Vancomycin purification and
extraction of other natural products used as
pharmaceuticals
The case for
substituting ion exchange resins with specialty
activated alumina
Dr. Mark
Moskovitz and Gary Witman, MD
Peptide fermentation broths
yielding useful antibiotics are an integral mainstay
of the pharmaceutical industry. Vancomycin remains
the most important antibiotic in the treatment of
methicillin resistant staphylococcus aureus (MRSA).
Given the increasing prevalence of MRSA in the
community setting, and it’s presence in previously
healthy individuals, the role for this drug in
controlling both the spread and disease eradication
is gaining global recognition. As the antibiotic is
no longer protected by patent rights, and generic
competitive pricing is intense, the most cost
effective production methods must be achieved to
assure product profitability. To that end the
production process should be as automated,
reproducible and efficient as possible.
Vancomycin is the product of a
fermentation broth. It is one of the glycopeptide
antibiotics produced by the genus Actinomycetes,
such as the strain Amycolatopis orientalis (ATCC
19795). Glycopeptide antibiotics are classified into
four groups based on their chemical structure. Group
I, or the vancomycin type has aliphatic amino acids
at positions 1 and 3. Vancomycin is a branched
tricyclic glycosylated non-ribosomal peptide. The
drug is effective in growth inhibition of gram
positive bacteria such as Streptococci,
Staphylococci, Clostridium difficile, as well as
organisms which are resistant to penicillin and
cephalosporin class antibiotics. The drug can be
administered in either an oral or intravenous form.
The impurities in the fermentation of vancomycin
tend to be polymeric species containing one of
several carboxylic acid groups. The preferred
vancomycin strain is Vancomycin B, with the desired
adsorbent used to select out this strain being
either a cation exchange resin such as Dowex 50 WX2,
or Amberlite XAD-16, a non functional resin, with
both these products available from Dow Chemical.
The term decolorization as used
in the pharmaceutical industry is a misnomer. It
does not mean to literally remove color. That would
be too simple, too literal. Rather, to decolorize
means to remove impurities of one sort or another.
In the decolorization of a fermented product process
stream one often uses ion exchange resins. However,
a superior solution lies in the use of specially
designed DAI activated alumina.
Steps for purification of the
drug via fermentation are well characterized. The
initial purity of vancomycin in a fermentation broth
is around 34%, and the purity must be driven up to
greater than 95% for pharmaceutical application. The
colors which are present in the fermentation process
tend to be similar to the colors seen in the sugar
industry, as the carbon source for the fermentation
process tends to be rapeseed oil or molasses. The
fermentation broth is adjusted through a series of
pH changes with the filtrate traditionally passed
through either a silica or a polymeric
chromatography packing. Vancomycin is subsequently
eluted from an adsorbent resin using reverse phase
column chromatography. After repeating the process a
basic salt of vancomycin is crystallized with a
solvent and the crystals are acidified at a low pH.
The acidified product is precipitated in an organic
solvent such as acetone or alcohol to produce
vancomycin HCl.
To control costs in some of the
processes for the production of vancomycin, the
agent used for decolorization is activated carbon
rather than ion exchange resins. Up to 10% of the
volume of the vancomycin can be activated carbon.
However, activated carbon has limitations which
include absorption of the final product, which
dramatically decreases yields. Activated carbon is
not pure, and colloidal carbon requires further
filtration downstream, which can slow down the flow
rate. Additionally, there is the possibility of
contamination with metals when using activated
carbon.
Decolorization of crude filtered
vancomycin improves the purification of vancomycin
with subsequent reversed phase chromatography. The
decolorization also diminishes fouling of the
reversed phase packing material, and allows an
effected single reverse phase step approaching the
purity level of 95%, which would be acceptable for
use as a pharmaceutical agent.
Many pharmaceutical firms
traditionally use basic anion exchange resins (such
as Dow Amberlite FPA98 CL) for decolorization of the
crude vancomycin broth. Such basic anion exchange
resins were introduced because they had proven more
effective and economical than carbon or bore char
based technologies for sugar solutions. However, the
argument is made that activated alumina provides
that ability and much more. Furthermore, due to its
amphoteric character, and the ability to manipulate
pore sizes, activated alumina can do so much more.
The basic ion exchange resins were promoted because
they offered a pore structure allowing high
molecular weight organics to be easily adsorbed.
These ion exchange resins were felt to exhibit good
resistance to physical breakdown by attrition and
osmotic shock.
There is no material which
offers the endurance, the amphoteric properties, the
heat and pressure stability of DAI activated
alumina. The molecular metallurgists at Dynamic
Adsorbents are able to manipulate the pore size of
the specialty alumina to accommodate virtually any
high molecular weight organic material, and provide
both a decolorizing and polishing for many
bio-processing applications such as natural product
extraction and the recovery of antibiotics from
fermentation broths.
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