Josef Pitha

Hydroxypropyl-β-cyclodextrin: preparation and characterization; effects on solubility of drugs

Abstract Conditions for condensation of β-cyclodextrin with propylene oxide were found which give preparations of hydroxypropyl-β-cyclodextrin with a narrow and symmetrical distribution of the degree of substitution. Furthermore, methods for purification of hydroxypropyl-β-cyclodextrins from the contaminating oligopropylene glycols were developed. Preparations of hydroxypropyl-β-cyclodextrin with low degrees of substitution (

Drug solubilizers to aid pharmacologists: Amorphous cyclodextrin derivatives

Conversion of crystalline alpha-, beta-, or gamma-cyclodextrins into amorphous mixtures of water soluble derivatives yields non-toxic solubilizers which dissolve drugs through the formation of inclusion complexes. From these types of compounds 2-hydroxypropyl ethers of cyclodextrins have presently been investigated and the ranges for the safe use in working with (a) receptor binding assays on membrane preparations, (b) cells in vitro, and (c) parenteral use in mice were established for these compounds. The drugs which were investigated were dissolved in amounts linearly proportionate to the concentration of the solubilizers used and did not precipitate upon dilution by aqueous media. These solubilizers may considerably facilitate pharmacological evaluation of new, water insoluble potential drugs.

Pharmaceutical evaluation of hydroxyalkyl ethers of β-cyclodextrins

Abstract Hydroxyalkylated β-cyclodextrins (HA-β-CyDs), 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD), and hydroxyethyl-β-cyclodextrin (HE-β-CyD), were prepared and their physicochemical and biological properties and solubilizing abilities were studied and compared with those of parent β-cyclodextrin (β-CyD). HA-β-CyDs had much higher aqueous solubility ( > 50 w/v%) and were less hygroscopic than the parent β-CyD. Their surface activities were between those of β CyD and alkylated-β-cyclodextrins and were increased proportionately to their average degrees of substitution. The hemolytic activity (human erythrocytes) and local irritancy (rabbit muscle) of these compounds, and particularly of HE-β-CyD, were considerably less than those of natural cyclodextrin or dimethyl-β-cyclodextrin (DM-β-CyD). In contrast to surface activity, the hemolytic activity of HA-β-CyD decreased with the degree of substitution; possibly the difference in their ability to dissolve membrane components may be the reason. HA-β-CyDs were found to be powerful solubilizers of several drugs and no crystalline complexes were precipitated at high concentrations of solubilizer, a phenomenon which is often observed when β-CyD is used. HP-β-CyDs were somewhat better solubilizers than HE-β-CyDs and the preparations with the lower degrees of substitution were again better than those with the higher ones. The above data suggest that HA-β-CyDs are safer and more effective solubilizers for poorly water-soluble drugs than the parent cyclodextrin.

(S)-2-Hydroxyprophyl-β-cyclodextrin, a new chiral stationary phase for reversed-phase liquid chromatography

(S)-2- and (R,S)-2-hydroxypropyl-beta-cyclodextrin have been bonded to silica gel and evaluated as stationary phases for reversed-phase liquid chromatography. Stationary phases also were prepared on two silicas having different pore sizes and surface areas. Dissimilarities were observed in enantiomeric selectivities between these columns and also between these and the native beta-cyclodextrin columns. With the exception of compounds 5 and 10, all other racemates reported here which have been successfully resolved on the new phases are enantiomers which have not been previously reported as separated on the beta-cyclodextrin stationary phase. In some cases, there were also differences in enantioselectivities observed between the (S)- and the (R,S)-hydroxypropyl-beta-cyclodextrin phases on the same silica. The results are discussed in terms of the retention mechanism and compared to results reported earlier for beta-cyclodextrin columns.

Severe hypervitaminosis A in siblings: Evidence of variable tolerance to retinol intake

A 2-year-old boy had signs and symptoms of chronic hypervitaminosis A. A course of increasing severity led to eventual death. A younger brother later had similar clinical features. Chicken liver spread containing up to 420 IU/g vitamin A was the likely source of intoxication. Markedly elevated circulating retinyl ester levels have persisted in the surviving sibling for 3 subsequent years despite severe restriction of vitamin A intake. A therapeutic trial of the carbohydrate-derived complexing agent 2-hydroxypropyl-beta-cyclodextrin was initiated. Circulating retinyl esters transiently increased during the infusion (from 407 to 4791 micrograms/dL), and urinary total vitamin A excretion, undetectable before infusion, increased to 23 micrograms/dL after infusion. The frequency of hypervitaminotic episodes has decreased somewhat in the 2 years since the infusion, probably related to dietary vitamin A restriction. The occurrence of this syndrome in two brothers, while a sister ingesting the same diet remains completely healthy, suggests an inherited variance in tolerance to vitamin A intake.

Effects of ethanol on formation of inclusion complexes of hydroxypropylcyclodextrins with testosterone or with methyl orange

Gradual additions of ethanol decreased and eventually abolished the formation of inclusion complexes of testosterone with hydroxypropylcyclodextrins in aqueous solutions. With hydroxypropyl-β-cyclodextrin this occured through two mechanisms. At low concentrations of ethanol (< 30%), the solvent primarily acted as a competing guest compound; at higher concentrations the dissociation primarily occurred through non-specific solvent effects. With hydroxypropyl-γ-cyclodextrin only the dissociation through nonspecific solvent effects was observed. Surprisingly, when ethanolic solutions containing fully dissociated complexes were evaporated, the solid residues had properties characteristic of complexed species, i.e., they showed the rapid and complete dissolution characteristic of complexes prepared by freeze drying of aqueous solutions. That inclusion complexes were formed during the final stages of evaporation of ethanolic solution of components was confirmed by measurements of circular dichroic spectra of a methyl orange: hydroxypropyl-β-cyclodextrin combination. In this combination the spectra of included species were highly characteristic and were recorded both in aqueous solutions and in solid state after the evaporation of ethanolic solutions but not in concentrated ethanolic solutions.

Distribution of substituents in 2-hydroxypropyl ethers of cyclomaltoheptaose

The distribution of substituents in 2-hydroxypropyl ethers of cyclomaltoheptaose, prepared by alkylation of the carbohydrate with propylene oxide in aqueous sodium hydroxide, was investigated. The samples were fully methylated and hydrolyzed, and the resulting mixture of alkylated sugars analyzed as their alditol acetates by g.l.c.-m.s. High and low alkali concentration favored the formation of 2-hydroxypropyl ethers at O-6 and O-2, respectively; substitution at O-2 increased the reactivity of O-3. The overall extent of substitution had only secondary effects on the relative reactivities of O-6 and O-2, and the 2-hydroxypropyl groups remained unevenly distributed among the glucose residues, even when the overall substitution increased. Only small proportions of the isomeric 2-(1-hydroxypropyl) ethers were formed, and the percentage of oligopropylene glycol ethers was also low.

Characterization of a novel and potent 5-hydroxytryptamine1A receptor antagonist

A series of pindolol derivatives (n = 7) was analyzed in radioligand binding, biochemical and behavioral studies. Three of these drugs (Compounds A, B, and C) are extremely potent (i.e., Ki values less than 1.0 nM) at 5-hydroxytryptamine1A (5-HT1A) sites labeled by [3H] 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT). Moreover, these drugs are selective in that they are approximately an order of magnitude less potent at beta-adrenergic receptors labeled by 3H-dihydroalprenolol (DHA). Compound A (N1-(bromoacetyl)-N8-[3-(4-indolyloxy)-2-hydroxypropyl]-(Z)-1,8-di amino-p- methane) is also significantly less potent at 10 other neurotransmitter receptor sites analyzed. In addition, Compound A (10(-10) M to 10(-3) M) has no effect on baseline forskolin-stimulated adenylate cycalse activity in rat hippocampus. By contrast, nanomolar concentrations of the drug significantly (p less than 0.01) reverse 8-OH-DPAT-induced inhibition of forskolin-stimulated activity. In behavioral studies. Compound A (0.5 mg/kg) alone has no effect on baseline measures of reciprocal forepaw treading in the rat. Pretreatment with Compound A, however, significantly (p less than 0.05) inhibits the reciprocal forepaw treading induced by 8-OH-DPAT. These data suggest that Compound A is a potent and selective antagonist of 5-HT1A receptors in the CNS.

Testosterone in a Cyclodextrin-Containing Formulation: Behavioral and Physiological Effects of Episode-like Pulses in Rats

Testosterone, administered in the form of an inclusion complex with 2-hydroxypropyl-β-cyclodextrin by subcutaneous injection, enters the circulation in a manner markedly similar to the natural episodic release by the testes. The effects of a regimen of once-a-day administration of complexed testosterone to adult (castrated or intact) rats and to senescent (intact) rats were investigated. Although this procedure left the castrated animals with concentrations of circulatory hormone far below physiological levels for much of the day, a significant improvement in androgen-sensitive behavior and physiology was obtained. Furthermore, the testosterone effects were more pronounced when high doses were used periodically rather than when the same total amount of testosterone was equally divided among doses. The same supplementation to intact rats intensified androgen-sensitive behavior and physiology over normal levels. In senescent rats uniform pulses of the testosterone complex also improved behavior and physiology. Specifically, spermatogenesis was stimulated and, notably, the treatment increased muscle weight without substantial enlargement of the prostate. Since the testosterone–cyclodextrin complex also can be effectively administered as a sublingual tablet, the data suggest that similar regimens may be recommended for elderly men suffering from decreases in muscle mass.

Distribution of substituents in O-(2-hydroxypropyl) derivatives of cyclomalto-oligosaccharides (cyclodextrins): influence of increasing substitution, of the base used in the preparation, and of macrocyclic size

Samples of O-(2-hydroxypropyl)derivatives of cyclomaltoheptaose (beta-cyclodextrin) with increasing substitution were prepared by withdrawing aliquots at different times from a reaction mixture containing cyclomaltoheptaose and an excess of (S)-propylene oxide in 0.39 M aqueous sodium hydroxide. The distributions of substituents between the different molecules and between the different alpha-D-glucopyranosyl residues in these samples were determined by mass spectrometry and methylation analysis, respectively. The solubilities of the samples and their association constants with phenolphthalein were also determined. The relative reactivities at O-2 and O-3 versus O-6, calculated using Spurlins equations, decreased with increasing degree of substitution, probably because of steric hindrance. No significant differences were observed when different strong bases were used as promoters of the hydroxypropylation of cyclomaltoheptaose. The hydroxypropylation of cyclomaltohexaose (alpha-cyclodextrin) and cyclomalto-octaose (gamma-cyclodextrin) was briefly investigated.