抄録
The reaction indices of π-electronic structures of the diuretics, xanthine, thiazide and triazine derivatives were calculated. An attempt was made to explain the potency of the diuretic action in the light of quantum chemistry. The reaction indices of xanthine derivatives, the first frontier superdelocalizability at the substituent occupying the 7-position of the highest occupied orbital and the second frontier superdelocalizability at the 3-position of the occupied orbital show fairly good correlations with the diuretic activities. The reaction index Sr″(E) is defined as: Sr″= fr1/λ1+fr2/λ2, where subscripts 1 and 2 stand for the highest occupied (or the lowest unoccupied) orbital, and the next highest occupied (or the next lowest unoccupied) orbital, fr is the electron density of the corresponding orbital and λi (i=1, 2) is the coefficient of energy in the i-th molecular orbital ε=α+λ1β, α and β being the standard Coulomb and resonance integrals. The diuretic activities of thiazide derivatives are in good parallel with the reaction indices, the π-electron densities at the 2-position, at the 4-position and at the 7-position. The potency of carbonic anhydrase inhibition of thiazide derivatives and sulphonamide derivatives however are fairly well parallel with the reaction indices, the π-electron density of the lowest unoccupied orbital and the formal charge at the position of amino group or at the position of nitrogen atom in sulphonamide. The diuretic activities of triazine derivatives show good correlation with the reaction indices, the first frontier superdelocalizability of the lowest unoccupied orbital at the 1-position (carbon atom) and the π-electron density of the unoccupied orbital at the 4-position (nitrogen atom). The positions of these diuretics, which are assumed to play the important role in diuretic action, are the positions in the group =N- ?? -N=. As the values of the Coulomb integral and the resonance integral of trill uoromethyl group (CF3) and the Coulomb integral of carbon atom adjacent to this pseudo-atom, α 2.0β, 1.0β and α-0.1β are employed.
