Synthesis and Applications of Fluorinated -Amino...

Synthesis and Applications of Fluorinated ⍺-Amino Acids

Overview and Recent Advances

Sébastien CardinalMacMillan Group Meeting

Princeton University11/15/2017

reference

Introduction Interest of artificial amino acids Unique properties of the C-F bond Natural fluorinated amino acid

Applications of fluorinated α-amino acids Protein engineering Medicinal chemistry 19F-NMR 18F-PET

Incorporation of fluorinated α-amino acids

Synthesis of fluorinated α-amino acids Strategy I Strategy II Strategy III Strategy IV Strategy V Strategy VI

Outlines

reference

reference

Peptides and proteins occupy innumerous biological functions Metabolic Structural

Serve as inspiration in many research fields New therapeutic agents Biomaterials

Appealing features Low toxicity Structural simplicity Low immune response

Intrinsic limitations Enzymatic degradation (protease) Thermic stability Denaturation in organic solvents

The use of non-canonical amino acids may overcome some of those limitations D-α-amino acids β-amino acids Artificial amino acids

Artificial amino acids expand the functional diversity and open the way to tailored protein design

IntroductionInterest of Artificial α-Amino Acids

reference

referenceBuer, B. C.; Marsh, E. N. G. Protein Sci. 2012, 21, 453.Cametti, M.; Crousse, B.; Metrangolo, P.; Milani, R.; Resnati, G. Chem. Soc. Rev. 2012, 41, 31.

Minor steric impact F: smallest Van der Waals radius after H and Ne

Major electronic impact F: most electronegative element Inverted polarization vs C-H

Unique features of the C-F bond Often described as the strongest organic bond (BDE up to 544 KJ/mol) Most polar covalent bond Can influence polarization on adjacent bonds Low polarizability of C-F can give rise to “Fluorous effect”

Fluorous effect Auto-segregation of fluorine-rich organic species Intermolecular: fluorous phase Intermolecular: fluorophile domain on protein

C-H → C-F Bond Substitution

reference

Can those unique features be explored in peptide/protein engineering ?

Fluorinated α-amino acids (α-AAF)

referenceOdar, C.; Winkler, M.; Wiltschi, B. Biotechnol. J. 2015, 10, 427.

4-Fluoro-L-threonine (4F-Thr): only natural α-AAF known Produced by Streptomyces cattleya (Gram-positive) Antibiotic agent Not identified in any peptide or protein so far

Biosynthesis involves incorporation of fluoride by a fluorinase enzyme

Natural Fluorinated α-Amino Acid

reference

O

HO OH

NSN

N N

NH2

NH2HO

O O

HO OH

NN

N N

NH2F

O

HO OH

FOPO3

2—

OPO32—F

OH

OH

O

H

OF

O-

O

NH3+

FOH

OH

OF

L-Thr

NAD+NADH

4FT transaldolase

Fluorinase

F-acetyldehydedehydrogenase

CH3CHO

F- L-Met PO43- adenine

Isomerase

Aldolase

FDA phosphorylase


Incorporation of Inorganic Fluoride by Fluorinase Enzyme

reference

referenceMerkel, L.; Schauer, M.; Antranikian, G.; Budisa, N. ChemBioChem 2010, 11, 1505. Berger, A. A.; Völler, J.-S.; Budisa, N.; Koksch, B. Acc. Chem. Res. 2017, 50, 2093.

Many properties can be influenced by the substitution of canonical α-amino acids by fluorinated analogues Protein folding Protein-protein interactions Ribosomal translation Lipophilicity Acidity/basicity character Optimal pH Stability: temperature, protease, organic solvents

Example: lipophilicity vs.VdW volume of side chains a-AAF can fill a desired space but with a different lipophilicity from α-AA

Often claimed to generally improve stability and properties in out-of-field literature

But, not that simple !

Application of α-AAFProtein Engineering: General Considerations

reference

« Fluorine has been shown to impart often favourable but seldom predictable properties to peptides and proteins »

-Beate Koksch (2017)-

(ProProGly)10(ProHypGly)10(ProFlpGly)10

NH

CO2H

F

Flp

NH

CO2H

Hyp

NH

CO2H

Pro

HO

referenceHolmgren, S. K.; Taylor, K. M.; Bretscher, L. E.; Raines, R. T. Nature 1998, 392, 666.

Classic example: stabilization of the folded triple helix structure of collagen at high temperature

Applications of α-AAFProtein Engineering

reference

referenceBerger, A. A.; Völler, J.-S.; Budisa, N.; Koksch, B. Acc. Chem. Res. 2017, 50, 2093.

Interest for peptides in medicinal chemistry Low toxicity Simple structure / synthesis Low immune response

Drawbacks of peptides in medicinal chemistry Biodisponibility Low membrane permeability Enzymatic cleavage

Impact of fluorine in medicinal chemistry 150 fluorinated small molecules reaching the market since 1950 In 2010, 20% of all administered drugs 30% by 2017

Applications of α-AAFMedicinal Chemistry of Peptides

reference

Can α-AAF help to overpass those limitations ?

Can this impact be translated to peptides ?

referenceKollonitsch, J.; et al. Nature 1978, 274, 906.Seki, M.; Suzuki, M.; Matsumoto, K. Biosci. Biotechnol. Biochem. 1993, 57, 1024.

Because of their resemblance with canonical a-amino acids, some α-AAF can act as inhibitors Known action on amino acid decarboxylase enzymes Inhibition of the production of biologically relevant amines, including:

α-(difluoromethyl)ornithine (DMDO) Commercial name: Eflornithine Treatment of hirsutism and African trypanosomiasis (sleeping sickness) Inhibitor or ornithine decarboxylase Acts on putrescine biosynthesis

Applications of α-AAFInhibitors

reference

DMDO

H2NO

OH

H2N CHF2

NH2HO

HODopamine

HNN

NH2 H2NNH2

Histamine Putrescine

19F-NMR spectra of a peptide bearing a Tyr(C4H9) at 500nM

referenceSalwiczek, M.; Mikhailiuk, P. K.; Afonin, S.; Komarov, I. V.; Ulrich, A. S.; Koksch, B. Amino Acids 2010, 39, 1589.Tressler, C. M.; Zondlo, N. J. Org. Lett. 2016, 18, 6240.

Widely used non-native NMR-active nucleus for interpretation of biological structure and functions

Many advantages No marking necessary No background in biological systems Sensible Can be used at biorelevant concentrations

Some α-AAF specifically designed as NMR probes

Applications of α-AAF19F-NMR Spectroscopy

NH2

CO2H

H

F3C

CF3-BpgUlrich

Tyr(C4H9)Zondlo

NH2

CO2H

H

O

F3C

F3CF3C

referenceKotzerke, J.; et al. Eur. J. Nucl. Med. Mol. Imag. 2003, 30, 1004.Nodwell, M. B.; Britton, R.; et al. J. Am. Chem. Soc. 2017, 139, 3595.

18F : t1/2 = 109.77 min

18F-PET mainly used in oncology

Main marker used: 18F-FDG (18F)-fluorodeoxyglucose Discrimination of cancer cells due to their higher metabolism

Consumption of α-amino acids also higher in cancer cells α-AAF explored as new markers Better resolution in some cases

α-AAF could also be used for more refine analysis Marking based on active transport events Transport protein LAT1 upregulated in cancer cells

Applications of α-AAF18F-Positron Emission Tomography (18F-PET)

reference

O

OH

O

NH218F

[18F]-F-TYR

referenceCarpentier, C.; Godbout, R.; Otis, F.; Voyer, N. Tetrahedron Lett. 2015, 56, 1244.Devillers, E.; Pytkowicz, J.; Chelain, E.; Brigaud, T. Amino Acids 2016, 48, 1457.

� A lot of α-AAF can be used in the context of SPSS

��Coupling in solution can overpass compatibility issues with problematic α-AAF

Incorporation of Fluorinated α-Amino Acids in Peptides and ProteinsSynthetic Incorporation with Solid-Phase Peptide Synthesis (SPSS)

reference

O

OFmocHN

Me

Me

O

ONH

Me

MeOHN

FO

FmocHN

Me

1) Piperidine/DMF 2) HATU, NMM, Fmoc-F-Ala-OH

3) Piperidine/DMF 4) HATU, NMM, Fmoc-F-Ala-OH

24% yield

O

O

Cl

Me

Me

NMM (2.2 equiv)(1.1 equiv)

H2NO

OHMeF3C

Poorly Nu- amineNot suitable for standard SPPS

+H3NO

Ot-BuMeF3C

Cl

1)

2)

(0.9 equiv)

NH

O

Ot-BuMeF3CO

FmocHNOH

OFmocHN

Me

Me

81% yield

Protected dipeptideSuitable for SPPS

(R)-α-Tfm-Ala-OH

Me

Me

referenceHackenberger, C. P. R.; Schwarzer, D. Angew. Chem., Int. Ed. 2008, 47, 10030.

Limitations of SPSS

Coupling of fragments in solution may be used for longer sequences

Incorporation of Fluorinated α-Amino Acids in Peptides and ProteinsSynthetic Incorporation Into Larger Peptide/Proteins

reference

Compatibility issues with some α-AAF

Specific protecting groups requiredNot suitable for more than 50-100 α-AA

Relies on native translational machinery of the cellIncorporates the modified α-AA at every position occupied by the parental α-AA

Needs strains of bacteria that are auxotrophic for the parental α-AAα-AAF has to be sufficiently similar to its natural analog

Particularly suitable for monoofluorated α-AAF


Residue specific

Incorporation of Fluorinated α-Amino Acids Into Peptides and ProteinsIn Vivo Ribosomal Translation of Non-Canonical α-Amino Acids

reference

Suppressor tRNARecognizes stop codon (via anti-codon)

Incorporates artificial α-AA in the protein

Mutant aaRSBrings together artificial α-AA and suppressor tRNA

Nonsense suppression: associate one of the three stop codons with an artificial α-AADesign of an appropriately engineered pair: aminoacyl tRNA synthetase (aaRS) / Suppressor tRNA

Corresponding sequence needs to be implemented in the genetic code in order to express the desired protein

referenceOdar, C.; Winkler, M.; Wiltschi, B. Biotechnol. J. 2015, 10, 427.Biava, H.; Budisa, N. Engineering in Life Sciences 2014, 14, 340.

Site specific

Incorporation of Fluorinated α-Amino Acids Into Peptides and ProteinsIn Vivo Ribosomal Translation of Non-Canonical α-Amino Acids

reference

Rely on the same translational machineryNeed prior extraction and partial purification of cellular material

More tunable systems

referenceEaston, C. J.; et al. Chem.–Eur. J. 2013, 19, 6824.

Recently developed as in vitro alternatives to the in vivo approaches

Other enzymes can be added to promote other transformations

Incorporation of Fluorinated α-Amino Acids Into Peptides and ProteinsCell-Free Ribosomal Translation of Non-Canonical α-Amino Acids

reference

PhtHNO

OMeMe

MeF

H2NO

OHMe

MeF

O

H2NO

Me Me

Problematic isolation

H2NO

NHNH2

Me

MeF

Deprot.

S30 extractin vitro

H2NO

OHMe

MeF S30 extract

in vitro

Undesired lactone

Protein containg(S)-4-fluoroleucine

NH2NH2

RF

CO2H NH2

N*

CO* R

RF *FAmine or nitrogen function

Carbox. acid or oxygenated function

Fluorinated side chain

Non fluorinated side chain

Fluorinating agent

Amino acid Cα

R

CO* N*

CO*

N*

RF *F

Synthesis of α-AAF: Proposed Classification

Approach AInstallation of functionalities

(Strategies 1-5)

Approach BFluorination of side chain

(Strategy 6)

RF

CO2H NH2

N*

CO* R





Fluorinating agent

Amino acid Cα

CO*

N*

RF



(Strategies 1-5)

RF

CO2H NH2

N*

CO* R





Fluorinating agent

Amino acid Cα

RF

CO* N*

Strategy I

N* CO*

RF

N*

RFCO*

Strategy III

RF

CO*

N*

Strategy II

Strategy IV

Synthesis of α-AAF: Proposed Classification [Approach A]

CO2H NH2

RF

Strategy V

H

O

Me

F3C

1) KCN, NH4ClNH4OH

2) HCl (aq)NH2

Me

F3C

COOH

Me

O 1) NaCN NH4Cl

2) HClNH2

COOH

FMe

F

R1 R2

O

R1 R2

CNHO

R1 R2

CNH2NCN-

(NH4)2CO3CN-

HNNH

O

O

R1

R2 H3O+ or OH-

NH3 or NH4Cl

R1 R2

OHH2N

Strecker reaction

Bucherer-Bergs reaction

H3O+

referenceBergmann, E. D.; Shani, A. J. Chem. Soc. 1963, 3462.Muller, N. J. Fluorine Chem. 1987, 36, 163.

Installation of carboxylic acid and amine functionalities on a carbonyl precursor

Examples in the synthesis of α-AAF: Strecker reaction

Strategy IMethodologies from Classic α-Amino Acid Chemistry

reference

R1 R2

O

R1 R2

CNHO

R1 R2

CNH2NCN-

(NH4)2CO3CN-

HNNH

O

O

R1

R2 H3O+ or OH-

NH3 or NH4Cl

R1 R2

OHH2N

Strecker reaction

Bucherer-Bergs reaction

H3O+

referenceTolman, V. Amino Acids 1996, 11, 15.

Installation of carboxylic acid and amine functionalities on a carbonyl precursor

Examples in the synthesis of α-AAF: Bucherer-Bergs reaction

Strategy IMethodologies from Classic α-Amino Acid Chemistry

reference

F3CCHO

(NH4)2CO3NaCN

HNNH

O

O

F3C Ba(OH)2 COOH

NH2

F3C

F3CS

CHO

1) (NH4)2CO3, NaCN2) NaOH

3) HClF3C

S COOH

NH2

referenceTolman, V. Amino Acids 1996, 11, 15.Walborsky, H. M.; Baum, M. E. J. Org. Chem. 1956, 21, 538.

Direct amination with ammonia

Azide as nucleophilic aminating agent

Strategy IIClassic Amination Reactions

reference

Br2

O

CO2EtF3C 1) NH3

2) H3O+F3C

COOH

NH2

OH

FO

CO2Li NH3 (aq)

NaBD4

FCO2H

H2N D

F3CCOOEt

Br

NaN3 F3CCOOEt

N3

1) H2 / Pd

2) H3O+F3C

COOH

NH2

F3CCOOH

F3CCOOH

Br

NH3 (l)F3C

COOH

NH2

referenceUneyama, K.; Katagiri, T.; Amii, H. J. Synth. Org. Chem. Jpn 2002, 60, 1069.Abid, M.; Teixeira, L.; Torok, B. Org. Lett. 2008, 10, 933.

Imines can be reduced by organomettallic reagents

Chiral imines can influence stereoselectivity on following reaction at Cα

Strategy IIVia the Formation of an Imine

reference

F3C CO2t-Bu

NPMP MgCl

F3CCO2t-BuHN

PMP

1) CAN

2) HCl (aq)

98%(from α-ketoester) 95%

F3CCO2HH2N

F3C CO2Et

N

Me

Ph

NH N

H

1) TfOH, CH2Cl2

2) Pd(OH)2/C, H2F3C CO2Et

OPh Me

NH2

92%

CO2EtNH2

F3C

82%90% ee

referenceLarsson, U.; Carlson, R.; Leroy, J. Acta Chem. Scand. 1993, 47, 380.

Amination directed by Evans auxilairy

Strategy IIStereoselective Amination

reference

LiN O

O

Bn

Et3NPivCl

F3CF2CF2C

O

N O

O

Bn

Bu2BOTf,(iPr)2NEt

then NBSF3CF2CF2C

O

N O

O

Bn

TMGA

Br

F3CF2CF2C

O

N O

O

BnN3

F3CF2CF2C

O

OHNH2

1) LiOOH

2) H2, Pd/C

87 %

36%, 2 steps75%, 2 steps

92:8 dr

CF2CF2CF3

O

HO

3 other α-AAFprepared

77-97% yield> 98:2 dr

referenceChiu, H. P.; Cheng, R. P. Org. Lett. 2007, 9, 5517.Biava, H.; Budisa, N. J. Fluorine Chem. 2013, 156, 372.

Ezymatic transamination

Kinetic resolution

Strategy IIObtention of Single Stereoisomer with Biocatalysts

reference

R

RO

OEtO

O

OH

R

R

H2N

1) Na2CO3 (aq)

2) phenylalanine dehydrogenase, formate dehydrogenase

NADH, HCOONH4 (aq), pH 8.5

F3CMe O

OHHN

O

F3CMe

Br

COOH

1) NH3 (aq)

2) Ac2O, NaOH

48%, 2 steps

F3CO

OHNH2

Me

29%

Aspergilus mellus acylase I

pH 7.5

39%, 99% ee (R = CF3)46%, 98% ee (R = CF2H)

referenceBiava, H.; Budisa, N. Watanabe, H.; Hashizume, Y.; Uneyama, K. Tetrahedron Lett. 1992, 33, 4333. Amii, H.; Kishikawa, Y.; Kageyama, K.; Uneyama, K. J. Org. Chem. 2000, 65, 3404.

Installation of an ester on an imidoyl halide

Strategy IIIPalladium-Catalyzed Alkoxycarbonylation

reference

Pd2(dba)3 (20 mol%)CO (1 atm), ROH

K2CO3Toluene

Rf I

NPMP

Rf CO2R

NPMP

F3C CO2Bn

NPMP

F3C CO2Et

NPMP

C7F15 CO2Et

NPMP

95% 98% 43% 79%

CO2Et

NPMP

FF

F

F FF3C CO2iPr

NPMP

49%

referenceVukelić, S.; Ushakov, D. B.; Gilmore, K.; Koksch, B.; Seeberger, P. H. Eur. J. Org. Chem. 2015, 2015, 3036.

Formation and hydrolysis of an α-aminonitrile in a semi-continuous process

Strategy IIIPhotooxidative Cyanation

reference

RF NH2

TPP, O2TMSCN, TBAF

420 nm, MeTHF-50 oC

Flow (τres = 4 min)

RF NH2

HCl (30% aq)AcOH

110 oCFlow (τres = 37 min)

CN

NH3

RF

O

OH

Cl

NH3

O

OH

ClNH3

O

OH

Cl

F

NH3

O

OH

ClF

NH3

O

OH

F3C

50%, 2 steps67%, 2 steps64%, 2 steps CF3

CF3

NH2

O

OHF3C

60%, 2 steps 63%, 2 steps

Cl Cl

referenceLi, G. Y.; van der Donk, W. A. Org. Lett. 2007, 9, 41.

� Preparation of protected γ-difluorothreonine from ascorbic acid

Strategy IVDeoxofluoration Followed by Amination

reference

OO

OHHO

OHOH

HO

OCO2Me

OBn

69%

1) DIBAL

2) DAST CH2Cl2

OO

CHF2

OBn

1) H3O+

2) TBSCl3) Tf2O, py4) NaN3, DMF

TBSO CHF2

OBn

N3

1) H2, Pd(OH)22) FmocCl, NaHCO3

3) t-BuBr, Ag2O

4) HF, py5) Jones [O]

HO CHF2

OtBu

NHFmoc

O

ascorbic acid

3 steps47%

67%

68%46%

referenceRaasch, M. S. J. Org. Chem. 1958, 23, 1567.Tolman, V. Amino Acids 1996, 11, 15.

Erlenmeyer synthesis (azlactone) - First α-AAF synthesis (1932)

SN2 reaction with an alkyl halide

Strategy VExploiting Basicity of Cα on the Glycine Moiety

reference

CH3COCH3H2O

NH

O

CF3

HOH2N

O

CF3

OH

CF3

O

H NHCOCH3

COOH AC2O NaOAc

NO

H3C

O

CF3

84%

1) H2, Pd/C2) HCl

40%, 2 steps

Ac

81%

EtONaEtOH HF, H2O

H2N COOH

CO2Et

CO2Et

H

AcHN

AcHN CO2EtEtO2C

F Br

F F

63% 27%

referenceTeegardin, K. A.; Weaver, J. D. Chem. Commun. 2017, 53, 4771.

Oxazolone enolates can be used to perform nucleophilic aromatic substitution

Fully substituted α-amino esters also accessible

Strategy VUse of Oxazolone as α-Amino Acid Template

reference

ArF-F

α-AAF (%)

ON

O

Ph

HN

O

OHO

Ph

ArF

1) ArF-F (1 equiv)TMG (2 equiv)ACN, -20 oC

2) HCl (aq)

COCH3F

F

F

FF

N F

F

F

FF

CF3F

F

F

FF

CNF

F

F

FF

87 86 82 78

ON

O

Ph

1) DIEA (10 equiv)ACN

2) TFA, MeOHBzHN

RCO2Me

NF

F

F

F

N F

F

F

FF

(1 equiv)

80% (R = Me)74% (R = i-Bu)79% ( R = CH2CH2SMe)71% (R = Bn)

R

RF

CO2H NH2

N*

CO* R





Fluorinating agent

Amino acid Cα

R

CO* N*

CO*

N*

RF *F



(Strategies 1-5)


(Strategy 6)

RF

CO2H NH2

N*

CO* R





Fluorinating agent

Amino acid Cα

R

CO* N*

*F



(Strategy 6)

reference

Smith, R. W.; et al J. Fluorine Chem. 1987, 37, 267. Kollonitsch, J.; Marburg, S.; Perkins, L. M. J. Org. Chem. 1976, 41, 3107.

Kollonitsch, J.; Barash, L. J. Am. Chem. Soc. 1976, 98, 5591.Janzen, A. F.; Wang, P. M. C.; Lemire, A. E. J. Fluorine Chem. 1983, 22, 557.

Fluorination of canonical α-AA with F2

XeF2 and CF3OF also explored

Strategy VIPioneering Works

reference

COOH

HONH2

F2/N2COOH

HONH2

F

H2N COOH

SH

H2N COOH

F

H2N COOH

FF

80%NH2

CO2Me

SMe

NH2

CO2Me

SFH2C

CF3OF, hvH2N COOH H2N COOH

F

F2/N2

XeF2

referenceZhang, X. G.; Ni, W. J.; van der Donk, W. A. J. Org. Chem. 2005, 70, 6685.

Preparation of α-AAF from Garner’s aldehyde

Strategy VIDeoxofluorination on Side Chain

reference

ONBoc

H

O

ONBoc

O

H DIBAL

THFO

NBocOH

HONHFmoc

FCrO3/H2SO4

HONHFmoc

F

O

86% 69%

56%

DAST

1) HCl (4N)

2) FmocCl NaHCO3

Ph2P=CHCHO

Toluene

NSF3

MeMe

ONBoc

F

80%32%

referenceKieltsch, I.; Eisenberger, P.; Togni, A. Angew. Chem., Int. Ed. 2007, 46, 754. Gadais, C.; Saraiva-Rosa, N.; Chelain, E.; Pytkowicz, J.; Brigaud, T. Eur. J. Org. Chem. 2017, 2017, 246.

Trifluoromethylation of L-cysteine

Togni’s reagent has shown potential for late-stage functionnalisation on tripeptides

Strategy VIAddition of Trifluoromethyl Radical

reference

BocHN

Me

O

NH

O

S

HN CO2tBu

Me

Me

2

CF3SO2NatBuOOH (80%)

MeCN/MeOH

R1 O

ONH

SH

IO

Me Me

CF3

CH2Cl2, -78 oC

R2

82% (R1 = Me, R2 = Boc)99% (R1 = Et, R2 = H)84% (R1 = Me, R2 = Ac)42% (R1 = Bn, R2 = Boc)

R1 O

ONH

SCF3

R2

BocHN

Me

O

NH

O

S

HN CO2tBu

Me

Me

1) TCEPMeOH/H2O

2) Togni’s reagentCH2Cl2, -78 oC

21%

CF3

R1 O

ONH

S

R2

2

referenceLi, S.-G.; Portela-Cubillo, F.; Zard, S. Z. Org. Lett. 2016, 18, 1888.

Trifluoromethylation of protected vinyl glycine by a CF3 radical generated from a xanthate

Other type of fluorinated side chains accessed from different olefins

Strategy VIVia the Addition of a Xanthate

reference

NO

O

Cl3C

F3C

52%, 2 steps

N CO2Me

Boc

CO2Me

NHCbz

F3C

O

60%, 2 steps 53%, 2 steps

CO2Me CO2MeLauroyl peroxide

AcOEt, refluxNHCbz NHCbz

F3C

SCSOEt H3PO2, TEAAIBN

Dioxane, reflux

CO2Me

NHCbz

F3C

72% 76%

CF3

SF3C

S

OEt

referenceLi, S.-G.; Portela-Cubillo, F.; Zard, S. Z. Org. Lett. 2016, 18, 1888.

Xanthate acts as a CF3 ‘’resevoir’’

Strategy VIVia the Addition of a Xanthate

reference

SF3C

S

OEt

CF3S

F3CS

OEt

F3C

SF3C

S

OEt

CO2Me

CO2MeF3C SF3C

S

OEt

CO2MeF3CSCF3

+

S

EtO

F3C

CO2MeF3CSCSOEt

NHCbz

NHCbz

NHCbzNHCbz

+

referenceBey, P.; Vevert, J. P.; Van Dorsselaer, V.; Kolb, M. J. Org. Chem. 1979, 44, 2732.Seki, M.; Suzuki, M.; Matsumoto, K. Biosci. Biotechnol. Biochem. 1993, 57, 1024.

Trapping of a difluorocarbene by a carbanion generated at Cα

Strategy employed in the synthesis of eflornithine

Strategy VIDifluoromethylation with Difluorocarbene Source

reference

MeO2C N

CH3

Ph

1) LDA2) ClCHF2

3) H3O+MeO2C N

CH3

PhF2HC Deprotection

HO2C NH2

CH3F2HC

83% 91%, 2 steps

CN

CO2MeNC

CN

CO2MeNC

F2HC1) NaH, DMF

2) ClCHF2 NH2

CO2MeH2N

F2HCHCl (2N)

MeOH

HCl (6N)Propylene oxyde

NH2

CO2HH2NF2HC

Eflornithine

referenceKockinger, M.; Ciaglia, T.; Bersier, M.; Hanselmann, P.; Gutmann, B.; Kappe, C. O. Green Chem. 2017, accepted.

Use of fluoroform as a CHF2 source

Strategy VIDifluoromethylation with Difluorocarbene Source

reference

MeO2C N

R

Ph MeO2C N

R

PhF2HC

HO2C NH2

RF2HC

1) LiHMDS (2 equiv)THF

2) CHF3 (3 equiv)Flow

6N HCl

150 oC, mw

86%, 2 steps (R = Me)76%, 2 steps (R = iPr)87%, 2 steps (R = iBu)86%, 2 steps (R = CH2Ph)

NH2

CO2HH2N

F2HC

Eflornithine

76%, 2 steps

referenceBume, D. D.; Pitts, C. R.; Jokhai, R. T.; Lectka, T. Tetrahedron 2016, 72, 6031.Bloom, S.; McCann, M.; Lectka, T. Org. Lett. 2014, 16, 6338.

Visible-light sensitized benzlic C-H fluorinated with Selectfluor

Selective late-stage fluorination of benzylic position in peptides

Strategy VIBenzylic C-H Fluorination

reference

PhthNO

OH

O

5 mol%

Selectfluor (2 equiv)MeCN, Visible light

PhthNO

OH

F

80%

NPhth

MeO

NH

HN

PhF

O

O

OEt

Me

Me NPhth

O

NH

HN

O

O

OEt

Me

Me

MeMeF

NH

O

OMe

FO

NHTFAHOOC

78%1.8:1 dr

63%1.3:1 dr

34%1.8:1 dr

referenceZhang, Q.; Yin, X.-S.; Chen, K.; Zhang, S.-Q.; Shi, B.-F. J. Am. Chem. Soc. 2015, 137, 8219. Miao, J.; Yang, K.; Kurek, M.; Ge, H. Org. Lett. 2015, 17, 3738.

Pd-catalyzed fluorination using 2-(pyridin-2-yl)isopropyl (PIP) as protecting and directing group

Shi (JACS, 2015)

Ge (Org Lett, 2015)

Strategy VIBenzylic C-H Fluorination

reference

NH

O Me MeH

BrNPhth

Pd(OAc)2 (6 mol%)Selectfluor (1.05 equiv)

DCM/iPrCN, 80 oC

NH

O Me MeF

BrNPhth

73%

NH

O Me MeH

BrNPhth


Fe(OAc)2 (0.3 equiv) Ag2CO3 (2 equiv)

DCE/iPrCN, 150 oC

NH

O Me MeF

BrNPhth

73%19:1 dr

referenceZhang, Q.; Yin, X.-S.; Chen, K.; Zhang, S.-Q.; Shi, B.-F. J. Am. Chem. Soc. 2015, 137, 8219. Miao, J.; Yang, K.; Kurek, M.; Ge, H. Org. Lett. 2015, 17, 3738.

Pd-catalyzed fluorination using 2-(pyridin-2-yl)isopropyl (PIP) as protecting and directing group

Shi (JACS, 2015)

Ge (Org Lett, 2015)

Strategy VIFluorination of Unactivated C-H Bonds

reference

NH

O Me MeH

NPhth


2-Me-BAH (0.2 equiv)DCM/iPrCN, 80 oC

NH

O Me MeF

NPhth

46%99% ee

NH

O Me MeH

NPhth


Fe(OAc)2 (0.3 equiv) Ag2CO3 (2 equiv)

DCE/iPrCN, 150 oC

NH

O Me MeF

NPhth

73%8:1 dr

Me Me

Me Me

referenceMiao, J.; Yang, K.; Kurek, M.; Ge, H. Org. Lett. 2015, 17, 3738.

Ge’s proposed mechanism invokes fluorination of a Pd(II) palladacyclic center

Strategy VIFluorination of Unactivated C-H bonds

reference

referenceZhu, R.-Y.; Tanaka, K.; Li, G.-C.; He, J.; Fu, H.-Y.; Li, S.-H.; Yu, J.-Q. J. Am. Chem. Soc. 2015, 137, 7067.

Similar system driven by a Quinoline-based ligand

Strategy VIFluorination of Unactivated C-H Bonds

reference

NHAr

OH

NPhth

Pd(TFA)2 (10 mol%)Selectfluor (1.5 equiv)

L (10 mol%)

Ag2CO3 (2 equiv)Dioxane, air, 115 oC

Me NHAr

OF

NPhth

53% (Ar = (4-CF3)C6F4)> 20:1 dr

Me

N O Me

Me Me

Me

L

referenceXia, J.-B.; Zhu, C.; Chen, C. Chem. Commun. 2014, 50, 11701.Halperin, S. D.; Fan, H.; Chang, S.; Martin, R. E.; Britton, R. Angew. Chem., Int. Ed. 2014, 53, 4690.

Visible-light promoted fluorination with benzophenone

Decatungstate-catalyzed C-H fluorination of branched aliphatic with NFSI

Strategy VIFluorination of Unactivated C(sp3)-H Bonds

reference

OMe

O

NPhthMe

MeSelectfluor (1.5 equiv)

Acetophenone (20 mol%)

MeCN, 48 hOMe

O

NPhthMe

Me

85%1 example of α-AA

F

OMe

O

NH3ClMe

Me

OMe

O

NH3ClMe

Me(PHSO2)2NF (1.5 equiv)

TBADT (0.02 equiv)365 nm

MeCN/H2O 56%

F

referenceNodwell, M. B.; Britton, R.; et al. J. Am. Chem. Soc. 2017, 139, 3595.

Decatungstate-catalyzed C-H fluorination: suitable system for preparation of 18F-labeled α-AAF

Strategy VIFluorination of Unactivated C(sp3)-H Bonds

reference

Preparation/purification of marked NFSI: 10 min Reaction time: 40 min Purification time: 10 min Total process from 18F generation: 60 min Product isolated directly as formulation for IV injection


5-[18F]FHL showed a normal distribution profile in healthy mice after 60 minutes

In Vivo Biological Investigation 18F Marked α-AAF Prepared by Fluorination of Unactivated C-H Bonds

reference


5-[18F]FHL showed a normal distribution profile in healthy mice after 60 minutes

4-[18F]FL accumulation in bones reveals in vivo production of fluoride by lactonisation


reference

O

O

NH3

O

O

NH3

18F

Me MeO

H3NO

Me Me

18F

Ca10(PO4)6(OH)18F

Ca10(PO4)6(OH)2

18F

MeMe

LAT1α-AA transport protein

Surexpressed in many cancer cell lines

60 min


LAT1 surexpression in tumor can be revealed by 5-[18F]FHL in PET imaging


reference

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