ALKALOIDS

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ALKALOIDS
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Alkaloid ?????????
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Alkaloid Difficult to define No definitive
difference between an alkaloid and naturally
occurring complex amines.
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• Alkaloids plant derived, are alkali and contain
  at least one N2-atom. They also normally have a
  significant physiological action on humans and
  animals.

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??? ????????? Alkaloid Description
Contains nitrogen - usually derived from an amino
acid. Bitter tasting, generally white solids
(exception - nicotine is a brown liquid). They
give a precipitate with heavy metal iodides.
Except Caffeine. Alkaloids are basic - they
form water soluble salts. In plants, they may
exist in the free state, as salts or as
N-oxides. Occur in a limited number of plants.
.
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????? ?? ????????? Tests for Alkaloids
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• Most alkaloids are precipitated from neutral or
  slightly acidic solution by
• Mayer's reagent (potassiomercuric iodide
  solution) ? Cream coloured precipitate.
• Dragendorff's reagent (solution of potassium
  bismuth iodide)? orange coloured precipitate.
• Wagners reagent (iodine in potassium iodide) ?
  red-brown precipitate
• Hagers reagent (picric acid) ? yellow
  precipitate
• Caffeine does precipitate

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????? ?????? ????????? Occurrence Distribution
of Alkaloids
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• Occur in bacteria and rarely in fungi.
• Some alkaloids occur in several genera from
  different species, but most occur in closely
  related species.
• Some occur in certain families ,.
• All alkaloids of one plant will have a common
  biogenenetic origin

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3-????? ?? ?????? ????? .
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?????? ????????? Chemistry of Alkaloids
The N2 atom can either be 1º, 2º, 3º or 4º
(quaternary).
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This N2 feature affects the alkaloid derivatives
which can be prepared and the isolation procedures
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Physical chemical
properties

• The basicity of alkaloids depends on the
  availability of the lone pair of e- on the N2
  atoms
• Because some alkaloids have a carbonyl group on
  the amide, they can also be neutral (colchicine
  piperine).
• Basic characteristic renders complex alkaloids
  unstable, so that in solution they are sensitive
  to heat, light oxygen.
• Basic character of alkaloids also allows them to
  form salts with mineral acids (such as
  hydrochlorides, nitrates and sulphates) or
  inorganic acids (tartrates, sulfamates).
• Solid salts can be conserved well and are a
  common commercial form of alkaloids.

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MW 100 900 , they are whit crystals. In rare
cases they are coloured. Most bases which do not
contain O2 are liquid at room temperature
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All active except Purins
Soluble in concentrated hydroalcoholic solutions
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They give a precipitate with heavy metal iodides.
Caffeine, a purine derivative, does not
precipitate like most alkaloids.
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????? ????????? Naming of Alkaloids

• Numerous methods can be used to name alkaloids
• Generic plant name atropine from Atropa
  belladonna
• Specific name of the plant cocaine from
  Erythroxylum coca.
• Common name of the herb ergotamine from ergot
  (rye)
• Physiological action of the plant emetine
  producing emesis
• Other e.g. morphine derived from ancient Greek
  mythology Morpheus god of dreams

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??????? ????????? Extraction of Alkaloids

• Extraction is based on the basicity of alkaloids
  ( they normally occur in plants as salts).

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• Herbs often contain other materials which
  interfere with extraction by forming emulsions.(
  waxes, terpenes, pigments and other lipophilic
  substances) avoided by defatting

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Extraction method normally depends on the raw
material, the purpose of extraction the scale
on which is to be performed. For research
purposes chromatography allows for quick and
reliable results.
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TLC plate
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??????? ????????? Extraction of Alkaloids
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Organic solvent containing alkaloids (bases) is
separated from residue by alcohol concentrated .
Solvent is stirred with an acidic aqueous
solution alkaloids go into the solution as
salts. Impurities remain in the organic
phase. Repeated until the organic phase no longer
contains alkaloids.
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???? ????????? H2SO4 ?? HCl
Alkalinized with a base using an organic solvent
not miscible with water (chloroform). Alkaloids
precipitate and dissolve in the organic phase.
Extraction of aqueous phase continues till all
alkaloids have moved into the organic phase
(tested when Mayers reaction on the aqueous
phase becomes negative). This purification step
may be carried out in a separation funnel or in
centrifugal extractors.
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Organic solvent containing alkaloid bases (drying
over anhydrous sodium sulphate) evaporated under
reduced pressure. A dry residue remains total
basic alkaloids
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Isolation of Alkaloids

• Volatile liquid alkaloids (nicotine) are isolated
  by distillation alkaloid is distilled off in
  steam. Nicotine is an important insecticide, and
  large amounts are prepared from the parts of the
  tobacco plant which is not used for tobacco
  manufacture

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??? ?????? ????????? Isolation of Alkaloids

• All methods of alkaloid extraction yield impure
  compounds, so alkaloids therefore have to be
  separated.
• TLC and HPLC are most commonly used.
• Chromatography is used for complex alkaloids and
  if only small amounts of alkaloids are needed.

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• Crystals of Hydrastine