Effect of a β-cyclodextrin-epichlorohydrin copolymer on the solubility of cortexolone

Abstract

Cyclodextrins (CD) represent a class of natural cyclic oligosaccharides comprising 6(00, 7(1~), and 8(y) glucose residues linked by ct-l,4-glycoside bonds. The CD molecules have a hollow truncated cone configuration, with the intramolecular cavity (containing only CH groups and glycoside oxygens) being rather hydrophobic. This structures enables CD molecules to form inclusion complexes with various substances poorly soluble in water.Many drugs of steroidal nature are obtained by methods of microbiological transformation. However, the limited solubility of these compounds in water results in their transport to and from the cells proceeding at a slow rate. As is known, 13-CD additives to steroids in the course of transformation are capable of increasing the efficacy of bioconversion [ 1 ]. Unfortunately, the effect is limited by comparatively low solubility of 13-CD in water. For this reason, a promising way to intensification of the steroid bioconversion process consists in using well-soluble chemically modified 13-CD complexes.A possible method of obtaining such systems is the reaction of polycondensation between [3-CD and epichlorohydrin [2,3]. A special feature of the resulting copolymers, in addition to their good solubility in water, is the ability to form complexes with large host molecules (greater than those typically involved in complexes with unmodified 13-CD) [2].The purpose of this work was to study the possibility of intensifying the process of cortexolone bioconversion into hydrocortisone [4]. To solve this task, we have synthesized a water-soluble copolymer of 13-CD with epichlorohydrin (IB-CD-ECH) and studied its interactions with the steroids of interest. EXPERIMENTAL PART 601 li-Cyclodextrin-epichlorohydrin copolymer synthesis. The 13-CD-ECH copolymer was obtained by enzymatic hydrolysis of a water-soluble starch with the aid of cyclomaltodexrin glucanotransferase from Bacillus sp. 1070 [5]. The procedure was as follows. To 500 ml of a 10% starch solution in an 0.05 M Na-phosphate buffer (pH 7.2) containing 10 x 10 -3 M CaCI 3 and 1% isooctane was added 50 ml of the above cell culture with an activity of 71 U/ml. Upon hydrolysis (6 h at 55~ the precipitate representing a CD-isooctane inclusion complex was centrifuged at 5000 rpm for 20 min. The deposit was washed twice with water and isooctane was separated by distillation. The resulting CD was recrystallized from aqueous solution to obtain 16 g (32%) of IB-CD with a 98% purity (determined by HPLC [51).A water-soluble I3-CD-ECH copolymer was obtained by condensation of 13-CD with epichlorohydrin using a modified Wiedenhof method [6]. According to this, a solution of 13-CD (12.0 g, 0.0105 mole) in 150 ml of water was mixed with 40 ml of a 20% sodium hydroxide solution. To this mixture was gradually (over 45 min) added epichlorohydrin (10.0 g, 0.127 mole) at 60~ and the reaction mass was stirred for 24 h at 65~ Upon termination of the reaction, the mixture was cooled to 20~ acidified to pH 2 with 1 M I--I2SO4, and kept for 15 rain so as to provide ...