TROPANE ALKALOIDS FROM ERYTHROXYLUM BEZERRAE

Erythroxylum bezerrae Plowman (Erythroxylaceae) is a genuine species of the Ceará state flora part of the “Caatinga”, the characteristic biome of the northeastern Brazil. The specific designation “bezerrae” was to honor Professor Prisco Bezerra the first curator of the herbarium of the Universidade Federal do Ceará. Stem barks (1.8 kg) from several specimens of E. bezerrae, harvested at the locality of “Serra-das-Almas”, Crateús-CE, were dried and milled, and then macerated with hexane (3x) for 48 h yielding the hexane extract (EbSB-H, 9.2 g). The mark was also macerated for 48 h (3x) in ethanol 96% to yield the ethanol extract (EbSB-E, 124.9 g). An aliquote of EbSB-E (46 g) was submitted to solid-liquid partitioning on with CHCl3, AcOEt and n-BuOH affording EbSBE-C (18.3 g), EbSBE-A (2.6 g), and EbSBE-B (2.4 g). TLC analysis revealed, after spraying with the Dragendorff reagent. positive reaction for EbSBE-C. An aliquote of EbSBE-C (10 g) was submitted to gravitational column chromatography over silica gel (50 g) by elution with CH2Cl2 & MeOH, in their pure forms, or in binary mixtures of increasing polarity, to afford eight compounds (1-8) with the tropane skeleton, the characteristic alkaloids of the genus Erythroxylum. Detailed analyses by one dimensional NMR (1H, 13C BB, 13C DEPT 135º), and two dimensional NMR (COSY, NOESY, HSQC and HMBC) lead to the characterization of six unknow tropane alkaloids (1-6): 6β-(benzoyloxy)-3α-(3,4,5-trimethoxycinnamoyloxy)-7β-hydroxy-tropane (1), 6β-(benzoyloxy)-7β-(4-hydroxy-3,5-dimethoxy-benzoyloxy)-3α-hydroxy-tropane (2), 6β-(benzoyloxy)-3α-(4-hydroxy-3,5-dimethoxybenzoyloxy)-7β-hydroxy-tropane (3), 6β-(4-hydroxy-3,5-dimethoxybenzoyloxy)-3α-(3,4,5-trimethoxycinnamoyloxy)-7β-hydroxy-tropane (4), 6β-(3,4,5-trimethoxybenzoyloxy)-3α-(3,4,5-trimethoxycinnamoyloxy)-tropane (5), and 6β-(benzoyloxy)-7β-(3,4,5-trimethoxy- benzoyloxy)-3α-hydroxy-tropane (6), and two other ones previously reported (7 & 8)1: 6β-(3,4,5-trimethoxybenzoyloxy)-3α-(E)-(3,4,5-trimethoxycinnamoyloxy)-7β-hydroxy-tropane (7) and 6β-(benzoyloxy)-3α-(E)-(3,4,5-trimethoxycinnamoyloxy)-7β-hydroxy-tropane (8). The final structures, including the relative stereochemistry, of 3-5 were further confirmed by X-ray chrystallography.