Topic 10 - The major groups of polyketides and terpenoids Flashcards
Polyketides
Highly unstable → ring closing reaction → aromatic rings
Specific polyketides
- Phloroglucinol derivates (e.g. humulone) – various effects
- Anthraquinones (e.g. emodin) – laxative
- Napthodianthrones (e.g. hypericin) – photosensitization
Polyenes
Fatty acid metabolism saturated and unsaturated fatty acids polyenes
Alternating single and triple bonds
In fungi and plants (Apiaceae)
Herbal toxins affect the CNS
Brightly coloured
Monoterpenes
Widespread in plants
Volatile compounds in oils
Acyclic, monocyclic (limonene in citrus fruits) and bicyclic (pinene in tansy) molecules and their derivatives
Monoterpenes often produce odour
They are rarely accumulated tissues
Monoterpenes effects and functions
o Allelopahtic effect
o Insect repellent effect (menthol, myrcene, camphor)
o Pollinator attractants (pinene, eycalyptol)
o Antimicrobial antifungal effect (carvacol)
o Toxic effects (pinene)
Iridoids
Non-volatile monoterpene derivative
♣ Protective chemicals (microbes, fungi, herbivores in the form of glycosides)
♣ The flavor of iridoids is distinctly bitter
♣ Medicinal effects: sedative, anti-inflammatory, antibacterial
Pyrethrines
Non-volatile monoterpene derivative
♣ Insecticidal activity by targeting the nervous system used against parasites
Sesquiterpenes
Natural occurrence mainly in Asteraceae family
Acyclic or cyclic compounds
Can be present in volatile oils, but less volatile than monoterpenes
Effects of sesquiterpenes
o Apetizing effect
o Antispasmodic
o Painkillers, but allergic reaction and photosensitization is also possible
Diterpenes
More then 2000 different molecules
Apolar or semi polar non-volatile compounds
Plant hormones: regulate growth and development – gibberellic acid
Poisonous derivates with nitrogen heterocycles pseudoalkaloids (taxines, aconitine)
Irritative effect, tumour promoters (phorbol)
Medicinal effects of diterpenes
o Spasmolytic o Cytostatic compounds o Anti-bacterial o Anti-fungal and anti-inflammatory activity o Cardioactive effects
Bitter substances
Not a single biosynthetic group
Stimulate taste receptor → increased production of saliva and gastric juices
The bitterness value is the reciprocal of the dilution of a bitter compound. It is determined by comparison with quinine hydrochloride (bitterness value 200 000)
Bitter substances Terpenoid groups
Monoterpenoid derivates (secoiridoids)
♣ Gentiopicrin
♣ Oleuropein
Sesquiterpene lactons
♣ Artemisinin
♣ Parthenolide
Diterpenoids
♣ Ginkgolide
Triterpenes
Triterpenoid saponins Phytosterols Cardiac glycosides Steroidal glycoalkaloids Steroidal saponins
Saponins
Not a single biosynthetic group
Amphipathic glycosides - emulsifying effect
Sapo (in latin) = soap → produce foam in the rumen
Triterpenoid saponins
Synthesised from squale, with five rings → bounds with sugar → saponin effect
Poisonous/antinutritive effects
Tetracyclic aglycon
Generally four ringed molecules
Dietry supplies
Medicinal effects of triterpenoid saponins
Anti-: fungal bacterial inflammatory acitivity tumor viral activity
Immunostimulant
Adaptogen: stabilisation of physiological processes
Radioprotective: reduce the effects of radiation
Cholesterol lowering effects
Other effects of triterpenoid saponins
Poisonous → cucurbitacins
Ginsenosides
Steroid glycosides and triterpene saponins exclusively in Panax (ginseng) spp.
Steroidal saponins
The glycon parts are mostly oligosaccharides
The aglycon part are spirostanol or furostanol
Cytotoxic and antifungal activity
Diosgenin – precursor of synthetic steroidal and anti-cancer drugs
Cardiac glycosides
Aglycons bounds with specific sugar moieties → glycosidic form with saponin effect
Inhibition of the membrane bound Na+/K+ pump → irregular or slow heart beat
Steroidal glycoalkaloids
Biosynthesised from cholesterol with a nitrogen heterocycles pseudo alkaloids
Bitter flavour
Toxic effects
Tetraterpenes
Derived from two GGPP molecules
Carotenoid plant pigments – UV védelem
In chromoplastids of roots, flower and fruits
Polyterpenes
Acyclic polymers containing a large number of isoprene subunits
Natural rubber in the latex of rubber tree
Terpenoids
Monoterpenes Sesquiterpenes Diterpenes Triterpenes Tetraterpenes Polyterpenes
