2011.11.08
M2 S. Majima

Peptide Catalyst in Synthetic Organic Chemistry
Contents

1. Introduction
4. Artificial Metalloenzymes

2. Design of Peptide
3. Miller's Works

5. Summary

Wikipedia: Amino acid: http://en.wikipedia.org/wiki/Amino_acid
Arginine(Arg, R)

Serine(Ser, S)

Alanine(Ala, A)

Histidine(His, H)Threonine(Thr, T)

Lydine(Lys, K)

Asparagine Glutamine(Asn, G)(Gln, Q)

Aspartic acid
(Asp, D)

Cysteine(Cys, C)

Glutamic acid
(Glu, E)

Glycine(Gly, G)

Proline(Pro, P)

Valine Isoleucine Leucine Methionine Phenylakanine Tyrosine Tryptophan(Val, V) (Ile, I)(Leu, L) (Met, M)(Phe, F)
(Tyr, Y) (Trp,W)

1. Introduction
1-1. Outline of Idea

review: Itsuno, S. et al. Polymeric Chiral Catalyst Design andChiral Polymer Synthesis, 2011, Wiley. ISBN-10: 0470568208

Life• HighCatalyze
Enzymes

efficientry
selectivity
substrate specificity• Mild condition• In water.

R
Many chemical reactions

By using artificial peptide,high performance reaction canbe achieved?

NHO nAmino acids

1-2. Typical W orks in the Peptide Catalyst Field in 20th CenturyWiechert, R. et al. ACIE, 1971, 10, 496.
" Amino acid catalyzed asymmetric Robinson annulation"
OOO

L-Proline
1N HClO4
CH3CNO

O87%, 84 % ee.

Inoue, S. et al. Die Mukromolekulure Chemie, 1975, 176, 2751.
" Poly(amino acid)-catalyzed asymmetric protonation"
PBLG (8 mol%)

C12H25SH +O

20 - 68 days, 50 - 98% conv.
up to 47 % ee.

CH2CO2BnHN
HOn
PBLG: poly (5-benzyl L-glutamate), n = 1 - 20

C12H25SO

Ohkubo, K. et al. J. Chem. SOC. Chem. Commun. 1980, 637.
" Enantioselective hydroysis of ester by amino acid dimer"
C11H23CO(L-His)(L-Leu)H,HN

RO

C18H37ONPhBr
RO

CH3CN/H2O
C6H4-p-NO2 buffer pH 7.61, 25 °C

Bn

O

HNOOH
Bn

k L/k D = up to 5.7(ca. 70% ee.)Julia, S. et al. ACIE, 1980, 19, 929.
" Asymmetric epoxidation (Julia-Colonna reaction)"PhPhpoly(L-Ala),
H2O2, NaOH

PhO

toluene/H2O, rt.

O

PhOMiller, S. J. et al. Chem. Rev.
2007, 107, 5759.

85%, 93% ee.

Miller, S. J. et al. JACS. 1998, 120, 1629.
" Kinetic resolution in the acetylation of alcohols"O
peptide
Ac2O

OHOAc

toluene, 0 °C

NHAc

NHAc

BocHN

> 90%, 84% ee.

racemicNHNOO
HNPhN
N
peptideList, B. et al. JACS. 2000, 122, 2395.
" Asymmetric aldol reaction"
OO+H

L-Pro (30 mol%)OOH

DMSO, rt.
97%, 96% ee.

1-3. Features of Peptide Catalyst
Advantages• Tolerances of oxygen ansd water: easy handling.
• Easy synthesis and valious amino acid monomers are available: high diversity.
Disadvantages• Reaction forms are limited to organocatalytic reactions.
• Tremendous screenning is requiered to optimize catalyst.

2. Design of Peptide
2-1. Basic Structure of Peptide Catalystchiral backbone (steric, hydrogen bond, - stacking)active site

2-2. Active Sitereview: Miller, S. J. et al. Chem. Rev. 2007, 107, 5759.

Peptide catalized reactions are organocatalyst.
Base or nucleophile:
OO
RHN

NHR

RHN

O
RHN

NHR

NHR
S

NHN

SNNHNRR:

NRvia

NH2application: conjugate addition (-> protonation), MBH reaction, protonation of silyl enorlether, hydrolysis of ester, Strecker reaction, Stetter reaction, acylation, phosphorylation

Enamine / iminium f ormation:
O

H
NO
NHR

H2N

NHR
R

application: aldol reaction, conjugate addition (epoxidation).

Oxidant
IO
RHN

O

O
NHR

NHR

RHN

OH
R

N
O

Br

O
I

O
OOH
NR
via

application: oxidation.

via

Ligand
O

Ph2P

O

O
NHR

RHN

NHR

RHN
RX
N
H

NR
PPh2

PPh2

application: metal catalyzed reaction.

2-3. Chiral Backbone
2-3-1. Structure of Peptide

review: Balaram, P. et al. Chem. Rev. 2001. 101. 3131.

~ 1960's

Area of peptide catalysts.

~ 2000's

Enzyme's area.
Hard to design.
Artificial metalloenzymes.

Fig. 2-1: Various levels of structural organization observed in protein structures.
Main structures of paptide cataysts are showed in the circles.

2-3-2. Helices
Berkessel, A. et al. Org. Lett. 2001, 3, 3839. Also see above Julia-Colonna reaction.

Fig. 2-2: A interactoin of peptide and substrate. left: Org. Lett.
right: Hughes, R, M. Design Strategies f or Peptide-Based Asymmetric Catalysis,
http://images.dcheetahimages.com/www.organicdivision.org/ama/orig/
Fellowship/2005_2006_Awardees/Essays/Hughes.pdf
Construction of helices (see also Mr. Sakaoka's literature seminar in 2010/7/14.)
1. Residues with large helix-forming propensities.
-> Leu, Val, Phe, Met, etc... (hydrophobic side chains.)
It seems that the electrostatic (i, i + 4) interactions eg) Gln•Asp, Glu•Asn) are rarein peptide catalyst field. Maybe ionic functional groups give wrong effect to reaction.
2. Covalent helix-stabilization.
-> Linking (i, i + 3 or 4) residues.
Kurihara, M. et al. Tetrahedon Lett. 2011, 52, 798.
Arora, P. S. et al. ACIE. 2005, 44, 6525.

Kuroda, R. et al. JACS. 2008, 130, 12266.

3. Aib type peptide.
-> Aib: -aminoisobutyric acid; one of the ( , )-dialkylglycines.

Fig. 2-3: Chemical structures of some
representative ( , )-dialkylglycines.

muchglycine

L-alanine

RDL-alanine

Both of DL-alanine

Fig. 2-4: Ramachandran maps of amino acids.

NHRRHNO

Tanaka, M. et al. Org. Lett. 2010, 12, 3564.
DMF*2

X-ray
higher selectivity and substratescope than original reaction.

2-3-3. -turns
Hydrogen bond between (i, i + 3) ( < 7 Å). Desighned from three amino acid.
1. Proline.

RR

N

R

O H
NR

HNOO
NHR

R

compatible with the i + 1 positionof type I/III and type II turns.
Fig. 2-5: Crystallographically observed
values of L-Pro residues
from 538 independent protein crystal structures.
These two are very
important elementsfor peptide catalysts!

2. Aib type peptide.
R
HN
R

O H
NO
NHR

HNR
R
R

VSO

R

HNO H
NO
NHRR R

R

O
NHR-> When dialkyl amino acid is i + 3 position, -turn is stabilized.

2-4. How to Screening?
Target reaction
Active site type

Backbone typebase, enamine, etc...

helix or turnScreening

The sequences of amino acides are infinite, so huge screenings are required fordevelopment of peptide catalyst.screening methods.

Fluoresence Assey in Enantioselective Acyl Transf er Reaction.
Miller, S. J. et. al. JACS. 1999, 121, 4306.
ivid. 2000, 122, 11270.
ivid. 2001, 123, 6496.
Miller, S. J. et al. JACS. 1998, 120, 1629.
see also Miller, S. J. et. al. J. Org. Chem. 1998, 63, 6784. (N-Me His as a active site.)
peptideAc2O

OH

toluene, 0 °C

NHAc

OOAc
NHAc

OPhN
When the reaction is faster, it is more selective.
-> By measure reactivity, good catalyst can be found.

PETO
HN

BocHN

> 90%, 84% ee.

racemic

NHNN
peptidePET X
OAc
PhOH+PhOH

resignFig. 2-6: Mechanisum of fluorescence.

Split & pool
methodAmino acids

PhAssey
Catalyst library
24 hPick up

1000 cat.
in 60 min!

FluFig. 2-7: Outline of catalyst development.

Edman sequenceReason of this choice is not written in the paper.
D-Pro(L-His + D-Pro is better than L-Pro, JOC.) and Aib are turn elements.
Gly is less hinder, Val, Ile, Phe, Ala is middle hinder, trt or tBu protectedamino acid and Trp is higher hinder amino acid.

How do we choose amino acid monomer in library synthesis?
1. Choose -turn element.
-> It seems -turn ( -hairpin) type peptide catalysts more effective than helix type one.
ex) Pro, Aib, Ach, etc.
2. Choose aliphatic amino acids.
ex) Val, Leu, Ile, Chg, Cha, etc.
3. Choose aromatic amino acids.
ex) Phe, His, Trp, Bn-Asn, Bn-Ser, Bn-His, trt-Asn, trt-His, Pya, etc.
4. Choose bulky side-cained amino acids.
ex) t Bu-Asn, t Bu-Ser, trt-Asn, trt-Gln, trt-His, Pya, etc.

0, 1

H2N

NH2

CO2H
CO2H

Chg = cyclohexyl glycine
Cha = cyclohexyl alanin

Pya = 1-pyrenyl alanine

How do we set amino acid monomer in library synthesis?
-> Absolute randam screening gives us too large library (see after the next page.)
The reasonable sequence methodology is desirable.
Miller, S. J. et al. JACS. 2006, 128, 16454.

Structural correlation

long range

Fig. 2-8: Substrate form (MM calc.)

95 % eeSplit & pool method

Knapp, R. J. et al, Nature 1991, 354, 82.

Stuart L. Schreiber Reserch Labolatry
http://www.broadinstitute.org/chembio/lab_schreiber/anims/animations/smdbSplitPool.php

This method gives us wide library.
ex) When we synthesize hexamer with 10 kinds of amino acid monomers,
max 106 (= 1000000, 100–œ!) unique catalyst are avalable.

Hit peptide for acylation.

Make second genelation liblary based on 4.
homogeneous condition:
not on regin
Average 35% mutation using 14 unique amino acid by split & pool method.
Two types of librarys were synthesized.
1)2)HFig. 2-8: Mutation ratio of peptide.

1) TMSCHN2
2) npropylamine

Regin free peptides are easily prepared. -> more realistic assey.
Screening 80 peptide by multi-well-plate.
-hairpin?

As another method,
fluorecent gel and beadcondition is repoeted.
JACS. 2000, 122, 11270.

HitMiss

In the case of asymmetric aldol reaction.
Wennemers, H. et. al. Org. Lett. 2005, 7, 1101.

split & pool

One substrate and peptide cat. are
immobilized on a same bead.

Another substrate hascoloring moiety.

Pick up colored beads (ca. 1 out of 100).
Then analysis.

Fig. 2-9:
Li it tif thth d i th

fti

lt

hili

d ti

Limitation of these method: in the case of asymmetric electrophilic epoxydation.
Miller, S. J. et al. ACS Comb. Sci. 2011, 13, 321.
Miller, S. J. et al. JACS. 2007, 129, 8710.

from experience(other reactions.)

optical observation is hard.
Fig. 2-10: Reaction mechanism.

Problem:many analyses
are required.

65% ee in DCM
from 50 peptides.
Fig. 2-11: Outline.
My opinion...
peroxide checkpeptidepeptide

CO2Hrxn

N C NR

CO2H / CO3H

ONNHR
H
color change

Does 2 step check enable
to optical check?

3. Miller's Works
Famous people in peptide catalyst chemistry.
• Scott J. Miller, Yale Univ.
• Helma Wennemers, Basel Univ.
• Carlos F. Barbas, The Scripps Research Institute.

3-1. Enantio and Regioselective Phosphorylation myo-Inositol.
1,3 Phosphorylation
Miller, S. J. et al. JACS. 2001, 123, 10125.
ivid. 2002, 124, 11653.

1P(C)

3P
acylation cat. (previously)
randomization algorithm
Fig. 3-1: Screening of -hairpin peptides.

Fig. 3-2: Hit peptide (left) and focused library peptide(middle) and final form (right).

cf) randomizer: Research Randomizer, version 2.1 [Internetbased computer program];
http://www.randomizer.org
They used the 16 amino acids monmer.

cf) model of acylation.
6-Phosphorylation
Miller, S. J. et al. PNAS. 2010, 107, 20620.

1,3In 4,6 case, the difference of stelicenvironment is less than 1,3.

4,6Fig. 3-3: Difficulty of 4,6 desymmetrization.
Pmh-P(V) reagent system had been faild. So Miller's group tred Atz-P(III) reagent system.
(Pmh: -methyl histidine, Atz: tetrazolyl alanine)
After screening...
4 °C71%, 70 % ee
unsatisfactory

16%

kinetic resolution

Hydrogen bond between P=O and peptide is necessary for high ee.
When P=O is change to P=S, k rel = 8.4 ± 2.8.
This kinetic resolution applies 5 (70 % ee) -> ee is increase.
4 °C1), 2)

3-2. Dynamic Kinetic Resolution of Biaryl Atropisomers
Miller, S. J. et al. Scince, 2010, 328, 1251.
Miller, S. J. et al. ACIE, 2011, 50, 5125.
NMPON
via
Lewis base catalyzed electrophilic bromination

Fig. 3-4: Screening of peptide.

BrVal-NMe2 part isactive part?

Scope: 11a (10 mol%), NBP (300 mol%), CHCl3 / 3% acetone (0.01 M), 25 °C

When CO2H change to CO2Me, CONBn, NO2, ee decreases.
Aplication

3-3. Other W orks
ACIE. 2006, 45, 5616.

Nature Chem. 2009, 1, 630.

A: NaHCO3, B: 2,6-lutidine

JACS, 2010, 132, 2870.
RAr

Boc2O (0.6 eq.)
peptide (5 mol&)

SNH

H

CHCl3, 4A MS. 25 °C

RArSN
H

Hup to 95 % ee
-NCHO: very slow

JACS, 2011, 133, 9104.

No N oxidation.

4. Artificial Metalloenzymes
4-1. Peptide as a Ligand of the Transition Metal
Limitation of peptide catalyst: reaction types are confinded to organocatalitic reactions.
-> redox reactions, eg. C-H activation, are difficult.

to solve this problem...
Is the transition metal - peptide system desireble?
Examplesreview: Kamer, P. C. J. et al. Chem. Eur. J. 2011, 17, 4680.
Meldal, M. et al. J. Comb. Chem. 2007, 9, 79.
"Tsuji-Trost reaction"
OAc
PhPh+

MeO2C

CO2Me

TBAF, BSA, THF, rtDL

MeO2C

CO2MePhPhbase94%, 60 % ee

Gilbertson, S. R. et al. JACS. 2000, 122, 6522., JOC, 2004, 69, 8077.

THF, 0°91%, 95 % ee-hairpin

In abobe cases, moderate to good selectivities are observed.
But are there any needs of pepride backbone?
I'm interesting in these reaction if there is some interaction (hydrogen bond) betweenligand and substrate. But if not, I think that the role of peptide is only a divergence.
(Of course, the divergence is important to asymmetric synthesis.)

4-2. Artif icial Metalloenzymes
reviews:
Ward, T. R. et al. Chem. Commun. 2011, 47, 8470.
Ward, T. R. Acc. Chem. Res. 2011, 44, 47.
Kamer, P. C. J. et al. Chem. Eur. J. 2011, 17, 4680.
Roelfes, G. et al. Chem. Cat. Chem. 2010, 2, 916.
W hat is artif icial metalloenzymes?
-> Combination of transition metal catalyst and protein.
Kaiser and Whitesides proposed in 1970's.
Artificial metalloenzymes harnes the chiral space of enzyme for stereo andsubstrate selectivities.
R'RmetalMR''

chiral space

R'protein

R*R''

Fig. 4-1: Model of metalloenzyme
4-2-1. Dative Anchoring-> Direct coordination of transition metals to protein.
ExampleKazlauskas, R. J. et al. Chem. Eur. J. 2009, 15, 1370.
"cis selective hydrogenation of olefin"Ph
9*His- hCAII-[Rh] (1 mol%)PhPhcistrans

H2 (5 atm), 0.1 M MES, rtPhPh
55.6%[Rh(cod)2]BF4: (80.0)

PhPh
2.1%
(57.5)+Ph
2.7%(12.6)

20.6 : 1(6.3 : 1)
+PhPh
(5.7)

hCAII = human carbonic anhydrase isoenzyme II
9*His means nine His residues at surface of enzyme are replaced by Arg, Ala, Phe.
W hy they chose hCAII?
1. hCAII has zinc. Zinc and rhodium have similar ionic radius.
2. hCAll's coordinate site has His. Imidazoyl group is good ligand for Rh.
3. CAs has cysteine and it interfere with binding of Rh. But hCAII's cysteine is not surface.
4. They previously reported metal exchange of hCAII.
After choosing protein, they screened hCAII and mutated hCAIIs.

Fig.4-2: Exchange of metal in the enzyme.
4-2-2. Supramolecular Anchoring-> Ligand of metal is coordinate (not covalent) with protein.
ExampleWard, T. R. et al. PNAS. 2005, 102, 4683., Chem. Commn. 2008, 4239.
"Asymmetric transfer hydrogenation"

p-cym [Ru], P64G Sav
90-97%, 85-94 % ee

Strept avidin: tightly bind tobiotin.
K a = 1015 M-1cf) Reduction of imine,ACIE, 2011, 50, 3026.

Other combination:• HSA (human serum albumin) + polphyrin-SO3Na.
• Antibody +4-2-3. Covalent Anchoring-> Ligand of metal is connected protein covalently.
Usually Cys is targeted as a linking amino acid.
Binding:
Tyr161- Cu
Arg114, His146, Lys190-SO3etc.

M
S

Othes reactions:
Oxidation (SA + Mn or V)a) Chem. Commun. 2008, 1665.
b) JACS. 2008, 130 (25), 8085.
Tsuji-Trost reacgtion
ACIE. 2008, 47, 701.

5. Summary & Future Direction
Peptide catalyst:(+)• Highy divergence and high selectivity.
• Especially desymmetlization is powerful.
(-)• Reaction types are limited in organocatalyst field.
• It needs tremendous screening.

Efficient screening method is require!

Metalloenzyme:(+)• Potentially highy divergence and high selectivity.
(-)• Available metals are limited.
• Sensitive purity of protein.
• Narrow substrate scope.

Under development.
Towards in vivo reaction!