Stachybotrys Metabolites: A History of Mis-Identification

Rob HalterSeptember 27th, 2003

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem.,2003, 7422.

Stachybotrys Molecules

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem., 2003, 7422.

Biological Activity

• Variety of biological activity• Antagonists of endothelin (cardiovascular)• Inhibititors of HIV-1 protease• Potent anti-influenza A activity• Selective inhibitor of myo-inositol monophosphatase (manic/depressive

disorders)• Anti-inflammatory

Reason for Total Synthesis

IC50 = 1.3 mM for HumanETA

IC50 = 1.5 mM for HumanETA

J. Antibiot. 1996, 13 and J. Antibiot. 1995, 1389.

Almost identical biological structure raised flagAlmost identical structure also raised flagTotal synthesis was done to prove structure

Synthesis of K-76

McMurry, J. E.; Erion, M. D. J. Am. Chem. Soc., 1985, 107, 2712.

OAcO

1. cyclopropytriphenylphosphorane

2. K2CO33. PBr3

Br

CH3COCH2COOMe, BuLi, NaH

O

O

O TBSCl

O

OTBSO

23 25

26 27

Hg(OTFA)2

ClHg

O

O O

57 %

OB

OPh

HO

1. Amberlyst-15

2. NaOH3. t-BuSLi

O

H

O

H

MeO

HO

HO

O

H

O

H

HO

O

41 K-76

Total Synthesis of Stachyflin

Taishi, T.; Takechi, S.; Mori, S. Tetrahedron Lett., 1998, 39, 4347.

O OMe

OMeBnO

O H

12

1. (MeO3)CH, TsOH

2. 13, TMSOTf

O OMe

OMeBnOOMeO

1. H2, Pd/C then 1N HCl, acetone

2. H2, Pd/C, AcOH

O OMe

OMeOHO

1. TBDPSCl, tBuOK

2. [TfO], KHMDS

17

O OMe

OMeTBDPSOTfO

18

19

1. 15, Pd(PPh3)4, HMPA, THF

2. TBAF3. I2, propylene oxide

I

O

OMe

O

MeO

21

1. DBU, DMSO

2. BH33. H2O2, NaOH4. PCC5. 0.5 N HCl, Acetone O

O O

OMe

O

MeO

OO

22

TMSO

13

OOZnI

15

Total Synthesis of Stachyflin

Taishi, T.; Takechi, S.; Mori, S. Tetrahedron Lett., 1998, 39, 4347.

Synthesis of L-671,776

Falck, J. R.; Reddy, K. K.; Chandrasekhar, S. Tetrahedron Lett., 1997, 38, 5245.

OH

TBDPSO

1. Swern

2. Wittig66 %

TBDPSO

OMe

1. TMSCl. NaI, MeOH

2. NaBH4, MeOH3. MsCl, NEt3, then LiBr

TBDPSO

Br

1. n-BuLi, 16, then CuCN, then 4

2. 1 N HCl3. NaBH4, MeOH4. TBDPSCl, DMAP TBDPSO

OMOM

MOMO OTBDPS

(EtO)3SiCl/NaI

TBDPSO

HO OTBDPS

O

1. Bu4NBr3

2. n-Bu3Sn(CH=CH)2 Pd(PPh3)43. OsO4, NaIO44. TBAF

64 %

70 %

74 %

40 %HO

HO OH

O

HO

10

HO

HO OH

O O

H

13

2 3 4

6 7

+

OMOM

MOMOOMe

OMe

16

Kende’s Retrosynthesis

Failed Coupling Attempts

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem., 2003, 7422.

No aldehyde addition, possiblybecause of steric repulsion betweenmethyl and benzyl group.

No reason given for lack orreactivity, presumably the sameas above.

Kende’s Synthesis

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem., 2003, 7422.

Almost identical coupling works,why??

Benzyl ether interferes with ring formation,stronger conditions also tried.

Kende’s Synthesis

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A.S., J. Org. Chem., 2003, 7422.

Wrong Regioisomer

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem., 2003, 7422.

X-ray of 22 and 1

1H NMR and 13C NMR spectra of 1do not match authentic sample ofSpirobenzofuranlactam, their target.

Correct Regio-isomer

Dong, W.-P.; Zhong, M.; Guo, X.-C.; Kende, A. S., J. Org. Chem., 2003, 7422.

Spectra of 27 does match thenatural product

Structure Revision

Structure proposed by Roggo et al. Hasthe wrong regiochemistry around thephenyl ring.

The new structure is consistent withother structures proposed for moleculesisolated from Stachybotrys species.

Correct Structure

Dimer Formation

Since structure of “monomer” waswrong, it was very possible that thestructure of the “dimer” was alsowrong.The correct structure should beidentical to a molecule alreadyisolated, Stachybocin A.

NMR Comparision

The NMR spectra confirm that Roggoalso mis-assigned the structure of the“pseudo-dimer”.

The NMR spectra of synthetic “pseudo-dimer” do not match that of previouslyisolated Stachybocin A.