Conversion of Racemic Ibuprofen to (S)-Ibuprofen

David Chavez-FloresPh.D. James Salvador

Outline

• Introduction• Objective • Experimental • Results• Conclusions and future work• Acknowledgments

Chiral Molecules • A molecule that is not identical to its mirror image is

asymmetric and named chiral. The most common chiral compounds which exist are enantiomers.

• Enantiomers are typically characterized by an asymmetric tetrahedral carbon

Solomons, T.W. 1994Rules for Specification of Chirality http://tigger.uic.edu

Metabolism SelectivityThe drug metabolism is highly enantioselective and lead different pharmacological activities of the enantiomers

Faber., 1999

Thalidomide• Thalidomide was used in the 1950s and 1960s on pregnant women

to avoid the morning sickness• The (R)-enantiomer is the effective against the morning sickness but

the (S)- enantiomer is tetarogenic and causes birth deffects.

Enantiomers

O

CO

Na(S)

O

OH

HH2N

O

CO

Na (R)

O

OH

NH2H

(R)

O

(S)

O

(R)(S)

N

O

O

(R)

NH

O

O

N

O

O

(S)

NH

O

O

(S)

O

Cl

NH

(R)

O

Cl

NH

HO

HO CH2

(S)

NH2H

C

Sodium (S)-glutamateflavor enhancer

Sodium (R)-glutamate

(S)-carvonecaraway seed

(R)-carvonespearmint

(S)-limonenelemon fragance

(R)-limoneneorange fragance

(R)-thalidomidetranquilizer

(S)-thalidomidetetarogenic

(S)-ketamineanesthetic

(R)-ketaminepsychotic

(S)-alpha-methyl-dopahypertensive O

OH

HO

HO CH2

(R)

NH2H

C(R)-alpha-methyl-dopa

inactive O

OH

(S)

O

OH HO

O

(R)

(S)-2-(4-isobutylphenyl)propanoic acid (R)-2-(4-isobutylphenyl)propanoic acid

Top 10 Drug 2003

Chemical and Engineering News (vol. 78, Oct. 23, 2004)

Top 10 Drug 2004

Chemical and Engineering News (vol. 78, Oct. 23, 2004)

Top 10 Drug 2005

Pharmaceutical Technology., April 2nd 2006

Example • Albuterol

– Racemic

– Single enantiomer

R-enantiomer of albuterol is responsible for the drug’s bronchodilating effectsS-enantiomer is responsible for adverse effects, including tachycardia, tremors, and nervousness.

Racemic Switch

• Is a reprocess and reformulation of a racemic mixture, into its single enantiomer product

• AstraZeneca marketed racemic Omeprozole as Prilosec and had the patent until April 2001 but now has a new patent on the (S)-enantiomer, know as Nexium or esomeprazole, for 17 more years

Enantiomer Separation

•Chromatography (A. M.)

•Asymmetric Synthesis

•Crystallization

•Enzymatic Resolution

Enzymatic Resolution

• Develop a clean synthesis “Green Chemistry”• Enzyme-catalyzed resolution of enantiomers

stereospecifically

Candida rugosa Lipase • Lipase is a water-soluble enzyme that catalyzes

hydrolysis of ester bonds in water-insoluble lipid substrates

• Candida rugosa Lipase has been used to resolve the enantiomers of naproxen, ibuprofen and suprofen due to its ability to catalyze reactions in non-aqueous based media

• Commercial availability• Recoverability

Structural Classification of Proteins http://scop.berkeley.edu

Ibuprofen

• Belongs to the Nosteroidal Antiinflammatory Drugs family

• Sold and administered as racemic mixture • (S)-Ibuprofen is the active enantiomer

COH

O

2-(4-isobutylphenyl)propanoic acid

(S)-Ibuprofen Activity

• Acts in 15 minutes, 3 times faster as the racemic mixture

• Reduce the side effects in a 50% • The dose is the half of the racemic mixture

Ibuprofen Toxicity • Most common adverse effects are dyspepsia, gastrointestinal ulceration/bleeding, salt and fluid retention, hypertension

Enantiomeric Excess (ee) and Enantioselectivity (E)

• In an enantiomerically enriched mixture, the excess of one enantiomer over the other is called an enantiomeric excess (ee).

• E describes how well the enzyme discriminates between the enantiomers of a substance under given reaction conditions

Objective

• Our goal is to develop an environmentallyfriendly method to convert the racemicmixture to the active enantiomer ofibuprofen ((S)-Ibuprofen) in a costeffective efficient way.

Part I

Ibuprofen was extracted with acetone from commercial ibuprofen tablets (200 mg/pill Member’s Mark) because it was really inexpensive

•4 ¢ gram Sam’s Club

• $12 gram Aldrich

Synthesis of (S)-Decyl Ibuprofen Ester

O

OHHO-(CH2)9-CH3+

Candida Rugosa Lipase

O

H2OO

OH

+

O

Cyclohexane 40 oC

Progress of the Reaction

Progress of the Reaction

0

10

20

30

40

50

60

0 10 20 30 40 50Time Hours

HP

LC S

pect

ra A

rea

%

(S)-decyl ibuprofen ester(R)-Ibuprofen(S)-ibuprofen

Ibuprofen Ester Separations

• Bulb to bulb distillation

• Radial Chromatography

• Extraction

Separation

• Chromatography• Extraction

• Distillation

(S)-Ibuprofen Ester HydrolysisO

R

O

Candida rugosa Lipase

Buffer pH 7.2O

OH

+ R-OH+ H2O

•Low concentration of Candida rugosa Lipase•Potassium phosphate pH 7.2 Buffer solution media•40 ºC and magnet agitation•In the hydrolysis, acid or base racemization, was the major concern

R O

O R'

H+

R O

O R'

H R O

O R'

H

H H H

R O

O R'

HR O

O R'

R O

O R'

R O

O R'H

OH

Summary Part I• Esterification

– Decan-1-ol• 48 hours to get a 47 % conversion at 40 C • High enantioselectivity up to 130 at 24 hours• Enantiomeric excess of 83 %

– Butan-1-ol• 96 hours to get a 48 % conversion • High enantioselectivity up to 46 at 48 hours• Enantiomeric excess of 63 %

• All separation methods distillation good for decan-1-ol– Chromatography good for both, extraction not good.

• Hydrolysis– 98 % enantiomeric excess in both reactions– 96 hours for the (S)-Decyl Ibuprofen Ester– 48 hours for the (S)-Butyl Ibuprofen Ester

Additional Work

• Temperature Effect

• Alcohol effect– Primary, secondary and tertiary– Different long chain

• Fisher esterification

Temperature Effect

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300Time hours

Con

vers

ion

25°C 30°C 35°C 40°C

45°C 50°C

Alcohols

• Candida rugosa lipase as catalyst showed a preference for the esterification of primary alcohols, while the secondary alcohols had a low rate and the tertiary ones could not be catalyzed

Esterification with different length of alcohols

• Methan-1-ol Slower• Ethan-1-ol• Butan-1-ol• Penta-1-ol• Octan-1-ol• Decan-1-ol Faster

Esterification with Methanol

05

10152025303540455055

0 20 40 60 80 100 120 140 160

Time in Hours

HPL

C s

pect

ra a

rea

Ester

R-Ibuprofen

S-Ibuprofen

Esterification eith Ethan-1-ol

05

101520253035404550

0 20 40 60 80 100 120 140 160

Time in Hours

HPL

C s

pect

ra a

rea

Ester

R-Ibuprofen

S-Ibuprofen

Esterification with Pentanol

05

10152025303540455055

0 5 10 15 20 25 30 35 40

T i me i n Hour s

HPL

C s

pect

ra a

rea

Ester

R-Ibuprofen

S-Ibuprofen

05

10152025303540455055

0 10 20 30 40

Con

vers

ion

Time in Hours

Esterification with Butanol

Ester

05

10152025303540455055

0 5 10 15 20

Con

vers

ion

Time in Hours

Esterification with Octanol

Ester

05

10152025303540455055

0 5 10 15 20

Con

vers

ion

Time in Hours

Esterification with Decanol

Ester

Fisher Esterification

O

OCH3 Buffer pH 7.2

45 °C

O

OH

O

OCH3

C. R. Lipase

• 99% conversion• 4 hours rxn

• ee = 76 %• E = 92

O

OH

Methanol

H45 °C

O

OCH3

Part II • Produce the (S)-ibuprofen ester by

enantioselective enzymatic esterification with racemization of the (R)-ibuprofen by acid, base addition or by photochemical reaction

+

O

H2O

ODecan-1-ol

Candida Rugosa Lipase

Cyclohexane 45 oC

CH2

CH3

9

+

O

OH

O

OH

R O

O R'

H+

R O

O R'

H R O

O R'

H

H H H

R O

O R'

HR O

O R'

R O

O R'

R O

O R'H

OH

Acids• p-toluenesulfonic acid• Phenyl dimethyl chlorosilane• Boric Acid• Pyruvic Acid• Isolute Si-Propylsulfonic Acid• Isolute Si-TsOH• p-toluene sulfonyl chloride

S

O

O

O

H

O

OH

O

OH

OH

OH

C R Lipase 45 °C

Cyclohexane

H

HH

H

R-Alchohol

O

OR

0

20

40

60

80

100

CRL Activity

[Acid]

Bases• PL-HCO3 MP Resin• PL-OH MP Resin• PL-CO3 MP Resin• Tributyl amine• Diethyl amine• Ethyl diisopropylamine

0102030405060708090

100

CRL Activity

[Base]

More Attempts

More Attempts

•Cyclohexane

•(S)-alkyl ibuprofen ester

•Ibuprofen sodium salt

•pH = 7.6 with NaOH

•Candida rugosa Lipase

•Alcohol

Photochemical racemization

• R-ibuprofen • S- ibuprofen • R-methyl ibuprofen ester• S-methyl ibuprofen ester

• All the samples were exposed directly to the sun rays for different time periods, only the esters showed complete racemization after 24 hours.

• UV Vis (absorption between 200 and 270 nm)• Experiments with the UV lamp at 254 nm

Photochemical racemization

Reaction Mechanism

O

OCH3

Candida rugosa Lipase

45 °CO

OH

CH3

O

OCH3

CH3CH3

O

OCH3

Aqueous Conditions

CH3

H H

[1,3] Sigmatropic Rearrengement

Allowed by Woodward-Hoffmann Rules

H

[1,3] Sigmatropic Rearrengement

hv hv

Current and future work

• Reaction characterization • Test the method with more NSAID drugs• Complete my Ph. D. degree• Publication• Patent

Acknowledgments• PhD James Salvador• All the attendants• Education Department of Chihuahua Mexico

Government • Chemistry department of University of Texas at El Paso • U. S. Army Research Laboratory and U.S. Army

Research Office under Contract W911NF0410052 • Consejo Nacional de Ciencia y Tecnologia (CONACyT)• Green Chemistry Institute-NSF (Travel Scholarship)

Thank You

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