Flash chromatography gradients

The crude residue was purified by flash chromatography (gradient elution with 10-30 % EtOAc/hexanes). 179 mg (98 % yield). 

To a solution of 10 mg 1,4-dione (0.021 mmol) in 0.5 mL methanol were added 23 fiL benzylamine (0.21 mmol), 12 ixL acetic acid (0.21 mmol), and 30 mg 4A molecular sieves activated by flame drying under vacuum. The reaction mixture was stirred at 70°C for 1 h. Upon completion, the reaction mixture was diluted with 50 mL EtOAc and washed with 1 M HCl (2 X 20 mL). The organic layer was then dried over MgS04, and the solvents were removed in vacuo. The crude material was purified by flash chromatography (gradient elution hexanes/EtOAc, 19 1-3 1, v/v) to afford 10 mg 5-benzoyl-l,4-dibenzyl-2-propyl-3b,4,5,6,6a,7-hexahydro-lH-l,5-diaza-cyclopenta[a]pentalene-4-carboxylic acid methyl ester, in a yield of 90%. 

Purify of the crude residue by flash chromatography on silica gel using hexane ethyl acetate as eluent (gradient elution from 98 2 to 90 10). Pure 6-(dimethylphenylsilyl)-2,2-dimethyl-4-(2-phenylethyl)-5-hexyn-3-one (33) (0.141 g, 65%) as a clear oil. Characterize the product by 1H NMR, IR, MS spectroscopy, and elemental analysis. 

As stated above, the utility of silica based stationary phases does not limit its use to organic mobile phases. For many years it has been commonplace in flash chromatography to use aqueous solvents to elute analytes from silica based media. Isocratic elution with mixtures of butanol, acetic acid and water is standard protocol for the separation of amino acids and a carefully prepared combination of methanol, chloroform and water is useful for general organic compounds. Peptides are also readily purified by gradient elution on normal phase silica, moving from acetonitrile to aqueous mobile phase 3,2l This technique is particularly useful for extremely hydrophilic peptides that are not strongly retained on reversed phase media. 

A solution of trichloroacetimidate 2-azido-3-0-benzyl-4,6-0-benzylidene-2-deoxy-n-glucopyranoside (3.217mmol) and l-D-l,2-0-(r.-l,7,7-trimethy][2.2.1 -bicyc]ohept-2-ylidene)-3,4-0-(l,l,3,3-tetraisopropyldisiloxanyl)-myo-inositol (4.507mmol) in 50 ml diethyl ether at —20°C was treated with 29 ml trimethylsilyl trifluromethanesulfonate, then gradually warmed over 5 hours to ambient temperature. The mixture was then quenched with 0.5 ml triethylamine and concentrated. The residue was purified by flash chromatography using a hexane/EtOAc gradient of 95 5-75 25 and the a(l-6) product isolated in 55% yield as a white solid. 

The residue was purified by flash chromatography with using EtOAc/hexane (0-100% gradient) and the product isolated in 85.2% yield as a white foam. 

Methyl-4-nitroanisole (29.1 mmol) dissolved in 46 ml apiece glacial acetic acid and acetic anhydride at 0°C was treated dropwise with 6.9 ml 18 M sulfuric acid and Cr03 (80.8 mmol) portionwise over 60 minutes. The mixture was stirred an additional 15 minutes, then poured over ice, and a precipitate isolated. The solid was washed with cool water, then purified by flash chromatography with a solvent gradient of 15-50% EtOAc/hexanes, and the product isolated in 24% yield as a white solid. 

The product from Step 3 (1.7 g) was added to a suspension of NaH in 50 ml DMF, stirred 15 minutes, the product from Step 6 (2.65 g) added, and the mixture stirred overnight. The mixture was diluted with 125 ml 10% HCl, extracted with EtOAc, purified by flash chromatography with EtOAc/CH2Cl2, a gradient elution of 1-4% EtOAc, and the product isolated. H-NMR data supplied. 

The product from Step 7 (0.96 g) was dissolved in 8 ml THE, 1.62 ml 1 M NBU4F in THF added, and stirred 4.5 hours. The mixture was extracted with 75 ml EtOAc and concentrated. The mixture was purified by flash chromatography using, EtOAc/chloroform with a gradient of 5 95 to 10 90 and the product isolated as a white solid. H-NMR data supplied. 

The product from Step 1 was dissolved in 150 ml THE, cooled to —20°C, 2M borane dimethylsulfide (110 mmol) dissolved in THE added, and the mixture refluxed 3 hours. The mixture was re-cooled to —20°C, 72 ml methyl alcohol added and stirred one hour at ambient temperature. Thereafter, 16.4 ml 1M HCl in diethyl ether was added, the solution concentrated, and the residue partitioned between CH2Cl2/THF/water, 3 1 1. The pH was adjusted to 10 with NaHC03, the aqueous layer saturated with NaCl, and extracted with CH2CI2/THF, 3 1. The combined organic layers were dried, concentrated, and purified by flash chromatography on silica gel using chloroform with a methyl alcohol gradient of 3-10%. The material was further purified by crystallization in EtOAc and the product isolated. 

The product from Step 4 (33 g) was dissolved in 800 ml ethyl alcohol containing 0.2 ml concentrated H2SO4 and refluxed 2 hours. It was cooled to 0°C, treated with 200 ml methyl alcohol saturated with ammonia, stirred 4 hours and concentrated. The residue was purified by flash chromatography using silica gel with a methyl alcohol gradient of methyl alcohol/CH2Cl2, 2%, 5%,10% 1, and 5g of product isolated. H-NMR and MS data supplied. 

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