Jennings, WB,McCarthy, NJP,Kelly, P,Malone, JF;

2009

September

Organic & Biomolecular Chemistry

Topically resolved intramolecular CH-pi interactions in phenylalanine derivatives

Validated

()

FACE AROMATIC INTERACTIONS DOUBLE-MUTANT CYCLES MOLECULAR RECOGNITION BENZENE DIMER CONFORMATIONAL-ANALYSIS ARENE INTERACTIONS BINDING COMPLEXATION CHEMISTRY BALANCE

7

5156

5162

NMR spectra of imines and nitrones derived from benzophenone and phenylalanine or tyrosine show clear evidence of an aromatic edge-to-face interaction in solution. At low temperatures the two ortho protons of the edge interacting phenyl ring become topically resolved with the ortho proton NMR signal involved in the CH-pi interactions shifted well upfield (delta 5.4-5.8 at -88 degrees C) of the other ortho signal. Introduction of a para substituent into the phenylalanine ring has a modest effect on the upfield shift. The edge-to-face arrangement also manifests in the X-ray crystal structures of two of these compounds. Barriers to rotation around the syn phenyl-imino bond are also reported (10.5-11.1 kcal mol(-1)).

DOI 10.1039/b916021n