide condensation reaction has been investigated. The synthesis of the N-terminal tripeptide sequence of oxytocin was selected as a model reaction. For identifying the compounds synthesized and checking their purity, in addition to traditional physicochemical methods (TLC, melting points, angles of optical rotation), wide use has been made of the13C NMR method.

Synthesis and isolation of monoesters of sucrose and arachidonic acid

Monoesters of sucrose and arachidonic acid have been synthesized by the transesterification of ethyl arachidonate with unprotected sucrose, and the structural isomers — 6-O-arachidonoylsucrose, 6′-O-arachidonoylsucrose, and 3-O-arachidonoylsucrose — have been separated chromatographically. The positions of the ester bonds in these compounds were determined by the13C NMR method.

1H and13C NMR spectra of biologically active compounds. III. Diastereomers of (�)-7-thia- and 13-thia-16-aryloxy analogs of 11-deoxyprostaglandins of the E1 series

The structure has been established and stereochemical assignments have been made of two complete sets of diastereomers of the 7-thia and 13-thia analogs of 11-deoxy-prostaglandins of the E1 series by the13C NMR method. It is proposed to determine the diastereomeric effects of the13C NMR chemical shifts, which are differential parameters bearing information on the stereochemistry of the molecules. Diagnostic diastereomeric effects have been found for assigning stereoisomers with respect to the C-15-hydroxy group and also with respect to the C-8 and C-12 chiral centers of the cyclopentane ring.

13C NMR spectra of polycyclic compounds and the stereochemistry of norbornadiene dimers and trimers

We have obtained the13C NMR spectra of all known dimers and trimers of norbornadiene. We have determined the principles governing the changes in chemical shifts depending on the orientation interactions of the fragments and carried out the stereochemical assignment of all known isomers. We have shown the agreement of the configurations of the latter determined by the13C NMR method with their structures previously established by other methods.

13C NMR spectra and structure of hydroxy- and amino-substituted azo derivatives of benzene and naphthalene

It was shown by the13C NMR method that the hydroxy- and amino-substituted azo derivatives of benzene and naphthalene have an azo structure under the studied conditions.

13C nmr of N,N'-diformyl-, N,N'-diacetyl-S and N,N'-di-(trifluoroacetyl)hydrazines and their methyl analogs

The molecular conformations of the N,N'-diformyl-, N,N'-diacetyl-, and N,N'-di(trifluoroacetyl)hydrazines, and their methyl analogs, were determined by the13C NMR method. A similarity was observed in the change of the13C spectral parameters of the conformers of diacylhydrazines and amides. Hindered rotation around the N-N bond in the13C NMR spectra of N,N'-di(trifluoroacetyl)dimethylhydrazine could not be detected.

Determination of stability constants of outer sphere adducts between CCl4 and Cr(acac)3 by the13C NMR method

The equilibrium constant for the formation of an outer sphere adduct between CCl4 and Cr(acac)3, which leads to the delocalization of a noticeable spin density from the paramagnetic center to CCl4, was determined.

Investigation of the structure of the products from telomerization of ethylene with 1,3-diheterocyclopentanes by the13C NMR method

1. The behavior of 1,3-diheterocyclopentanes (X=O), NC4H9, S; R=H, CH3) in radical telomerization with ethylene was compared. The nature of the heteroatom and the presence of a substituent in the OCHRX group have a significant effect on the ratio of the competing addition and ring-opening reactions in the radical . 2. The relationships governing the variation of the chemical shifts of the signals in the13C NMR spectra of the telomers of 1,3-dibeterocyclopentanes in relation to the nature of the heteroatoms were investigated. The combination of the characteristic signals in the13C NMR spectra makes it possible to assign the investigated compounds reliably to the linear and cyclic series.

Terpene amines. III. Synthesis and study of the structure of N-cycloalkyl-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylamines

The reductive amination of cycloalkanones by camphor oxime has been studied. A probable scheme has been put forward for the occurrence of the reaction and the stereochemical composition of its products have been determined. It has been established with the aid of the13C NMR method that the reaction forms a mixture of isomeric optically active N-cycloalkyl-1,7,7-trimethylbicyclo[2.2.1]hept-2-ylamines with a ratio of the endo to exo isomers of 4:1. The absolute configurations of the amines synthesized have been determined.

Polysaccharides ofEremurus. XV. Structure of the glucomannan ofEremurus lactiflorus

Ten oligosaccharides have been isolated from the products of the partial hydrolysis of a native acetylated glucomannan obtained fromEremurus lactiflorus O. Fedtsch. Their structures have been studied with the aid of acid hydrolysis before and after reduction with NaBH4, by the GLC method, and also by chromatography with markers. The compositions and sequence of the monomers in tetra- and heptaoligo-saccharides have been determined by the13C NMR method. The glucommannan ofE. lactiflorus differs from theEremurus glucomannans studied previously by the ratio of monosaccharides, the presence of 0-Ac groups, the degree of polymerization, and the presence of a cellobiose unit (Glcp-Glcp) in the polymer chain. The repeating unit consists of 14 hexose residues.

13C NMR spectra of arylthiosulfonium salts formed in the reaction between arylsulfenyl chlorides and diaryl, aryl methyl, and dimethyl sulfides in the presence of lewis acids

1. Arylthiosulfonium complexes, slightly stable at > 0°C, and also relatively more stable complexes, the dimethylarylsulfonium salts, were identified by the13C NMR method. 2. The specificity of the δ13C changes was shown on transition from neutral reagents to ionic complexes: the C1 signal is shifted to the strong field, and the C2, C3, and C4 signals to the weak field. 3. The conclusions derived in several papers with respect to the more simple cationoid systems on the redistribution of the electron density in aromatic rings can be extended to the complexes studied. 4. The complexes studied may be considered as p-disubstituted benzenes containing a cationoid center, for which the rule of simple additivity of substituents effects holds.

Polysaccharides ofEremurus. XIII. Study of the structure of the partially acetylated glucomannans by the13C NMR method

The13C spectra of the glucomannans fromEremurus lactiflorus andE. luteus are analyzed in comparison with the spectra of low-molecular-weight model compounds. It has been shown that the linear polymer chain consists of 1 → 4-bound glycosidic residues in the pyranose form, which confirms the results of earlier chemical investigations of these polysaccharides.

Use of pentafluorophenyl esters in the synthesis of intermediate fragments of ACTH

The results are given of the synthesis of the heptapeptide 13–19 of the natural sequence of ACTH using, in a number of stages, the pentafluorophyl esters of amino acids and peptides in combination with the temporary silyl protection of the carboxy group of the amino components. The intermediate compounds were obtained with good yields (70–90%) in chromatographically homogeneous form and their physicochemical characteristics did not differ from those of similar products obtained by other methods and described in the literature. The identification and checking of the purity of the compounds synthesized was carried out not only by traditional methods but also by the13C NMR method and by high-pressure liquid chromatography. Some physicochemical characteristics of the compounds synthesized are given.

Reductive amination ofl-menthol by aliphatic nitriles

The reductive amination ofl-menthol with aliphatic nitriles has been studied. A probable scheme of the mechanism of the reaction has been put forward and the stereochemical composition of its products has been determined. It has been established with the aid of the13C NMR method that the reaction forms a mixture of isomeric optically-active N-alkylmenthyl-, -neomenthyl-, -isomenthyl-, and-neoisomenthyl-amines in a ratio of 54:24:17:5. The absolute configurations of the amines obtained have been determined.

Manifestation of geminal coupling of atoms in13C NMR spectra of some alkoxygermanes

1. The13C NMR spectra of a number of alkylalkoxy- and alkylalkoxychlorogermanes were measured. 2. The13C NMR method gives contradictory information on the presence of geminal coupling of the atoms in the studied compounds, which in most cases are in agreement with its existence.

Investigation of substituted bicyclo[4.2.0]oct-7-en-2-ones by13C NMR spectroscopy

1. The isomeric structures in the series of bicyclo[4.2.0]oct-7-en-2-one series were identified by the13C NMR method on the basis of the effect of the substituents. 2. The variations in the chemical shifts of the olefinic13C and1H in the 7-or 8-alkyl-substituted bicyclo[4.2.0]oct-7-en-2-ones under the influence of Eu(dpm)3 confirm the structural assignments in the investigated series of compounds. 3. The formation of the complex between 8-butylbieyclo[4.2.0]oct-7-en-2-one and Eu(dpm)3 leads to conformational changes.

A study of the binding of manganese (II) with the sodium salts of nucleosides in aqueous solutions by the13C NMR method

The binding of manganese(II) with nucleosides — adenosine (A), guanosine (G), cytidine (C), and uridine (U) — in an alkaline D2O solution has been investigated by the13C NMR method. It has been established that the structure of the paramagnetic Mn(II)—nucleoside complexes differs substantially in neutral and in alkaline media. The broadening of the resonance lines (C-2′, C-3′ > C-1′, C-4′ > C-5′) shows the localization of the Mn(II) in the C-2′ and C-3′ hydroxyls of the ribose in an alkaline medium. It has been shown for the case of U that the degree of complex-formation depends on the pH of the solution. It is assumed that the nucleoside forms intramolecular complexes (I) with Mn(OH)2.

Use of tert-butoxycarbonyl protection in the synthesis of the peptide corresponding to sequence 17?19 of ACTH

The paper gives the results of the synthesis of the tripeptide arginyl-arginylproline performed with the use of various condensing agents. Nα-tert-Butoxycarbonyl-Nω-nitroarginine was used as the starting compound. Some physicochemical characteristics of the tripeptide derivatives (melting point, angle of optical rotation, elementary composition) are given. The13C NMR method was used to identify the structures of the compounds. The chemical shifts of the signals and their assignments are given.

Use of13C NMR, $$J_{13_C 15_N }$$ and $$J_{1_H 15_N }$$ data in structure and configuration analysis of heteroorganic derivatives of alkanenitronic acids

1. The general criteria for the structure analysis of the heteroorganic derivatives of alkanenitronic acids by the13C NMR method were established. 2. The pyridine complexes of the boric esters of nitronic acids exist as the trans isomers. 3. The 1,3 (O, O)-transfer of the B(C2H5)2·C5H5N fragment in (CH3O2C)CH=N(O)OBEt2· C5H5N was observed, as well as the 1,5 (O, O)-transfer of the Si(CH3)3 group in C(NO2)2 =N(O)OSiMe3, and it was found that the two NO2 groups in C(CH3)(NO2)=N(O)OSi(CH3)3 are nonequivalent.