Ivan S. Alferiev

Bisphosphonates and Tetracycline: Experimental Models for Their Evaluation in Calcium-Related Disorders

AbstractPurpose. This work was aimed at synthesizing novel bisphosphonates (BPs) and examining them in comparison to clinically used BPs such as pamidronate and alendronate, and to tetracycline, in order to evaluate their potential as anticalcification and antiresorption agents. The correlation between the various models was examined in order to establish facile experimental models for pre-screening of potential compounds.nMethods. Nitrogen-containing heterocyclic, novel BPs such as 2-(3-methylimidazolio) ethylidene-l,l-bisphosphonic acid betaine (VS-5b), 2-(2-dimethylamino-4-pyrazinio)ethylidene-1,1 -bisphosphonic acid betaine (VS-6b), and 2-(2-α-pyridylethylthio) ethylidene-1,1-bisphosphonic acid (ISA-225), were synthesized and evaluated in comparison to clinically used BPs, in various experimental models of resorption and calcification.nResults. The physicochemical properties of the novel compounds are slightly different than the BPs in clinical use: the pKa values are lower, the affinity for hydroxyapatite is lower and the solubilities of the calcium salts are higher. The anticalcification potencies of the novel compounds were high and ranked as follows: alendronate = pamidronate > VS-6b = VS-5b = ISA-225 > tetracycline. The in vivo antiresorption activity of VS-5b and VS-6b in comparison to that of the clinically employed, pamidronate, was shown to be similar and higher, respectively.nConclusions. The anticalcification activity of the novel compounds as well as that of tetracycline was lower than that of alendronate. The antiresorption activity of VS-6b was similar to that of pamidronate. A good correlation between the different models was found, enabling the facile screening of novel compounds. The activities of tetracycline and EDTA highlight the distinct behavior of BPs as crystal poison”. In addition, tetracycline was found to be a potent anticalcification agent in the ectopic calcification model.

Elastomeric polyurethanes modified with geminal bisphosphonate groups

Three types of elastomeric segmented polyurethanes represented by a polyether-urethane, a polyurethane-urea, and a polycarbonate-urethane were introduced into a modified low-temperature variant of base-induced N-alkylation of urethane hard segments with an excess of 1,6-dibromohexane in N,N′-dimethylacetamide (DMAc), resulting in the modification of polymers with 0.08–0.26 mmol/g of pendant 6-bromohexyl groups. Either lithium diisopropylamide (LDA) or sodium hydride was used to initiate the reaction, although LDA was found to be more suitable for the bromoalkylation. Selected bromoalkylated polyurethanes of all three types were reacted with thiol-containing bisphosphonates, to yield the polymers modified with 0.08–0.12 mmol/g of geminal nonesterified covalently attached bisphosphonate groups. Two thiol-containing geminal bisphosphonates used in the modifications were prepared via reactions of nucleophilic addition to vinylidene-bisphosphonic acid. All three types of polyurethanes were found equally suitable for the modifications. The bisphosphonate-modified polyurethanes with nonmetallic cations on the bisphosphonate groups remain soluble in the solvents suitable for the dissolution of nonmodified polymers and can be processed into films by solvent casting. After the exchange of nonmetallic cations to sodium, the polymers become insoluble in any solvent, probably as a result of the intermolecular coordination of bisphosphonate groups with the metal cations.

Synthesis and preclinical pharmacology of 2-(2-aminopyrimidinio) ethylidene-1,1-bisphosphonic acid betaine (ISA-13-1)-a novel bisphosphonate.

AbstractPurpose. To validate our hypothesis that a bisphosphonate (BP) having a nitrogen-containing heterocyclic ring on the side chain, and with no hydroxyl on the geminal carbon would possess increased activity, and better oral bioavailability due to enhanced solubility of its calcium complexes/salts and weaker Ca chelating properties.nMethods. A novel BP, 2-(2-aminopyrimidinio)ethylidene-l,l-bisphosphonic acid betaine (ISA-13-1) was synthesized. The physicochemical properties and permeability were studied in vitro. The effects on macrophages, bone resorption (young growing rat model), and tumor-induced osteolysis (Walker carcinosarcoma) were studied in comparison to clinically used BPs.nResults. The solubility of the Ca salt of ISA-13-1 was higher, and the log βCa: BP stability constant and the affinity to hydroxyapatite were lower than those of alendronate and pamidronate. ISA-13-1 exhibited effects similar to those of alendronate on bone volume, on bone osteolysis, and on macrophages, following delivery by liposomes. ISA-13-1 was shown to have 1.5−1.7 times better oral absorption than the other BPs with no deleterious effects on the tight junctions of intestinal tissue.nConclusions. The similar potency to clinically used BPs, the increased oral absorption as well as the lack of effect on tissue tight junction of ISA-13-1 warrant its further consideration as a potential drug for bone diseases.

Activated polyurethane modified with latent thiol groups

A novel type of modified polyurethane with pendant acetylthio groups (as a latent form of thiol groups) has been proposed for the use in surface modifications with various biomolecules. The polymer was prepared via a modified variant of low-temperature bromoalkylation of urethane hard segments followed by the reaction of pendant bromoalkyl groups with thiolacetic acid in mild conditions. The extent of modification with acetylthio groups can be made as high as 0.45 mmol/g. After deprotection of acetylthio groups and reaction of the resulting thiol groups with an excess of Ellmans reagent, 0.1 nmol/cm(2) of thiol-reactive 3-carboxy-4-nitrophenyldithio groups were detected on the surface of films cast from the modified polymer. A sensitive fluorescent probe--dansyl-L-cysteine was used for the quantification of thiol-reactive groups bound to the surface. The acetylthio-modified polyurethane is sufficiently stable to withstand conditions typical for the high-temperature processing (molding, extrusion) of polyurethanes.

Synthesis of an azido spermidine equivalent

Abstract The synthesis and conversion of a new spermidine equivalent ( 2 ) to squalamine is reported. It is prepared in a practical manner, is stable to sodium borohydride reduction, is converted to spermidine under mild conditions, and is not prone to internal cyclization reactions.

High reactivity of alkyl sulfides towards epoxides under conditions of collagen fixation: a convenient approach to 2-amino-4-butyrolactones

Epoxy crosslinking agents have been investigated for use in the fabrication of bioprosthetic devices, such as heterograft heart valve prostheses. It has been generally assumed that epoxy crosslinking takes place via amino-epoxy reactions. The present study investigated the hypothesis that the reactions of methionine residues with epoxides also can occur in biomaterial crosslinking. A series of model reactions were studied in which a mono-epoxide was combined with individual alkyl sulfides. In the present studies epoxides rapidly alkylate aliphatic sulfides, including methionine derivatives, in buffered aqueous solutions at room temperature and pH close to neutral, forming sulfonium compounds, which are stable at pH 5-7 at temperatures up to 50 degrees C, except for cases in which methionine derivatives with non-protected carboxy groups are used. The rate of reaction remains practically unchanged within the range of pH from 5 to 12, whereas in strongly alkaline media the reverse reaction occurs. This discovery can provide a better understanding of processes occurring in the fixation of bioprosthetic tissues with polyepoxides. It can also develop into a site-specific method to label methionine residues in proteins. The carboxy group-containing sulfonium betaines derived from N-protected methionines undergo cyclization in unexpectedly mild conditions, which can be used as an efficient method for preparation of N-protected 2-amino-4-butyrolactones with sensitive protective groups.

AMPLIFIED FLUORESCENT MOLECULAR PROBES BASED ON 1,3,5,7-TETRASUBSTITUTED ADAMANTANE

Abstract A novel series of fluorescent labels containing multiple fluorescein moieties attached to a bridgeheadsubstituted adamantane has been synthesized. Molecules containing two, three or four fluorescein residues were prepared and their fluorescence was measured. The rigid adamantane core prevents fluorescein moieties from intramolecular collisions, thus precluding mutual fluorescence quenching. Proposed design allows building the molecular probes with amplified fluorescence signal by combining several fluorophores in a molecule.

Aldol-Type Cyclization of Bisacylphosphonates. A Unique Concerted Catalytic Effect of Diamines

Abstract Some bisacylphosphonates are biologically active in calcium related disorders, such as bone resorption and ectopic calcification.1 In the course of our studies directed towards the preparation of stable, pharmaceutically acceptable salts of bisacylphosphonates, we found that in the presence of N,N-dibenzylethylenediamine (benzathine), adipoylbisphosphonate (AdBP) underwent cyclization to 2-hydroxy-2-phosphonocyclopentanecarbonylphosphonic acid. Similarly, pimeloylbisphosphonate (PiBP) cyclized to 2-hydroxy-2-phosphonocyclohexanecarbonylphosphonic acid, although at a rate about 30 times slower than AdBP. Study of the catalytic effect of amines on the cyclization of PiBP revealed a striking dependence on the pH, the chain length of the diamine, and the amine used. Thus the following relative efficacy was observed for the different amines at pH 5: Me2N(CH2)2NH2 (120), H2N(CH2)2NH2 (100), H2N(CH2)3NH2 (4), H2N(CH2)4NH2 (1), PhCH2NHCH2CH2NHCH2Ph (0.1), Me2NCH2CH2NMe2 (0.02), MeNH2 (0.02). These data ...