Zorbax Rx-SIL

Mass Spectrometry, APCI-MS/MS Zorbax RX-SIL, 5 p, 250 x 2.1 mm, hexane/isopropanol.ethyl acetate gradient p-carotene, a-T, p-cryptoxanthin. Lutein, zeaxanthin (20 min) Hao et al., 2005... 

Column 80 X 4.6 3.65 pm Zorbax Rx-SIL (similar to Zorbax SB-C8 (Mac-Mod Analytical)) Mobile phase MeCN 0.1% trifluoroacetic acid 18 82 Flow rate 1... 

FIGURE 32.2 DRIFT Spectra of porous silica (A) type B, Zorbax Rx-Sil, and (B) type A, Davisil, after the removal of physisorbed water from the surface by mild evacuation at 100°C. 

FIGURE 32.4 SEM photo of Zorbax Rx-Sil, type B silica using a scale of 6.3 pm. 

Thus, in order to evaluate the enantiopurity of the Michael product 14a obtained during the optimization of the catalyst A (Scheme 5), the purification of the analytical quantities of the crude 14a from its diastereomer and residual p-ketoester 12a was performed by semipreparative normal phase HPLC using achiral silica-based column ( -hexanes/lPA, Zorbax Rx-SIL column). This purification provided partial separation, and the pure fractions containing major diastereomer (i.e., 14a) along with some mixed fractions containing both diastereomers were collected. Remarkably, the first collected fraction contained highly enantiopure 14a (99% ee). 

Considering that an achiral silica-based HPLC column (Zorbax Rx-SIL) was used for the purification, we assumed that this fraction was representative of the entire sample and that catalyst A promoted the formation of 14a in 99% ee. However, later a more direct analytical chiral HPLC-based method... 

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