Progress toward the Total Synthesis of Pleurotin
SHINYA IIMURA
Wipf Research Group Meeting
July 9th, 2005
Shinya Iimura @ Wipf Group 1 7/10/2005
Presentation Outline
! Isolation and Structure
! Biological Activity
! Current Total Synthesis Efforts in the Wipf Group
! Previous Studies in the Wipf Group
! Hart's Total Synthesis (Racemic)
! Kraus' Studies toward Total Synthesis
! Future Plans
Shinya Iimura @ Wipf Group 2 7/10/2005
Isolation and Properties of Pleurotin
!"First isolated from the fungus Pleurotus griseus in 1947 by Robbins et al., and later obtained from
Hohenbuehelia geogenius.
O
O
HO
O
O
CH3
Pleurotin
Robbins, W. J. et al. Proc. Natl. Acad. Sci. USA, 1947, 33, 171.
! Pleurotin began to melt with decomposition at temperatures between 200 ˚C and 215 ˚C depending
upon the rate of heating.
! Pleurotin was optically active with [#]23D
= -20˚ (c 0.59, CHCl3).
! The solubility of pleurotin at 25 ˚C: 0.125 mg/mL (water), 6.8 mg/mL (95% ethanol), 0.37 mg/mL
(5% ethanol), 3.5 mg/mL (ether), more than 200 mg/mL (chloroform).
! Pleurotin in solution was rendered inactive by exposure to light for a few hours.
! Pleurotin was not thermostable. Solutions of pleurotin in 0.1 M. phosphate buffer when boiled for 10 min
lost 50% of their biological activity at pH 3, 75% at pH 6.5, and all of their activity at pH 8.5.
! Pleurotin was 75% destroyed in 1 h at pH 8.5 and 25 ˚C.
Shinya Iimura @ Wipf Group 3 7/10/2005
Poster Presented at the 2004 International Congress on Natural Products Research, A joint meeting of the ASP, AFERP, GA and the PSE July 31–August 4, 2004 Phoenix, AZ; Podium Presentation at the July 2004 Society of Microbiology meeting, Anaheim, CA
Shinya Iimura @ Wipf Group 4 7/10/2005
Structure and the Synthetic Challenges
! Structure originally assigned on the basis of degrative studies in 1968 and later
confirmed by X-ray crystallography in 1981.
O
O
HO
O
O
CH3
Pleurotin
Oddoux, L. et al. Arzneim. Forsch. 1981, 31, 293.Cohen-Addad, P. C. et al. Acta Crystallogr. 1981, B37, 1309.
! The Challenge to Synthetic Chemists: The unique compact hexacyclic framework
The six contiguous stereogenetic centers
No enantioselective total synthesis
Shinya Iimura @ Wipf Group 5 7/10/2005
O
O
HO
O
O
CH3
Pleurotin
Oddoux, L. et al. Arzneim. Forsch. 1981, 31, 293.
Biological Activity
! Antibiotic activity against Gram-positive bacteria.
! Antitumor activity against two rapidly grafted tumors: Ehrlich ascites carcinoma and
L-1210 lymphoid leukemia, as well as a slow growing spontaneous mammary tumor.
! A potent inhibitor of the thioredoxin–thioredoxin reductase system (IC50 170 nM).
Robbins, W. J. et al. Proc. Natl. Acad. Sci. USA, 1947, 33, 171.
Powis, G. et al. Anti-Cancer Drug Des., 1997, 12, 659.Powis, G. et al. Mol. Cancer Ther., 2003, 2, 235.Wipf, P. et al. Org. Biomol. Chem., 2004, 2, 1651.
Shinya Iimura @ Wipf Group 6 7/10/2005
Bioreductive Alkylation
Lin. A. J. et al., J. Med. Chem. 1972, 15, 1247.Moore, H. W. Science (Washington, D.C.) 1977, 197, 527.
The concept of bioactivation as a mechanism of drug action is one
that is especially appealing to the medicinal and synthetic organic
chemist. The challenge of designing compounds in a biologically
inactive form which become activated only subsequent to an in vivo
transformation allows the synthesis chemist to take advantage of his
arsenal of methodology and mechanistic probes and to directly apply
them to potentially important problems of drug action.
The concept of bioreductive alkylation which is compounds which
become potent alkylating agents after they undergo a reduction in
vivo, is a particularly fascinating area within the field of bioactivation.
Moore, H. W. Science (Washington, D.C.) 1977, 197, 527.
!
!
Shinya Iimura @ Wipf Group 7 7/10/2005
Bioreductive Alkylation
Tomasz, M., Chem. Biol. 1995, 2, 575.
H2N
O
O
N
OMe
OCONH2
NH
Mitomycin C
H2N
OH
OH
N
OMe
OCONH2
NH
H2N
OH
O
N
OCONH2
NH
H
– MeOH
H2N
OH
O
N
OCONH2
NH2
DNA
First alkylation stepH2N
OH
OH
N
OCONH2
NH2
DNA
H2N
OH
OH
N
NH2
DNA
– OCONH2
H2N
O
O
N
NH2
DNA
Second alkylation step(cross-linking) O2
Shinya Iimura @ Wipf Group 8 7/10/2005
Suggested Bioactivation of Pleuotin
O
OO H
O
O
OH
HOO H
O
O
OH
OO H
HO
O
O
OO H
HO
O
O
OH
HO
O
O
OH
HO
ONu1
Nu2
OH
OH
Moore, H. W. Science (Washington, D.C.) 1977, 197, 527.Hart, D. J. et al. J. Am. Chem. Soc. 1989, 111, 7507.
pleurotin
dihydropleurotin acid
Nu
Shinya Iimura @ Wipf Group 9 7/10/2005
Hart: First Total Synthesis of Pleurotin (Racemic)
O
OO H
O
O
O
OO H
HO
O
Hart, D. J. et al. J. Am. Chem. Soc. 1988, 110, 1634.Hart, D. J. et al. J. Am. Chem. Soc. 1989, 111, 7507.
pleurotin dihydropleurotin acid
CH3CO2Et
OO H
OOCO2Et
CH3
Key feature
Biomimetic conversion of dihydropleurotin acid to pleurotin*
Stereoselective free-radical cyclization
*Arigoni group has demonstrated that dihydropleurotin acid is converted to pleurotin by cultures of Pleurotus griseus. Vogt, P.M. Ph. D. Thesis, Eidgenossischen Technischen Hochschule, Zurich, Switzerland, 1982.
Shinya Iimura @ Wipf Group 10 7/10/2005
Hart: First Total Synthesis of Pleurotin (Racemic)
Hart, D. J. et al. J. Am. Chem. Soc. 1988, 110, 1634.Hart, D. J. et al. J. Am. Chem. Soc. 1989, 111, 7507.
CO2H
1. Li, NH3; Br(CH2)2CH(OCH2CH2O)
2. DPPA, Et3N, pyrrolidine, THFO N
O
O1. I2, THF/H2O2. HCO2H, H2O
3. Ph3P=C(CH3)CO2Et
CO2Et
I
O
O
nBu3SnH, AIBN
benzene, !O
O
CO2EtH
H1. LiOEt, MeOH, H2O; HCl, H2O2. (COCl)2; NaBH4
3. TBSCl, imidazole, DMF
O
O
CH2OTBSH
H 1. mCPBA2. LiNEt2, Et2O
O
O
CH2OTBSH
H
HO
1. Li, EtNH22. CH2N2
3. (COCl)2, DMSO, Et3N
CO2Me
CH2OTBSH
H
O
THFCO2Me
CH2OTBSH
H
OH
OMe
OMe
66% (2 steps) 78% (3 steps)
80%85% (3 steps)
66% (2 steps)
59% (3 steps) 91%
2,5-(MeO)C6H3CH2MgClCeCl3
Shinya Iimura @ Wipf Group 11 7/10/2005
Hart: Stereoselectivity in the Free-Radical Cyclization
R1
R2
I
O
O
nBu3SnH, AIBN
benzene, ! O
O
CO2EtH Me
H
O
O
CO2EtH Me
H
OOR2
R1
+
OO+
OO
R1R2
R1R2
1: R1 = Me, R2 = CO2Et 80% 4% 4% 4%
2: R1 = CO2Et, R2 = Me 37% 2% 15% 12%
O
O
MeH CO2Et
H
+ O
O
CO2EtH Me
H
+
OO Me CO2Et OO MeO. (OEt)
OEt (O.)
OO Me
H
CO2Et
HHSnnBu3
Shinya Iimura @ Wipf Group 12 7/10/2005
Hart: First Total Synthesis of Pleurotin (Racemic)
Hart, D. J. et al. J. Am. Chem. Soc. 1988, 110, 1634.Hart, D. J. et al. J. Am. Chem. Soc. 1989, 111, 7507.
CO2Me
CH2OTBSH
H
OH
OMe
OMe
1. SOCl2, pyridine*2. LiAlH4
3. (COCl)2, DMSO, Et3N CHO
CH2OTBSH
H
OMe
OMe
Dowex-50 (H+), MeOH
H
H
OMe
OMe
O
BF3•Et2O
toluene
OMe
H
H
OMe
MeO
O1. BH3•THF; NaOH, H2O22. (COCl)2, DMSO, Et3N
3. TosMIC, KOtBu, DME
4. DIBAL-H, toluene
5. Ag2O, NaOH
OMe
MeOO H
HO
O
H
H
OMe
MeO
O
HO2CH
*Inseparable 1:1 mixture
37% (3 steps)99%
52%
36% (5 steps)
Shinya Iimura @ Wipf Group 13 7/10/2005
Hart: First Total Synthesis of Pleurotin (Racemic)
Hart, D. J. et al. J. Am. Chem. Soc. 1988, 110, 1634.Hart, D. J. et al. J. Am. Chem. Soc. 1989, 111, 7507.
O
OO H
O
O
OMe
MeOO H
HO
O
CAN
CH3CN/H2O
O
OO H
HO
O
MnO2
CH2Cl2
26 steps from benzoic acid0.3% overall yieldan average of 80% yield per step
89% 32%
Shinya Iimura @ Wipf Group 14 7/10/2005
Kraus: Retrosynthetic Analysis of Pleurotin
O
O
HO
O
O
CH3
OMe
OMe
OH
O
G
O
CHO
OMe
OMe
O
O
G
Kraus, G. A. et al. Synlett 1991, 89.Kraus, G. A. et al. Synth. Commun. 1993, 23, 2041.
Tandem Photoenolization/Diels–Alder Reaction
Shinya Iimura @ Wipf Group 15 7/10/2005
Kraus: Synthetic Studies toward Pleurotin
Kraus, G. A. et al. Synlett 1991, 89.Kraus, G. A. et al. Synth. Commun. 1993, 23, 2041.
OMe
OMe
OH
nBuLi, THF
DMF
OMe
OMe
O
OH
66%
1. HS(CH2)2SH, BF3•OEt22. RCO2H, DCC, DMAP
3. MeI, aq. MeCN
CHO
OMe
OMe
O
O31% (3 steps)
CHO
OMe
OMe
O
O
O
O
HO
O
OHH
OMe
OMe
HO
O
OHH
1. h!, Benzene
2. 165 ˚C, 40 h
50%
AgO, HNO3
THF
28%
Comparable activity with pleurotin against SR leukemia cell line
{log10GI50 = -5.33 (pleurotin: -5.51)} and most colon cancer cell lines
{log10GI50 ranging from -4.65 to -4.77 (pleurotin: -5.17)}.O
O
HO
O
OHH
Shinya Iimura @ Wipf Group 16 7/10/2005
Acknowledgments
Wipf research group members
University of Pittsburgh
$ National Institutes of Health (GM66509) $
Prof. Dr. Peter Wipf
Dr. Sonia Rodríguez
Dr. Steven Geib (X-ray)
Shinya Iimura @ Wipf Group 17 7/10/2005