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Highly Stable Self‐Association of 5‐(Guanidiniocarbonyl)‐1 H ‐pyrrole‐2‐carboxylate in DMSO – The Importance of Electrostatic Interactions
Author(s) -
Schmuck Carsten
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199909)1999:9<2397::aid-ejoc2397>3.0.co;2-3
Subject(s) - chemistry , carboxylate , dimer , pyrrole , protonation , moiety , titration , medicinal chemistry , hydrogen bond , proton nmr , stereochemistry , polymer chemistry , molecule , inorganic chemistry , organic chemistry , ion
The zwitterionic compound 5‐(guanidiniocarbonyl)‐1 H ‐pyrrole‐2‐carboxylate ( 1 ) self‐assembles to form dimers, which are completely stable in DMSO even at 170 °C or at concentrations of 0.001 m M . This high stability stems from a combination of multiple weak interactions. NMR titrations of 1 H ‐pyrrole‐2‐carboxylate ( 5 ) with (1 H ‐pyrrole‐2‐carbonyl)guanidinium ( 6 ) and [5‐(methoxycarbonyl)‐1 H ‐pyrrole‐2‐carbonyl]guanidinium ( 8 ) led to binding constants of K ≈ 10 6 mol –1 in DMSO and K ≈ 10 3 mol –1 in 40% water/DMSO for carboxylate binding by the 2‐(guanidiniocarbonyl)pyrrole moiety. The stability constant for the dimer 1 2 in DMSO could therefore be estimated as K ≈ 10 12 mol –1 . In solution, the self‐association process of 1 can be completely disrupted by protonation of the carboxylate group. In the solid state, however, the hydrochloride salt 1 + also exists as a similar but only very weakly hydrogen‐bonded dimer.