Theoretical and UV spectral study of isomeric 1-(quinolinyl)-β-carbolines conformations

On the basis of beta-carboline (1) and 1-(quinolin-2 '-yl)-beta-carboline (3) alpha-and t-band energies differences (Delta(alpha,t)) a equilibrium conformations of 1-(quinolin-4 '(5 '-8 ')-yl)-beta-carbolines (4-8) in solution have been estimated. Furthermore, as an example of model compounds 1-(alpha '-naphtyl)-beta-carboline (MC1) and 1-(beta '-naphtyl)-beta-carboline (MC2) and also 5 and 6 by molecular mechanics (mm+), semi-empirical (AM1) and none empirical (RHF/6-31G(d)) methods a computations of internal rotation of quinoline fragment around single bond have been performed. It was found that the greater bathochromic shift of the long-wavelength band maxima of 1, in the case of 3 (Delta lambda(max) = 39 nm) relatively to 6, 7 (Delta lambda(max) = 17 +/- 2 nm) and 4, 5, 8 (Delta lambda(max) = 9 +/- 1 nm) caused by coplanarity of the molecule 3. Also, from experimental and theoretical investigations a less dihedral angle between beta-carboline and quinoline nucleons for 6, and 7 than 4, 5 and 8 owing to steric and electronic interactions have been found. (c) 2006 Elsevier B.V. All rights reserved.