PRODUCTION OF ENANTIOMERS IN SUPERCRITICAL FLUIDS

Production of enantiomers
Edit Székely
Budapest University of Technology and Economics
Nature is asymmetric
Hands
Shells
C-tetrahedra
C
Plants
P-bipyramids
C
Different biological effects
COOMe
HN H
O
COOH
H2N
H
aspartam
limonene
OH OH
HN
O 2N
CHCl 2
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
O
chloramphenicol
O
H
N
O
O
O
thalidomide
N
H
Definitions
Optical purity (OP)
 Tλ, measured
OP 
 Tλ, max
optical rotatory power
Enantiomeric excess (ee)
R S
ee 
R S
R- and S enantiomers of a racemic
compound
Preparation of enantiomers
Natural
source
Prochiral
compounds
Extraction/
purification
Asymmetric
synthesis
Modification
Enantiopure product
Introduction
Production of enantiomers
Prochiral
compounds
Natural
source
Racemate
Extraction
Diastereomer
formation
Kinetic
resolution
Modification
Direct
crystallization
Chromatography
Enaniopure product
Introduction
Asymmetric
synthesis
Preparation of enantiomers
Natural
source
Extraction/
purification
Enantiopure product
Introduction
Isolation from natural sources –
example: paclitaxel (taxol)

(-) –paclitaxel=
(1S,2S,3R,4S,7R,9S,10S,12R,15S)-4,12Diacetoxy-15-{[(2R,3S)-3- (benzoylamino)2-hydroxy-3- phenylpropanoyl]oxy}-1,9dihydroxy-10,14,17,17-tetramethyl -11oxo-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
Natural
source
Extraction/
purification
Modification
Enantiopure product
Introduction
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
Natural
source
Prochiral
compounds
Extraction/
purification
Asymmetric
synthesis
Modification
Enantiopure product
Introduction
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)
Reactants
Products
Reactants
Products
SCF
Catalyst
SCF
Reactants
Products
Catalyst
SCF
liquid
SCF
Catalyst
liquid
solid
Catalyst
Reactants
Products
Jessop and Leitner in Jessop, P., Leitner, W. (Eds):
Chemical Synthesis Using Supercritical Fluids, Wiley-VCH, Weinheim, 351, (1999)
Homogeneos hydrogenation
Catalyst: [Ru(OCOCH3)2((S)-H8-binap]
H
COOH
+
H3C
H
Ru-catalyst
H2
CH3
H
H3C
scCO2
COOH
H
CH3
50 °C
tiglic acid
2-methylbutanoic acid
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
Xiao et al., Tetrahedron Letters, 37(16), 2813 (1996)
Heterogeneous hydrogenation
Hydrogenation of ethyl pyruvate catalyzed by
Pt/Al2O3 modified with cinchonidine
O
O
+
H3C
OC2H5
H2
catalyst
HO
sc ethane
H3C
6 MPa, 40 °C
O
OC2H5
ethyl lactate
ethyl pyruvate
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
-
70
323
100
75
Toluene
X: conversion
Baiker, Chem. Rev., 99, 453 (1999)
Hydrogenation
dimethyl itaconate
Cymantrene type ligands
S.E. Lyubimov et al. / J. of Supercritical Fluids 45 (2008) 70–73
Hydrogenation
dimethyl itaconate
35°C
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
S.E. Lyubimov et al. / J. of Supercritical Fluids 45 (2008) 70–73
X: conversion
Heterogeneous hydrovinylation
Rodrıguez et al. / Journal of Organometallic Chemistry 693 (2008) 1857–1860
Heterogeneous hydrovinylation of
styrene
pC2H4=25 bar, t=2 h
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
Solvent
Rodrıguez et al. / Journal of Organometallic Chemistry 693 (2008) 1857–1860
X: conversion
S: selectivity
Production of enantiomers
Prochiral
compounds
Natural
source
Racemate
Extraction
Diastereomer
formation
Kinetic
resolution
Modification
Direct
crystallization
Chromatography
Enaniopure product
Introduction
Asymmetric
synthesis
Production of enantiomers
Prochiral
compounds
Natural
source
Racemate
Extraction
Modification
Direct
crystallization
Enaniopure product
Introduction
Asymmetric
synthesis


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
solvent
solvent
solvent
T decrease
x
x
1
3
2
4
solvent
solvent
x
1
1
2
x
x
Direct crystallization in
enantioseparations


Continuous attention is
necessary, thus skilled
operators are needed.
Adventages:
solvent
1
3
2
4
 high
purity material is
crystallized
 No added compound, thus
no need to get rid of it.
x
Production of enantiomers
Prochiral
compounds
Natural
source
Racemate
Extraction
Modification
Direct
crystallization
Chromatography
Enaniopure product
Introduction
Asymmetric
synthesis
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
signal
Retention factor
k  t R  t M /t M
Separation factor
α  k 2 k1
2(t R 2  t R1 )
Resolution of peaks R 
w1  w 2
t
M
tR1
tR Retention time
tM Unretained peak hold-up time
tR2
w Widthness of peak
w1
w2
time
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
Stacked mode injection
OH
OH
OH
OH
(S)-(-)-BINOL
(R)-(+)-BINOL
1,1'-binaphthyl-2,2'-diol
m.p. 205-211°C
barrier of rotation > 24 kcal.mol-1
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
Recirculation of liquid
Recirculation of solid
…and in reality
Aerojet Fine
Chemicals
Column diameter of
80 cm.
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
Prochiral
compounds
Natural
source
Racemate
Extraction
Diastereomer
formation
Modification
Direct
crystallization
Chromatography
Enaniopure product
Introduction
Asymmetric
synthesis
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
O
H
COOH
ingredient of captopril
H
SH
O
+
Br
Cl
racemate: (R,S)
N
H
H
COOH
resolving agent (S-proline)
N
H
COOH
N
H
COOH
+
O
H
O
H
Br
Br
(S)-(S)
(R)-(S)
Diastereomer can be formed by…
Formation of covalent bonds
 Salt formation

Basic idea of resolution via
diastereomeric 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
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)
Salt
decomposition
Sample
preparation
Extraction
Racemic
compound
+
Solved in
an
appropiate evaporation Solid
solvent
sample
Resolution
agent
Supporting
material
added
Sample
preparation
Extraction
Salt
decomposition
gas meter
CO2 vessel
extractor
separator
raffinate
cooler
thermostate
pump
extract
Factors of chiral resolution
Sample
preparation
Extraction
Salt
decomposition
Molar ratio
Pressure
Support
Temperature
Solvent
Extraction time
- used CO2
Flow rate
Example
Effects are shown on the example of resolution of
tetramisole with (-)-dibenzoyl-tartaric acid (DBTA)
COOH
H
PhOOC
+
N
N
H
HOOC
methanol
solid dextramisole
+
perfil
COOPh
levamisole - DBTA
SFE
S
DBTA
tetramisole
levamisole
extract
raffinate
levamisole - DBTA dextramisole
+
DBTA
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
support
Effect of molar ratio
Selectivity: FE  2  YE  eeE
me

m0
100
80
0.3
eeE
YE
0.2
60
FE
eeE (%), YE (%)
RS

RS
40
0.1
FE
20
0
0
0
0.25
0.5
molar ratio
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
0.75
1
Compounds
Effects of P and T
cis-chrysanthemic acid
+
S-(+)-2-benzylamino-1-butanol
COOH
OH
N
H
TE
-23.10
PE
19.51
PE2 x TE2
6.838
TE2
5.069
PE2
4.475
PE x TE2
PE x TE
PE2 x TE
4.089
3.630
-0.875
p=0.05
Standardized Effect Estimate
F = F E + FR
Keszei S., PhD Theses, Budapest, 1999.
Compounds
Effects of P and T
ibuprofen
+
R-(+)-α-phenylethylamine
HOOC
H
NH2
PE
9.889
PE2
PE x TE2
1.393
-0.756
PE2 x TE2
0.607
TE
0.535
PE2 x TE
-0.378
TE2
PE x TE
-0.111
0.100
p=0.05
Standardized Effect Estimate
F=
Fogassy E., Ács M., Szili T., et al.,
Tetrahedron Letters, 35 (2), 257-260 (1994).
Keszei S., PhD Theses, Budapest, 1999.
F E + FR
Compounds
Effects of P and T
tetramisole
+
O,O’-dibenzoyl-(2R,3R)-tartaric acid monohydrate
H
N
Ph
PhOOC
N
S
TE
18.58
TE2
PE x TE2
HOOC
-3.192
-1.732
PE x TE
1.000
PE2 x TE2
-0.795
PE2
0.638
PE
0.612
PE2 x TE
-0.577
p=0.05
Standardized Effet Estimate
Keszei S., Simándi B., Székely E. et al.,
Tetrahedron: Asymmetry, 10, 1275-1281 (1999).
COOH H2O
H
COOPh
Compounds
Effects of P and T
F-quinoline
+
O,O’-di-p-toluoyl-(2R,3R)-tartaric acid
F
H
CH3PhOOC
N
H
Curvature
CH3
HOOC
-1.512
PE x TE
1.155
TE
-0.577
PE
-0.577
p=0.05
Standardized Effect Estimate
Kmecz I., Simándi B., Bálint J. et al.,
Chirality, 13, 568-570 (2001).
COOH
H
COOPhCH3
Diastereomer can be formed by…
Formation of covalent bonds
 Salt formation
 Complex formation

OH
HOOC
OH
OH
OH
+
HO
HO
SFE, 1st extract
COOH
SFE, 2nd extract
OH
OH
OH
HO
S,S-4
R,R-4
Székely E., Bánsághi Gy., Thorey P. et al.,
Ind. Eng. Chem. Res., 49, 9349-9354 (2010).
Fractionated SFE
Total elimination of organic solvents
Sample
preparation
no
solvent
Extraction
Decomposition
of complex
separation of both
enantiomers by fractionated
supercritical fluid extraction
Extraction curves
OH
HOOC
OH
OH
OH
+
HO
HO
Székely E., Bánsághi Gy., Thorey P. et al.,
Ind. Eng. Chem. Res., 49, 9349-9354 (2010).
COOH
Comparison of process steps
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
OH
OH
R1
HOOC
R1
+
R2
1: R1: Cl,R2:H
2: R1: Br, R2: H
3: R1: I, R2: H
4: R1: OH, R2: H
5: R1: CH3CH2CH3, R2: CH3
R2
O
R1'
6: R1': H
7: R1': Ph
O
R1'
COOH
Production of enantiomers
Prochiral
compounds
Natural
source
Racemate
Extraction
Diastereomer
formation
Kinetic
resolution
Modification
Direct
crystallization
Chromatography
Enaniopure product
Introduction
Asymmetric
synthesis
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
OAc
vinyl-acetate
OH
O
OH
OH
O
OAc
Lipase enzym
rac-3-benziloxy-1,2-propanediol
OH
O
O
OAc
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
260 min, 100 bar, 40 °C
I. Kmecz et al. / Biochemical Engineering Journal 28 (2006) 275–280
OAc
Effect of substrate
Acylation of 3-hydroxy octanoic acid methyl ester,
(LPS Amano, 40 °C, 120 bar, 20 h)
Substrate
ee (%)
X (%)
E
Styryl acetate
38
7
2.3
Isopropenil acetate
60
10
4.3
Vinyl acetate
65
38
4.8
E: enantioselectivity
Capewell et al., Enzyme Microb. Technol., 19, 181 (1996)
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
Prochiral
compounds
Natural
source
Racemate
Extraction
Diastereomer
formation
Kinetic
resolution
Modification
Direct
crystallization
Chromatography
Enaniopure product
Conclusion
Asymmetric
synthesis
THANK YOU FOR YOUR KIND
ATTENTION!