Isolation radial chromatography

Resin 19 (0.108 mmol, 1 equiv.) was reswoUen in CHCI3 (1 mb) and trie-thylamine (1.08 mmol, 1 equiv.) was added. The reaction mixture was heated at reflux for 24 h and then cooled to rt. The resin was then filtered off and the filtrate was collected. The resin was washed several times with MeCN and CH2CI2, and the combined filtrate and washings were concentrated. The residue 20 was first dried at 50 °C in vacuo and then purified by radial chromatography eluting with hexane/EtOAc (5 1). Isolated yields were in the range 48-58%. 

Resin 22 (0.132 mmol, 1 equiv.) was swollen in MeCN/CHCb (1 1 2 mL), phenyl isothiocyanate (0.092 mmol, 0.70 equiv.) was added, and the mixture was heated to reflux for 16 h. After filtering, the resin was washed several times with MeCN and CH2CI2. The combined organic phases were concentrated and the residue 24 was purified by radial chromatography using hex-ane/EtOAc (5 1) as the eluent. Isolated yield 95%. 

Chemical methods As with many areas of natural product chemistry, new impetus in the chemistry of lichen substances is provided by the more rapid and improved methods for detecting, isolating and purifying these compounds and in determining their structure. The techniques of preparative TLC, radial chromatography and preparative HPLC provide rapid and efficient methods for the purification of lichen substances and developments in mass spectrometry, proton and carbon-13 nuclear magnetic resonance (NMR) spectroscopy and X-ray analysis greatly aid structural smdies. 

Circular chromatography can be carried out with forced-flow as well as capillary-flow mobile-phase migration (Botz et al., 1992). No special plate preparation is required for off-line radial OPLC or RPC, but for on-line radial OPLC, a sector must be isolated by scraping the layer and then impregnated with solvent (Nyiredy, 1992). 

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