Temperature glycopeptides

Fig. 2-5. Examples showing the complementary separations on glycopeptide CSPs. (A) Separation of N-CBZ-norvaline on vancomycin (left) and teicoplanin (right). The mobile phase was methanol 1 % triethylammonium acetate (20/80 v/v) pH 4.1. (B) Separation of warfarin on teicoplanin (left) and vancomycin (right) CSPs. The mobile phase was acetonitrile 1 % triethylammonium acetate (10/90 v/v) pH 4.1. (C) Separation of naproxen on teicoplanin (left) and ristocetin A (right). The mobile phase was methanol 0.1 % triethylammonium acetate (30/70 v/v) pH 4.1. All columns were 250 x 4.6 mm i.d. The flow rate for all the separations was 1 mL min1 at ambient temperature (23 °C).

A comprehensive study on the temperature effect was done in 2004 for 71 chiral compounds on four glycopeptide CSPs TE, TAG, ristocetin A, and vancomycin phases, using the three RP, POM, and NP elution systems [95]. The separations were studied in the 5 5°C temperature range. Peak efficiencies always increased with temperature, but in only 17% of the separations studied, a small increase of the resolution was observed. In the rest of the cases, the resolution decreased or even vanished when temperature increased. All van t Hoff plots were linear, showing that... 

Another study focused on aryl-substituted P-lactams, using the same set of teicoplanin-based CSPs and variable-temperature conditions [99]. Tricyclic P-lactams were investigated by the same group of authors, together with some bicyclic P-amino acids, on five different commercially available glycopeptides CSPs, namely ristocetin A, TE, TAG, vancomycin, and VAG, and on a new dimethylphenyl carbamate-derivatized 5-cyclodextrin-based CSP. The chromatographic results, achieved with different methods, were compared in systematic examinations [170]. 

Glycopeptides have been found in milk at temperatures above 50 °C (Hindle and Wheelock 1970), and peptides similar to macropeptides from chymosin (EC 3.4.23.4) hydrolysis are produced in milk heated to 120°C for 20 min (Alais et al 1967). Under severe ultra-high-temper-... 

Glycosyl amines are not very stable therefore the water bath temperature should not exceed 30°C. Always prepare them freshly before further conversion to glycopeptides. 

Schachter and coworkers45 published some 360-MHz, H-n.m.r. data for a series of glycopeptides having N-glycosylically linked carbohydrate chains of the N-acetyllactosamine type, and one having a chain of the oligomannoside type spectra were recorded at a variety of probe temperatures (20, 25, 30, 70, and 85°). The compounds... 

Peptide A-Terminal Deprotection. After a solution of crude 19 (160 mg, 0.12 mmol) dissolved in NMP (1.6 mL) and piperidine (0.4 mL) was stirred at room temperature for l h, diethyl ether (20 mL) was added to produce a white precipitate. After centrifugation, the supernatant was removed carefully, and the precipitate was washed with diethyl ether (5 mL) twice and dried under a stream of nitrogen to give glycopeptide 20 (130 mg, 98%) as an off-white solid. 

Peptide C-Terminal Deprotection and Activation. Glycopeptide 21 was obtained by repeated -terminal deprotection and coupling to amino acids. A part of 21 (5 mg, 0.005 mmol) was dissolved in 20% TFA in DCM (2 mL), and the solution was stirred at room temperature for 2 h. The reaction mixture was diluted with toluene (4 mL) and concentrated to dryness in vacuum. The residue was then dissolved in H20 (5 mL). After washed with diethyl ether (5 mL) twice, the aqueous solution was lyophilized to afford a white solid. Upon its dissolution in NMP (1 mL), pentafluorophenol (9 mg, 0.05 mmol) and DCC (21 mg, 0.1 mmol) were added, and this homogeneous solution was stirred at room temperature for 5 h. The reaction mixture was diluted with diethyl ether (10 mL), and the resultant precipitate was isolated and washed as described above to give 22 as a wet white solid. 

Berthod et al. [28] examined the effect of temperature on chiral separations between 5°C and 45°C using four macrocyclic glycopeptides phases and although the efficiencies increased with temperature, in 83% of cases the chiral selectivity decreased. 

Polystyrene-based resins have been used successfully for the solid-phase synthesis of glycopeptides and oligosaccharides. Experiments that compare the rates of a reaction on a PS-resin compared to TentaGel have revealed that the rate of reaction completely depends on the nature of the reaction itself [36], Some reactions perform better on hydro-phobic resins, while others are better on hydrophilic resins. Another issue of particular importance for the synthesis of oligosaccharides on solid phase is the influence of the solid support on the stereochemical outcome of the reaction. There are few detailed studies that address this issue however, preliminary results are contradictory, but indicate that as in solution-phase reactions, the anomeric ratio is strongly influenced by the solvent, C-2 group on the donor and temperature [37-39]. In some cases there seems to be an enhancement of anomer selectivity on the solid phase [38]. 

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