Design, synthesis, and side chain binding cooperativity of bis-crown ether peptides

Tetrahedron

Letters,

Vo1.32,

No.3. pp 331-334,

00404039/9

1991

1 $3.00

Pergamon

Printed in Great Britain

DESIGN,

SYNTHESJS,

COOPERATIVITY Normand Dtpartement

de chimie,

AND

SIDE

OF BJS-CROWN and

Voyer*

Universite

CHAIN

BINDING

ETHER

PEPTIDES

Johanne

de Sherbrooke,

+ .oa

Press plc

Roby

Sherbrooke,

QC, Canada

JlK

2Rl

The design , the synthesis, Summary: and the ion binding ability of three bisAll peptides demonstrated crown ether peptides is reported. a strong side chain cooperativity in the binding of Cs+ , an ion known to form “sandwich” 2:1 complexes with 18-crown-6 ligands. The

ability

response

of

enzymatic

activity,

important

biological

therefore

of

development useful

perspective,

a

we

sought

octapeptides

models

better

not

that

to

design

well

mimick

the

changes

by

using

at two

different

side

the synthesis

positions

natural

systems

specific

on the design,

with

in

chain and

could

_

complementary

alanines because

and two it can be

Also,

alanine

other

hand,

catechol peptides

guest

18-crown-6 accomodated

model the

ditopic

peptides

crown

The peptides of L-phenylalanine. a-helices, g-sheets

derivatives easily in have

amino

been

acid

may

used

extensively

be

function of the available L-DOPA. u are separated systematically

prepared

As illustrated by one, two

in readily

are or

ability

of three

moieties3.

composed

such manner

as to

of

L-

six

Alanine was chosen even turn structures.

structural

studiesh.

taking

advantage

in Figure and

ligand

interactions.

binding

benzo-18-crown-6

ions.

In that

undergo

Peptides 1_3 were designed in a way that under specific conformations and R-sheet, the two crown rings can be organized in a cooperative

complex

are

hand, the has been

host-guest

the

other

events

processes2

that

in

of the

and

those

On the other of biomolecules

behavior several

molecular

changes feature

processes,

involved

understood.

of

simple

transport

mechanisms

comprehension

our results

modified

The

conformational

is a quintessential

membrane

1 and

specific

or ions

stimulation,

importance

simple

undergo

molecules

phenomenal

gain

we report

to

other

receptor

conformational

Here,

cl-helix

with

crucial of

to

gated

polypeptides

to interactions

On the of

1, the crown

three

alanines

the

units

of

respectively.

For peptide 1, using and the R-sheet the helix axial projection5 schematic it can be seen that only under a sheet conformation the two crown representations, moieties are oriented for cooperative binding and distanced by 6-7A. However, with peptide 2, only under an o-helix structure that the crown units are organized for binding

and

cooperative 13-14A

spaced binding

for

conformation

the of

by

4.5A.

in both helix 3

and

could

Finally,

forms. the in

This sheet

principle

the

hosts

of

time

the

crown

structures be

A,

rings

are

respectively.

modulated

331

peptide

upon

can

be

oriented

separated Hence,

binding

by the

ditopic

for

681 and backbone

guests

of

332

complementary to

note

shapes

that

cooperative

the

such

crown

binding

as di-ammonium rings

under

in

several

alkyl

chains.

1_3

may

peptides types

of

turn

In also

addition,

it is important

be

organized

well

structures. CE

6.IA

BocNH-Alas-CE-Ala-CE-Ala2CONH-nPr

0 0

1 .ac

B-sheet

BocNH-Ala2-CE-Alaz-CE-AlaZCONH-nPr

CE

a-helix

2 .A’ dE

BocNH-Ala-CE-Ala3-CE-AlazCONH-nPr

CE

CE

Peptides resin

Kaiser

and steps

coupled

for

oxime resin CHCi3/MeOH CHC13/MeOH and

The

The

a 27%

was by

3

by

solid

acids yield of

the

their

ninhydrin

yield

to obtain

homogeneous

respectively

and

were

method the

on

L-DOPA7.

The

hydroxybenzotriazole

1

a p-nitrophenyl

procedure

L-phenylalanine

from

described & was

amino

by

prepared

acids

activated

were

ester8.

test9.

a 10 min treatment with a freshly (3/l) solution. Crude n-propylamide mixture

phase

following

BOC-18-crown-6

isolated

equivalents by

the

amino

necessary

overall

monitored

Peptides were cleaved from the prepared 0.5M n-prepylamine in a peptides

peptides.

were

Peptides

characterized

by

u FAB

crystallized were mass

in

obtained

a in

spectrometry

spectroscopylo.

complexing

analog

synthesized protected

1 h using

57%

and lH NMR ether

with

coupling

X6, 65

were BOC

DeGrado6.

in four Each

u with

4.5A

i

3

Figure

oxime

for

5

toward

ability

of the

several

ions

bis-crown was

peptides investigated

u

and using

the the

monomeric picrate

crown

extraction

333

methodll,l2. mono

The

and

reported

bis-crown

in Figure

18-crown-6

host

is observed 5.

applicability

compounds

When

(e.g.

when

However,

ether

2.

of this

technique

was

the guest

using

the

bis-crown

ether

of Rb+ and Cs+,

establish

demonstrated

ion is known

Na+, K+, Ca2+, and Ba2+)

in the case

to

almost

only

a 1:l

no increase instead

form

binding

previouslyI*.

to form

peptides

who

the

of

ability

of

The results

are

complex

with

in the binding the

monomeric

2 to 1 “sandwich”

analog

complexes

Figure

Na+

K+

Ba2+

ca2+

an

ability with

2

cs+

Rb-+

two 18-crown-6 ringsl3, peptides 1, 2, and 2 demonstrate a much stronger binding ability than the single crown ether 5. These results corroborate the reported data that molecules bearing two 18-crown-6 units organized in a cooperative fashion bind Cs+ ions much tighter than the corresponding monomeric analogslz. The extraction ability of peptides u relative to their monomeric analog 5 is reported in Table 1. With Rb+, a 2.2 to 3.3 fold increase in the extraction is noted. However for Csf, the bis-crown peptides U are 13, 19 and 14 times better Cs+ ligand than 5 respectively14. The relative extraction ability values obtained with Cs+ compare favourably with the ones obtained with the rigid 18-crown-6 derivative of polystyrene15 as well as with flexible bis-l8-crown-6 molecules*2. Those receptors extract Cs+ in average 5 times more than Table

1:

Relative

Ligandtd

L

corresponding

monomeric

K+

Ca2+

Ba2+

3

0.7 0.7 0.5

0.8 1.2 1.4

2.5 1.5 2.3

analogs.

this

(18-crown-6)2+Cs+

value

is

the

complex

nearest (around

to the 4.2A).

of peptides

Rbf 3.3 3.1 2.2

u*

Cs+ 13 19 14

M+ ext. by 5.

Among

the highest extraction ability toward Cs+. under its a-helical conformation is estimated peptides,

ability

Na+

*% M+ ext. by w% their

extraction

the

three

The distance to 4.5A. one

found

in

peptides,

peptide

2

between the crown rings Interestingly, for all the the

crystal

structure’6

exhibit of 2 three of the

334

In U

summary,

clearly

ether

the

demonstrate

side

chains

complexation. account ability

for

the

as

towards

chiral

well

peptides as

worth

to

observed

U

pursued

and Cs+ using

investigate

the

using

occurs

backbone

considering

is currently

Cs+

the

between

flexibility inherent

between

enantioselective

two must

peptides

u

the

dichroism

peptides

distant

crown

diminish

upon

conformational

to determine circular

bis-crown

changes in their

binding

conformation and

recognition

III

of the

NMK

ability

to

of

spec1_3

substrates.

,Acknowleds?ement+:

financial

is

with

binding

their

differences

Work

between

troscopy

it

obtained

cooperative

therefore,

significant Cs+.

results

that

and,

However,

toward

complexes

for

extraction

The authors

thanks

the NSERC

of Canada

and the FCAR

of Quebec

support.

References and

. notes,

1) Franklin, T. J., in Design and Synthesis uf Organic Molecules Based on Molecular Recognition, Van Binst, Ed., Springer Verlag, Berlin, 1986. 2) Cram, D. J., ‘Angew. Chem. Intl. Ed. EngI., 1988, 27, 1009; Lehn, J.-M., ibid, 1988, 27, 89; Rebek, J., Jr., ibid, 1990, 29, 245. 3) Some examples of crown ether peptides reported in the literature include poly-15-crown-5 LDOPA, Berthet, M. and Sonveaux, E., Biopolymers, 1986, 25, 189; crown ether modified poly-Lglutamate, Anzai, J., Ueno, A., and Osa, T., Makromol. Chem. Rapid Commun., 1982, 3, 55; and small molecular weight peptides: Detellier, C. and Stbver, H. D. H., Synthesis, 1983, 990; Berthet, M., Yordanov, S., and Sonveaux, E., Mnkromol. Chem. Rapid Commun., 1986, 7, 205. 4) Marqusee, S. and Baldwin, R. L., Proc. Natl. Acad. Sci. USA, 1987, 84, 8898; Elliott, A,, in Fibrous Protein Structure, Academic Press, New York, 1987, p.117 and references cited therein. 5) Schiffer, M. and Edmundson, Biophys. J., 1967,7, 121. 6) Kaiser, E. T., Act. Chem. Res., 1989, 22, 47; DeGrado, W. F. and Kaiser, E. T., J. Org. Chem., 1982, 47, 3258; DeGrado, W. F. and Kaiser, E. T., J. Org. Chem., 198U, 45, 1295. 7) All compounds were fully characterized spectroscopically and data were in agreement with the structures assigned. Selected data for 9: m. p. 96-98OC; [a]D=+14.4 (c=l, MeOH); Exact mass m.s.: calc.=499.2417, obt.=499.2405; 1H NMR (CDC13, S in ppm): 1.40(s, 9H), 3.01(m, ZH), 3.63-3.73(m, 12H), 3,86(m, 4H), 4.lO(m, 4H), 4,48(broad q, IH), 5.08(6, lH, J= 7,YHz), 6.656.80(m, 3H), 7.?h(broad s, I#), 8) W. Kbnig and R. Geiger, Chem. Ber., 1970, 103, 788. 9) Kaiser, E., Colescott, R. L., Bossinger, C. D., and Cook, P. I., Anal. Biochem., 1970,34, 595. 10) Peptides 1, 2, and 2 gave spectral data in agreement with the proposed structures. FAB m. s. data for u: M+= 1348; M++ Na’= 1371; Mf+ K+: 1387. 11) Pcdcrscn, C. J., Fed. Proc., Fed. Amer. Sot. Exp. Biol., 1968, 27, 386. 12) Kimura, K., Sakamoto, H., Koseki, Y., and Shono, T., Chem. Left., 1985, 1241; Kikukawa, K., He, G.X., Abe, A., Goto, T., Arata, R., Ikeda, T., Wada, F., and Matsuda, T., J. Chem. Sot, Perkin Trans. II, 1987, 135. Typical experiment: 10 mL of a ligaud CHC13 soution(2.4X10-4M in crown unit) is stirred well with 1OmL of an aqueous solution of a metal hydroxide (O.OlM) and picric acid (7X10-5M). After 30 mm., the layers arc separated and analyzed by UV spectroscopy. The values reported are the averages of 3 assays reproducible within f5 %. Chemistry of Macrocyclic Compounds”, Plenum 13) Popov, A. 1. and Lehn, J.-M., in “Coordination Press, New York, USA, 1979, pp. 537; Frensdorff, H. K., .I. Am. Chem. Sot., 1971, 91, 600; Kopolow, S., Machacek, Z., Takaki, U., and Smid, J., J. Macromol. Sci.=Ch_cm., 1973, M, 1015; Pcdersen, C. J., J. Am. Chem. Sot., 1967,89, 7017. 14) No Cs+ was extracted in a control experiment using the analog of 2 without the crown rings. 15) Kopolow, S., Hogen Esch, T. E., and Smid, J., Macromolecules, 1973, 6, 133; see also Kopolow et al in ref. 13. 16) Dawes, S. B., Ward, D. L., Huang, R. H., and Dye, J. L., 1. Am. Chem. Sot., 1986, 108, 3534. (Received

in USA

11 July

1990;

accepted

13 November

1990)