The present doctoral dissertation deals with the fermentation of leaves of Digitalis lanata Ehrh. (woolly foxglove) causing the enzymatic transformation of lanatoside A, B and C (LA, LB and LC) into the secondary glycosides digitoxin (Dx), gitoxin (Gx) and digoxin (Dgx), the extraction of the secondary glycosides by percolation using the aqueous solutions of methanol and ethanol (10-50 % v/v), the purification of the percolates, the preparation of dry extracts of secondary glycosides using chloroform or trichlorethylene and the isolation of highly pure Dgx (>96 %) from the solution of the dry extracts by fractional dissolution employing either the batch liquid-liquid extraction or continuous countercurrent liquid-liquid extraction in a Karr’s extraction reciprocating plate column. Ground dried leaves cultivated of Digitalis lanata Ehrh. were used. The main goal was to develop the process for obtaining Dgx from the leaves of Digitalis lanata Ehrh.
At first, the optimal operating conditi...ons of the fermentation of leaves of Digitalis lanata Ehrh. under anaerobic conditions at 37 oC were determined to be as following: the mean size of plant particles of 7 mm and the water-to-plant material 1:2 g/cm3. Then, the optimal operating conditions of Dgx extraction from the fermented plant material by percolation ensuring the Dgx extraction degree higher than 95 % were found to be as follows: the mean size of plant particles of 7 mm, the depth of the plant material in the extractor of 30 cm, the 10 % vol. ethanol solution as the extracting solvent and the percolate flow rate of 4 dm3/h (i.e. the residence time of 4 h). Also the optimal conditions of purification of the liquid extract using chloroform or trichlorethylene. The obtained liquid extracts were evaporated under vacuum, treated by MgO, filtrated under vacuum and evaporated under vacuum (60 oC). The obtained dry extract contained about 80 % of the secondary glycosides. It was treated with a mixture of acetone and water (7:1 to 10:1 vol.) under reflux to get the Dgx product of high purity (>96 %). Further purification of
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Dgx was conducted by the batch and continuous processes. The first process was carried out using separating funnels (15 funnels for the light phase and 15 funnels for the heavy phase) and the extraction system EtOH:H2O:CHCl3:THE = 35:15:20:30 vol., having the saturated phases, at the concentration of secondary glycosides dissolved in the light phase of 15 g/dm3 and the volumetric ratio of light-to-heavy phase 1:1.1. The light phase was evaporated until the third of the initial volume. The Dgx crystals were separated by filtration under vacuum and dried. The Dgx yield was 98 %. The purification of Dgx was also carried out in the Karr’s extraction reciprocating plate column with countercurrent flows of the phases. The highest Dgx extraction degree (> 99 %) in the light phase was achieved when the solution of secondary glycosides (45 g/dm3 in the heavy phase) was fed in the middle of the column (4 h high) using the solvent system EtOH:H2O-CHCl3:THE = 35: 15:20: 30 vol. at the volumetric ratio of light-to-heavy phase 1:1.1, the spacing between the perforated plates 2.5 cm, the stroke 2 cm and the frequency 125 min-1. The Dgx product of high purity (99 %) was obtained, containing 98.6-100.2 % Dgx.
