Multiple-column chromatography systems

Another unique characteristic of this technology is the potential for online structure information collection. This HTP method utilizes a high-pressure chromatography system in a parallel processing mode, i.e., multiple simultaneous column runs coupled to a robot controlled liquid handling... 

Multiple chromatographies are needed to purify benzophenones, and a variety of normal and reversed-phase solvent systems and solid phases including column chromatography over silica gel, reversed-phase, and Sephadex LH-20, as well as preparative TLC and HPLC have been employed. Isolation methods for selected benzophenones are given, and our experiences with the activity-guided isolation of xanthochymol (138) from G. xanthochymus fruits are discussed. 

Hey-Hawkins reported that the asymmetric Diels-Alder reactions of 2H-phospholes with the dienophile (5/ )-(l-menthyloxy)-(5//)-furanone allowed the generation of multiple stereogenic centers in 1-phosphanorbomadienes 256. The cycloaddition products were converted to their air-stable sulfur derivatives, which were isolated and the endo- and exo-isomers were separated by column chromatography (Scheme 81). In this case, the principle of face differentiation for a P=C bond is a synthetic tool for highly selective and efficient synthesis of P-chiral phosphanes from readily available starting materials. The observed selectivity was explained by the transition states of the two main isomers exo-A and endo-B (Scheme 82). The two molecules approach mainly in an endo fashion, which in consequence leads to the main diastereomer. Because of the favorable secondary orbital interactions between the C=0 functionality and the diene system, the endo product is kinetically favored, as is known for such systems with normal electron demand [170]. 

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