Wydział Chemii

Alexander F. Pozharskii

Valery A. Ozeryanskii

Ekaterina A. Filatova

Olga V. Dyablo

Olga G. Pogosova

Gennady S. Borodkin

Aleksander Filarowski

Dmitriy V. Steglenko

2019

Journal of Organic Chemistry

84

726-737

10.1021/acs.joc.8b02562

Naukowa

Angielski

Artykuł

9-Dimethylaminobenzo[g]indoles 3–6 and 1-dimethylamino-8-(pyrrolyl-1)naphthalene 7 were examined as possible models for establishing the ability of the pyrrole nitrogen atom to participate in [NHN]⁺ hydrogen bonding as a proton acceptor. Indoles 3–5 (to a lesser extent 6) form rather stable tetrafluoroborates, with the proton mostly located on the NMe₂ group but simultaneously engaged in the formation of a charged intramolecular [NHN]⁺ hydrogen bond (IHB) with the pyrrole N atom. The theoretically estimated energies of IHB in salts 3H⁺BF₄^––6H⁺BF₄^– vary between 7.0–10.7 and 6.2–7.0 kcal mol^–1 in vapor and MeCN, respectively. The pyrrole N atom undergoes a perceptible pyramidalization but still remains involved in the 6π-electron aromatic system, suggesting that the hydrogen bonding in salts 3H⁺BF₄^––6H⁺BF₄^– represents a previously unknown mixed NH···N(n,π) interaction. Despite the favorable orientation of the N–H bond and the pyrrole ring in salt 7H⁺BF₄^–, no signs of NH···N(n) bonding in it were noticed, and the existing interaction was classified as pure NH···N(π). The results obtained may be useful in studies of secondary protein structures, especially those α-helix sections which contain tryptophan residues.

https://doi.org/10.1021/acs.joc.8b02562

https://www.acs.org/content/acs/en.html