Chromatography preparative TLC

A solution of 3 (1.0 g, 4 mmol) in CHCI3 (100 mL) was shaken with aqueous sodium dithiorete until the organic layer became coiortess. The glassy residue obtained after evaporation was dissolved in dk>xane TEA (1.1) (100 mL) by heating 12 h on a steam bath. Evaporation and chromatography (preparative TLC - PhH.MeOH 9 1) gave 0.6 g of 4 (89%), mp 77-7B.3 C. 

Soczewinski, E. and Wawrzynowicz, T., Preparative TLC, in Encyclopedia of Chromatography, Marcel Dekker, New York, 2001, pp. 660-662. 

There are several faetors affeeting the overall chromatography of both analytical and preparative TLC, and further details can be found elsewhere [44]. 

An aqueous extract of P. hysterophorus (collected in Puerto Rico) was partitioned into methylene chloride at pH 7, pH 10 and pH 2. Bioassays of the methylene chloride soluble fractions, using the bean second internode bioassay (13), showed that the highest activity was concentrated in the methylene chloride extract at pH 7. Extensive chromatographic purification (flash chromatography, medium pressure LC, preparative TLC) monitored by bioassay led to the isolation of the four sesquiter-... 

Additional details of planar chromatography—methods of descending and radial development, how to prepare TLC plates, tips on how to apply the sample, what to do if the spots are not visible—and the details of preparatory TLC, etc., are beyond our scope. 

Preparation of vinyl tellurides. To a mixture of NaH (1 mmol) (80% suspension in oil) and (phenyltelluromethyl)-phosphonate (1 mmol) in THF (5 mL) at reflux under Nj, aldehydes (1 mmol) were added dropwise. Following 3 h at reflux, the solution was cooled to room temperature. Then, saturated aqueous NH4CI was added and the mixture was extracted with diethyl ether. The organic extract was dried (MgS04) and evaporated to give vinyl tellurides, which were purified by column chromatography on silica gel with ethyl acetate/hexane (1 20) or by preparative TLC,... 

Typical procedure To a solntion of diaryl diteUnride (0.50 mmol) in dry MeCN (2 mL) nnder N2 was added dropwise SO2CI2 (0.081 g, 0.60 mmol) and the mixtnre was stirred at room temperature for 1 h. a-AUenoic acid (0.50 mmol) in dry MeCN (2 mL) was then added to above ArTeCl solntion with stirring. After the reaction was complete, the mixture was concentrated and the residne pnrified by flash chromatography or preparative TLC to afford )3-organotellurobutenolides. 

Cuts from the silica gel column were incorporated into artificial diets optimized for several economically-important agricultural pest insects, the pink bollworm Pectinophora gossypiella> the tobacco budworm Heliothis virescens> the corn earworm H. zea and the fall armyworm Spodoptera frugiperda. > Monitoring with this artificial diet bioassay, further column chromatography and preparative TLC on silica gel in diethylether-petrol yielded five... 

A mixture of 1 mmol of optically active sulfonium salt, 1 mmol of cyclic /J-oxo ester and 1.3 mmol of anhyd potassium carbonate is stirred in 10 mL of CH2C12 at r.t. for 2 d. After filtration of insoluble materials, the alkylated products are purified by preparative TLC (Merck, silica gel 60F254) and medium-pressure column chromatography. The ee is determined by H NMR analysis [Eu(hlc)3] or by HPLC (Oaicel Chiralcel CA-1. methanol). 

A soln of the acid from hydrolyzed dipeptide 20 (40 mg, 0.115 mmol) in DMF (lmL) was treated with bithiazole 19 (30 mg, 0.088 mmol), HOBt (12 mg, 0.088 mmol), EDC (17.8 mg, 0.093 mmol), and NaH-C03 (30 mg, 0.35 mmol) at 0°C, and the mixture was stirred at 25 °C for 50 h. Brine was added, and the mixture was extracted with EtOAc (5x5 mL). The extracts were washed with sat. aq NaHC03 and brine, dried (MgS04), and concentrated. Chromatography (silica gel, preparative TLC, CH2Cl2/MeCN 2 1 and MeCN/CH2Cl2/MeOH 3 6 0.2) gave the jV-Boc tetrapeptide methyl sulfide yield 50 mg (85%). This was methylated with Mel/MeOH in 97% yield and then deprotected in 99% yield to give tetrapeptide S (21). 

An aqueous suspension (50 mL) of 16-dehydroprogesterone 1 (100 mg) in a Pyr-ex flask was irradiated with fluorescent lamp (Philips, TLD 30W/55) under magnetic stirring at 24 °C for 10 days. EtOAc extraction and flash chromatography (silica gel, EtOAc-hexane 3 2) followed by preparative TLC gave 2 (20 mg) as a colorless oil. 

A mixture of the starting material (2 mmol) and 9% Yb(0Tf)3-Si02 (800 mg) was suspended in 2 mL of CH2CI2 and the solvent was removed in vacuo. After standing at either room temperature or at 40 °C, the product was extracted into ethyl acetate. Concentration and purification by silica gel column chromatography or preparative TLC gave the corresponding free amide. 

Purified the product by preparative TLC chromatography (ethyl acetate/hexane 1 9, silica gel) yield > 20%. 

The low yields in these syntheses make purification of the diazirines a difficult task. Preparative TLC was used extensively by Smith and Knowles and this can now be effectively replaced by HPLC or flash chromatography. 

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