Polimorfismo de alcamidas naturais da Aniba riparia (NEES) MEZ (LAURACEAE)

Abstract

Riparins are natural alkamides, which have been isolated from Aniba riparia and subsequently synthesized. The substitution of hydrogens by hydroxyl groups in the first aromatic ring distinguishes riparins II and III. Riparin I, II and III showed several potential therapeutic activity in preclinical studies, such as antidepressant, anxiolytic and anti-inflammatory effects. Given the direct influence of the crystalline structure on the physico-chemical properties, the importance of the characterization of these properties and the crystalline elucidation of a drug candidate molecule becomes evident. Therefore, this contribution has as main objective to elucidate the crystalline structures of riparins, besides conducting a thermal and physicochemical studies in order to identify possible polymorphs. This study also has the objective to evaluate the solubility of the compounds. To achieve the results, several techniques were used, such as: Raman and infrared spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), ultraviolet–visible spectrophotometry (UV/VIS), X-ray powder diffraction (XRPD) and single-crystal X-ray diffraction (SCXRD). The crystalline structures of riparins were determined. Despite riparin I has its structure elucidated and reported in the literature, it was possible to determine the crystalline structure of a polymorph, which presented a monoclinic crystalline system, one molecule per asymmetric unit and four molecules per unit cell. Riparin II also exhibited a monoclinic system, with two molecules per asymmetric unit and eight per unit cell, while riparin III, though also presented a monoclinic crystalline system, exhibited one molecule per asymmetric unit and two per unit cell. The structural and conformational characteristics of the three riparins lead to physical-chemical, thermal and spectroscopic differences. It was also possible to evaluate and discuss the polymorphism of riparin I and III.