New 1H-pyrazole-containing polyamine receptors able to complex L-glutamate in water at physiological pH values

The interaction of the pyrazole-containing macrocyclic receptors 3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1(27),11,14(28),24-tetraene 1 [L-1], 13,26-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111, 14] -octacosa-1(27),11,14(28),24-tetraene 2[L-2], 3,9,12,13,16,22,25,26-octaazatricyclo-[22.2.1.1(11,14)]-octacosa-1 (27),11,14(28),24-tetraene 3[L-3], 6,19-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1 (27),11,14(28),24-tetraene 4[L-4], 6,19-diphenethyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1 (27),11,14(28),24-tetraene 5[L-5], and 6,19-dioctyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.1(11,14)]-octacosa-1 (27),11,14(28),24-tetraene 6[L-6] with L-glutamate in aqueous solution has been studied by potentiometric techniques. The synthesis of receptors 3-6[L-3-L-6] is described for the first time. The potentiometric results show that 4[L-4] containing benzyl groups in the central nitrogens of the polyamine side chains is the receptor displaying the larger interaction at pH 7.4 (K-eff = 2.04 x 10(4)). The presence of phenethyl 5[L-5] or octyl groups 6[L-6] instead of benzyl groups 4[L-4] in the central nitrogens of the chains produces a drastic decrease in the stability [K-eff = 3.51 X 10(2) (5), K-eff = 3.64 x 10(2) (6)]. The studies show the relevance of the central polyaminic nitrogen in the interaction with glutamate. 1[L-1] and 2[L-2] with secondary nitrogens in this position present significantly larger interactions than 3[L-3], which lacks an amino group in the center of the chains. The NMR and modeling studies suggest the important contribution of hydrogen bonding and pi-cation interaction to adduct formation.