Camptothecin

Reviewing Camptothecin

1

Ke ChenBaran Group Meeting9/ 26/2007

This quinoline based alkaloid was found in the bark of the Chinesecamptotheca tree.

Camptotheca goes by many names in China, including "happy tree","dragon tree" and "fine tree".

Chinese have used the "happy tree" in traditional medicine for thousandsof years. It has been used for psoriasis, leukemia and diseases of liver,gallbladder, spleen, and stomach.

During the last half century, scientists have discovered its potential as aselective anticancer drug.

The unique mode of action for this potent cytotoxic compound was found toact via inhibition of an enzyme known as DNA topoisomerase I.

Fig 1 Fig 2

In Fig 1, normally, topoisomerases I introduces a nick in the DNAbackbone allowing the rotation of one strand around another. Thisreleases the torsional strain which otherwise accumulates in front ofthe advancing replication fork (the large arrow). The DNA break isextremely transient and is religated as it release the other strand.

In Fig 2, when camptothecin is present(black oval with C), it binds to thetopoisomerase I-nicked DNA complex. This prevents the religation of thenicked strand and the release of the enzyme. Eventually, the replicationfork collides with the complex, causing the formation of a double-strandbreak.

N

N

O

O

OOH

Name Camptothecin

IUPAC name 4-ethyl-4-hydroxy-1H-pyrano[3',4':6,7]

indolizino[1,2-b]quinoline-3,14-(4H,12H)-dione

CAS number 7689-03-4

Formula C20H16N2O4

Mol. mass 348.352 g/mol

Hsiang, Y.H. Cancer Res. 1989, 49, 5077.

Discovering Camptothecin

2


Born in 1916 in Newark, NJ, Dr. Wall receivedhis B.S., M.S., and Ph.D. degrees fromRutgersUniversity. In 1941, he joined the United StatesDepartment of Agriculture. From 1941 to 1960,Dr. Wall gained national recognition as agovernment scientist in steroid chemistry. In1960, Dr. Wall joined the Research TriangleInstitute (RTI) to start a chemistry researchgroup. He became RTI Vice President ofChemistry and Life Sciences in 1971. Amongnumerous contributions to the field of naturalproduct research, he is best known for thediscovery and development of taxol andcamptothecin. In 1981 He retired fromadministration and devoted his time to researchuntil two weeks before his death at 85.

Monroe E. Wall (1916–2002)

Monroe Doctrine: "Get good people, support them with good facilities,do good science, work hard, and keep doing it."

Mansukh C. Wani

Born in Nandurbar, India, Dr. Wani receivedhis B.S. and M.S. degrees from the Universityof Bombay. He came to the United States andfinished his Ph.D in chemistry at IndianaUniversity under the instruction of ProfessorErnest Campaign. After a postdoctoralfellowship at the University of Wisconsin-Madison, he accepted a position at RTI fromDr. Wall in 1962. Together they developed twoof the most promising anticanceragents, taxol and camptothecin., which arebenefiting millions of people all over theworld. Dr. Wani is still active at RTI,supervising junior researchers.

Timeline of Camptothecin:

1960-1966 Isolation of active compound from amptotheca acuminata;determination of structure of camptothecin

1985 Determination of mechanism of action of camptothecin

N

N

O

O

OOH

N

N

O

OOH

OH

ONa+

low solubility in water water-soluable but inactive

Clinical trials started in the 1960s but were abandoned shortly thereafter.

1996 FDA approval of two analogs of camptothecin for treatmentof ovarian, lung, breast and colon cancer.

After Camptothecin returned, like " the phoenix from the ashes", it rekindledinterest in developing analogs of camptothecin that were both water solubleand retained anticancer activity

Some numbers and facts...

11729 publications regarding "camptothecin".

114 publications involving total or formal synthese of camptothecin and itsderivatives.

By 2001, the analogs developed included Pharmacia’s Camptosar andGlaxoSmithKline’s Hycamtin, collectively reporting worldwide salesapproaching $ 800 million.

Synthetic chemists embrace practility and perfection.

Camptothecin: From Bench to Bedside

3


N

N

O

O

OOH

CHO

NH2

N

O

CO2Et

CO2Et

N

N

CO2H

CO2Et

N

N

O

Et CO2Et

OCO2Et

Et CO2Et

OCO2Et

Et CO2Et

OH

EtO2C

N

N

O

O

O

Et

CO2Et

Stork G., Schultz A. G. J. Am. Chem. Soc. 1971, 36, 4074-4075.

aq. NaOH

50 %

1 eq LDA

-78 oC

LDA, RT

dl-camptothecin

1. First synthesis reported

2. One of the key steps involves the annulation of an estercarbonate and unsaturated lactam

Classical condensation

Friedlander quinoline synthesis

N

N

O

O

OOH

N

O

O

OCN

O

CO2EtO

NTs

N

O

O

OCN

CO2Et

N

O

O

OCN

O

CO2EtO

NTs

Et

N

O

O

OOH

O

Tagawa H. Tetrahedron Lett. 1989, 30, 2639-2640.

Br

NTs

CO2H

Na2CO3, DMF, 70oC

76-97 %

NaH, EtI, DMF

rt, 65-100 %

NH2

NTol

p-TsOH, tolreflux, 73 %

1. First asymmetric synthesis

2. 1,4-Asymmetric induction in the diastereo-selective ethylation was achievedusing an N-tosyl-(R)-proline derivative

steps

d. r. = 82 :18

4


Classical condensation

Friedlander quinoline synthesis

NH2

NTol

p-TsOH, tolreflux, 75 %

NH

CO2MeMeO2C

•CO2Me

HH

Et3N

92 % N

O

CO2Me

CO2Me

t-BuOK/EtI

DME, 91 %N

O

CO2Me

CO2Me(CH2O)n/H

+

95 %N

O

CO2Me

O

O

N

O

CO2Me

O

O

O

N

N

O

O

O

MeO2C

1. HBr, 140 oC

2. Me2NH, CuCl2O2, DMF

N

N

O

O

OOH

N

N

O

O

OOH

HOHO

Et

Danishefsky S. J. J. Org. Chem. 1993, 58, 611-617.Danishefsky S. J. J. Am. Chem. Soc. 1971, 93, 5575.

Two analogs:


Corey E. J. J. Org. Chem. 1975, 40, 140-2141.

O

HO2C

CO2H

O

Et

OHCO2H

HO

OO

O

Et OCO2Me

OO

O

Et OCO2Me

O

Cl

N

NH

1. quinine-water

2. recrystalization

3. MeOCOCl, Et3N

pyr(S)-camptothecin

1. O2, eosine2. SOCl2

N

O

CO2Me

O

O1. PhCHO, NaHMDS2. O33. TMSCHN2

85 % overall

dl-CPT

N

R2

R1

O

CO2Me(CH2O)n/H

+

N

R2

R1

O

O

O

N

R2

R1

O

Et

O O

major


5


Bennasar M. L.. J. Chem. Soc., Chem. Commun. 2000, 2459.Bennasar M. L.. J. Org. Chem. 2002, 67, 7465.

N Br

N

N

O

O

OOH

OTf

N

F

CO2Me

N Br

NCO2Me

F

N Br

NCO2Me

O

O

O

O

OTf

DCM, rt

30 min

O O

O

O O

OLi

LDA, THF

-78 oC, 30 mins

-30 oC

1.5 h

then DDQ

N

N

O

O

OOH

Modern organic chemistry

N

OMe

N

CO2Me

Me

I-

NMe

Me

H

HCO2Me

SePh

O

Methylervitsine

LDA

intermediate

PhSeBr?

Bennasar M. L.. J. Chem. Soc., Chem. Commun. 1995, 125.

N

O

Bn

Br

NH2

C6H11N=C

AcONa, MeOH, 65 oC

71 %

N

Bn

NC

NH

OC6H11

Lavilla R. Org. Lett 2006, 8, 5789-5792.

Other recent applications of 1,4-addition to pyridinium salts

Discovering Camptothecin

6


N

N

N

O

O

OOH

Diels-Alder Reaction:

OMe

NSO2Me

CO2Et

EtO

OEt

EtO OEt

rt

N

OMe

MsN

CO2EtOEt

OEt

OEtOEt

N

OMe

N OEt

OEt

OMe

N

OMe

N OEt

OEt

O

HO

ModifiedSharpless

Dihydroxylation

N

OMe

N OEt

OEt

O

HO

NaClO2

NaH2PO4

OH

1. HBr2. K2CO3

Boger, D. L.. Tetrahedron 2002, 58, 6343.

NH

O

N O

CNCO2H

Ac2O

reflux N

N

O

CN

N

N

O

CNN

N

O

CN

HO

OAc

O

O

74 %48 %

75 %

Fortunak J. Tetrahedron Lett. 1996, 37, 5679-5682.

86 % ee

NH

O

N O

CN

Me3OBF4

reflux N

N

O

CN

82 %

MeOMeO

Revised alternative:


7


[4+1] Radical Annulation:

Curran D. P. J. Am. Chem. Soc. 1992, 114, 5863-5864.

Shibasaki M.; Curran D. P. J. Am. Chem. Soc. 2001, 123, 9908-9909.Shibasaki M. J. Am. Chem. Soc. 2000, 122, 7412-7413.

CN

CO2H

CO2H

1. PCl52. HBr

3. MeOH

HN

Br

O

CO2Me

N

Br

O

CO2Me

Et

PhNCMe3SnSnMe3

N

N

O

Et

CO2Me

dl-Camptothecin

N

Br

O

R

N

O

RN

N

R

O

N

N

R

O

PhNC

N

N

O

Et

CO2Me

N OTBS

OMe

SMT

HN O

O

I O

Et OH

O

N

CN

OTBS

OMe

SMT

Et OTMS

N O

OMe

I O

Et OH

5 mol % SmLn1.5 equiv TMSCN

EtCN, -40 oC, 18 h

98 %, 84 % ee

1. ICl2. HCl-EtOH

71 % (2 steps)

TMSI, cat H2OCH3CN, 87 %

> 99 % ee afterrecryst. from MeOH-CHCl3Over 100 derivatives of camptothecin have been prepared by Dr. Curran's

research group utlizing this approach.

Curran and Shibasaki:

Camptothecin: the Future

8


N OMe

1. MesLi

2. N NCHO

3. n-BuLi N OMe

NLi

N

OLi

1. I22. NaBH4, H2O

N OMe

I

OH

one pot

TMSCl, NaI

(CH2O)n, CH3CNN O

O

I

1. n-BuLi

2.

CO2R*

O

N O

O

LiOOR*

O

Et

HCl

iPrOH

NH

O

O

O

Et

HO

N Cl

It-BuOK

DME

N

N

O

O

OOH

ClN

N

O

O

OOH

(Ph3P)2Pd(OAc)2

KOAc, CH3CN

Comins D. L. Org. Lett 2001, 3, 4255-4257.

This remains the most efficient route reported (six steps, 12.5 % overall yield).

Scientists from GSK are utilizing this approach to synthesize analogs of CPT.

N

N

O

O

OOH

A B C

D

E

Structure-Activity Relationships:

N

N

O

O

OOH

HO

N

N

N

O

O

OOH

ON

O

N

Hycamtin

Camptosar

10 additional CPTderivatives in variousstages of clinical trials

"Trees hold the answer to saving the planet. Scientists are discovering moreremarkable facts about trees, forests and animal interactions than ever before.The work of these scientists is immeasurably protecting humanity and all life,now and into the future."

Reese Halter

Education

Camptothecin