HPLC resolution

Some racemates (Figure 3.23) are more efficiently resolved on the bonded-type CSP than the coated-type CSP by using chloroform as a component of the eluent. On the bonded-type CSP of 24n, topologically interesting catenanes and molecular knots are successfully resolved using a hexane-chloroform-2-propanol mixture.185 The first direct HPLC resolution of the smallest chiral... 

The cycloalkylcarbamates do not absorb UV light above 220 nm and therefore can be used as the CSPs for thin-layer chromatography (TLC).191 The TLC chromatogram was readily detected by UV radiation at 254 nm and showed the resolution of racemates into each enantiomer. The TLC results can be compared with those obtained by HPLC with the same CSP. The a values in HPLC are slightly larger than those in TLC, although a good correlation is observed between these a values. The cycloalkylcarbamates can be very useful CSPs for TLC as well as for HPLC resolution. 

Nonchiral columns can be used with nonchiral derivatization for better detectability of the analytes, using chiral modifiers of the carrier solvent. For example, RP-HPLC resolution of dansylated (92) D,L-amino acids using L-phenylalanine-Cu(II) complex... 

Chiral derivatives of hemiacetal from fluoral have been prepared by adding an alcohol to fluoral in the presence of (l )-BlNOL— Ti(0—iPr)2 or by HPLC resolution of the racemate. The displacement of the sulfonate moiety from the tosyl derivative, by an alkyl lithium aluminate, affords the trifluoromethyl ether with inversion of configuration and an excellent chirality transfer (Figure 2.49). ° ... 

Fig. 5.4.7 HPLC resolution at 35°C of a standard mixture of free BA naphthacyl esters (3.18 x 10 6 M). Chromatogram (a) 1 UDCA, 2 CA, 3 CDCA, 4 DCA, 5 lauric acid (the internal standard), 6 LCA. Chromatogram (b) blank, consisting of reagent kept at reaction conditions. R is the reagent peak in both chromatograms (reprinted from [20])...

In the presence of chiral lithium alkoxides as initiators, chloral forms completely isotactic, crystalline polymers that are insoluble in all solvents (Scheme 71) (166). The polychloral film displays rotation values as high as 3000-5000°. The stereoregular helicity comes about at the stage of the trimer (167). A pure enantiomer of a tert-butoxy-initiated, acetate end-capped pentamer of chloral, which has 4r-helical conformation in both chloroform solution at 35 °C and in the crystalline state, can be obtained by HPLC resolution on a chiral stationary phase (168). 

The purpose of their investigation was to determine the relative order of elution of the molecular species of rearranged butterfat triacylglycerols for which the exact quantitative composition can be calculated by statistical considerations. The initial part of the study was concerned with verifying that a random distribution of the fatty acids had indeed been obtained, which was established by detailed GC and HPLC resolution and MS identification of the species. 

Optically active catalyst 1 can be obtained either by enantiomer-selective reaction of rac.-2 with optically active lithium (l,l -binaphthyl)-2,2 -diolate or by direct resolution by chiral HPLC. Optically active 21 and 22 in addition to 1 were successfully obtained by HPLC resolution and used for the polymerization of 1,5-hexadiene [60-62], Both catalysts gave an optically active polymer through cyclopolymerization. The optical activity and the content of tranj-structure in the main chain of the polymers obtained with 21 and 22 were comparable with those of the polymers synthesized with 1 [61,62],... 

Like its two sister column chromatographic techniques (GC, HPLC), resolution in SFC is determined by the product of three terms—efficiency, selectivity, and retention—as shown in equation 1,... 

Chen and Contario [31] reported an HPLC resolution of enantiomers of vigabatrin. The samples were treated with N-f-butoxycarbonyl-L-leucine N-hdroxysuccinimide esters in the presence of sodium carbonate and then with trifluoroacetic acid. The resulting diastereoisomers were separated on a column (25 cm x 4 mm) of Lichrosorb RP-8 (10 fim) with acetonitrile-dioxan-0.5 M H3PO4 (pH 7)-acetonitrile (24 1) as mobile phase with a flow rate of 2 ml/min and detection at 210 nm. Good recoveries of the inactive R-(—)-form (0.5-2%) added to the active S-(+)-form of the aminobutyrate aminotransferase inhibitor were obtained. The results on a sample containing 0.24% of the R-(—)-form agreed with those obtained by GC. 

The most serious limitation associated with the use of Fu s planar chiral ferrocenyl catalysts (4a-d) is that their preparation is via a multi-step synthesis followed by chiral-HPLC resolution however, catalysts 4b and 4c are commercially... 

The chiral 5-carbon units were now in hand as was a route that would permit HPLC resolution of C-2 stereoisomers (Figure 12) the synthesis was concluded as outlined in Figure 15. 

In a similar way, the use of formic acid/ammonium formate was shown to be superior to the use of acetic acid/ammonium acetate in the RP HPLC-ESI MS/MS analysis of a number of heterocyclic aromatic amines [7]. It is clear from numerous other examples in the literature that HPLC resolution and MS sensitivity can be dramatically influenced by the correct selection of mobile phases, organic modifiers, and ion-pairing additives. 

Figure 9.70 Chromatogram of the HPLC resolution of a-naphthol glucuronide. Peaks 1, a-naphthol glucuronide 2, /3-naphthol, the internal standard 3, a-naphthol, the substrate. Solvent 0.1 M acetic acid-methanol (55 45, v/v) flow rate 1.5 mL/min wavelength, 240 nm. (From To and Wells, 1984.)...

Finally, libraries aimed to chiral resolution of racemates will be covered here in particular, the use of chiral stationary phases (CSPs) has recently been reported for the identification of materials to be used for chiral separation of racemates by HPLC. The group of Frechet reported the selection of two macroporous poly methacrylate-supported 4-aryl-1,4-dihydropyrimidines (DHPs) as CSPs for the separation of amino acid, anti-inflammatory drugs, and DHP racemates from an 140-member discrete DHP library (214,215) as well as a deconvolutive approach for the identification of the best selector phase from a 36-member pool library of macroporous polymethacrylate-grafted amino acid anilides (216,217). Welch and co-workers (218,219) reported the selection of the best CSP for the separation of a racemic amino acid amide from a 50-member discrete dipeptide iV-3,5-dinitrobenzoyl amide hbrary and the follow-up, focused 71-member library (220). Wang and Li (221) reported the synthesis and the Circular Dichroism- (CD) based screening of a 16-member library of CSPs for the HPLC resolution of a leucine ester. Welch et al. recentiy reviewed the field of combinatorial libraries for the discovery of novel CSPs (222). Dyer et al. (223) reported an automated synthetic and screening procedure based on Differential Scanning Calorimetry (DSC) for the selection of chiral diastereomeric salts to resolve racemic mixtures by crystallization. Clark Still rejxrrted another example which is discussed in detail in Section 9.5.4. 

Direct analysis with the on-line ORD detector linked to the HPLC was hampered by peak broadening, which led to incomplete resolution of the two peptides. Diffusion in the large flow cell may be a major factor in this difficulty. Because detector response can be either positive or negative, it is important to have an excellent signal-to-noise ratio and baseline HPLC resolution of the peptide isomers to be able to quantitate the degree of racemization by this technique. While the on-line ORD detector is promising, further improvements in resolution as well as sensitivity are required for it to be useful for routine peptide analysis. 

The ability of proteins to stereoselectively bind small molecules has been used to develop a series of commerdally available protein-based CSPs (the type V HPLC CSPs), including phases that contain immobilized AGP (84), HSA (85), BSA (86), and ovomucoid (OVM) (87) (see Table 5). All these CSPs are useful in the HPLC resolution of enantiomeric compounds and appear to have an extremely wide range of applications, and the AGP CSP seems to have the broadest utility of any of the current CSPs (9-11). However, although the type V CSPs display high enantioselectivities, they also have low capadties due to the relatively small amounts of the chiral selector that can be immobilized per g silica. Thus, these CSPs are useful... 

Wang, S.Y., Maas, J.L., Daniel, E.M., and Galletta, G. J. 1990. Improved HPLC resolution and quantification of ellagic acid from strawberry, blackberry and cranberry. Hort. Sci. 25 1078. 

Compendium of international methods of wine and must analysis - OIV, Dosage of sugars in wine by HPLC (Resolution 23/2003), edition 2006, Vol. 1, MA-E-AS311-03-SUCRES, p. 14. 

Experimental design methodology was applied for the optimization of the elution program for the RP-HPLC resolution of a mixture of nine phenols, with a ternary solvent system (water-AcOH-MeCN). Important factors were the initial isocratic elution, the gradient running time and the gradient curvature . ... 

VIE Efficient HPLC resolution ofaseries of underivatized diarylcarbinols on a chiral stationary phase based on C5-amide-bonded N-3,5-dinitrobenzyl-DPEDA, Chirality, 1996, 8, 490-493. 

In analytical HPLC, resolution is the prime requistie, with speed of analysis another important variable. The scope of the system i.e. its ability to separate mixtures of wide polarity range, is also important and can be varied by altering the mobile phase. Capacity is sacrificed in analytical HPLC. For preparative HPLC, capacity and scope are more important and speed is sacrificed to provide the maximum capacity. 

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