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!