Post on 16-Feb-2020
Production of enantiomers
Edit Székely
Budapest University of Technology and Economics
Nature is asymmetric
Hands Shells Plants
C C
C-tetrahedra P-bipyramids
Different biological effects
Name R or R,R
enantiomer
S or S,S
enantiomer
Aspartame bitter sweet
Limonene smelling of
orange
smelling of
lemon
Chloramphenicol antibacterial
agent inactive
Hexobarbital inactive sleeping pill
Thalidomide sedative teratogenic N
N
O
OH
H
O
O
thalidomide
NH H
COOMe
O
COOHNH2
H
aspartam
OH
NH
O
CHCl2
OH
O2N
chloramphenicol
limonene
Definitions
Optical purity (OP)
Enantiomeric excess (ee)
T maxλ,
T
measuredλ,OP
optical rotatory power
SR
SRee
R- and S enantiomers of a racemic
compound
Preparation of enantiomers
Introduction
Natural
source Prochiral
compounds
Enantiopure product
Extraction/
purification
Modification
Asymmetric
synthesis
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Kinetic
resolution
Diastereomer
formation
Direct
crystallization
Enaniopure product
Chromatography
Preparation of enantiomers
Introduction
Natural
source
Enantiopure product
Extraction/
purification
Isolation from natural sources –
example: paclitaxel (taxol)
(-) –paclitaxel=
(1S,2S,3R,4S,7R,9S,10S,12R,15S)-4,12-
Diacetoxy-15-{[(2R,3S)-3- (benzoylamino)-
2-hydroxy-3- phenylpropanoyl]oxy}-1,9-
dihydroxy-10,14,17,17-tetramethyl -11-
oxo-6-oxatetracycloheptadec-13-en-2-yl
rel-benzoate
Originally found and
isolated from Taxus
brevifolia (pacific yew)
Isolation from natural sources –
example: paclitaxel (taxol)
Originally found and isolated
from Taxus brevifolia (pacific
yew)
Harvesting
Peeling
Grinding etc.
Extraction
Chromatography
Crystallization
Impossible in
scales big
enough to fulfill
the needs
Isolation from natural sources –
example: paclitaxel (taxol)
Originally found and isolated
from Taxus brevifolia (pacific
yew)
Currently produced by
fermentation of plant cells
(PCF) followed by
Extraction
Chromatography
Crystallization
Phyton Biotech LLC
Isolation from natural sources –
example: paclitaxel (taxol)
Originally found and isolated
from Taxus brevifolia (pacific
yew)
Currently produced by
fermentation of plant cells
(PCF)
Analogues might be produced
by fungies, or isolated from
byproducts of food industry (no
commercial applications yet)
Preparation of enantiomers
Introduction
Natural
source
Enantiopure product
Extraction/
purification
Modification
Isolation from natural sources followed
by further modification -examples
Alkaloids like
morphines (applied
also unchanged)
Antibiotics, e.g. penicillin G
based
Produced by fermentation
Extraction with butyl acetate
Forming K-salt, precipitates
Further purification and
modifications
Preparation of enantiomers
Introduction
Natural
source Prochiral
compounds
Enantiopure product
Extraction/
purification
Modification
Asymmetric
synthesis
Catalytic asymmetric synthesis
The enantioselective conversion of a
prochiral substrate to an optically
active product
chiral catalysts: chiral acid
chiral base
metal complex
Different types of metal-complex reactions
– in supercritical fluids (applies also to other solvents)
Jessop and Leitner in Jessop, P., Leitner, W. (Eds):
Chemical Synthesis Using Supercritical Fluids, Wiley-VCH, Weinheim, 351, (1999)
Reactants Products
Catalyst
SCF
Reactants Products
Catalyst
SCF
solid
Reactants Products
Catalyst
SCF
liquid Reactants Products
CatalystSCF
liquid
Homogeneos hydrogenation
CH3
H
CH3
COOH H
CH3
H H
CH3
COOH
50 °C
+Ru-catalyst
scCO2
H2
tiglic acid 2-methylbutanoic acid
Catalyst: [Ru(OCOCH3)2((S)-H8-binap]
Xiao et al., Tetrahedron Letters, 37(16), 2813 (1996)
Reaction medium H2 (bar) Product
Yield (%) ee (%)
scCO2 33 99 81
scCO2 7 23 71
scCO2/CF3(CF2)6CH2OH 5 99 89
Methanol 30 100 82
Hexane 30 100 73
Heterogeneous hydrogenation
CH3
OC2H
5
OO O
OC2H
5CH
3
OH+ H2
catalyst
sc ethane
ethyl pyruvate ethyl lactate6 MPa, 40 °C
Hydrogenation of ethyl pyruvate catalyzed by
Pt/Al2O3 modified with cinchonidine
Baiker, Chem. Rev., 99, 453 (1999)
Solvent Psolvent
(bar)
PHydrogen
(bar)
T
(K)
X
(%)
ee
(%)
sc ethane 60 70 293 98 74
scCO2 80 20 313 2 29
scCO2 80 70 313 3 28
Toluene - 70 323 100 75
X: conversion
Hydrogenation
S.E. Lyubimov et al. / J. of Supercritical Fluids 45 (2008) 70–73
dimethyl itaconate
Cymantrene type ligands
Hydrogenation
S.E. Lyubimov et al. / J. of Supercritical Fluids 45 (2008) 70–73
Solvent Ligand Pco2
(bar)
PH2
(bar)
t
(h)
X
(%)
ee
(%)
scCO2 3 100 100 2 100 90
scCO2 4 100 100 1.5 100 81
CH2Cl2 3 - 20 14 100 95
CH2Cl2 4 - 20 16 100 79
dimethyl itaconate
35°C
X: conversion
Heterogeneous hydrovinylation
Rodrıguez et al. / Journal of Organometallic Chemistry 693 (2008) 1857–1860
Heterogeneous hydrovinylation of
styrene
Rodrıguez et al. / Journal of Organometallic Chemistry 693 (2008) 1857–1860
Solvent Catalyst Pco2
(bar) T (°C) S (%)
X
(%)
ee
(%)
scCO2 1 100 45 96.6 36.7 76
CH2Cl2 1 - 25 99.9 29.3 83
scCO2 2 100 45 95.1 38.1 71
CH2Cl2 2 - 25 98.5 29.5 75
scCO2 3 100 45 94.4 40.2 74
CH2Cl2 3 - 25 98.6 27.4 79
pC2H4=25 bar, t=2 h
X: conversion
S: selectivity
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Kinetic
resolution
Diastereomer
formation
Direct
crystallization
Enaniopure product
Chromatography
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Direct
crystallization
Enaniopure product
Direct crystallization in
enantioseparations It is only
possible if the
racemate forms
conglomerate
(ca. 20% of all
racemates)
It is not
possible if the
racemate forms
racemic
compound.
Conglomerate,
homochiral
Racemic compound,
heterochiral
Direct crystallization in
enantioseparations
x x
x
1 1
2
x
x
4
3 1
2
solvent
solvent solvent
solvent solvent
T decrease
Direct crystallization in
enantioseparations
Continuous attention is
necessary, thus skilled
operators are needed.
Adventages:
high purity material is
crystallized
No added compound, thus
no need to get rid of it.
x
4
3 1
2
solvent
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Direct
crystallization
Enaniopure product
Chromatography
Chromatography
A separation technique based on the different
distribution of different compounds (solutes) between
a mobile and a stationary phase.
The sample is injected to the mobile phase.
Main types:
HPLC (high performance liquid chromatography)
GC (gas chromatography)
SFC (supercritical fluid chromatography)
Chiral selectors
Small molecules: amino acids, alkaloids
Natural polymers: peptides, proteins,
carbohydrates
Synthetic selectors: brush-type (Pirkle)
phases, polyacrylates, polysiloxanes,
copolymers, polysaccharide type
stationary phases, cyclodextrins
Chromatographic terms
12 kkα
MMR /tttk Retention factor
Separation factor
Resolution of peaks R 2 R1
1 2
2(t t )R
w w
signal
time
tM
tR1
tR2
w1 w2
tR Retention time
tM Unretained peak hold-up time
w Widthness of peak
Chromatography
o Separation is influenced by:
o Stationary phase and studied compound
o Properties of mobile phase:
o Temperature (GC, SFC)
o Modifier type and composition (SFC, HPLC)
o Pressure (SFC)
Scale-up of of chromatography
Remember! Preparative chromatography is not
the same chromatography we use for analytics!
Continuous chromatography: stacked-mode
injection
OH
OH
OH
OH
(R)-(+)-BINOL (S)-(-)-BINOL
1,1'-binaphthyl-2,2'-diol
m.p. 205-211°C
barrier of rotation > 24 kcal.mol-1
Stacked mode injection
Thar Technologies
Scale-up of chromatography
Remember! Preparative chromatography is not
the same chromatography we use for analytics!
Continuous:
Stacked-mode injection
Increasing size of the separation column
Increasing the injected amount of substance
Employing many columns in paralell
From Batch to continous:
Simulated moving bed technology
Simulated moving bed (SMB)
chromatography (idea)
Typical schemes of SMB
Recirc
ula
tion o
f liquid
Recirc
ula
tion o
f solid
Aerojet Fine
Chemicals
Column diameter of
80 cm.
…and in reality
Requirements to achive total,
continuous separation
Section I.: regeneration have to be perfect.
Neither A nor B are allowed to remain on
the surface.
Section II.: all B have to enter section III, while
most of A is preferred to remain in the
column.
Section III.: only B component can leave the
column, not even traces of A.
Section IV.: only component B is allowed the
enter section IV, but it should not leave the
coulmn before the next switch.
(A more retained, B less retained enantiomer)
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Diastereomer
formation
Direct
crystallization
Enaniopure product
Chromatography
Diastereomer can be formed by…
Formation of covalent bonds
Generally not viable, because decomposing
the diastereomer is difficult and may cause
racemization.
In special cases, when the resolving agent will
a part of the final molecule, it might be the
best choice.
Diastereomer can be formed by…
Formation of covalent bonds – example
(blood pressure regulator)
N COOH
O
SH
H
H
N COOH
O
Br
H
H
N COOH
O
Br
H
HNH
COOH
HO
ClBr
racemate: (R,S) resolving agent (S-proline) (S)-(S) (R)-(S)
ingredient of captopril
++
Diastereomer can be formed by…
Formation of covalent bonds
Salt formation
Pasteur (1848) DL + 2R DR + LR
Pope and Peachy (1899) DL + R + A DR + LA
Modified Pope and Peachy method
DL + R DR + L
Basic idea of resolution via
diastereomeric salt formation
Formation of diastereomer salts
are influanced by…
Selection of resolving agents
Efficient, available, stable, preferably cheap and
reusable.
Most important resolving agents of bases: tartaric
acid + its derivatives, mandelic acid + its isomers,
champhor sulfuric acid
Most important resolving agents of acids used to be
natural alkaloids but now synthetic resolving agents
are widely applied (e.g. 2-phenylethyl-amine)
3 point interaction is necessary
Experiments needed.
Formation of diastereomer salts
are influenced by…
Selection of resolving agents
Solvents
Temperature (pressure) of crystallization
Inoculation
Added materials
Etc.
Optimization is still based on experiments.
Supercritical fluid extraction (SFE)
Sample preparation
Extraction Salt
decomposition
Racemic
compound +
Resolution
agent
Solved in
an
appropiate
solvent
Supporting
material
added
Solid
sample
evaporation
CO2 vessel extractor separator
pump cooler thermostate
raffinate extract
gas meter
Sample preparation
Extraction Salt
decomposition
Factors of chiral resolution
Molar ratio
Support
Solvent
Pressure
Temperature
Extraction time
- used CO2
Flow rate
Sample preparation
Extraction Salt
decomposition
Example Effects are shown on the example of resolution of
tetramisole with (-)-dibenzoyl-tartaric acid (DBTA)
S
NN H
H
COOH
HOOCCOOPh
PhOOC
+
methanol
perfil
solid dextramisole
+
levamisole - DBTA
SFE
extract
dextramisole
raffinate
levamisole - DBTA
+
support
levamisole
DBTA
tetramisole
DBTA
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
Effect of molar ratio
0
0.1
0.2
0.3
0
20
40
60
80
100
0 0.25 0.5 0.75 1
FE
ee
E(%
), Y
E(%
)
molar ratio
eeEYE
FE
Selectivity: EEE eeYF 2
0
e
m
m SR
SR
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
Compounds
Effects of P and T cis-chrysanthemic acid + S-(+)-2-benzylamino-1-butanol
COOHOH
NH
-0.875
3.630
4.089
4.475
5.069
6.838
19.51
-23.10
p=0.05
Standardized Effect Estimate
PE2 x TE
PE x TE
PE x TE2
PE2
TE2
PE2 x TE
2
PE
TE
F = FE + FR
Keszei S., PhD Theses, Budapest, 1999.
Compounds
Effects of P and T
0.100
-0.111
-0.378
0.535
0.607
-0.756
1.393
9.889
p=0.05
Standardized Effect Estimate
PE x TE
TE2
PE2 x TE
TE
PE2 x TE
2
PE x TE2
PE2
PE
HOOC
H
NH2
ibuprofen + R-(+)-α-phenylethylamine
F = FE + FR Fogassy E., Ács M., Szili T., et al.,
Tetrahedron Letters, 35 (2), 257-260 (1994).
Keszei S., PhD Theses, Budapest, 1999.
Compounds
Effects of P and T
-0.577
0.612
0.638
-0.795
1.000
-1.732
-3.192
18.58
p=0.05
Standardized Effet Estimate
PE2 x TE
PE
PE2
PE2 x TE
2
PE x TE
PE x TE2
TE2
TE
N
SPh N H
HCOOH
HOOCCOOPh
PhOOCH2O
tetramisole + O,O’-dibenzoyl-(2R,3R)-tartaric acid monohydrate
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
Compounds
Effects of P and T
-0.577
-0.577
1.155
-1.512
p=0.05
Standardized Effect Estimate
PE
TE
PE x TE
Curvature
NH
F
CH3
H
HCOOH
HOOCCOOPhCH
3
CH3PhOOC
F-quinoline + O,O’-di-p-toluoyl-(2R,3R)-tartaric acid
Kmecz I., Simándi B., Bálint J. et al.,
Chirality, 13, 568-570 (2001).
Diastereomer can be formed by…
Formation of covalent bonds
Salt formation
Complex formation
OH
OH
OH
OH
HOOC
COOH
OH
OH
+
SFE, 1st extract
OH
OH
S,S-4
SFE, 2nd extract
OH
OH
R,R-4
Székely E., Bánsághi Gy., Thorey P. et al.,
Ind. Eng. Chem. Res., 49, 9349-9354 (2010).
Fractionated SFE
Sample
preparation Extraction
Decomposition
of complex
Total elimination of organic solvents
separation of both
enantiomers by fractionated
supercritical fluid extraction
no
solvent
Extraction curves
OH
OH
OH
OH
HOOC
COOH
OH
OH
+
Székely E., Bánsághi Gy., Thorey P. et al.,
Ind. Eng. Chem. Res., 49, 9349-9354 (2010).
Compounds 1st step 2nd step At P=1 bar
Rac.
Comp.
Res.
agent
P
(MPa)
T (°C) P
(MPa)
T (°C) T decomp
(°C)
1 6 10 33 20 70 86
2 6 10 33 20 80 93
3 6 10 33 20 80 98
4 7 20 33 20 95 137
5 6 4 10 20 50 68
Comparison of process steps
OH
R1
R2
1: R1: Cl,R2:H2: R1: Br, R2: H3: R1: I, R2: H4: R1: OH, R2: H5: R1: CH3CH2CH3, R2: CH3
OH
R1
R2
+
OR
1'
O
R1'
HOOC
COOH
6: R1': H7: R1': Ph
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Introduction
Kinetic
resolution
Diastereomer
formation
Direct
crystallization
Enaniopure product
Chromatography
Kinetic resolutions
- by enzyme catalysis in supercritical fluids
enzymes are chiral catalysts
very mild conditions (low temperatures)
water-insoluble compounds can be processed
in single phase
enzymes do not dissolve in CO2
efficient separation/fractionation of
substrates, products, catalyst
mainly kinetic resolution is viable
The stability, activity and selectivity of
enzymes is influenced by…
water content
temperature
pressure (changes in pressure)
mass transfer
immobilization
Selection of enzyme
Enzyme X, % eediacetate, %
PPL 50.1 45.1
Lipase PS "Amano " 66.5 73.6
Lipase AK " Amano" 84.7 71.6
Trichoderma reesei 84.6 25.0
Thermoascus thermophilus 83.6 21.2
Talaromiches emersonii 80.6 19.2
O OH
OH O OH
OAc
O OAc
OHO OAc
OAc
Lipase enzym
vinyl-acetate
rac-3-benziloxy-1,2-propanediol
I. Kmecz et al. / Biochemical Engineering Journal 28 (2006) 275–280
260 min, 100 bar, 40 °C
Effect of substrate
Acylation of 3-hydroxy octanoic acid methyl ester,
(LPS Amano, 40 °C, 120 bar, 20 h)
Capewell et al., Enzyme Microb. Technol., 19, 181 (1996)
Substrate ee (%) X (%) E
Styryl acetate 38 7 2.3
Isopropenil acetate 60 10 4.3
Vinyl acetate 65 38 4.8
E: enantioselectivity
Effect of pressure on conversion
(CALB at fixed, 22 hours of reaction time)
Utczás M., Székely E., Tasnádi G., et al., J. Supercrit. Fluids, 55, 1019-1023 (2011).
Purification of enantiomeric
mixtures
The process is called enantiomeric
enrichment
Necessary in all cases when ee does not
meet the requirements (ee>99% or
higher)
Mostly with any of separation methods
after crystal formation.
Purification of enantiomeric
mixtures with crystallization
Conglomerate Racemic compound
Purification of enantiomeric
mixtures Recrystallization
Repeated resolution
with same or different chiral resolution agent
what to do with different ee mixtures
What to do with the mixtures of
different ee?
Székely E., Bánsághi Gy., Thorey P., et al.,
Ind. Eng. Chem. Res., 49, 9349-9354 (2010).
Purification of enantiomeric
mixtures Recrystallization
Repeated resolution
with same or different chiral resolution agent
what to do with different ee mixtures
Use of achiral reagent
based on the non-ideal behaviour of enantiomeric
mixtures
forms an unsoluble salts with the racemic part or
enantiomer in excess
easy and cheap
Conclusions
Chirality is present in our everyday life, and major products of pharmaceutical, flavour and fragnance, food etc. industries are chiral molecules.
According to the regulations if only one of the enantiomers is active, it has to be marketed in enantiopure form.
Process development for pure enantiomers needs the cooperation of chemists and chemical engineers.
Major techniques:
Production of enantiomers
Natural
source
Prochiral
compounds
Racemate
Asymmetric
synthesis
Extraction
Modification
Conclusion
Kinetic
resolution
Diastereomer
formation
Direct
crystallization
Enaniopure product
Chromatography
THANK YOU FOR YOUR KIND
ATTENTION!