Flash chromatography column isolation

Haliclonacyclamine E (13) and arenosclerins A (14), B (15), and C (16) have been isolated from the marine sponge Arenosclera brasiliensis, endemic in Brazil. Crude extracts of this sponge displayed potent cytotoxic and antibiotic activities, and were subjected to fractionation by sihca-gel flash chromatography, medium pressure chromatography on a SiOH cyanopropyl-bonded column, and reversed-phase Cis column chromatography to give compounds 13-16 [18]. The structure elucidation was based on spectroscopic analysis, including HRFABMS, COSY, HSQC, HSQC-TOCSY, and HMBC NMR... 

To achieve efficient oligosaccharide synthesis, an excess of acceptor is still required, which can be impractical in certain circumstances. Nevertheless, the products are easily isolated by normal flash chromatography on silica gel column, and a large amount of gel is unnecessary because the excess of acceptors are easily recovered by using less polar eluants. Alternatively, the products can be isolated after 0-acetylation. 

The same procedure described in the foregoing was followed using excess of acceptor 36 (20 Eq.). The disaccharide was isolated by flash chromatography on silica gel column using the same eluant in 69% yield mp 114°-1150C, [ot]D +43° (c 0.5, CHC13). 

The checkers found that gravity chromatography can be replaced by ordinary flash chromatography (30% ethyl ether-hexane eluant, 2.5-cm I.D. column 40 g of flash grade silica gel, 20-nt fractions). In at least one case, the checkers found that pure product could be isolated in high yield (98%) without recrystallization. 

A solution of commercial household bleach (Clorox) is diluted to approximately 0.55 M in NaOCI with 0.005 M Na2HP04, and the pH of the resulting buffered solution is adjusted to pH = 11.3 by addition of 1 M NaOH solution. To this solution are added a solution of 159 mg (0.26 mmol) of 5 and 2.01 g (12.5 mmol) of 2,2-dimethyl-2//-l-benzopyran in 12.5 mL of C H,CI2. The two-phase mixture is stirred at 4 °C, and the reaction progress is monitored by TLC. After 6 h, 12.5 mL of CH2CI2 are added to the mixture and the brown organic phase is separated, washed twice with 50 mL of H20 and once with 50 mL of sat. aq NaCl, and then dried over Na2S04. After solvent removal, the residue is purified by flash chromatography (silica gel) yield 1.59 g (72% isolated yield) 97.6% ee (GC analysis, chiral phase capillary column). 

Prior to structural elucidation and possible eventual synthesis, the isolation of component phenolic lipids in a pure state is essential. The cold methods of thin layer chromatography (TLC), column chromatography (CC), flash chromatography, high performance liquid chromatography (HPLC) and hot methods (GC), often after derivatisation, are well established. Argentation versions of these separatory methods are less common but are desirable for the rapid separation of unsaturated constituents. 

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