Vancomycin
Vancomycin is a macrolytic glycopepetide having a molecular weight of 1449.22 and containing 54.69% carbon, 5.22% hydrogen, 4.89% chlorine, 8.70% nitrogen and 26.50% oxygen. It is an amphoteric glycopeptide and an antibiotic substance produced by Streptomyces orientalis contained in Indian and Indonesian soil. Vancomycin has been used as a very effective chiral stationary phase as it has 18 chiral centers and three shallow molecular cavities so some inclusion can take place. There are many dipoles on the molecule covering a wide range of polar intensities, a number of polarizable groups that can provide induced dipole ineteractivity and a range of dispersive groups that can provide dispersive (hydrophobic) interactivity. Vancomycin can be bonded to silica to provide a stable chiral bonded phase. In chromatography, vancomycin can be used in both the polar and dispersive mode by employing the appropriate complementary mobile phases. The macrolytic glycopeptides are used extensively as stationary phases in chiral chromatography
Author: RPW Scott
Book:Liquid Chromatography
Section:HPLC Chiral-Stationary-Phases Macrocyclic-Glycopeptide
phases was first
introduced by Armstrong [39]. One method of preparation is to covalently bond
Vancomycin to the surface of silica gel particles. Vancomycin contains 18
chiral centers surrounding three 'pockets' or 'cavities' which are bridged by
five aromatic rings. Strong polar groups are proximate to the ring structures
to offer strong polar interactions with the solutes. This type of stationary
phase is stable in mobile phases containing 0–100% organic solvent. The
proposed structure of Vancomycin is shown in figure 49.
A, B and C are inclusion cavities. Molecular weight
1449. Chiral centers 18. pK's 2.9, 7.2, 8.6, 9.6, 10.4, 11.7. Isoelectric point
7.2
Courtesy of ASTEC Inc.
Figure 49 The Proposed
Structure of Vancomycin
HPLC Chiral-Stationary-Phases Macrocyclic-Glycopeptide
Author: RPW Scott
Book:Principles and Practice of Chromatography
Section:Principles Applications Liquid-Chromatography b--blockers
Vancomycin is
a very stable chiral stationary phase, has a relatively high sample capacity,
and when covalently bonded to the silica gel, has multiple linkages to the
silica gel surface.
A, B and C are inclusion cavities. Molecular weight
1449. Chiral centers 18. pK's 2.9, 7.2, 8.6, 9.6, 10.4, 11.7. Isoelectric point
7.2
Courtesy of ASTEC Inc.
Figure 52 The Proposed
Structure of Vancomycin
It can either
be used with mobile phases with a high water content, as a reversed phase, or
with a high solvent content, as a largely polar stationary phase. For example,
when used as a reversed phase the strongly polar THF–water mixtures would
be very effective mobile phases. Conversely, when used as a polar
stationary phase, n-hexane–ethanol mixtures would be more appropriate.
Vancomycin has a number of ionizing groups and thus can be used over a range of
Principles Applications Liquid-Chromatography b--blockers
Author: RPW Scott
Book:Preparative Chromatography
Section:Preparative Chlorokynurenine-Enantiomers
stationary phase. The mobile phase (termed by
the manufacturers as elution by the polar organic
mode) is strongly polar so the major retentive mechanism is likely
to be predominantly dispersive in nature modified by the selective interactions
afforded by the chiral centers of the Vancomycin (see
The Mechanism of Chromatographic Retention
).
Courtesy of ASTEC Inc.
Figure 38.
The Chromatographic Properties of the Enantiomers of Nicardipine when Retained
on the Chirobiotic Vancomycin
Preparative Chlorokynurenine-Enantiomers
Author: RPW Scott
Book:Preparative Chromatography
Section:Preparative Chlorokynurenine-Enantiomers
spatial arrangement of chemical groups or atoms around a single atom, referred
to as the stereogenic center or the chiral center(s). Such differences impart
very subtle physical chemical variations between the individual isomers and,
thus, must be carefully exploited if a chromatographic separation of the
individual enantiomers is to be achieved. A number of antibiotics have been
shown to be very effective stationary phases for the separation of chiral
mixtures. An example of one of these is Vancomycin the structure of which is
depicted in figure 37. Vancomycin has three fused rings (shown as rings A, B
and C in figure 37) and 18 chiral centers which endows it with the
characteristic strong chiral selectivity exhibited by many antibiotics.
Figure 37.
The Structure of Vancomycin
Preparative Chlorokynurenine-Enantiomers
Author: RPW Scott
Book:The Thermodynamics of Chromatography
Section:Thermodynamics Other-Methods Chiral-Separations
nbsp;As an
example of the application of the opimizing equations the retention data
reported by Beesley and Scott (15) for the two
enantiomers, (S) and (R) 4-benzyl-2-oxazolidinone will be employed. The column
that was used was 25 cm long, 4.6 mm I.D., packed with 5 mm silica particles
bonded with the stationary phase Vancomycin (Chirobiotic V, Advanced
Separations Technology Inc., Whippany New Jersey). Vancomycin is a macrocyclic
glycopeptide thaving a molecular weight of 1449.22, and containing 18 chiral
centers surrounding three 'cavities' bridged by five aromatic rings.
The column was
operated in the normal phase mode using mixtures of n-hexane and
ethanol as the mobile phase. As the interactive character of the solvent
mixture was highly dispersive, the mechanism of retention, and the chiral
Thermodynamics Other-Methods Chiral-Separations
Author: RPW Scott
Book:The Mechanism of Chromatographic Retention
Section:Retention Chiral-Chromatography Chiral-Polysiloxane-Stationary-Phases
a very stable chiral stationary phase, has a relatively high sample capacity,
and can be covalently bonded by multiple linkages to the silica gel surface. It
can be used with mobile phases with a high water content, as a reversed
phase, or with a high solvent content, as a largely polar stationary
phase. For example, when used as a reversed phase THF–water mixtures are
very effective mobile phases. Conversely, when used as a polar stationary phase,
n-hexane–ethanol mixtures are often employed. Vancomycin has a number of
ionizing groups and thus can be used over a range of different pH values (pH
4.0 to 7.0) and exhibit a wide range of retention characteristics and chiral
selectivities. Ammonium nitrate, triethyl-ammonium acetate and sodium citrate
buffers have all been used satisfactorily with this stationary phase.
The effect of
the chosen buffer has little or no effect on chiral selectivity only on pH
control. An example of the use of Vancomycinas a stationary phase to
separate
Retention Chiral-Chromatography Chiral-Polysiloxane-Stationary-Phases