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aa Biomolecules > Lecture 8- Terpenoids > Flashcards

Lecture 8- Terpenoids Flashcards

1
Q

What are terpenoids structure

A
  1. Terpenoids derive from 5-carbon isoprene
  2. Hydrocarbons, sometimes with oxygenation
  3. Often polycyclic
  4. Can contain unsaturation
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2
Q

What are terpenoids used for

A
  1. Essential oils and flavours - pine, ginger, menthol
  2. Colours- sunflowers, tomatoes, turmeric
  3. Pharmacologically active - cannabinoids, ginkgolide, bilobalide
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3
Q

What are names for terpenoids with increasing isoprene units 1-6, 8

A
  1. 1= hemiterpenoid - 5C
  2. 2= Monoterpenoid- 10C
  3. 3= Sesquiterpenoid- 15C
  4. 4= diterpenoid- 20C
  5. 5= Sesterpenoid- 25C
  6. 6=Triterpenoid- 30C
  7. 8=Tetraterpenoid- 40C
  8. Polyterpenoid
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4
Q

What are the two derivatives of terpenes that nature uses

A
  1. IPP- isopentenylpyrophosphate
  2. DMAPP- dimethylallylpyrophosphate
  3. Used to construct all terpenes
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5
Q

What is produced when DMAPP reacts with IPP

A
  1. Form geranyl pyrophosphate
  2. Direct attack of IPP on non-ionised DMAPP does not occur
  3. DMAPP is ionised to give carbocation - di
  4. Proton drops off and double bond of IPP attacks carbocation
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6
Q

What does geranyl pyrophosphate do after formation

A
  1. Ionises and cyclises to give a tertiary cation
  2. From this cation the other monoterpenes arise by rearrangement reactions, eliminations, addition of water and oxidations
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7
Q

What is formed if geranyl pyrophosphate loses a proton after formation of carbocation

A
  1. Forms myrcene- non cyclic
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8
Q

How does geranyl pyrophosphate form limonene

A
  1. If double bond attacks carbocation- forms cyclic structure
  2. If new carbocation deprotonates- limonene
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9
Q

How is pinene formed

A
  1. If double bond attacks carbocation- forms cyclic structure
  2. If double bond acts as a nucleophile to carbocation
  3. Then proton eliminated- determines if alpha or beta
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10
Q

What are other monoterpene derivatives of geranyl pyrophosphate

A
  1. Menthol
  2. R-carvone
  3. Camphor
  4. All oxidised by water acting as nucleophile to carbocation- OH can then be oxidised to =O
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11
Q

Describe properties of monoterpenes

A
  1. Low molecular weight (C10) and low polarity- often volatile
  2. Have characteristic odours
  3. Opposite enantiomers have different scents
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12
Q

How do you form sesquiterpenes

A
  1. A C15 precursor is needed
  2. This is derived from the reaction of geranylpyrophosphate with another molecule of IPP to give Farnesyl pyrophosphate
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13
Q

How do you form diterpenes

A
  1. A C20 precursor is needed
  2. Formed from reaction of farnesyl pyrophosphate with IPP to give geranylgeranyl pyrophosphate
  3. geranylgeranyl pyrophosphate undergoes electrophilic cyclisation to produce polycyclic structures
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14
Q

How are triterpenes formed

A
  1. Synthesised by squalene
  2. Squalene is made from 2 farnesyl units head to head
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15
Q

How do you synthesise steroids from squalene

A
  1. Oxidise to form 2,3-oxidosqualene
  2. Then undergoes electrophilic cyclisation and rearrangement to access the steroidal nucleus
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16
Q

How can terpenes be used to make polyester

A
  1. Beta-pinene multistep synthesis
  2. Produce 4-isopropyl-cyclohexanone which is oxidised using mCPBA, CH2CI2 to produce 4-isopropylcaprolactone
  3. This undergoes ring opening polymerisation to produce polyester
17
Q

What are steroids

A
  1. Organic compounds with 4 rings organised in a specific molecular configuration
  2. Steroids core structures are composed of 17 carbon atoms bonded in 4 fused rings
  3. 3 6-Member cyclohexane ring
  4. 1 5-member cyclopentane ring
  5. e.g. cholesterol, estradiol, testosterone
18
Q

What are the two principal biological functions of steroids

A
  1. Important component in cell membranes which alters membrane fluidity
  2. Signalling molecules which activate hormone receptors
19
Q

What are all steroids manufactured from

A
  1. Ianosterol (animal and fungi)
  2. Cycloartenol (plants)
  3. Both are derived from cyclisation of the triterpene squalene
20
Q

What are polyketides

A
  1. Diverse range of highly oxygenated secondary metabolites - contain ketones
  2. Biosynthesis vai thio-Claisen condensation of acyl-coenzyme A units by PKS (polyketides synthases)
  3. Type 1 - macrolides
  4. Type 2- often aromatic molecules
  5. Type 3 - Often small aromatic molecules
21
Q

How are polyketides formed from terpenoids

A
  1. Epoxidation
  2. Followed by ring opening and closing
22
Q

What are examples of type 1 polyketides

A
  1. Glycosylated macrolides
  2. Erythromycin
  3. clarithromycin
  4. Amphotericin B
23
Q

What are prostaglandins

A
  1. PG’s are a group of physiologically active lipid compounds which have diverse hormone-like effects in animals
  2. PG’s are derived enzymatically from the fatty acid, arachidonic acid
  3. Every PG contains 20 carbon atoms including a 5-carbon ring
  4. Prostaglandins are powerfulling acting vasodilators and inhibit the aggregation of blood platelets
  5. Also have a role in inflammation
24
Q

What is an example of a prostaglandin

A
  1. Alprostadil
25
Q

Describe how aspiring works

A
  1. Aspiring blocks an enzyme called cyclooxygenase, COX-1 and COX-2 which is involved with the ring closure and addition of oxygen to arachidonic acid which forms prostaglandins
  2. The acetyl group on aspirin is hydrolysed and linked to the alcohol group of serien as an ester
  3. This blocks the channel in the enzyme so arachidonic cannot enter the active site
26
Q

What are alkaloids

A
  1. Natural products that usually contain a basic nitrogen
  2. Alkaloids are produced by a large variety of fungi, plants and microorganisms
  3. Generally have a better taste
  4. Biological roles vary e.g. protective (predators or parasites), neurotransmitters (serotonin, dopamine)
  5. Many are pharmacologically active - antimalarial, antibacterial, anticancer, psychotropic
  6. Biosynthesis pathways complex, but begin with amino acids
27
Q

What are some examples of alkaloids

A
  1. Aconitine
  2. Ephedrine
  3. morphine
  4. Caffeine
  5. Cocaine
28
Q

Describe classification of alkaloids

A
  1. No uniform classification
  2. Most recent classifications based on similarity of- carbon skeleton (indole-, isoquinoline-, pyridine-like) and biochemical precursor (which amino acid)
  3. Used to be based on the common natural source e.g. type of plant
29
Q

What is cocaine

A
  1. Stimulating, appetite supressing local anesthetic
  2. High addictive due to interactions with the mesolimbic reward pathway which increases dopamine production in the brain
  3. First derived from tropinone
30
Q

Describe biosynthesis of cocaine

A
  1. Start with L-glutamine which is decarboxylated by PLP enzyme producing putrescine
  2. N-methylation by SAM enzyme to produce N-methylputrescine
  3. Diamine oxidase oxidises NH2 to =O
    4.
30
Q

Describe first part of biosynthesis of cocaine

A
  1. Start with L-glutamine which is decarboxylated by PLP enzyme producing putrescine
  2. N-methylation by SAM enzyme to produce N-methylputrescine
  3. Diamine oxidase oxidises NH2 to =O
  4. Shiff base formation to form iminium species
31
Q

Describe second part of the biosynthesis of cocaine

A
  1. React iminium with Coenzyme A- Happens twice
  2. Hydroxylated by hydroxylase enzyme
  3. elimination to generate another iminium
  4. Aminolate attack of iminium
  5. Then remove coenzyme to get OMe
  6. Then reduction steps to get to cocaine
32
Q

What did Willstatter do

A
  1. synthesised cocaine over many many steps
  2. Proved cocaine had tropane core structure
33
Q

What did Robinson do

A
  1. Different method to build tropinone core
  2. Did retrosynthetic approach
  3. Dialdehyde, H2NMe, acetone are basic components - starting materials
34
Q

Describe double Mannich reaction

A
  1. One-pot -refined to have 90% yield

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