A QSAR analysis to explain the analgesic properties of Aconitum alkaloids

Aconitum roots are traditionally prescribed for the management of different types of painful affections in Asiatic countries. A quantitative structure-activity relationship (QSAR) analysis was performed to study the effect of chemical substitutes in the analgesic potency of alkaloids available in Chinese Aconitum roots. Using the CAChe program package for biomolecules, molecular modelling was performed in 12 alkaloids previously tested in a model of acetic acid-induced writhing in rats. The ED50 (mumol/kg) was used as the activity parameter. Structural parameters were compared between alkaloids with an aroyl/aroyloxy group at R-14 and alkaloids with the aroyloxy group at R-4. Single linear regression analyses were performed in order to find the parameters explaining activity. Alkaloids with an aroyl/aroyloxy group at R-14 exhibited the highest potency (significantly less ED50). The stability parameters were different between groups, e.g. total energy was -8.0 +/- 0.4 in the potent analgesic alkaloids and -6.7 +/- 0.3 in the weak analgesic alkaloids (P = 0.001). The reactivity index of C2', C3' and C5' of the aromatic ring was also different between groups, e.g. the reactivity index of C5' was 40.8 +/- 0.6 in potent analgesic alkaloids and 48.1 +/- 0.6 in weaker analgesic alkaloids (P < 0.001). Several structural parameters explained analgesic activity of alkaloids, being the reactivity index of C5' on the aromatic group the most important factor (r = 0.89; P < 0.001).