Efficient modulation of hydrogen-bonding interactions by remote substituents

[GRAPHICS] A series of tetralactam macrocycles having different substituents were prepared, and their binding affinities for an adipamide guest were investigated in CDCl(3) by (1)H NMR titrations. The association constants strongly depend on the substituents, varying up to DeltaDeltaG = 3.4 kcal/mol; electron-donating substituents (OMe, NMe(2)) decrease the binding affinity, while electron-withdrawing groups (Cl, NO(2)) increase it. These large substituent effects have been rationalized by secondary repulsions and partial perturbations of intramolecular hydrogen bonds.