Facile Discrimination of Aldose Enantiomers by Reversed-Phase HPLC

Abstract

Aldoses are one of the most important structural components of biomolecules, such as polysaccharides, nucleic acids, glycolipids and glycoproteins. In addition, numerous secondary metabolites in plants, such as terpenoids, steroids, and flavonoids, exist as glycosides, which conjugate with aldoses. Aldoses are optically active compounds, and confirmation of absolute configuration is required in natural product chemistry. Measurement of specific rotations of pure samples is the most reliable method, although this is impractical in many cases because only limited amounts of samples are available. Analysis using a column with a chiral stationary phase developed for the separation of enantiomers, or an HPLC system equipped with an optical rotation detector and a column specified for sugar analysis, can be applied 1,2) ; however, the latter method is not applicable to mixtures of Dand L-enantiomers. Identification of sugars with small optical rotation may be also difficult. Methods using capillary electrophoresis have also been developed, 3,4) but these methods require specialized equipment or columns that are unfamiliar to most organic chemistry laboratories. Some methods based on conversion of aldose enantiomers to diastereomeric derivatives through coupling to an optically active reagent have been developed 5,6) ; however, there are not many methods applicable to the widely used HPLC systems equipped with a UV detector and C 18 reversed-phase column. This paper describes a new method to discriminate between aldose enantiomers using a usual HPLC system. Results and DiscussionHara et al. developed an excellent method using gas chromatography, in which enantiomeric aldoses were converted to trimethylsilyl ethers of methyl 2-(polyhydroxyalkyl)-thiazolidine-4(R)-carboxylates. 7) In order to apply this method to HPLC analysis, we converted the thiazolizine derivatives to arylthiocarbamate (3, 4) by reaction with arylisothiocyanates.The reaction procedure is very simple: sugar samples, such as D-and L-glucoses (1, 2, respectively), are heated with L-cycteine methyl ester in pyridine at 60°C for 60 min, then arylisothiocyanate was added to the reaction mixture and further reacted at 60°C for 60 min. Then, the reaction mixture was directly analyzed by standard C 18 HPLC and detected by a UV detector (at 250 nm). When phenylisothiocyanate was used, the retention time (t R ) of the derivatives of D-and L-glucoses were 16.35 and 15.37 min, respectively. The derivatives of D-and L-glucoses (3, 4, respectively) were isolated and their structures were determined by 1 H-and 13 C-NMR spectra and FAB-MS analyses. Although the production of two diastereomers, which have an opposite configuration at the sugar C-1 position, was expected from each enantiomer, the 1 H-and 13 C-NMR spectra showed that one of the two possible diastereomers was produced preferably in the case of glucose.When the reaction mixture was stored at room temperature for a few days, the derivatives decomposed to give thiohydantoin compounds by elimination of metha...

In vitro antitumor activity of chemical constituents of EtOAc extract from Artemisa gmelinii

“…Their structures were elucidated on the basis of comparing their NMR data with those reported in the literature [16][17][18][19][20][21][22].…”

Allenyl and Alkynyl Phenyl Ethers from the Endolichenic Fungus Neurospora terricola

“…3.77 (1H, d, J ) 3.6 Hz, H-2′), 3.68 (1H, dd, J ) 6.0, 12 Hz, H-6′a), 3.50 (1H, dd, J ) 9.6, 9.6 Hz, H-4′), 3.34 (1H, dd, J ) 3.6, 9.6 Hz, H-3′), 3.13 (1H, ddd, J ) 2.4, 6.0, 9.6 Hz, H-5′); HMBC data (acetoned 6 , 500 MHz) H 2 -1 f C-2, 1′; H-3 f C-1, 4, 5, 6; H-4 f C-2, 5; H-6 f C-2, 5; H-7 f C-1, 4, 5, 6; H 2 -8 f C-5, 9; H 2 -11 f C-9; H-9 f C-11; H-1′ f C-1, 2′; H-2′ f C-3′, 4′; H-3′ f C-4′; H-4′ f C-3′, 5′ C-8 Sugar Identification. 5,6 Authentic samples of D-Glc and L-cysteine methyl ester hydrochloride (5.0 mg each) were dissolved in pyridine (1.0 mL) and heated at 60°C, and then o-tolylisothiocyanate (0.2 mL) was added to the mixture and heated at 60°C for 1 h. The derivatives of L-Glc, D-Man, and L-Man (5.0 mg each) standards were prepared following the same procedure as described for that of D-Glc.…”

“…Terricollenes A-C (1-3), new allenyl phenyl ethers, and terricolynes (4)(5)(6), new alkynyl phenyl ethers, have been isolated from the crude extract of the endolichenic fungus Neurospora terricola. The structures of these compounds were elucidated primarily by NMR experiments.…”

Two new maltol glycosides and cyanogenic glycosides from Elsholtzia rugulosa Hemsl.

“…The location of the -apiose moiety at the C-6' of -glucose was apparent from the large low field shift of the C-6' ( 68.8,  6.3) compared with that of maltol 3-O--D-glucoside ( 62.5) [2,14]. The absolute configurations of the glucose and apiose were determined to be D-glucose and D-apiose by reversed-phase HPLC after conversion of the sugars to thiocarbamoyl-thiazolidine derivatives [15].…”