University of Pittsburgh

Total synthesis of Marinomycins A-C and of Their

Monomeric Counterparts

Monomarinomycin A and iso-Monomarinomycin A

K.C.Nicolaou, Andrea L. Nold, Robert R. Milburn, Corrina S. Schindler,

Kevin P.Cole and Junichiro Yamaguchi

Filip Petronijevic

March, 12th 2007

J. Amer. Chem. Soc. 2007, 129, 1760.

Chemistry Department

• Marinomycins A-C are new class of antibiotics

• Antibiotics are usually isolated from Actinomycetes (more than 10,000

bioactive compounds)

• The Fenical group isolated marinomycins A-C from a novel marine actinomycete

Marinospora CNQ-140

• Marinomycins show potent antibiotic activity against methicillin-resistant

Staphilococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium

(VREF)

• Marinomycin A has MIC90 0.1-0.6 µM

• Marinomycins show potent cytotoxicities against some cancers (LC50 2.7 µM) and

melanomas (for SK-MEL-5, LC50 5.0 nM)

• probably a novel mechanism of action

• only marinomycin A shows activity against Candida albicans (MIC90 10 µM)

Marinomycins-isolation and activity

J.Amer.Chem.Soc. 2006, 128, 1622.

• different geometries of double bonds

• 44-membered ring

• possible photoisomerisation of

marinomycin A to B and C analogue

• note the symmetry of marinomycin A

Structures of marinomycins A-C

MeOH OH OH Me

OH

O

O

MeO

O

Me

OH

OH OH OH

HO

OH

Suzuki coupling

1: marinomycin A

B

MeMe

HO

HO

OTBS OTBS

O

OTBS

TBSOO

OTIPS

Br

HWE olefination

Mitsunobu reaction

4

BnO

P(OMe)2Me

OH O O

H Me

O

OTBS

OTBS

OTES

5 6

OAcO

Br

HO

7

Retrosynthetic analysis

Preparation of ketophosphonate 5

PMBO

8

OTBS

O

9

n-BuLi, THF, -78 °C, 45 min

then BF3.OEt2, 9 in THF,

-78 °C, 4h, 89%

R1O

OTBS

OR2

10: R1 = PMB, R2 = H

11: R1 = PMB, R2 = TBS

12: R1 = H, R2 = TBS

TBSCl, imid., DMF 25 °C, 6h, 96%

DDQ, DCM pH 7 phosphate buffer 25 °C, 3h, 79%

HO

OTBS

ITBSO

13

Red-Al, THF, 25 °C, 45 minthen NIS, THF, -78 °C, 30 min 66%

R3O

OR4

MeTBSO

TMSCl, Et3N, THF, 25 °C, 2h

then Pd(dppf)Cl2, Me2Zn, THF, 65 °C, 12h

then K2CO3, MeOH, 25 °C, 4h, 81%

14: R3 = H, R4 = TBS

R3O

OR4

MeTBSO

14: R3 = H, R4 = TBS

15: R3 = Bn, R4 = TBS

16: R3 = Bn, R4 = H

NaH, THF, 0 to 25 °C, 30 min

then BnBr, n-Bu4NI, 6h, 88%

HF.py, THF, 0 °C, 3h, 77%

BnO

O

MeTBSO H

PCC, NaHCO3, 25 °C, 3h, 73%

17

1. MeP(O)(OMe)2, n-BuLi, THF, -78 °C, 2h then 17 in THF, -78 °C, 2h

2. PDC, 4 A MS, DMF, 25 °C, 12h 64 % over two steps BnO

MeTBSO O

P(OMe)2

O

18

BnO

MeOH O

P(OMe)2

O

5

HF, MeCN25 °C, 3h, 92%

Preparation of ketophosphonate 5

Preparation of Aldehyde 6

O Me

OTBS

(-)-Ipc2BOMe, allylMgBr

Et2O, -78 to 25 °C, 2h

then 19, Et2O, -78 °C, 4h

-78 to 25 °C, 1h, 95%

19

Me

OTBS

OR

20: R = H

21: R = TES

TESCl, imid., DMF 25 °C, 4h

O3, DCM, -78 °C, 4h

then Ph3P, -78 °C, 2h

-78 to 25 °C, 1h

64% (two steps)O

Me

OTBS

OTES

22

(-)-Ipc2BOMe, allylMgBr

Et2O, -78 to 25 °C, 2h

then 22, Et2O, -78 °C, 4h

-78 to 25 °C, 1h, 85%

Me

OTBS

OTES

OR1

23: R1 = H

24: R1 = TBSTBSCl, imid., DMF 25 °C, 4h

O3, DCM, -78 °C, 4h

then Ph3P, -78 °C, 2h

-78 to 25 °C, 1h

91% (two steps)Me

OTBS

OTESO

OTBS

6

O O

Me Me

O

O O

Me Me

O

B

O

O

O O

Me Me

O

TMS

O O

Me Me

O

Br

OH O

Br

OH

OAc O

Br

OH

2,5-dimethyl-2,4-hexadiene

BH3.THF, THF, 0 °C, 3h

then 25, 0 °C, 1.5h

then H2O, 0 to 25 °C, 1h

then (CH2O)n, 25 °C,12h

then pinacol, MgSO4, 25 °C

87%25

Pd(PPh3)4, Cs2CO3

27, THF/H2O (5:1)

55 °C, 1h, 89%

26 28

NBS, MeCN25 °C, 15 min 88%

KOH, THF/H2O (5:1)

55 °C, 18h, 87%Mg(ClO4)2, Ac2O

25 °C, 48h, 96%

29307

TMSBr

27

Preparation of Fragment 7

BnO

MeOH O

P(OMe)2

O

5

5, 6, Ba(OH)2.H2O

THF/H2O (20:1)

25 °C, 1h, 95%BnO

MeOH O Me

OTBS

OTES

OTBS

31

Et2BOMe, THF/MeOH (4:1)

-78 °C, 15 min

then NaBH4, 3h, 89%

R3O

MeR1O Me

OTBS

OTES

OTBSOR2

32: R1 = R2 = H, R3 = Bn

33: R1 = R2 = TBS, R3 = Bn

34: R1 = R2 = TBS, R3 = H

TBSCl, imid., DMF 25 °C, 8h, 89%

33 in THF/i-PrOH (3:1)

then liq. NH3, then Ca

-78 °C, 1h, 75%

O

MeTBSO Me

OTBS

OTES

OTBSOTBS

DMP, NaHCO3 DCM25 °C, 30 min, 87%

35

Preparation of Suzuki Coupling Precursor 39

O

MeTBSO Me

OTBS

OTES

OTBSOTBS

35

MeTBSO Me

OTBS

OR4

OTBSOTBSi-PrNH2, n-BuLi, THF

-78 to 0 °C, 30 min

then TMSCHN2, THF

-78 °C, 30 min; then 35

-78 to 25 °C, 2h, 85%

36: R4 = TES

37: R4 = H

PPTS, EtOH25 °C, 3h, 75%

DEAD, PPh3, 7THF, 25 °C, 1h, 93%

MeTBSO Me

OTBS

OTBSOTBS

O

O

OR5

Br

38: R5 = Ac

39: R5 = TIPS

1. K2CO3, MeOH, 25 °C, 15 min

2. TIPSOTf, 2,6-lut., DCM, 25 °C, 18h

92% over two steps

OAc O

Br

OH

7

Preparation of Suzuki Coupling Precursor 39

Olefin Cross-Metathesis toward Enone 31

MeTBSO Me

OTBS

OH

OTBSOTBS

MeTBSO Me

OTBS

OTBSOTBS

O

O

OR5

TMS

OH O

TMS

OH

45 46

37

DEAD, PPh3

Et2O, 20h

no reaction

45

Attempted Mitsunobu Reaction between 37 and 45

Me

OTBS

OH

OTBS

ORO

HO

48a: R = H48b: R = Me48c: R = Ac

47

OAcO

HO

TMS

50

DEAD, PPh3, THF

48a-c

DEAD, PPh3, THF

50, 1h, 81%

Me

OTBS

OTBS

O

O

OR

49a: R = H, 24h, trace product49b: R = Me, 3h, 65%49c: R = Ac, 1h, 72%

Me

OTBS

OTBS

O

O

OAc

TMS

51

Model Studies toward Mitsunobu Reaction

39

MeTBSO Me

OTBS

OTBSOTBS

O

O

OTIPS

Br

B

HO

HO

catecholborane, Cy2BH

THF, 25 °C, 30 min

then H2O (excess)

25 °C, 1h

Me

OO

TBSO

OTBS OTBS

OTBS

Me

OTIPS

Me

OO

HO

OH OH

OH

Me

OH

OH

OO

Me

OHOHHO

HO

Me

4

52

m-1

m-2

Pd(PPh3)4, TlOEt

THF/H2O (4:1)

25 °C, 1h, 72%

TBAF, THF 25 °C, 18h 85%

m-1/m-2 1:1

Formation of Monomarinomycins m-1 and m-2

OH

OO

Me

OHOHHO

HO

Mem-2

X-ray crystal structure of m-2

MeTBSO Me

OTBS

OH

OTBSOTBS

37

MeTBSO Me

OTBS

OTBSOTBS

OO

MeMe

OTBS

OTBS TBSO OTBS

OTIPS

HO

MeTBSO OTBS OTBS Me

OTBS

O

O

MeO

O

Me

OTBS

OTBS TBSO OTBS

RO

OTIPS

Br

1. catecholborane

Cy2BH, THF

25 °C, 30 min

2. 39, KOH, Pd(PPh3)4 THF/H2O (4:1)

25 °C, 1h, 63%

53

DEAD, PPh3, 7

THF,25 °C, 1h

56: R = TIPS

K2CO3, MeOH

25 °C, 15 min

54: R = Ac

55: R = H

TIPSOTf, 2,6-lut. DCM, 25 °C, 18h78 % (over three steps)

Toward the Completion of the Total Synthesis of Marinomycin A (1)

MeTBSO OTBS OTBS Me

OTBS

O

O

MeO

O

Me

OTBS

OTBS TBSO OTBS

RO

OTIPS

Br

56: R = TIPS

1. catecholborane, Cy2BH

THF, 25 °C, 30 min

2. TlOEt, Pd(PPh3)4 THF/H2O (10:1)

25 °C, 4h

57: R = TIPS

MeOH OH OH Me

OH

O

O

MeO

O

Me

OH

OH OH OH

HO

OH TBAF, THF 25 °C, 18h23% (over three steps)

1

Completion of the Total Synthesis of Marinomycin A (1)

MeTBSO OTBS OTBS Me

OTBS

O

O

MeO

O

Me

OTBS

OTBS TBSO OTBS

TIPSO

OTIPS

Br 1

1. Cy2BH, catecholborane

then H2O

2. conditions (see table)

3. TBAF

Attempts To Improve the Yield of Marinomycin (1)

hv

Biological Evaluation of the Synthesized Marinomycins

Conclusion:

• The synthesis of the Marinomycins A-C presents an interesting challenge in synthetic

organic chemistry

• The synthetic marinomycin A shows the same biological activity as the naturally

occurring one

• The polyunsaturated nature of these molecules makes them particularly sensitive to

both chemical and light activation

• The Suzuki reaction was used for macrocyclization in the last step of the synthesis as

well as in the polyunsaturated chain synthesis

• Monomeric macrocyclization gave the monomarinomycins A and the structure of one

of them is proved by X-ray crystallography

• Two monomarinomycins A show no activity

• Synthetic monomarinomycin A undergoes photoisomerisation to its analogues