Amidines. XVII—substituent‐induced chemical shifts in <sup>13</sup>C NMR spectra of N<sup>2</sup>‐phenyl‐formamidines, ‐acetamidines and ‐guanidines

Oszczapowicz, Janusz; Raczyńska, Ewa D.; Osek, Jerzy

doi:10.1002/mrc.1260240105

Cited by 33 publications

(20 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…NMR spectroscopy, fail to detect the individual forms [27]. At the same time, owing to the sp2 hybridization of both nitrogens E/Z isomerism of amidines can be observed [28]. This seems to be demonstrated by the presence of two series of signals for the acetamidino This is probably due to the axial orientation of the acetamidino group in this monosaccharide, since in the case…”

Section: Discussionmentioning

confidence: 99%

Somatic antigens of Pseudomonas aeruginosa

Knirel

Paramonov

Vinogradov

et al. 1987

European Journal of Biochemistry

View full text Add to dashboard Cite

O‐specific polysaccharides, obtained on mild acid degradation of lipopolysacchrides of the serologically related strains Pseudomonas aeruginosa O3 (Lányi classification), O25 (Wokatsch classification) and immunotypes 3 and 7 (Fisher classification), are built up of trisaccharide repeating units involving 2‐acetamido‐2,6‐dideoxy‐D‐galac‐tose (N‐acetyl‐D‐fucosamine), 2,3‐diacetamido‐2,3‐dideoxy‐D‐mannuronic acid or 2,3‐diacetamido‐2,3‐dideoxy‐L‐guluronic acid and 3‐acetamidino‐2‐acetamido‐2,3‐dideoxy‐D‐mannuronic acid or 3‐acetamidino‐2‐acetamido‐2,3‐dideoxy‐L‐guluronic acid. Lányi O3(a),3d,3f and Wokatsch O25 polysaccharides contain also O‐acetyl groups. On the basis of solvolysis with anhydrous hydrogen fluoride, resulting in trisaccharide fragments with N‐acetylfucosamine residue at the reducing terminus, chemical modifications of the acetamidino group (alkaline hydrolysis to the acetamido group or reductive deamination to the ethylamino group), as well as analysis by 1H‐NMR (including nuclear Overhauser effect experiments) and 13C‐NMR spectroscopy, and fast‐atom bombardment mass spectrometry, it was concluded that the repeating units of the polysaccharides have the following structures: where HexNAcAmA →α‐L‐GulNAcAmA (∼70%) or β‐D‐ManNAcAmA (∼30%). Lányi O3(a),3d,3f polysaccharide involves two types of repeating units, which differ from each other only in the configuration at C‐5 of the 3‐acetamidino‐2‐acetamido‐2,3‐dideoxyuronic acid residue. Lányi O3(a),3c, O3a,3d,3e and Fisher immunotypes 3 and 7 polysaccharides contain, together with the major repeating units shown above, a small proportion of units in which the derivative of α‐L‐guluronic acid is replaced by the corresponding β‐D‐manno isomer. The data obtained provide the opportunity to substantiate the serological interrelations between these strains of P. aeruginosa by the presence in the O‐specific polysaccharides of common monosaccharides or disaccharide fragments. The distinctions between them stem from the presence or absence of the O‐acetyl group, a different configuration of the glycosidic linkage of the N‐acetylfucosamine residue and/or a different configuration at C‐5 of one or both derivatives of diaminouronic acids.

show abstract

Section: Discussionmentioning

confidence: 99%

Somatic antigens of Pseudomonas aeruginosa

Knirel

Paramonov

Vinogradov

et al. 1987

European Journal of Biochemistry

View full text Add to dashboard Cite

show abstract

“…The main reasonsf or this are their rich acid-base chemistry (several protonation/deprotonation steps may occur depending on the substitution pattern), andt he fact that configurational isomerism (E/Z)w ith respect to theC =Nd ouble bond as wella sr otational isomerism (syn/anti)w ith respectt ot he CÀNs ingle bond are possible. [6][7][8][9][10][11] For example, the Z isomer is favored as the steric bulk of the substituent R 1 increases. The isomerization mechanisms comprise C=Ni somerization (a), CÀNr otation (b), andt automerization (c).…”

Section: Introductionmentioning

confidence: 99%

“…[15,17,18] In the solid state, intermoleculara ssociation of amidines hasb een occasionally observed by means of X-ray crystallography. [9,18] Subsequently,e laborate 2D NMR measurements were used in order to identify the isomers of amidines present in solution. Even experimentally determined solid-state structures have only limited significance for the situation in solution because the relevant intermoleculari nteractions might be completely different.…”

Section: Introductionmentioning

confidence: 99%

Solution Chemistry of N,N’‐Disubstituted Amidines: Identification of Isomers and Evidence for Linear Dimer Formation

Kalz

Hausmann

Dechert

et al. 2016

Chemistry A European J

View full text Add to dashboard Cite

Amidines have found widespread use, but their solution chemistry remains poorly understood. In this work, X-ray crystallographic and detailed 1D and 2D NMR spectroscopic studies have been performed to elucidate the preferred isomers and their interconversion mechanisms. Amidines are shown to exist as a mixture of E-syn and Z-anti isomers in solution and to form dimeric H-bonded aggregates that are also observed in the solid state. Rapid proton exchange/tautomerization reactions occur within the dimers, allowing fast interconversion of E-syn and Z-anti isomers even at very low temperatures. Three different exchange processes were identified in solution, and on this basis the unusual concentration and temperature dependence of the NMR spectra of these amidines could be explained. This work thus resolves some of the puzzles of the complex solution chemistry of this prominent class of compounds.

show abstract

“…which are the first structurally characterized CH-NH tautomers of an acyclic amidine. Even though N,N'-tautomerism in amidines has been investigated in detail, [11] up until now the existence of an equilibrium between CH-NH tautomers has been proven only indirectly for the short-lived ene-1,1-diamine species, which could not be isolated. [12] In contrast, a cyclic ene-1,1-diamine has been previously characterized by NMR spectroscopy.…”

mentioning

confidence: 98%