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Biosynthesis > Biotransformations > Flashcards

Biotransformations Flashcards

1
Q

Types of hydrolytic enzymes

A

Lipases
Esterases
Proteases

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2
Q

PPL

A

Porcine pancreatic lipase

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3
Q

PCL

A

Pseudomonas cepacia lipase

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4
Q

PSL

A

Pseudomonas species lipase

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5
Q

CAL-B

A

Candida Antarctica lipase B

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6
Q

ACE

A

Acetylcholine esterase

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7
Q

PLE

A

Pig liver esterase

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8
Q

CE

A

Cholesterol esterase

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9
Q

Examples of proteases

A

Chymotrypsin
Thermolysin
Carboxypeptidase A

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10
Q

Alpha-chymotrypsin

A

Selectively hydrolyses amide bonds where the R group on the carboxylic acid portion of the molecule is aromatic

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11
Q

Trypsin R group

A

Polar

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12
Q

Elastase

A

Small, uncharged group

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13
Q

Alpha-chymotrypsin mechanism

A

Serine protease

Catalytic triad = Asp(102), His(57), Ser(195)

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14
Q

Xenobiotic substrate

A

Not encountered in a biological environment

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15
Q

Disadvantages of kinetic resolution

A

Max yield of product is 50 % (at 100 % ee)

But often the isolate yield and enantioselectivity are lower than this

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16
Q

Desymmetrisation reaction

A

100 % yield

Achiral –> single enantiomer

17
Q

tBu group

A

Often inert to enzymes
Very bulky
Very few examples of natural products containing a tBu group
Can exploit this inertness in kinetic resolutions, for example tBu esters won’t be affected by enzymes

18
Q

Why is an aqueous buffer solution required for large scale ester hydrolyses?

A

Production of a carboxylic acid will lower the pH of the solution
Enzymes are pH-sensitive so a low pH may compromise their activity

19
Q

Irreversible transesterification

A

Use a vinyl alcohol (its ester is often referred to as the ‘acyl donor’)
Can undergo keto-enol tautomerisation
Can drive reaction to completion

20
Q

Mitsunobu inversion

A

Can use to obtain the opposite enantiomer of the alcohol

21
Q

Dynamic kinetic resolution

A

Can take place when the 2 enantiomers of the starting material are in dynamic equilibrium
Enzyme will only react with one enantiomer
In this way, both enantiomers of the starting material are converted into one enantiomer of the product

22
Q

Criteria for a dynamic kinetic resolution

A
  1. Racemisation of starting material
  2. Stereoselective catalyst that only reacts with one enantiomer
  3. Reaction conditions do not induce racemisation of the product or interfere with/prevent enzyme function
23
Q

Why are cyanohydrins good substrates for DKRs with enzymes?

A

They can be racemised in the presence of base

Draw

24
Q

Rationale behind using a basic resin

A

Enzyme incompatible with bases in solution

Use of a basic resin minimises interaction with the enzyme

25
Q

Oxazolinones

A

Draw

26
Q

Why are oxazolinones easy to racemise, even at neutral pH?

A

The anion formed upon deprotonation is a 6pi aromatic system

27
Q

Why are “whole cell” organic reactions difficult to set up?

A

Yeast need to grow in water but the SM or product may have low water solubility
Yeast often only tolerate low concentrations of SM/product, so need to use several litres of water per gram of substrate
Often difficult to isolate the product at the end of the reaction - have to extract from all the water and get rid of lots of impurities

28
Q

Fumarase

A

Selectively adds water to fumaric acid, leading to the formation of malic acid as a single enantiomer

29
Q

Hydration of nitriles

A

Nitrile group can be hydrolysed to a primary amide using various bacteria e.g. rhodococcus butanica

30
Q

Epoxide hydrolase

A

Hydrolysis of epoxides

31
Q

Alcohol dehydrogenase

A

Can catalyse the conversion of ketones to alcohols

Uses NADH as a cofactor

32
Q

Balance between NADH/NAD+

A 
NADH = neutral, non-aromatic
NAD+ = charged, aromatic
33
Q

How to regenerate NADH (use it catalytically)

A

Use a second enzyme (formate dehydrogenase) and formate as a cheap reductant

34
Q

Leucine dehydrogenase

A

Catalyses the conversion of a ketone into an amine in the presence of ammonium salts
Occurs via the imine, then enzyme-catalysed reduction of the imine to the amine

35
Q

Oxidation reactions that can be achieved by biotransformations

A
  1. Biotransformation equivalent of the Baeyer-Villager reaction (achiral ketone to chiral lactone using mono-oxygenase)
  2. Enantioselective oxidation of sulphides into sulphoxides using Aspergillus niger (S = stereocentre)
36
Q

Mitsunobu inversion reagents

A

PPh3

DEAD (diethyl azodicarboxylate)

Biosynthesis (2 decks)

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