new strigolactone analogues, design, synthesis and … · 11th wcpp, june 7-12 , 2011 1 radboud...

11th WCPP, June 7-12 , 2011 1

Radboud University Nijmegen Department of Organic Chemistry

New New StrigolactoneStrigolactone Analogues, Design, Synthesis Analogues, Design, Synthesis

and Bioactivityand Bioactivity

Binne Zwanenburg,

Heetika Malik, A.Simon Mwakaboko and Floris P.J.T. Rutjes

Radboud University Nijmegen

The Netherlands

11th WCPP, June 7-12 , 2011 2


Parasitic Weeds:Parasitic Weeds:

Beautiful flowers but a real pestBeautiful flowers but a real pest

11th WCPP, June 7-12 , 2011 3


StrigaStriga seed germinationseed germination

Seed germinationGermination test of stimulants

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Interaction between host and parasitic weedInteraction between host and parasitic weed

simplified schemesimplified scheme

Hostreleases Chemical signal =

germination stimulant

interaction

Seeds of the parasiteAttachment on

host roots

detrimental effect

induction of

germination

Occurrence of Striga spp: tropical and subtropical areas in Africa and Azia (India).

Food crops: maize, sorghum, millet and rice; yield losses 50-90%; 100 million African people suffer.

Occurrence of Orobanche spp: mediterranean area, Eastern Europe and Middle East.

Food crops: legumes (tomato, fava beans), sunflower and tabacco; damage severe.

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� isolated from cotton(Cook et al., 1966)

� absolute configuration (Brooks et al., 1985)

� isolated from maize (Siame et al., 1993)

� activity 10-7-10-12 M

� isolated from sorghum(Hauck et al., 1992)

� absolute configuration: confirmed by total synthesis (Zwanenburg et al., 1997)

� activity 10-9-10-12 M

� isolated from cowpea(Müller et al., 1992)

� exact structure: unknown� absolute configuration:

unknown� activity 10-12 M?

Strigol Sorgolactone Alectrol Orobanchol

� isolated from red clover(Yokota et al., 1999)

� absolute configuration:confirmed by total synthesis (Mori et al., 1999)

� activity

OOO

O O

OH

A B

D

C

OOO

O O

A B

D

C

OOO

O OOH

A B

D

C

OOO

O O

OH

A B

D

C

NaturallyNaturally occurringoccurring germinationgermination stimulantsstimulants

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Tentative Molecular MechanismTentative Molecular Mechanism

Characteristics of the proposed mechanism:

� Addition/Elimination of nucleophilic site of the receptor

� Nucleophilic site e.g.: HS(-), H2N

(-)

� D-ring serves as a good leaving group

E.M. Mangnus, B. Zwanenburg; J.Agric.Food Chem., 1992, 40, 1066-1070.

OOO

O O

D

CNu

- O O

Nu

+-O

OO

OOO

O O

Nu

-

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Relevant Structural FeaturesRelevant Structural Features

OOO

O O

A B

D

CR

*

*

*

Stereochemistry

is very important

A-ring modifications

don’t reduce activity

α,β-unsaturated systemand D-ring are essential

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� Best chance for selectivity

� Best way to design active compounds, especially when the bioactiphore can be identified

� Low concentration (environmental issue)

� Best chance of decomposition in the soil (this is a prerequisite for the natural stimulant)

� Molecular fine tuning is based on a model

� No time consuming random search for a lead

Natural Stimulants as a lead for Weed Control,Natural Stimulants as a lead for Weed Control,

Why??Why??

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NijmegenNijmegen--11

ED50: 10-7 M Striga hermonthica10-6 M Orobanche crenata

OOO

N

O

O

O

O

Nijmegen-1

Nefkens, G.H.L., Thuring, J.W.J.F., Beenakkers, M.F.M., Zwanenburg, B.

J. Agric. Food Chem., 1997, 45, 2273-2277.

Easy synthesis; potential candidate for use in suicidal germination

The essential features of the bioactiphore are connected to a simple scaffold, i.e. phthalimide

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Field test Suicidal Germination, Field test Suicidal Germination, O. O. ramosaramosa

tobacco field treated with Nijmegen-1 untreated tobacco field

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Relevant Structural Features, Model for Design of new Relevant Structural Features, Model for Design of new StrigolactonesStrigolactones

OOO

O O

A B

D

CR

*

*

*

Stereochemistry

is (very)

important

A-ring modifications

don’t reduce activity

α,β-unsaturated systemand D-ring are essential

11th WCPP, June 7-12 , 2011 12


Strategy: *Incorporate essential structural feature, using simplStrategy: *Incorporate essential structural feature, using simple e

scaffolds. *Obey the molecular mechanism. *Use simple scaffolds. *Obey the molecular mechanism. *Use simple

starting materials. *Dstarting materials. *D--ring must be presentring must be present

Two step synthesis, one pot.Two step synthesis, one pot.

New New StrigolactonesStrigolactones from simple from simple KetonesKetones

O OX

7, X = Cl

O O

OO O

B. HCO2Et, t -BuOK, THF;

7, DMF, sequential

10, n = 18, n = 19, n = 2

A. HCO2Me, Na, DMF, 7,sequential ( )n( )n

11, n = 2

halo butenolide

C. HCO2Me, t-BuOK; 7, t-BuOK, two steps

11th WCPP, June 7-12 , 2011


Bioassays of new Strigolactone Analogues from Ketones

0

20

40

60

80

100

indanone tetralone GR 24

% g

erm

ination

S. hermontica

0

20

40

60

80

100

indanone tetralone GR 24

% g

erm

ination

O.crenata1 ppm0.1 ppm0.01 ppm

O

O

O

O

Tetralone analogueAs good as GR 24!!

O

O

OO

Indanone analogue

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New New StrigolactoneStrigolactone Analogues from simple Analogues from simple KetonesKetones

All are active as germination stimulants, best are those from carvone (30) and pulegone (31)

Mwakaboko, Zwanenburg, Plant & Cell Physiol. 52, 699-715 (2011)

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New New StrigolactoneStrigolactone Analogues from Analogues from KetoKeto EnolsEnols in a single Stepin a single Step

O O

OH

14

15

O O

OO

O

K2CO3, DMF

OCl O

8

O

O

O

O

O

O

DMF, 8

K2CO3

RR R

R

R = H 16

R = Me 18R = H 17

R = Me 19

R=H; R=Me

OX= OH=start.mat.

activity: ** *** **** ****** ****

OX=

stimulantO

O

HO

OX

O

OOX O O

OX

O O

OX

O

OXRR

O OO

O

OX

*

11th WCPP, June 7-12 , 2011 16


O

O

O

O

from triacetic acid lactone

O

O

O

OO

from 4-hydroxy coumarin

O

O

O

O

from dimedone

Excellent performance for analogues from dimedoneand hydroxy coumarin

S. hermonthica 0.1 mg/L: 57% germination 0.01 mg/L: 63%

O. cernua 0.1 mg/L: 79% germination 0.1 mg/L: 80%

S. hermonthica 0.1 mg/L: 62% germination

O. cernua 0.1 mg/L: 76% germinationSubmitted for publication

New New StrigolactonesStrigolactones for Suicidal Germination derived from for Suicidal Germination derived from KetoKeto

EnolsEnols in a single Stepin a single Step

11th WCPP, June 7-12 , 2011 17


StrigolactoneStrigolactone Analogue derived from SaccharineAnalogue derived from Saccharine

S

N K

O

S

N

OO

SN

OO

HO

ClCH2COCH3 (i) HCO2CH3, Na

(ii) H+

SN

OO

O

O

O

KOBut

DMF, 10

DMF, RefluxO O O O O O

O O

12 1617

18

10 is chloro-butenolide

Highly active germination stimulant for

S. hermonthica and O. cernua at 0.1 mg/L

11th WCPP, June 7-12 , 2011 18


A major obstacle is the A major obstacle is the

preparation of the Dpreparation of the D--ring! The CHring! The CH33--

group is absolutely necessarygroup is absolutely necessary

See Synthesis, 2010, 3271See Synthesis, 2010, 3271--32733273

O O

COOHO

COOH

2) p-TsOH, benzene, ∆

1) NaBH4

O O

H2, Pd/Cglyoxylic acid

benzene / anisole, ∆

O O

O OO

OCl O

1) Na or KOtBU, ethyl formate

2)

, THF

GR 24

Synthesis of GR 24Synthesis of GR 24

Zwanenburg et al : J. Agr. Food Chem. 47, 1705-1710 (1999);idem 40, 1230-1235 (1992);

New synthesis of GR24:Tetrahedron

66, 7198-7203 (2010)

11th WCPP, June 7-12 , 2011 19


Synthesis of Aromatic Synthesis of Aromatic OrobancholOrobanchol, introduction of OH in B, introduction of OH in B--ringring

O O

+

O O O O

O O

i ii

O OH

OH

iii, iv

(3%)

82 %9a

9b

Reagents and conditions: (i) FeCl3 (2 mol %), aq tBuOOH (70%, 3 equiv)

pyridine, 82 ºC, 24 h, (ii) NaBH4, CeCl3.7H2O, EtOH, (iii) PPh3,

PhCO2H, EtO2CN=NCO2Et, toluene, (iv) K2CO3, MeOH.

11th WCPP, June 7-12 , 2011 20


Synthesis of Aromatic Synthesis of Aromatic OrobancholOrobanchol, introduction of D, introduction of D--ring, OH ring, OH

down, no protection neededdown, no protection needed

O

O

O

O O

+

O

O

O

O OOH OH

9b

11aαααα 11aββββ

O OBr

10

i

O

O

O

O O

+

O

O

O

O OOAc OAc

12aαααα ((((99995555%%%%)))) 12aββββ ((((99995555%%%%))))

ii

Reagents and conditions:

HCO2Me, t-BuOK, THF, then butenolide 10, DME (ii) Ac2O, pyridine, CH2Cl2.Malik, Kohlen, Jamil, Rutjes, Zwanenburg, Org. Biomol. Chem. 9, 2286-2293 (2011)

11th WCPP, June 7-12 , 2011 21


Aromatic Aromatic OrobancholOrobanchol, introduction D, introduction D--ring ,OH up, protection neededring ,OH up, protection needed

O

O

O

O O

+

O

O

O

O OOH OH

O O

iii

O

O

O

O O

9a

OMOM

16bαααα

13b: PG = MOM15b: PG = SEM

OPG

16bββββ

iv

v

O

O

O

O O

+

O

O

O

O OOAc OAc

17bαααα ((((99993333%%%%)))) 17bββββ ((((99994444%%%%))))

i or ii

14biii for15b

Reagents and conditions: (i) MOM chloride, DIPEA, CH2Cl2, rt, 16 h, (ii) DIPEA, SEMCl, CH2Cl2,

22 h, (iii) HCO2Me, t-BuOK, THF, then butenolide 10, DME, workup with 1 M HCl

(iv) ZnBr2, CH2Cl2, 25 °C, (v) Ac2O, pyridine, CH2Cl2.

11th WCPP, June 7-12 , 2011 22


Bioassay: germination activity towards seeds of Bioassay: germination activity towards seeds of O. O. ramosaramosa

11aα OH down, D-ring down (natural); 11aβ OH down D-ring up

16bα OAc up, D-ring down;16bβ OAc up; D-ring up

11th WCPP, June 7-12 , 2011 23


Bioassay: germination activity towards seeds of Bioassay: germination activity towards seeds of O. O. ramosaramosa

12aα: OH down, D-ring down (natural); 12aβ: OH down, D-ring up17bα: OAc up, D-ring down; 17bβ: OAc up, D-ring up

18α: oxo, D-ring down (remarkably active); 18β: oxo, D-ring up

11th WCPP, June 7-12 , 2011 24


OO

O O O

A 5-Deoxy-strigol has been isolated and identified as a branching factor for arbuscular

Mycorrhizal Fungi. Akiyama et al. Nature, 453, 824 (2005); Parniste, Nature, 435, 750 (2005).

Strigol, sorgolactone and GR24 are also highly active!

••StrigolactonesStrigolactones apparently have symbiotic functionsapparently have symbiotic functions

••Weeds thrive best in soil of low fertilityWeeds thrive best in soil of low fertility

••N and P deficiency promote stimulant productionN and P deficiency promote stimulant production

••AM fungi improve P level in the soilAM fungi improve P level in the soil

BB StrigolactonesStrigolactones as new hormone class in regulating above ground plant architectas new hormone class in regulating above ground plant architectureure

••Active as inhibitor for Active as inhibitor for shoot shoot branching branching andand bud outgrowthbud outgrowth

•• UmeharaUmehara et alet al, Nature, 2008; Gomez, Nature, 2008; Gomez--RoldanRoldan et al,et al, Nature, 2008Nature, 2008

C QuestionC Question: structure activity relationship, : structure activity relationship, bioactiphorebioactiphore, receptor protein, , receptor protein,

same as for germination?same as for germination?

Newly discovered functions of Newly discovered functions of strigolactonesstrigolactones

11th WCPP, June 7-12 , 2011 25


The Huygens Building ; Radboud University NijmegenThe Huygens Building ; Radboud University Nijmegen

11th WCPP, June 7-12 , 2011 26


New New StrigolactoneStrigolactone Analogues, Design, Synthesis Analogues, Design, Synthesis

and Bioactivityand Bioactivity

� Thank you for your attention

new strigolactone analogues, design, synthesis and … · 11th wcpp, june 7-12 , 2011 1 radboud...

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