Phytochemistry Flashcards
What is phytochemistry?
isolation and identification of compounds from plants
What is pharmacognosy and ethnopharmacognosy?
scientific basis for the use of plants in pharmacy
historical medicinal use of plans by different societies around the world
What is the difference between primary metabolism and secondary metabolism?
primary metabolism is the production of molecules common across many forms of life - carbohydrates, proteins
secondary metabolism is the production of compounds which are unique to a certain species of an organism - can be used for a number of different reasons
How can plants be transformed to give medicines?
plants can be transformed to give herbal medicines or a pure single compound
these can be used as drugs or be chemically modified to give drugs
What are the areas of the plant where the most useful natural products are found?
aerial parts leaf flower fruit bark root rhizone bulb
What products can be extracted directly from the plant?
resin
gum
oils
How can compounds be extracted from plants?
1 - identify the plant
2 - dry the whole plant or the selected organ
3 - material containing the desired compound is crushed or finely chopped
- to increase surface area for extraction
4 - a solvent is used to extract the compound
= hot solvent is used with a soxhlet apparatus or supercritical carbon dioxide is used
5 - initial product results in a crude extract
= mixture of similar compounds
6 - crude extract goes through further extraction to get isolated product
= primarily chromatography, acid/base extraction
7 - compound is identified by spectroscopic methods
= NMR, UV, IR, MS or analytical chromatography (TLC, HPLC, GLC)
Why is supercritical carbon dioxide increasingly being used as a solvent for drug extraction from plants?
environmentally friendly
= can be boiled off at the end, no need to dispose of toxic chemicals
easily removed from extract
= heat to room temperature and it evaporates off
non-reactive
= does not interfere with the extract
extraction conditions can be changed to suit your needs
= temperature and pressure can be changed to selectively extract compounds of different polarities
What is a disadvantage of using hot solvent as an extraction method in plants?
leaves behind large quantities of organic solvent that need to be disposed of
What is a major constituent of the initial crude plant extract?
crude extract - initial extract of plant material hat gives a mixture of related/similar compounds
fatty acids
What is the structure of a fatty acid and how is it referred to as?
fatty acids are referred to as fixed oils (if liquid) or fats (if solid)
often found as esters
- R groups attached to an OOR’ group = especially as glycerides
structure is a hydrocarbon chain attached to a carboxylic acid group
- the hydrocarbon chain can be saturated (no double bonds) or unsaturated (at least one double bond)
- double bonds tend to be cis (same side)
What is the difference between glycerol and glyceride?
glycerol is a triol - an alcohol with three hydroxyl groups
glyceride is formed after a reaction between fatty acids and glycerol
How are soaps formed?
reacting fatty acid or their glycerides with a strong base (example - sodium hydroxide)
give the sodium salts of fatty acids
R group attached to OONa (charged O and Na)
What are waxes and how are they formed?
esters of fatty acids with long chain alcohols
- formed from a reaction between a fatty acid (hydrocarbon chain + carboxylic acid group) and a long chain alcohol (long hydrocarbon chain with a hydroxyl group)
What are volatile oils?
have a lower boiling point than fixed oils (fatty acids in liquid form)
can be isolated by steam distillation
tend to have two forms phenyl propenes or monoterpenes
What are volatile oils used for?
antibacterial use
therapeutic flavour
perfume properties
What are monoterpenes?
major constituent of volatile oils
shows the chemical variety that can occur in different species with the same starting material
- monoterpenes are the starting materials for a whole range of terpene compounds
all have 10 carbon atoms in their structures
How are monoterpenes formed?
synthesised from two 5-carbon units related to isoprene
- dimethylallyl pyrophosphate = DMAPP
- isopentyl pyrophosphate = IPP
these 5 carbon units react to give the 10 carbon monoterpenes
What is an example of a monoterpene and how is it formed?
geranyl PP (10C)
- formed from reacting DMAPP (5C) and IPP (5C)
- is the common intermediate in monoterpene synthesis
How can geranyl PP react further?
monoterpene common intermediate
- can react further to give linear compounds of cyclic compounds
What are sesquiterpenes?
15 carbon compounds
can be cyclic or acyclic (linear) compounds
How are sesquiterpenes formed?
synthesised from a monoterpene (10C) reacting with another molecule of IPP (5 carbon) to form a 15C compound
What is an example of a sesquiterpene and how is it formed?
farensyl PP (15C)
- formed as geranyl PP (10C) reacts with IPP (5C)
- is the common intermediate
example
- artemisinin can be used as a treatment for malaria
- parthenolide can be as an anti migraine/headache
What are diterpenes?
20 carbon compounds
- intermediate from which other diterpenes are formed
- many have a cyclic structure but can be linear
How are diterpenes formed?
synthesised from a sesquiterpene reacting with another molecule of IPP (5 carbon)
What is an example of a diterpene and how is it formed?
geranylgeranyl PP (20C)
- formed as farensyl PP (15) reacts with IPP (5C)
- is a common intermediate
example
- taxanes (Taxol) have potent anticancer activity
What are triterpenes?
30 carbon compounds
- incldues steroids
How are triterpenes formed?
synthesised from 2 sesquiterpenes (15C) reacting together
- farensyl PP reacts with farensyl PP
What is an example of a triterpene and how is it formed?
squalene
- formed as two molecules of farensyl PP (15C) react together
- join with the two OPP reacting to form a bond = final product does not have OPP
reaction is catalysed by the enzyme squalene synthase
How is squalene involved in steroid synthesis?
squalene can be epoxidised
- cyclic ether ring = 2C bonded with O
squalene epoxide cyclises to give the common intermediate for steroid synthesis
= has 4 rings
What is tetraterpene?
40 carbon compound
- family of compounds includes carotenes/carotenoids and lycopene
What is an example of a tetraterpene and how is it formed?
lycopene
- formed as two molecules of geranylgeranyl PP (20C) react
- react at the OPP end so end product does not have OPP
What are features of tetratepenes?
compounds are highly coloured due to their conjugation
- form part of the distinctive pigmentation in flowers, tomatoes and carrots
conjugation means that
- strongly absorb UV light so can protect itself from effects
- are strong antioxidants
What are alkaloids?
low molecular weight nitrogen containing compounds
- found mainly in plants
- generally basic
- wide range of biological activity
What are examples of alkaloids?
belladonna
- 0.3 - 0.6% alkaloid contained
- highly poisonous
- mixed alkaloid extract can be used as GI sedative and roots can be used for external pain relief (plasters)
coca
- 0.7 - 2.5% alkaloid but 40 - 50% cocaine
- cocaine = local anaesthetic
- combats fatigue, hunger and cold
What are stilbenes and flavonoids?
are both alkaloids
stilebenes
- resveratol = potent antioxidant from wine and red grape
- combretastatin = potent cytotoxic (anticancer compound) from bush willow, inhibits tubular formation
flavonoids
- brightly coloured antioxidants from brightly coloured parts of plants
isoflavonoids
- act as phyto-oestrogens
How can biosynthetic routes be established?
to find the origin of the biological molecule which are generally formed from two or three carbon fragments
- isotopes are used
- plants can be fed with a labelled acetate group
- analytical techniques can be used to find where the isotope has been incorporated into the compound
How do analytical techniques show the biosynthetic process?
shows whether the isotope (acetate molecule) has been
- used as a building block
- how many of the acetate molecules have been used
- how the acetate groups are linked
can show the full process if the studies are repeated with different intermediates labelled at different points
