Basicity, H‐bonding, tautomerism and complex formation of imidic acid derivatives

Oszczapowicz, Janusz

doi:10.1002/9780470772478.ch12

PATAI'S Chemistry of Functional Groups

1991

DOI: 10.1002/9780470772478.ch12

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Basicity, H‐bonding, tautomerism and complex formation of imidic acid derivatives

Janusz Oszczapowicz

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1992

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Cited by 17 publications

References 97 publications

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Basicity of 3-aminopropionamidine derivatives in water and dimethyl sulphoxide. Implication for a pivotal step in the synthesis of distamycin A analogues

Koppel

Leito

et al. 1996

J. Phys. Org. Chem.

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The acid-base properties of eight 3-aminopropionamidine derivatives R,R,N(CH,),C (=NH)NR,R, (1, R,=R,=R,=R,=H; 2, R1=R,=R,=H, R,=Me; 3, R,=R,=R,=H, R,=Me; 4, R,=R,=H, R,=R,=Me; 5, R, = Tos, R2 = R, = R, = H; 6, RI = Tos, R, = Me R, = R, = H; 7, R, = Tos, R, = R, = H, R, = Me; 8, R, = Tos, R, = H, R, = R, = Me; Tos = 4toluenesulphonyl) related to the antiviral natural product distamycin A were investigated in water and dimethyl sulphoxide (DMSO). The measured pK, values for the ammonium function in 1-4 in water ranged between 7.48 and 7-73, whereas the corresponding values in DMSO were 9.4 f 0.3. The amidinium moiety of these compounds displayed pK, values in the range 11.4-12.0 and 13-4-13.6 in water and DMSO, respectively. The tosylamide group in compounds 5-8 was deprotonated in the expected pH region and exhibited pK, values between 9.49 and 10.02 in water, but was considerably less acidic in DMSO (14.5 c pK, s 15.7). The behaviour of the amidinium cation of 5-8 in water and DMSO resembled that of 1-4. The measured pK, values are discussed and the solvent-induced pK, shifts are explained in terms of solvent and substituent effects. The observed pK, differences between the ammonium and the amidinium functions in 1-4 render these compounds suitable intermediates in an alternative synthesis of distamycin A.

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Basicity of 3-aminopropionamidine derivatives in water and dimethyl sulphoxide. Implication for a pivotal step in the synthesis of distamycin A analogues

Koppel

Leito

et al. 1996

J. Phys. Org. Chem.

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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

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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.

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ChemInform Abstract: Basicity, H‐Bonding, Tautomerism and Complex Formation of Imidic Acid Derivatives

Oszczapowicz

1992

ChemInform

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Basicity, H‐bonding, tautomerism and complex formation of imidic acid derivatives

Cited by 17 publications

References 97 publications

Basicity of 3-aminopropionamidine derivatives in water and dimethyl sulphoxide. Implication for a pivotal step in the synthesis of distamycin A analogues

Basicity of 3-aminopropionamidine derivatives in water and dimethyl sulphoxide. Implication for a pivotal step in the synthesis of distamycin A analogues

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

ChemInform Abstract: Basicity, H‐Bonding, Tautomerism and Complex Formation of Imidic Acid Derivatives

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