Probing the Stereointegrity of Troger's Base-A Dynamic Electrokinetic Chromatographic Study

摘要

Under acidic conditions the enantiomers of Troger's base 1 (2,8-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diaziozine) are subject to enantiomerization. During enantioselective dynamic electrokinetic chromatography using 10 mM hydroxypropyl-beta-cyclodextrin as the chiral mobile phase additive in 50 mM tris/phosphate buffer at pH 2.2, enantiomerization of Troger's base gives rise to characteristic elution profiles featuring plateau formation and peak broadening. Introduction of a permanent positive charge attributed to quaternization in the monobenzylated derivative of Troger's base 2 (5-benzyl-2,8-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazozinium bromide) decreases the enantiomerization barrier significantly. To determine the rate constatns of enantiomerization the experimental chromatograms were evaluated by a direct calculation method and by using the computer simulation program ChromWin. From temperature-dependent measurements the Eyring activation parameters for 1 and 2 were determined: 1: DELTAG~# (298 K) = 100.9 (+-) 0.5 kJ mol~(-1), DELTAH~# = 89.5 (+-) 2.0 kJ mol~(-1), DELTAS~# = -42 (+-) 10 JK~(-1) mol~(-1); 2: DELTAG~# (298 K) = 90.2 (+-) 0.5 kJ mol~(-1), DELTAH~# = 91.4 (+-) 2.0 kJ mol~(-1), DELTAS~# = 9.8 (+-) 10 JK~(-1) mol~(-1).