Column chromatography boronic acids

A flask was charged with 4-bromo-iodobenzene (0.079 mol), 4-methoxy-2-methyl-phenyl boronic acid (0.087 mol), palladium acetate (0.004 mol), and triphenyl phosphine (0.008 mol) and then treated with 200 ml acetone and 250 ml 2M NaHCO i. The mixture was refluxed at 65°C for 18 hours and was then treated with water and diethyl ether and the organic layer isolated. This layer was washed with 40 ml saturated sodium chloride solution and water, dried over MgSC>4, filtered, and concentrated. The residue was purified by column chromatography using silica gel with CH2C12/ hexane, 1 1, and then recrystallized in / , 7 3, respectively, and 16.4 g of product isolated. 

From the known, differential complexing between boronic acids and polyhydroxy compounds, it follows that carbohydrate mixtures may be separated by column-chromatographic methods that exploit the differences. Nucleoside and nucleotide boronates have been separated on columns of anion-exchange resins,90 and sugars and alditols have been shown to be differentially retained on such resins in the sulfonated phenylboronic acid form,64 but perhaps the best uses of column chromatography in this connection have incorporated the resolving powers of insoluble polymers to which boronic acid groups have been covalently bonded. Such insoluble forms of boronates have been synthesized either by substitution of polysaccharide derivatives, or by polymerization of suitable arylboronic acids. 

Other results involving liquid chromatography separations with imprinted metal oxides have been published in recent years. Norrlow et al. prepared surface imprinted silica gels functionalised with boronic acids that could form covalent linkages with riboses via boronate ester formation [43]. The gels were imprinted with templates containing two (nicotinamide adenine dinucleotide (NAD)) or four ribose units (bis-NAD 1, bis-NAD II). Columns were packed with the imprinted... 

Other cydic esters of boronic acids are used in those cases where they are crystalline, and purification by column chromatography is not required. 

A round-bottom flask containing a magnetic stir bar was charged with an aromatic boronic acid (1 mmol), methanol (2 mL), 25% aqueous ammonia (5 mmol), and CU2O (0.1 mmol, 15 mg). The flask was not sealed, and the mixture was allowed to stir under an atmosphere of air at RT until complete (as monitored by TLC). The mixture was then filtered, and the solvent of the filtrate was removed via rotary evaporation. The residue was purified by column chromatography on silica gel to provide the desired product. 

To an oven-dried resealable Schlenk tube was added Pdjidba), (13.9 mg, 0.015 mmol, 3.0 mol% Pd), 24 (24.6 mg, 0.060 mmol, 6.0 mol%), 2,6-dimethylphenyl boronic acid (300 mg, 2.0 mmol, 2.0 equiv), and powdered anhydrous K3PO4 (637 mg, 3.0 mmol, 3.0 equiv). The Schlenk tube was evacuated and refilled with argon three times. Dry toluene (2.0 mL) was then added to the reaction vessel and the mixture was stirred for 2 min at room temperature. After the addition of 2-bromo-l,3-dimethoxybenzene (217 mg, 1.0 mmol, 1.0 equiv), the reaction mixture was heated at 100 °C for 10 h. The reaction was then cooled, filtered through a pad of silica gel (washing with diethyl ether), and concentrated in vacuo. The crude product was purified by flash column chromatography (95 5 hexanes diethyl ether) to afford the pure product 55 (213 mg, 88%) as a white sohd (Eq. (5), Scheme 2.9). 

In a dried Schlenk tube, NHC-Pd catalyst (see Scheme 6.26) (0.0075 mmol), MS (240 mg), 4-flourophenyl-boronic acid (0.3 mmol), iV-Boc-a-(phenylsulfonyl) arylamine (0.15 mmol), KjCOj (0.9 mmol), and NEtj (0.225 mmol) are dissolved in 1,4-dioxane (2.0 ml) under inert atmosphere [32, 33]. The solution is stirred at 65 ° C and monitored by TLC. After the reaction is completed, the solvent is removed under reduced pressure and the residue is purified by flash column chromatography on silica gel eluted with ethyl acetate petroleum ether (1/20) to afford the title compound as a white solid (89% yield, 86% ee). M.p. = 118 —119°C H NMR (CDClj,... 

Optically active allylboronates bearing chiral auxiliary located at the boron atom found widespread applications in asymmetric synthesis. Enantiomerically enriched a-alkylidene-y-lactones and lactams can also be synthesized following such a synthetic approach. VUlieras et al. (41, 45] demonstrated the potential of chiral allylboronates derived from 2-phenyl-2,3-bomanediol, ephedrine, or norephedrine for this purpose. Chiral allylboronates 46a,b were obtained in a sequence of reactions involving transformation of achiral precursors 32 into the corresponding boronic acids 44 followed by their esterification with enantiomerically pure diol or 1,2-aminoalcohol 45 (Scheme 4.10). In the case of methyl-substituted derivatives 32b (R = Me), initial composition of E- and Z-isomers was transferred to the target allylboronates 46b. Importantly, the isomeric mixture was separated by means of the column chromatography. 

Fluorovinyl tosylate 40 was stereoselectively prepared from commercially available 2,2,2-trifluoroethyl tosylate in two steps. A pure ( )-40, isolated by column chromatography, was used in the Suzuki-Miyaura coupling with (4-methoxyphenyl)boronic acid, and ( )-(2-fluorovinyl)-4-methoxybenzene 41 was obtained stereoselectively [66] (Scheme 14). 

Tetrakis(4-iodophenyl)methane (50.0 mg, 60.7 pmol), Pd(PPh3)4 (14.0 mg, 12.1 pmol), and potassium carbonate (67.1 mg, 0.49 mmol) were dissolved in toluene/EtOH/H20 (8 mL, 20 5 3) in a sealed tube (10 mL). The corresponding boronic acid (58.5 mg, 0.480 mmol) was added and the reaction mixture was stirred for 72 h at 65 °C. The solvent was removed under reduced pressure, the solid was taken up in H2O (20 mL) and CH2CI2 (50 mL). The aqueous layer was extracted with CH2CI2 (2 x 50 mL), the organic layers were dried (MgS04), and the solvent was removed under reduced pressure. The product was isolated after column chromatography (3 x 20 cm, cyclohexane/EtOAc, 25 1) to yield a brown solid (23 mg, 0.07 mmol, 61%) mp 221 °C (dec.) Rf 0.40 (cyclohexane/EtOAc 25 1). 

Synthesis of 72 To a solution of quinoline 69 (0.2 mmol), boronic acid 70 (0.4 mmol), catalyst 71 (0.02 mmol), and NaHCOs (34 mg, 0.4 mmol) in CH2CI2 (2 mL) were added H2O (0.2 mL) and phenyl chloroformate (0.051 mL, 0.4 mmol) under an argon atmosphere at —78°C. Stirring was continued at the same temperature for 24 hours, and then the reaction mixture was diluted with chloroform washed with 1N NaOH, 1-N HCl, and water dried over MgS04 and concentrated at reduced pressure. Purihcation of the residue by column chromatography (silica gel, hexane/ethyl acetate, 10 1) afforded 72 (59%, 82% ee) as colorless crystals. 

Affinity chromatography Has a wide number of uses and can be applied to the isolation and purification of virtually all biomolecules. Specific applications include nucleic acid purification, protein purification from cell and tissues extracts, and antibody purification from blood serum. There are a number of matrices used for the construct, and some examples of these and their uses are as follows heparin columns to separate cholesterol lipoproteins, lectin columns to separate carbohydrate groups, and phenyl boronate columns to separate glycated haemoglobins. 

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