Condensation In Aqueous Media Research Articles

ChemInform Abstract: Preparation and Modification of Nucleic Acids by Condensation in Aqueous Solution

This review article describes preparation and modification of oligonucleotides by condensation in aqueous solution. Nucleotides and oligonucleotides are generally soluble in water, but not in organic solvents. Reactions in aqueous solution are therefore indispensable. Condensation in aqueous media is thermodynamically unfavorable. Several methods have been devised to overcome this problem. Large amount of water soluble condensing agents such as EDC or cyanogen bromide are employed for the condensation of oligonucleotides. Use of imidazole-activated nucleotides is an another approach for the preparation and the modification of oligonucleotides. The control of pH of the reaction media is necessary to accomplish the efficient and regioselective condensation. Metal ions or polynucleotide template, wihch organize the substrate nucleotides by complex formation promote the target condensation.

Amberlite IRA-400 (OH−) as a Catalyst in the Preparation of 4H-Benzo[b]pyrans in Aqueous Media

A quaternary ammonium hydroxide–type of anion exchange resin (Amberlite IRA-400) was found to be an effective and reusable catalyst for the synthesis of various 4H-benzo[b]pyran derivatives via a one-pot, three-component condensation in aqueous media. Short reaction time, easy and quick isolation of the products, environmentally friendly procedure, excellent chemoselectivity, and excellent yields are the main advantages of this procedure.

Tetra-methyl ammonium hydroxide: An efficient and versatile catalyst for the one-pot synthesis of tetrahydrobenzo[b]pyran derivatives in aqueous media

Tetra-methyl ammonium hydroxide has been used as a mild, efficient, neutral and cheap catalyst for the synthesis of various 4H-benzo[b]pyran derivatives via a one-pot three-component condensation in aqueous media. This method offers the advantages of proceeding, neutral and mild conditions, giving high to excellent yields of the products and simple work-up.

Uncatalysed Knoevenagel condensation in aqueous medium at room temperature

Knoevenagel condensation of various aromatic and heteroaromatic aldehydes with active methylene compounds like malononitrile, ethyl cyanoacetamide, ethyl cyanoacetate, barbituric acids, Meldrum’s acid, dimedone and pyrazolone proceeds smoothly with stirring in an aqueous medium. The reactions occur at room temperature giving excellent yields of the products. The work-up procedure is very simple and the products do not require further purification.

The polycondensation of lithium 11-bromoundecanoate in aqueous media

To obtain a biodegradable plastic, polycondensation, the substitution of bromine by carboxylate was carried out on lithium 11–bromoundecanoate. Using water as a solvent, the formation of a double bond was detected between 70 and 100°C, yielding a good quantity of polymer. Water is recommended as the best solvent for the reaction. Thermodynamic investigations were carried out by using ethylene glycol and water. The reaction is believed to proceed according to the SN2 mechanism. The ΔH and ΔG values for condensation in ethylene glycol were slightly higher than for those in water, but the reaction rate in water at 70°C was 7 times greater than that in ethylene glycol. The enhancement of dissociation accounts for the advantageous condensation in aqueous media. Furthermore, ΔS shows negative values and ΔG shows positive values, meaning that the reaction should proceed exothermically and not spontaneously. Experiments to condense 11–bromoundecanoate in aqueous media were carried out for ten days in a water bath, kept at 70°C, using 25 mL of 0.05M 11–bromoundecanoate. The degree of polymerization for the resulting polymer was found to be 23 by the end group assay for both bromine and carboxylate. Neither a melting point nor glass transition point for the product were observed. The polymer formed decomposes at 300°C and instantly disperses. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 130–134, 2003

Investigations on transition state geometry of the aldol condensation in aqueous medium

In aqueous medium, base-induced aldol condensations of keto aldehyde 1 show high anti-selectivity independent of metal ion and water content of the solvent. The acid-induced aldol condensations affords syn-aldol products in variable selectivity depending upon acid strength and water content of the medium.

水溶液中の縮合反応‐核酸の合成および修飾への応用

This review article describes preparation and modification of oligonucleotides by condensation in aqueous solution. Nucleotides and oligonucleotides are generally soluble in water, but not in organic solvents. Reactions in aqueous solution are therefore indispensable. Condensation in aqueous media is thermodynamically unfavorable. Several methods have been devised to overcome this problem. Large amount of water soluble condensing agents such as EDC or cyanogen bromide are employed for the condensation of oligonucleotides. Use of imidazole-activated nucleotides is an another approach for the preparation and the modification of oligonucleotides. The control of pH of the reaction media is necessary to accomplish the efficient and regioselective condensation. Metal ions or polynucleotide template, wihch organize the substrate nucleotides by complex formation promote the target condensation.