Nineteen-step Total Synthesis of (+) - Phorbol Shuhei Kawamura, Hang Chu, Jakob Felding, and Phil Baran

[1] Science 2013, 341, 878. [2] Nature 2016, 0, 1.

Evan Carder Wipf Group Current Literature

April 09, 2016  

HO OH

HO

O OH OH

MeMe

MeTMSO

O OTBS

Me

H

1 Cyclase Phase

2 Oxidase Phase

Advanced Intermediate [1] (+) – Phorbol [2]

Oxidase Phase

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

Phorbol Background

04/09/16 Evan Carder @ Wipf Group 2

§  Phorbol and phorbol derivatives are members of the tigliane diterpenoid family.

§  The tigliane diterpenoid family are isolated from the Euphorbiaceae and the

Thymelaeaceae family members 1. Structural elucidation was confirmed by X-ray crystallography of a phorbol derivative in 1967 2.

Structural characteristics:

§  Tigliane diterpenoids have a 5/7/6/3- tetracyclic ring system consisting of a five-membered ring (A), a seven-membered ring (B), a six-membered ring (C), and a cyclopropane system (D).

§  Phorbol has a polyhydroxylated tigliane carbon skeleton that contains eight contiguous asymmetric centers, six of which are sited around the six-membered C ring.

§  Phorbol derivatives are isolated as mixed esters, most commonly existing as

12,13 or 13,20-diesters.

[1] Arch. Exp. Pathol. Pharmakol. 1935, 177, 212. [2] Angew. Chem. Int. Ed. Engl. 1967, 6, 809.

HO OH

HO

O OH OH

1

2 3

19

4 5 6

20

7

8 9 10

11 18

12 13

14

15 16

17

A" B"

C"D"

04/09/16 Evan Carder @ Wipf Group 3

§  As a downstream effector of G-protein coupled receptors and receptor tyrosine kinases, PKC propagates important signaling events.

§  Deregulation of PKC has been associated with

multiple cancer-promoting pathways, which can lead to an array of adverse phenotypes.

§  Therefore, PKC has been implicated in the

development and progression of disease.

§  PKC is commonly activated by second messenger molecule 1,2-diacylglycol (DAG) at the cellular surface.

§  Phorbol esters have been shown to strongly activate PKC and potently promote tumor development - tetradocecanoyl phorbol acetate is active at 20 nM. Paradoxically, deoxygenated derivatives can inhibit tumor formation; therefore, synthesis of phorbol and phorbol derivatives may provide therapeutically active agents toward the treatment of cancer.

Protein Kinase C (PKC) Activation and Tumor Promotion Stimuli

Carcinogenesis Tumor Progression

PKC

Anti-Apoptosis Survival

DNA Synthesis Proliferation

Motility Angiogenesis

P

PLC

DAG

Phorbol

[1] Nature Review 2011, 11, 937. [2] J. Bio. Chem. 2000, 275, 12136.

Effector

Efforts toward the synthesis of Phorbol

§  Paul Wender and co-workers:

Racemic total synthesis, 52 steps, 0.16% overall yield 1 Racemic formal synthesis, 42 steps, 0.02% overall yield 3 Asymmetric formal synthesis; 36 steps, 1.2% overall yield 4

§  Jin Kun Cha and co-workers:

Asymmetric formal synthesis, 43 steps, 0.4% overall yield 5 §  Work from the labs of Shibasaki, Wilson, Rigby, Harwood, Little,

Page, Dauben, McMills, Paquette, Singh, Ovaska, West, Evans, Li, and others.

A-B-C-D, B-C-D, A-B-C skeletal components

[1] J. Am. Chem. Soc. 1989, 111, 8954. [2] J. Am. Chem. Soc. 1989, 111, 8957. [3] J. Am. Chem. Soc. 1990, 112, 4956. [4] J. Am. Chem. Soc. 1997, 119, 7897. [5] J. Am. Chem. Soc. 2001, 123, 5590.

H

HO O

Me Me

MeO

OMe

MeMe

MeO2C

8 kbar2:1 dr (exo)

60%

Z is unreactive

H

HO O

MeMe

MeO

OMe

MeMe

CO2Me

2:1 E/ZTet. Lett. 1989, 30, 5073.

Rigby Lab – [4+2] cycloaddition

J. Org. Chem. 1993, 58, 7635.

Dauben Lab – carbonyl ylide cycloaddition

O OAcH

HMeMe

H

HO

N2EtO2C

OAc

MeMe

H

O CO2Et

O

H

H

Rh2(OAc)4

toluene, 100 oC86%

(both isomers)

HH

Tet. 1994, 50, 4071.

Paquette Lab – anionic oxy-Cope

OMeMe

H

H

O

Me

HLDA

THF, -78 oC71%

MeMe

H

O

OH

H

H

H H

Me

1

2

3

19

4

5 6

20

7

8 9 10

11 18

12 13

14

15 16

17

A" B"

C"D"

Wender’s racemic total synthesis

04/09/16 Evan Carder @ Wipf Group 5

H

O O

Me Me

Me

Me

Me

OTBS

H

O

O

MeMe

OAc

O

Me Me

Me

Me

Me

OTBS

OOAc

O OPh2SC(Me)2

THF, CH2Cl2, -78 oC85%

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

14 steps 20 steps

Phorbol52 steps

0.16% Total yield

OAcMe

OHO

TBSO

OAcMe

OO

OAcOTBS

O+

O- H OAc

OTBS

OAc

H

Me

O

OTBS

O92%dr 2:1

DBUOxidopyrylium-Olefin [5+2] Cycloaddition1. MCPBA, THF2. Ac2O, DMAP, pyr

5 steps

B and C ring

A ring

D ring

[1] J. Am. Chem. Soc. 1989, 111, 8954. [2] J. Am. Chem. Soc. 1989, 111, 8957.

OAc

H

Me

OTBS

OOHCTMSO

OAc

H

Me

OTBS

OONTMSO

H1. NH2OH2. NaOCl

46%

OAc

H

Me

OTBS

O

TMSO

N+-O

1,3-dipolar cycloaddition

7 steps

Wender’s racemic formal synthesis

04/09/16 Evan Carder @ Wipf Group 6

6 stepsO

TBSO

O

OTBS

Me

heat

71% O+

TBSO H

OTBS

H

Me

O

OTBS

O

Oxidopyrylium-Olefin [5+2] Cycloaddition

-O

TBSO

B and C ring

A ring

26 steps

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

Phorbol42 steps

0.02% Total yield

[1] J. Am. Chem. Soc. 1990, 112, 4956.

5 stepsH

Me

OTBS

O

TMSO

Me

Cp2ZrBu2, THF, -78 - rtthen, AcOH

69%

OAc

H

Me

OTBS

O

OTMS

HMe

Me

1. O3; NaBH42. 2-methoxypropene, PPTS

2. PCC, NaOAc24%, three steps

H

O O

Me Me

Me

Me

Me

OTBS

OOAc

O

16 steps, 1% total yieldoriginal: 26 steps. 11% total yield

N

OMe

O

O

Bn

O CHOTBSO + 7 steps O

O

HMe

OAcTBSO

OAcO+

O- H OAc

OTBS

OAc

H

Me

O

OTBS

O79%

DBUOxidopyrylium-Olefin [5+2] Cycloaddition

Wender’s asymmetric formal synthesis

04/09/16 Evan Carder @ Wipf Group 7

B and C ring

A ring

[3] J. Am. Chem. Soc. 1997, 119, 7897.

6 stepsH

Me

OTBS

O

TMSO

Ph

1. Cp2ZrCl2, nBuLi then, AcOH2. PCC, NaOAc

84%

OAc

H

Me

OTBS

O

OTMS

HPh

Ph

OAc

21 steps

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

Phorbol36 steps

1.2% Total yield

Current work: Two phase synthetic strategy

04/09/16 Evan Carder @ Wipf Group 8

[1] Science 2013, 341, 878. [2] Nature 2016, 0, 1.

Cyclase Phase 1

MeMeMe NCS, DMAP

DCM, rt MeMe

Cl

(+)-3-carene

O3, CH2Cl2/MeOH-78 oC

then, thiourea-78 oC - rt

OMeMe

Cl

Two steps, 48%

Li-napthalenide, THF, -78 oCthen, HMPA, MeI, -78 oC -rt

then, LiHMDS, -78 oC OMeMe

Me

44%Me

OHH

OMe

THF, -78 oC - 15 oC MeMe

Me

81%

MeOHHHO

BrMgTBSOTf, Et3NCH2Cl2, 0 oC

then, TMSOTf, Et3N MeMe

Me

71%

MeOTBSHTMSO

[RhCl(CO)2]2, CO

p-xylene, 140 oC

72%

MeMe

MeTMSO

O OTBS

Me

H

Advanced Intermediate>100 g, LEO Pharmaceutical

Oxidase Phase

(+) – Phorbol [2] Advanced Intermediate [1] (+) – 3-Carene

MeMeMe

(+)-3-carene

MeMe

MeTMSO

O OTBS

Me

HCyclase Phase

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

Advanced Intermediate LEO Pharmaceutics

> 100 grams

04/09/16 Evan Carder @ Wipf Group 9

Oxidase Phase 2

MeTMSO

O OTBS

Me

H

TBSO

Me

Mn(acac)2 (4.0 eq), O2PhSiH3 (3.5 eq.), PPh3 (1.5 eq.)

EtOH

2 steps, 34%SM, 62%

2.16 g scale

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

RuCl3 (0.61 eq.)NaBrO3 (54 eq.)NaHCO3 (3.1 eq.)

EtOAc/CH3CN/H2O 0.002 M, (6/6/1)

0.103 g scale

96%

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

OO TFAA (10 eq.)

DMAP (3.0 eq.)CH2Cl2, 0 oC

then, Zn (120 eq.)AcOH, CH2Cl2

MeTMSO

O OTBS

Me

H

TMSO

O

O

CF3

MeMe

OHHO

1.01 g scale

MeMe

MeTMSO

O OTBS

Me

H

MeMe

MeTMSO

O OTBS

Me

H

TMSO

Mn(acac)2 (4.5 eq.)PhSiH3 (7.0 eq.), O2EtOH

then, TMSOTf (28 eq.), Et3N (42 eq.), 0 oC

1.25 g scale

70%

MeMe

MeTMSO

O OTBS

Me

H

TMSO

TFDO (1 eq.)

CH2Cl20 oC

HO

1.04 g scale

then, ZnI2 (5.0 eq.)MgI2 (5.0 eq.)

Et2O

MeTMSO

O OTBS

Me

H

TBSO

Me

then, Ac2O (4.0 eq.)DMAP (2.5 eq.)

CH2Cl2, 0 oC

MeTMSO

O OTBS

Me

H

TMSO

O

O

CF3

MeMe

OO

HOMe

Et3N

DMF, 60 oC

64%

MeMe

MeTMSO

O OTBS

Me

H

TMSO

O OAc

TsNHNH2 (6.0 eq.)MeOH, reflux

then, NaBH3CN (18 eq.)AcOH, reflux

40%

0.7 g scale

MeMe

MeTMSO

OTBS

Me

H

TMSO

O OAc

04/09/16 Evan Carder @ Wipf Group 10

Oxidase Phase 2

MeMe

MeHO

H

OTMS

O OAc

O

Me

OAc

NaBH4, MeOH, -40 oC

then, Ac2O (7.0 eq.)DMAP (5.0 eq.), CH2Cl2

93%

MeMe

MeHO

H

OH

OH

O

Me

OH

NaBH(OAc)3benzene, reflux

then, TBAF, THF, 0 oCthen, Ba(OH)2, MeOH

72%

13 mg scale

HO

(+) - Phorbol15 mg

MeMe

MeTMSO

OTBS

Me

H

TMSO

O OAc

CrO3 (100 eq.)3,5-DMP (105 eq.)

CH2Cl2, 0 oC - rt

46%

0.2 g scale

MeMe

MeTMSO

OTBS

Me

H

OTMS

O OAc

O

1. TMSN2 (218 eq.) DCE, 70 oC then, I2 (339 eq.), pyrdine

2. Me4Sn, AsPh3 PdCl2(PhCN)2 CuI, NMP, 80 oC

two steps, 64%SM, 33%

MeMe

MeTMSO

OTBS

Me

H

OTMS

O OAc

O

13 mg scale

Me

1. HF-Py, THF, 0 oC

2. Martin sulfurane (8.0 eq.) DCE, 60 oCthen, SeO2 (12 eq.)benzene, 80 oC

two steps, 51%

MeMe

MeHO

H

OTMS

O OAc

O

Me

13 mg scale 13 mg scale

HO

04/09/16 Evan Carder @ Wipf Group 11

Notable steps: C-H Activation

C-H Activation Considerations §  Steric shielding of C6, C7,

C8, and C11.

§  Higher s-character of tertiary cyclopropane C-H bonds (C13/C14).

§  Compared to the remaining

carbon centers, C13 NMR suggests C12 is the most nucleophilic position.

§  Hyperconjugation from the pi-like cyclopropane system should facilitate oxidation.

MeMe

MeO

O OTBS

Me

H

TMSO

OHH

SiMeMeMe

12

11

13

14 8

7

6 5 3

12 Eq.

Ax.

Eq. vs Ax. Considerations

§  Activation by cyclopropane occurs through electron donation of its C-C σ bonding orbital to neighboring C-H σ antibonding orbitals.

§  Proper orbital overlap is

required in order for activation through cyclopropane hyperconjugation.

§  Hindered C-H bonds can

experience reduced rates of oxidation.

Angew. Chem. Int. Ed. 2011,50, 3362.

MeMe

MeTMSO

O OTBS

Me

H

TMSO

MeMe

MeTMSO

O OTBS

Me

H

TMSO

TFDO (1 eq.)

CH2Cl20 oC

HO

then, ZnI2 (5.0 eq.)MgI2 (5.0 eq.)

Et2O

MeTMSO

O OTBS

Me

H

TBSO

Me

04/09/16 Evan Carder @ Wipf Group 12

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

RuCl3 (0.61 eq.)NaBrO3 (54 eq.)NaHCO3 (3.1 eq.)

EtOAc/CH3CN/H2O 0.002 M, (6/6/1)

0.103 g scale

96%

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

OO

Notable steps: 1,2 –Diketone

04/09/16 Evan Carder @ Wipf Group 13

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOTFA

HOOH

acetylationthen, reduction

Sc(OTf)3

not observed

ring closure

MeMe

MeTMSO

O OTBS

Me

H

TMSO

O OH

O OTBS

MeTMSO1,2 - shift

TMSOMe

O

H

HO

62%

TFAA then, Zn

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

OO

TFAA then, Zn, Sc(OTf)3

MeMe

MeTMSO

O OTBS

Me

H

TMSO

O OH

product not obtained

Alternative product

Notable steps: Reforming the cyclopropane ring

04/09/16 Evan Carder @ Wipf Group 14

MeTMSO

O OTBS

Me

H

TMSO

O

O

CF3

MeMe

OO

HOMe

MeTMSO

O OTBS

Me

H

TMSO

Me

MeO

HOOH

MeTMSO

O OTBS

Me

H

TMSO

O

O

CF3

MeMe

OHHO

CF3

O

acetylationthen, reduction

TFAA then, Zn

aldol

Ac2O

acetylation

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOTFA

HOOAc

ring closure

MeMe

MeTMSO

O OTBS

Me

H

TMSO

O OAc

Et3N

retro-Aldol

Desired product

MeTMSO

O OTBS

Me

H

TMSO

Me

MeOH

OO

1.TFAA (10 eq.) DMAP (3.0 eq.), CH2Cl2, 0 oC2. Zn (120 eq.) AcOH, CH2Cl2

3. Ac2O (4.0 eq.) DMAP (2.5 eq) CH2Cl2, 0 oC4. Et3N, DMF, 60 oC

MeMe

MeTMSO

O OTBS

Me

H

TMSO

O OAc

64%

Notable steps: Reforming the cyclopropane ring

04/09/16 Evan Carder @ Wipf Group 15

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

MeMe

MeHO

H

OH

OH

O

Me

OH

HO

Conclusions

04/09/16   Evan  Carder  @  Wipf  Group   16  

§  Accomplished an enantiospecific total synthesis of (+) – Phorbol in 19 steps.

§  Demonstrated an effective, symbiotic relationship between an academic organic chemist and a pharmaceutical company in a collaborative pursuit toward a complex natural product synthesis.

MeMe

MeTMSO

O OTBS

Me

H

Advanced Intermediate [1] (+) – Phorbol [2]

Oxidase Phase

MeMe

MeHO

H

OH

OH

O

Me

OH

HO