Vacuum chromatography

Method D TBA-F (26 mg, 0.1 mmol) is added to Me,SiSiMe, (0.2 g, 1.5 mmol) in HMPA (2 ml) and the solution is stirred for 5 min at room temperature. The solution is then added to the aldehyde and the mixture is stirred for 4-5 h. On completion of the reaction, HChMeOH (1 10, 1 ml) is added and the mixture is extracted with Et20 (3 x 35 ml). The extracts are washed with aqueous NH4C1 (sat. soln. 25 ml) and brine (25 ml), and concentrated under vacuum. Chromatography from silica gives the trimethylsilyl enol ether or, in the ease of the aryl aldehydes, the pinacol. 

Cyclohexyl 1-tetrahydropyranyl ether 3.4 To a solution of cyclohexanol 1 (2.0 g 20 mmol) in dry CH2CI2 (25 mL) containing K-10 clay (500 mg) was added, under stirring at 20°C, a solution of dihydro-4H-pyran 2 (2.52 g 30 mmol) in dry CH2CI2 over a period of 5 min. After 30 min the completion of the reaction was tested by TLC (Merck Kieselgel E, EtOAc hexane 1 3). The catalyst was removed by filtration and the solvent evaporated in vacuum. Chromatography of the residue (silica gel, hexane CHCl3 1 1) afforded 3.23 g of 3 (95%). 

For isolation of hydroxycoumarins the TE1 was subjected to liquid vacuum chromatography (LVC) with PE, CHC13, EtOAc and MeOH to yield the corresponding fractions [10]. No coumarins were found in the PE fraction. The CHCI3 fraction was chromatographed over a silica gel column with a dichloroethane (DCE) - MeOH gradient. A TLC study of the DCE fractions on silica gel yielded the coumarins esculetin (2), fraxetin (4), scoparone (6), isoscopoletin (7), scopoletin (8), fraxidin (9) and fraxinol (10). Identification of all coumarins was achieved by UV, IR, H NMR and mass spectra, and direct comparison with authentic samples. NOE experiments confirmed the structures of 9 and 10. 

Liquid Vacuum Chromatography Minimum Inhibition Amount Minimum Inhibitory Concentration Mass Spectrometry Not Active... 

Vacuum chromatography is simple, rapid, and convenient. Optimum sample loads are similar to flash chromatography. However, it is not unusual to use sample overload conditions to separate simple mixtures by stepwise gradient elution, or to simplify mixtures for further separation. Under these conditions the sample loads may reach 10 % (w/w), or even higher, of the bed mass. 

Fractions 8 and 9 from the initial flash vacuum chromatography were combined and vacuum flash chromatographed again on a reverse-phase column using methanol. Further purification of the first fraction by preparative layer chromatography on silica using acetone/hexane (1 1) afforded isomeridine (446). 

To a suspension of 1.31 g A-acetyl-D,L-alanine (10 mmol) in 10 mL acetic anhydride was added 3.2 mL diethyl acetylenedicarboxylate (20 mmol). The reaction mixture was maintained at 110°C for 2 h, cooled, and then evaporated under reduced pressure. The oily residue was dissolved in hot cyclohexane and left in the refrigerator overnight with crystal seeds. Diethyl 2,5-dimethyl pyrrole-3,4-dicarboxylate was isolated as white needles by filtration, in amount of 274 mg, in a yield of 11.4%. The filtrate was evaporated and chromatographed (dry column vacuum chromatography) using CH2CI2 and then CH2Cl2/EtOH (99 1 to 98 2) to afford 1.58 g 2-(2,5-dimethyl-3,4-diethoxycarbonyl)-pyrrolyl maleic acid diethyl ester as a yellowish oil, in a yield of 39%. 

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