Synthesis of diacetylene-containing peptide building blocks and amphiphiles, their self-assembly and topochemical polymerization in organic solvents

DOI: 10.1002/chem.200801668

Synthesis of Diacetylene-Containing Peptide Building Blocks and

Amphiphiles, Their Self-Assembly and Topochemical Polymerization in

Organic Solvents

Eike Jahnke, Jan Weiss, Sonja Neuhaus, Tobias N. Hoheisel, and Holger Frauenrath*^[a]

Abstract: A series of functional iodo-

acetylenes was prepared and converted

into the corresponding diacetylene-sub-

stituted amino acids and peptides via

Pd/Cu-promoted sp–sp carbon cross-

coupling reactions. The unsymmetrical-

ly substituted diacetylenes can be in-

corporated into oligopeptides without a

change in the oligopeptide strandꢀs di-

rectionality. Thus, a series of oligopep-

tide-based, amphiphilic diacetylene

model compounds was synthesized,

and their self-organization as well as

their UV-induced topochemical poly-

merizability was investigated in com-

parison to related polymer-substituted

macromonomers. Solution-phase IR

spectroscopy, gelation experiments, and

UV spectroscopy helped to confirm

that a minimum of five N-H···O=C hy-

drogen-bonding sites was required in

order to obtain reliable aggregation

into stable b-sheet-type secondary

structures in organic solvents. Further-

more, the non-equidistant spacing of

these hydrogen-bonding sites was

proven to invariably lead to b-sheets

with a parallel b-strand orientation,

and the characteristic IR-spectroscopic

signatures of the latter in organic solu-

tion was identified. Scanning force mi-

crographs of the organogels revealed

that compounds with six hydrogen-

bonding sites gave rise to high aspect

ratio nanoscopic fibrils with helical su-

perstructures but, in contrast to the re-

lated macromonomers, did not lead to

uniform supramolecular polymers. The

UV-induced topochemical polymeri-

zation within the b-sheet aggregates

was successful, proving parallel b-

strand orientation and highlighting the

effect of the number and pattern of N-

H···O=C hydrogen-bonding sites as

well as the hydrophobic residue in the

molecular structure on the formation

of higher structures and reactivity.

Keywords: acetylenes · oligopepti-

des · organogels · self-assembly ·

supramolecular chemistry

Introduction

at the interface of microelectronics and the life sciences. Sig-

nificant advances in this field have been achieved in recent

years on the basis of concerted efforts in synthetic organic,

supramolecular, as well as preparative polymer chemistry.^[2–4]

Hierarchically structured, dynamically folded polymers

have, for example, been prepared by extending the foldamer

approach^[5,6]toward high molecular weight materials^[7–9]in-

cluding helical poly(acetylene)s as a prominent class of

folded, fully p-conjugated polymers.^[10–16]

We recently described a complementary strategy to obtain

well-defined, hierarchically structured p-conjugated poly-

mers that was based on the self-assembly and topochemical

polymerization of the diacetylene macromonomers 1 (see

below).^[17–20]Related attempts to extend the scope of the

UV-induced topochemical diacetylene polymerization from

single crystals^[21,22]or crystalline mono- and multilayers^[23–27]

toward less geometrically constrained systems such as vesi-

cles and other types of colloidal structures^[28–33]or fibrillar

aggregates in organogels^[34–40]have been spurred by the pros-

pect of potential applications, for example, in biosensing.

Typical examples of biopolymers exhibit hierarchical struc-

ture formation;^[1]they have a well-defined molecular struc-

ture (primary structure), fold segment-wise into distinct con-

formations (secondary structure), arrange the folded seg-

ments into specific topologies (tertiary structure), and then

spontaneously self-assemble into the final material (quater-

nary structure). Combining this kind of higher-order struc-

ture formation with properties only observed in synthetic

polymers, such as the optoelectronic activity of p-conjugated

polymers, might lead to interesting materials for applications

[a] Dr. E. Jahnke, J. Weiss, S. Neuhaus, T. N. Hoheisel, Dr. H. Frauenrath

Department of Materials, ETH Zurich

Wolfgang-Pauli Str. 10, HCI H515

8093 Zꢁrich (Switzerland)

Fax : (+41)446331390

E-mail: frauenrath@mat.ethz.ch

Supporting information for this article is available on the WWW

under http://dx.doi.org/10.1002/chem.200801668.

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Chem. Eur. J. 2009, 15, 388 – 404

FULL PAPER

Thus, a variety of diacetylene-

containing lipid amphiphiles

with chiral polar head groups,

such as phosphatidyl chol-

ines,^[41–44]

aldonamides,^[45,46]

amino acids,^[47,48]and oligopep-

tides^[49]was found to furnish

one-dimensional supramolec-

ular aggregates with helical su-

perstructures that could be co-

valently cross-linked by UV ir-

radiation. While, in all of these

examples, hydrogen bonding

between the head groups plays

an important role to translate

the molecular chirality into a

helical superstructure, the

phase segregation and crystal-

lization of the long-chain hy-

drophobic tails (or spacers)

was the decisive factor for the

formation of supramolecular

aggregates. Furthermore, the

À

Figure 1. Diacetylene macromonomers with (5+x) N H···O=C hydrogen-bonding sites (x=0, 1, 2, 5) used as

precursors for the preparation of p-conjugated polymers with a well-defined, multiple-helical quaternary struc-

ture.^[17–20]

diacetylene moieties were always incorporated into these

hydrophobic segments so that the packing of the latter con-

trolled the topochemical polymerization. Hence, the ob-

served helical structures are to be regarded as micellar or

vesicular structures and typically exhibited a mixture of su-

perstructures and a distribution of diameters from dozens of

nanometers to, in some cases, several micrometers. Conse-

quently, the topochemical diacetylene polymerization inside

these aggregates may serve as a convenient way of covalent

capture but it does not lead to well-defined polymers with a

uniform tertiary or quaternary structure.

In the present paper, we report on the synthesis of a

series of functionalized iodopropargylamine derivatives and

their conversion into a variety of peptide-substituted diace-

tylenes which may be used as building blocks in oligopep-

tide synthesis. Starting from these building blocks, we syn-

thesized the diacetylene-containing oligopeptide amphi-

philes 2a–e (Figure 2) as a set of simplified, low molecular

weight model compounds. These were designed to test some

of the molecular parameters controlling the self-assembly of

the macromonomers 1. The results from IR spectroscopy,

scanning force microscopy (SFM), gelation experiments,

UV, and CD spectroscopy proved that compounds with a

In marked contrast to the above examples, macromono-

À

mers 1 (Figure 1) comprised hydrogenated poly

G

minimum of five N H···O=C hydrogen-bonding sites relia-

a non-crystallizable hydrophobic segment, and the diacety-

lene functions were incorporated directly into the hydrogen-

bonding array.^[17–20]As a consequence of the chosen molecu-

lar architecture, the self-assembly was driven exclusively by

b-sheet formation in organic solution. Thus, the molecules

self-organized into distinct, uniform helical superstructures

constituted from a defined, finite number of stacked b-sheet

bly gave rise to b-sheet aggregates with a parallel b-strand

orientation which, in contrast to macromonomers 1, led to

the formation of organogels that could then be polymerized.

In conclusion, the molecular design of the model com-

À

pounds 2 helped to elucidate the detailed role of the N

H···O=C hydrogen-bonding sites and the hydrophobic poly-

mer segments in order to achieve well-defined, self-assem-

bled superstructures from 1. This understanding is essential

for the preparation of tailored supramolecular scaffolds and

will hopefully serve as a guideline for the preparation of hi-

erarchically structured synthetic materials in the future.

tapes, presumably controlled by the number and pattern of

À

the moleculesꢀ N H···O=C hydrogen-bonding sites.

These aggregates may, hence, be regarded as hierarchically

structured supramolecular polymers rather than micellar or

vesicular structures. As the packing of the oligopeptide b-

strands inside the constituting b-sheet tapes controlled the

arrangement of the diacetylene moieties, their topochemical

polymerization proceeded under complete preservation of

the previously assembled superstructures and, consequently,

furnished oligopeptide-functionalized poly(diacetylene)s

with defined multiple-helical quaternary structures. The ob-

tained polymers also exhibited a rich dynamic folding be-

havior in solution which was associated with their solvato-

chromic transitions.^[19,20]

Results and Discussion

Preparation of synthetic building blocks: In order to synthe-

size the desired diacetylene-containing peptide building

blocks via an sp–sp carbon cross-coupling analogous to So-

nogashira–Hagihara reaction conditions,^[51–54]a series of io-

doacetylene derivatives was required, in particular, iodopro-

pargyl amine derivatives. As various attempts to prepare

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389

H. Frauenrath et al.

the analogous oligo(ethylene

oxide) derivative 5j were

straightforwardly

prepared

from the corresponding termi-

nal acetylenes via (modified)

literature

procedures

(Scheme 3).^[56]

With the functional iodoace-

tylenes 5a–j in hands, the cor-

responding

diacetylene-con-

taining amino acids 8a–j were

synthesized via a Pd-catalyzed

sp–sp carbon cross-coupling

utilizing conditions analogous

to the Sonogashira–Hagihara^[51]

coupling (Scheme 4), starting

from the N-propargyloxycar-

bonyl-l-alanine tert-butyl ester

(7) which had been synthesized

in analogy to a published pro-

cedure for propargyloxycar-

À

Figure 2. Diacetylene-containing oligopeptide amphiphiles as model monomers with (3+x) N H···O=C hydro-

gen-bonding sites (x=0–3) investigated for their self-assembly and topochemical polymerizability.

these compounds via direct iodination of propargyl amine

had failed in our hands, we resorted to preparing 3-iodopro-

pargyl amine hydrochloride 4 from commercially available

propargyl bromide in a simple one-pot procedure which was

an adaptation of a previously published procedure for the

synthesis of other propargyl and allyl compounds carrying

silylated amine functionalities (Scheme 1).^[55]Thus, proparg-

yl bromide was added to a solution of two equivalents of

lithium hexamethyldisilazane (LHMDS) in diethyl ether at

À788C. The reaction was allowed to reach room tempera-

ture in order to be complete,

bonyl-protected amino acids.^[57]Among various different re-

action conditions and catalyst systems investigated, the cou-

pling reaction in tetrahydrofuran (THF) using [PdCl₂-

AHCTUNTGRENNG(UN PPh₃)₂] as the catalyst, CuI as the cocatalyst, and diisopro-

pylamine (DIPA) as the base delivered the most satisfactory

results for almost all iodoacetylene derivatives. Thus, the de-

sired unsymmetrically substituted diacetylenes were ob-

tained in isolated yields of 50–70%. Typically, only minor

amounts of the symmetric diacetylenes resulting from either

the homocoupling of 7 (ꢀ10%) or the self-coupling of the

before iodine was added,

again, at À788C. An aqueous

workup and a subsequent re-

moval of the excess hexame-

thyldisilazane (HMDS) by dis-

tillation afforded the crude si-

lylated iodopropargylamine 3

which was directly subjected to

alcoholysis in a freshly pre-

pared mixture of anhydrous

HCl in MeOH/CH₂Cl₂. The

corresponding acetamide 5a

was then straightforwardly pre-

Scheme 1. Synthesis of iodopropargylamine derivatives: a) 2 equiv HMDS, 2 equiv BuLi; then I₂, Et₂O,

À788C to RT; b) HCl in MeOH/CH₂Cl₂; c) Ac₂O, TEA, CH₂Cl₂.

pared by acetylation of

(Scheme 1).

4

By analogy, iodopropargyl

amide 5b, carbamate 5c, sulfo-

namide 5d, as well as the l-

alanyl and glycyl peptides 5e–g

were obtained from 4 by ap-

propriate acylation or peptide

coupling reactions (Scheme 2).

Additionally, 1-iodo-2-trime-

thylsilylacetylene 5h, iodopro-

pargyl alcohol 5i, as well as

Scheme 2. Derivatization of iodopropargylamine 4: a) Methyl succinyl chloride, CH₂Cl₂, DIEA, 08C; b) Fmoc-

Cl, CH₂Cl₂, DIEA, 08C; c) dansyl chloride, CH₂Cl₂, DIEA, 08C; d) Fmoc-l-Ala-OH, PyBOP, CH₂Cl₂/DMF,

DIEA, 08C; e) Fmoc-Gly-OH, PyBOP, CH₂Cl₂/DMF, DIEA, 08C; f) Ac-l-Ala-OH, PyBOP, CH₂Cl₂/DMF,

DIEA, 08C.

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Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

tive yields and used in subsequent peptide coupling reac-

tions without further purification. It is worth noting that, in

particular, the Fmoc-protected, unsymmetrically substituted

diacetylenes 10c, 10e, and 10 f are useful peptide building

blocks that can be incorporated into oligopeptides without a

change in the strand directionality and may, for instance, be

applied as non-natural amino acids in solid-phase peptide

synthesis.

Design and synthesis of diacetylene model monomers: All

of the free carboxylic acid building blocks 10a–j were uti-

lized in the synthesis of macromonomers 1 by coupling them

to prefabricated oligopeptide–polymer conjugates such as

Scheme 3. Preparation of other iodoacetylene building blocks: a) nBuLi,

THF, À78 to 08C; then I₂, À788C to RT, 16 h; b) 4 equiv KOH, I₂,

MeOH, RT, 16 h; c) tetra(ethylene glycol) monomethyl ether, NaH,

THF, 08C, 16 h; then 4 equiv KOH, I₂, MeOH, RT, 16 h.

hPI-NH-Ala₃-H (hPI=hydrogenated polyACHTNUTRGNEUNG(isoprene) with an

average degree of polymerization P_n=10–12) analogous to

previously published procedures.^[17–20]Additionally, a subset

of these building blocks was also used to prepare a series of

simple diacetylene monomers as low molecular weight,

monodisperse model compounds for the macromonomers.

For this purpose, the hydrophobic polymer segments used in

1 were substituted with simple dodecyl residues. The model

compounds were to comprise the same end groups and also

retain a comparable hydrophilic–hydrophobic balance, so

that the amino acid sequence was appropriately shortened.

Hence, the model compounds 2 utilized l-alanyl-l-alanine

respective iodoacetylene 8 (ꢀ10–25%, depending on the

excess of 8) were observed. A notable exception turned out

to be the Fmoc-substituted derivative 8c, which was ob-

tained as an inseparable ternary mixture of the three cou-

pling products that could only be purified after the following

step. Furthermore, iodopropargylamine hydrochloride

4

failed to deliver any isolable product at all, making its deri-

vatization prior to the acetylene heterocoupling reactions in-

evitable.

À

In addition to the thus obtained unsymmetrically substi-

tuted diacetylene amino acid derivatives, the symmetric bis-

ACHTUNGTRENNUNG(l-alanyl)-substituted diacetylene 9 was prepared by an acet-

self-assembling segments, resulting in a total of (3+x) N

H····O=C hydrogen-bonding sites (x=0–3). Starting from

the appropriate diacetylene-containing peptides 10 or 11,

the diacetylene monomers 2a and 2c–e were obtained by

simple PyBOP-promoted peptide-coupling reactions and

conveniently purified by precipitation into water

(Scheme 5). The terminal diacetylene 2b was then obtained

via desilylation of 2a. While the removal of the TMS group

with tetrabutylammonium fluoride (TBAF) in CHCl₃/THF

ylene homocoupling reaction under Hay^[58]conditions

(Scheme 4). The tert-butyl esters 8a–j and 9 were finally

converted into the free carboxylic acids 10a–j and 11, re-

spectively, by treatment with trifluoroacetic acid (TFA) in

CH₂Cl₂. After removal of the solvent and TFA in high

vacuum, the free acids were typically obtained in quantita-

Scheme 4. Synthesis of diacetylene-containing amino acid building blocks: a) Propargyl chloroformate, TEA, CH₂Cl₂, 08C; b) 5a–j, [PdCl

(2 mol%), CuI (10 mol%), DIPA, THF, 08C; c) TMEDA, CuCl, air, acetone; d) TFA, CH₂Cl₂, 3–16 h; e) isolated yield of 10c over two steps.

₂ACHTUNGTRENNUNG(PPh₃)₂]

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391

H. Frauenrath et al.

indicative of

a heat-induced

polymerization. For all model

monomers, the UV irradiation

of solutions did not lead to a

color change, but the organo-

gels immediately turned violet

to dark purple, clearly indicat-

ing poly(diacetylene) forma-

tion (see below). The gel

formed from 2e in THF ap-

peared to be the most reactive

as it already turned dark

purple when stored at room

temperature in the dark. It is

very important to acknowledge

that these observed gelation

properties are distinctly differ-

ent from the behavior of the

macromonomers 1 and more in

Scheme 5. Synthesis of diacetylene model monomers. a) Fmoc-l-Ala-OH, PyBOP, DIEA, CH₂Cl₂/DMF, RT;

b) piperidine, CHCl₃, RT; c) PyBOP, DIEA, CH₂Cl₂/DMF, RT; d) AgNO₃, EtOH/MeOH/H₂O; then KI.

or K₂CO₃in CH₂Cl₂/MeOH had failed in our hands because

of an epimerization of the peptides, 2b was cleanly obtained

in 91% yield following a mild deprotection protocol using

AgNO₃/KI in a MeOH/EtOH/H₂O mixture as the sol-

vent.^[59,60]

line with the properties of typical diacetylene-containing

amphiphiles.^[34–49]Despite their significantly larger number

À

of N H···O=C hydrogen bonds and resulting tendency to ag-

gregate at even micromolar concentrations, the macromono-

mers 1 had not shown any tendency to form macroscopic

gels in organic solvents at all even at high concentrations,

presumably due to the presence of more soluble^[61]and uni-

form supramolecular polymers without branching points

with extreme persistence lengths, and, accordingly, little ten-

dency to form entanglement networks.

Gelation in organic solvents: The diacetylene model mono-

mers 2 were investigated concerning their ability to self-

assemble into nanostructures in organic solution that would

allow for a topochemical polymerization in analogy to their

more complex macromolecular siblings 1. We, therefore, at-

tempted to dissolve the model compounds in various sol-

vents such as CH₂Cl₂, CHCl₃, THF and cyclohexane, typical-

ly at a concentration of 1 gL^À1. Compound 2a formed clear

solutions in all of these solvents and did not cause gelation

or undergo polymerization upon UV irradiation (see

below). Thus, more than 45 gL^À1could be dissolved in

CH₂Cl₂, CHCl₃and THF without any visible gel formation.

Likewise, 2b showed no tendency toward gel formation in

any solvent, although its overall solubility was lower, and it

was virtually insoluble in cyclohexane. Upon heating these

solutions, their color typically turned to orange-brown, prob-

ably due to random cross-linking of the diacetylene func-

tions. In the solid state, the compound was found to be un-

stable toward degradation, changing its color to brown

within a few days even when stored in the dark.

By contrast, compounds 2c–e showed trends in their solu-

bility and gelation properties which qualitatively scaled with

their number of hydrogen-bonding sites (Figure 3). Thus, 2c

was found to form a mechanically weak gel in CH₂Cl₂at a

concentration of 1 gL^À1at room temperature but gave rise

to solutions in CHCl₃as well as THF. Compound 2d formed

weak gels in CH₂Cl₂and CHCl₃under the same conditions

which were stable up to about 358C, but it remained soluble

in THF. Finally, 2e was an efficient organogelator and

formed stable gels in CH₂Cl₂, CHCl₃and even in THF at

concentrations as low as 0.5 gL^À1. These gels were stable up

to the solventsꢀ boiling points, attaining only a slight red hue

Figure 3. Representative pictures of the mechanically stable gels formed

from 2c and 2e before and after UV irradiation.

IR Spectroscopy in organic solvents: Macromonomers 1 had

been found to give rise to IR spectra with different charac-

teristic signatures depending on the number and pattern of

À

N H···O=C hydrogen-bonding sites in the molecules, which

we had tentatively attributed to parallel versus antiparallel

b-sheet formation.^[17–20]It should be noted, however, that

problems in the detailed interpretation of the IR spectra

arose from the conflicting, contradictory, and often arbitrary

assignments of IR bands to certain secondary structures in

the literature,^[62]from the presence of non-peptidic (carba-

mate, amide) hydrogen-bonding sites in the macromono-

mers, and from the use of an organic solvent instead of

water. IR spectra of the drastically simplified diacetylene

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À

the use of N H···O=C hydrogen-bonding sites in order to

achieve specific types of aggregation in organic solvents.

Thus, all model compounds which remained soluble and

did not form gels gave rise to non-aggregated secondary

structures in organic solvents. For example, the IR spectra

of the TMS-functionalized derivative 2a, which comprised

À

(3+0) N H···O=C hydrogen-bonding sites and was well-

soluble in CHCl₃, revealed an amide A absorption at

3430 cm^À1, that is, far above the value of 3300 cm^À1that

À

would be expected for N H bonds in an aggregated state.

Only the small IR band observed at 3309 cm^À1may be re-

garded as indicative of a low degree of b-sheet formation. In

the amide I region, first of all, a broad peak at 1725 cm^À1

was observed that can be assigned to the carbamate function

in a non-hydrogen-bonded state.^[63]The observed broad and

featureless amide

I absorption with a maximum at

1667 cm^À1implied that the molecules gave rise to a mixture

of non-aggregated secondary structures, such as random coil

and “turn-like” structures.^[61]Likewise, the amide II region

contained one broad and featureless band with a maximum

at 1503 cm^À1, corroborating this interpretation. Derivative

2b, featuring the same number and pattern of hydrogen-

bonding sites, showed a strikingly similar IR signature. The

main amide A absorption was observed at 3308 cm^À1accom-

panied by a smaller band at 3423 cm^À1, showing that b-sheet

formation was still not predominant but might be slightly

more favorable as compared to 2a, probably because of the

reduced steric hindrance of the H-terminated versus the

TMS-protected diacetylene. The IR absorptions in the

amide I and II regions at 1722, 1663 (broad), and 1515 cm^À1

proved that the situation was essentially the same as in 2a,

that is, the carbamate was not hydrogen-bonded, and the

molecule attained random coil or “turn-like” conformations.

By contrast, those model compounds which formed stable

organogels showed a completely different behavior. Thus,

the symmetric model compound 2e as the other extreme,

featuring (3+3) hydrogen-bonding sites and forming the

most stable organogels in CHCl₃, showed a single, sharp

amide A band at 3290 cm^À1, consistent with predominantly

À

aggregated N H bonds in a b-sheet arrangement and match-

ing exactly the values observed in the cases of the corre-

sponding macromonomers 1. The amide I region of 2e was

dominated by a band at 1639 cm^À1. The position of this main

amide I band was curiously shifted away from the typical

values of 1625–1630 cm^À1reported for antiparallel b-sheet-

type secondary structures from related oligopeptides and

their polymer conjugates in solution,^[63–68]and it did not

match the value of 1626 cm^À1calculated for a single antipar-

Figure 4. a) IR spectra and b) the corresponding peak deconvolution in

the amide I region proved that 2a–c gave no indication of aggregation in

chloroform solutions (indicative peaks marked in blue). By contrast, the

weak gel obtained from 2c in CH₂Cl₂as well as the gels from 2d and 2e

in chloroform exhibited IR spectra consistent with an aggregation into

parallel b-sheets (indicative peaks marked in red). The degree of order

allel poly

close to the value of 1637 cm^À1calculated for the hypotheti-

cal infinite, single, parallel poly

(alanine) b-sheet,^[69,70]as well

(alanine) b-sheet,^[69]either. However, it was very

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

as the experimental value of 1642 cm^À1observed in a tripep-

tide that formed parallel b-sheet structures in the crystalline

state.^[71]Likewise, the amide II region revealed a single peak

at 1538 cm^À1which also closely matched the calculated

value for a single parallel b-sheet^[69,70]and was distinctly dif-

ferent from typical examples of antiparallel b-sheets.^[63–68]

À

increased with the number of N H···O=C hydrogen-bonding sites in the

molecules.

model monomers 2a–e (Figure 4a) ought to help clarify the

remaining issues and also establish a set of guidelines for

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393

H. Frauenrath et al.

Finally, the absorption of the carbamate function was ob-

served at 1694 cm^À1, which was clearly indicative of a carba-

mate in a hydrogen-bonded state.^[63]Hence, the band ob-

served at around 1690 cm^À1does not necessarily originate

from the presence of antiparallel b-sheet structures in this

particular case and is, hence, not contradictory to the above

interpretation. This interpretation is, moreover, supported

by the fact that 2e should be expected to aggregate into par-

allel b-sheets due to its symmetry, if the molecules are

straightforward deconvolution of the IR absorptions in the

region between 1580 and 1780 cm^À1with a limited number

of peaks at almost constant positions and reasonable peak

widths (Figure 4b). Consistent with the global analysis of the

spectra discussed above, the IR spectra of chloroform solu-

tions of 2a–c were dominated by

a peak at around

1670 cm^À1, and the predominant peak in the case of gels of

2c–e was located at around 1640 cm^À1. Interestingly, the nor-

malized areas of these two peaks showed a systematic de-

pendence on the number of hydrogen-bonding sites.^[75]Ac-

cordingly, a plot of the area fraction of the peak at around

1640 cm^À1(Figure 5), which may be taken as a coarse esti-

mate for the degree of parallel b-sheet formation, exhibited

a strong increase between four and five hydrogen-bonding

sites and then appeared to level off, reaching a value of ap-

proximately 94% in the case of 2e.^[76]

À

aligned in-register and the maximum number of N H···O=C

hydrogen bonds is to be achieved.

The remaining model compounds 2c and 2d exhibited a

behavior between the above extremes, according to the re-

spective number of (3+1) or (3+2) hydrogen-bonding sites.

Thus, the IR spectra of 2c in CHCl₃solution showed amide

A absorptions at 3434 and 3314 cm^À1and two broad bands

at 1730 and 1675 cm^À1which can be assigned to the n_Cvi-

=

O

brations of, on one hand, the ester and the free carbamate

as well as, on the other hand, the amide and peptide n_{C O}vi-

=

brations, proving that the molecules were i) not aggregated

and ii) the peptide mainly attained a “turn-like” conforma-

tion, just like 2a and 2b. However, the IR signature of 2c

changed drastically when the weak gel obtained in CH₂Cl₂

was investigated. The amide A region was now dominated

by an absorption located at 3285 cm^À1, well in line with an

aggregation into b-sheet structures. The additional, smaller

bands at 3352 and 3427 cm^À1indicated that a certain fraction

of molecules remained non-aggregated and the degree of

order was still not very high. This interpretation was con-

firmed by the main amide I absorption located at 1641 cm^À1

accompanied with a smaller one at 1676 cm^À1. The ester and

the carbamate groups were now separated into two bands at

1734 and 1706 cm^À1, respectively, the latter being indicative

of a carbamate in a hydrogen-bonded state. Finally, the

amide II region revealed two peaks at 1543 and 1503 cm^À1,

the former exactly matching the value calculated for a

single, parallel b-sheet^[69,70]and the latter proving the coexis-

tence of molecules with a different secondary structure. In

conclusion, the amide A, carbamate, amide I, and amide II

absorptions together converged into a consistent picture.

Apparently, model compound 2c with its (3+1) hydrogen-

bonding sites was just on the border of being able to aggre-

gate, as it predominantly remained disordered in CHCl₃as

the more polar solvent^[72]but formed the desired parallel b-

sheet-type aggregates in CH₂Cl₂to a certain extent. Finally,

the IR spectrum of the gel (in CHCl₃) of 2d with its (3+2)

Figure 5. Area fractions of the peaks at 1640 and 1670 cm^À1as a coarse

estimate for the degree of b-sheet formation (in solutions or gels in

chloroform) systematically increased with the number of hydrogen-bond-

ing sites, reaching a value of 94% in the case of 2e (line serves as guides

to the eye).

In summary, IR spectroscopy indicated that, in apolar or-

À

ganic solvents, a minimum number of (3+1) N H···O=C hy-

drogen bonds is the lower limit for the formation of b-sheet

aggregates. However, even minor changes of the solvent po-

larity are enough to change the nature of the secondary

structures, and stable b-sheet aggregates are only obtained

À

N H···O=C hydrogen bonds, exhibited a n_NÀHvibration at

for (3+2) or (3+3) N H···O=C hydrogen bonds. These find-

3291 cm^À1with only a minor shoulder at 3431 cm^À1. The

amide I region was dominated by a band at 1639 cm^À1, the

carbamate band was observed at 1687 cm^À1, and the single

amide II absorption band was located at 1541 cm^À1, all con-

sistent with the presence of highly ordered parallel b-sheet

aggregates, as in the case of 2e.

ings are in line with related investigations concerning oligo-

peptide–PEG conjugates in the solid state.^[63,77]They are

also in good agreement with our own previous investigations

on macromonomers 1 where derivatives such as 1h–j were

found to aggregate into relatively flexible fibrillar features

(via antiparallel b-sheet formation); only macromonomers

with (5+1) or more hydrogen-bonding sites gave rise to

many micrometers long, uniform, well-defined helical rib-

bons or fibrils. Furthermore, the exclusive observation of

parallel b-sheet secondary structures in the model com-

It is worth mentioning that the observed band structure in

the IR spectra, in particular in the case of 2d and 2e, was

considerably more clear and better interpretable than in re-

lated literature examples.^{[64–66,73,74]}This allowed for

a

394

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Chem. Eur. J. 2009, 15, 388 – 404

Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

pounds 2c–e goes to prove that, in apolar organic solvents

and in the absence of competitive hydrogen-bonding part-

ners, the non-equidistant placement of hydrogen-bonding

sites in a molecule, that is, a default configuration for the

maximization of hydrogen-bonding interactions upon paral-

lel aggregation, constitutes a sufficient driving force to con-

trol parallel versus antiparallel orientation and even over-

compensates other factors favoring the latter.

be excluded that they had only been formed upon the evap-

oration of the solvent during sample preparation. Somewhat

larger aggregates with a length of up to about 200 nm and

an apparently smaller tendency to align on the HOPG sub-

strate predominated in SFM images of samples from 2d

(Figure 6b). Finally, the symmetric compound 2e was the

only derivative that gave rise to better-defined, many micro-

meters long fibrillar features with helical superstructures

(Figure 6c) reminiscent of those formed by the macromono-

mers 1 to a certain degree. In marked contrast to the latter,

however, these one-dimensional aggregates were not uni-

form species but exhibited a distribution of diameters and a

variety of helical superstructures. Thus, several distinctly dif-

ferent types of aggregates with heights on the order of 5–

11 nm, apparent widths of 16–34 nm, and helix pitches of

25–64 nm were observed. However, all different types of fi-

brils had a right-handed helical superstructure in common.

This seems to be a remarkable detail because the fibrils ob-

tained from macromonomers 1a and 1b with the same total

number of hydrogen-bonding sites were, to the best of our

knowledge, the first example of b-sheet aggregates with a

right-handed helical superstructure^[17–20]whereas, with one

notable, recently reported exception,^[78]all literature exam-

ples of fibrils from synthetic oligopeptides or amyloid pro-

teins give rise to left-handed helical superstructures,^[50]pre-

sumably due to their preferred molecular conformations.^[79]

Combined with the observed gelation properties, these re-

sults serve to elucidate the role of hydrogen bonding as well

as the difference between using flexible, amorphous, poly-

disperse polymer segments in macromonomers 1 as opposed

to simple alkyl tails in the model compounds 2. In agree-

ment with both the IR spectra discussed above and our find-

ings concerning the self-assembly of macromonomers 1, it

SFM Imaging of organogel samples: SFM investigations of

solutions or gels of the model compounds confirmed the re-

sults of the IR measurements and helped to establish a link

between the molecular structure and the macroscopic gela-

tion behavior. In the case of 2c, samples spin-coated from

CH₂Cl₂gave rise to aggregates the majority of which had a

thin, flat tape-like appearance and a length of up to 100 nm

(Figure 6a). As these aggregates exhibited a preferred orien-

tation parallel to the HOPG lattice axes, it could not even

À

appears that four or five N H···O=C hydrogen-bonding sites

are sufficient for unspecific aggregation. However, a total of

six hydrogen-bonding sites, that is, (3+3) for the model com-

pounds 2 or (5+1) for the macromonomers 1, are an indis-

pensable prerequisite for obtaining high aspect ratio, one-di-

mensional aggregates in organic solvents.

Contrary to Bodenꢀs findings concerning the hierarchical

self-organization of (more elaborately designed) oligopep-

tides into distinct levels of b-sheet superstructures,^[67,68,79]the

inherent helicity of the aggregates from the very short and

simple oligopeptide derivatives 2 alone does not appear to

be able to prevent the formation of a variety of superstruc-

tures as well as defect structures via b-sheet stacking, b-

sheet edge-interactions, and imperfections in the hydrogen-

bonding network. For this reason, the utilization of the flexi-

ble and polydisperse, non-crystallizable polymer segments in

the macromonomers 1 is a decisive element in the molecular

design, as well, as opposed to the solubilizing but also crys-

tallizable dodecyl residues in the model monomers. The at-

tached polymer segments, presumably, guide the system into

the formation of better soluble and uniform superstructures

from a finite number of stacked b-sheets, resulting in the

formation of well-defined supramolecular polymers with an

extraordinary persistence length, without branching points,

Figure 6. SFM images of samples of 2c–e spin-coated onto a monolayer

of octadecylamine on HOPG; only in the case of 2e with its (3+3) hy-

drogen-bonding sites, high aspect ratio fibrillar aggregates with helical su-

perstructures were observed.

Chem. Eur. J. 2009, 15, 388 – 404

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395

H. Frauenrath et al.

and, as a consequence, without any tendency to form orga-

nogels.

Topochemical polymerization in the organogels: In order to

investigate the UV-induced topochemical polymerization of

the model compounds in organic solvents and organogels,

thoroughly degassed CH₂Cl₂or CHCl₃solutions of 2a–e at a

typical concentration of 0.5–1 gL^À1were homogenized in an

ultrasonic bath, heated and transferred immediately into

quartz cuvettes under nitrogen. Upon cooling, the solutions

of 2c–e formed organogels inside the cuvettes. The samples

were then subjected to UV irradiation for 2 h, using a

250 W Ga-doped Hg lamp equipped with a black bandpass

filter. Whereas none of the solutions were polymerizable, all

organogel samples underwent topochemical diacetylene

polymerization, which helped to independently corroborate

the presence of parallel b-sheet structures, as inferred from

the IR spectroscopic signature.

Thus, solutions of the TMS-protected diacetylene 2a did

not show any significant change in the UV/Vis spectra upon

UV irradiation, and solutions of the terminal diacetylene 2b

only developed

a broad, featureless absorption below

500 nm indicative of a random cross-linking process.^[75]Like-

wise, CHCl₃solutions of 2c were not polymerizable, either.

By contrast, organogels formed from 2c in CH₂Cl₂exhibited

the typical absorption spectra known from poly(diacety-

lene)s upon UV irradiation (Figure 7b). The global absorp-

tion maximum was located at 573 nm with the first vibronic

progression observed at 528 nm, resembling the spectra of

the poly(diacetylene) obtained from the corresponding mac-

romonomer 1b.^[17–20]As expected from the higher degree of

order according to the IR spectra, organogels obtained from

2d turned purple more quickly. However, the polymeri-

zation also resulted in the relatively rapid disruption of the

gel under precipitation of purple polymer that could not be

redissolved (Figure 7a). Supposedly, the overall hydropho-

bic/hydrophilic ratio may be inappropriate in 2d, highlight-

ing the role of the attached alkyl residues as solubilizing

groups. Finally, UV/Vis spectra of the organogels from 2e

after UV irradiation exhibited the characteristic UV absorp-

tion bands for poly(diacetylene)s (Figure 7c), and the molar

extinction coefficient of the obtained polydiacetylene) P2e

of around e=8ꢃ10⁶cm²mol^À1was on the order of other

(pure) poly(diacetylene)s reported in the literature,^[80]sug-

gesting that the achieved conversions were high in this case.

The shape of the spectra was reminiscent of that of the mac-

romonomers and, at the same time, proved the presence of

different types of spectroscopic aggregates in the gels from

P2e. Thus, the global maximum at l_max=534 nm corre-

sponded exactly to the value observed for poly(diacetylene)s

prepared from macromonomers 1b, 1 f, and 1g, and the

shoulder at 495 nm could straightforwardly be assigned as a

vibronic side band. The maxima at 588 and 571 nm, howev-

er, appeared to belong to a different spectroscopic species.

Interestingly, the spectrum of the CHCl₃gel exhibited essen-

tially the same peaks but the higher wavelength absorptions

were much less pronounced and the vibronic fine structure

Figure 7. a) Organogels of 2c–e in CHCl₃or CH₂Cl₂turned red or purple

upon UV irradiation; in the case of 2d, the polymerized material precipi-

tated; b),c) UV spectra of the organogels of 2c and 2e after 2 h of UV ir-

radiation proved the formation of poly(diacetylene)s; however, high con-

versions were only achieved in the case of 2e. d)–f) Color changes, UV,

and CD spectra of P2e upon the addition of TFA; the purple gel i) of

P2e formed a yellow solution, ii) upon the addition of TFA, accompanied

with a hypsochromic shift in the UV/Vis spectrum; subsequent addition

of TEA yielded a red solution, iii) from which the polymer slowly precipi-

tated.

better developed, suggesting a more uniform and less aggre-

gated distribution of superstructures in CHCl₃as the better

solvent. The gels remained stable throughout the polymeri-

zation, and no precipitation of polymer occurred, probably

because of both the more appropriate hydrophobic–hydro-

philic balance and the presence of the very long entwined fi-

brils which may not have enough mobility to aggregate into

larger bundles during polymerization.

The addition of minuscule amounts of a hydrogen-bond-

breaking cosolvent, such as trifluoroacetic acid (TFA), to

the polymerized purple gel of P2e (about 7 mL of TFA for

0.7 mL of the gel) led to its slow dissolution, a color change

to yellow, and a drastic hypsochromic shift in the UV/Vis

396

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Chem. Eur. J. 2009, 15, 388 – 404

Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

spectrum (Figure 7d and e). The subsequent addition of trie-

thylamine (TEA, about 14 mL) induced another color

change to red. In comparison to the original polymerized

gel, this newly formed red species exhibited an absorption

for the formation of high aspect ratio nanoscopic fibrils, ac-

cording to SFM imaging. The exclusive formation of parallel

b-sheet structures was observed, indicating that the non-

À

equidistant placement of the N H···O=C hydrogen-bonding

maximum slightly shifted to shorter wavelengths (l_max

=

sites in such molecules is a useful parameter to control the

intermolecular orientation in detail. In marked contrast to

the macromonomers 1, the diacetylenes 2 were found to be

efficient organogelators, and gel formation was, in this case,

a prerequisite for their polymerization upon UV irradiation.

The origin of the macroscopic gelation in the case of 2e on

the nanoscopic length scale was found to be the presence of

entwined, entangled, and branched nanoscopic fibrils with a

distribution of diameters on the order of a few nanometers

and a variety of helical superstructures. Apparently, the

more elaborate molecular design of the macromonomers 1,

including a flexible, non-crystallizable, polydisperse hydro-

phobic polymer segment, was required for the formation of

well-defined supramolecular polymers from a defined, finite

number of laminated b-sheet tapes which, despite the small-

er number of hydrogen bonds and the higher propensity

toward aggregation, showed no tendency toward gelation. In

conclusion, the work presented here extends the knowledge

about the requirements for an appropriate molecular design

in order to achieve well-defined, oligopeptide-based nano-

structures via supramolecular self-assembly. This improved

understanding will hopefully establish a set of guidelines for

the detailed control of the self-organization of oligopeptide-

based materials, which may then be utilized as a universal

supramolecular scaffold to control the placement of reactive

molecules and moieties other than diacetylenes and, thus,

provide a pathway toward hierarchically structured carbon-

rich or organic optoelectronic materials.

522 nm) with an even higher extinction coefficient and a

well-resolved vibronic fine structure. No gelation occurred

in the red state and, moreover, precipitation of the polymer

was observed over time.^[75]Although the UV spectra of the

purple, yellow, and red species resembled those of the poly-

(diacetylene)s P1 (upon TFA addition) to a certain degree,

the observed processes were fundamentally different in

nature and, in the present case, more in line with previously

reported examples of poly(diacetylene) solvatochrom-

ism.^[39,81–85]P1 had been observed to undergo two distinct,

consecutive solvatochromic transitions with the red form as

a defined intermediate, and the presence of three different,

well-defined states had further been confirmed by CD spec-

troscopy. Accordingly, the CD-spectroscopic behavior of

P2e (Figure 7f) was found to be different from P1. The orig-

inal red-purple organogels exhibited a strong but difficult to

reproduce CD signal which, in marked contrast to P1, did

not have a clean signature with zero-crossings from bisignate

Cotton effects and, hence, probably rather resulted from cir-

cular intensity dichroic scattering (c.i.d.s.)^[86]like many other

examples of poly(diacetylene) CD spectra.^[87]The CD signal

almost completely disappeared upon TFA addition but, in

contrast to the reversible red-yellow transition in the case of

P1, was not recovered upon neutralization with TEA. Only

a weak CD signal was observed which, like the red form of

P1, exhibited a negative bisignate Cotton effect at the posi-

tion of the highest wavelength UV absorption. All these re-

sults served to confirm the assumption that only the poly-

(diacetylene)s P1 were present in the form of defined aggre-

gation states (single tapes, dimeric ribbons, tetrameric fi-

brils) which were able to reversibly unfold and refold. By

contrast, the poly(diacetylene) P2e, due to its simpler mo-

lecular architecture, gave rise to a variety of poorly defined

superstructures, as had been observed in the SFM images of

samples before UV irradiation, as well.

Experimental Section

Instrumentation: NMR spectroscopy was carried out on

a Bruker

Avance 300 spectrometer operating at a frequency of 300.23 MHz for ¹H

and 75.49 MHz for ¹³C nuclei. The UV/Vis spectra were recorded on a

Perkin–Elmer UV-20 spectrometer with a scan speed of 480 nm per

minute using 1 cm quartz cuvettes from Hellma. High resolution mass

spectra were recorded on IonSpec ULTIMA FTMS: 6211 HiRes-

MALDI and 494 HiRes-ESI-MS machines, respectively. Elemental analy-

ses were carried out as service measurements at the Laboratory of Or-

ganic Chemistry at the Department of Chemistry and Applied Biosci-

ences at ETH Zurich using a LECO CHN/900 instrument. Solution

phase IR spectra were recorded on a “Spectrum One” IR spectrometer

from Perkin–Elmer using a solution phase cuvette with KBr windows

and a light path of 0.5 mm. TLC Analyses were performed on TLC

plates from Macherey–Nagel (Alugramm Sil G/UV₂₅₄). UV-light

(254 nm) or standard coloring reagents were used for detection. Column

chromatography was conducted on Geduran Silica gel Si 60 from Merck

(40–60 mm). UV polymerizations were performed using a 250 W Ga-

doped low pressure Hg lamp from UV Light Technology, Birmingham,

UK, using a “black bandpass filter” with a transparency window from

315 to 405 nm.

Conclusions

In summary, we prepared a number of functionalized iodo-

propargyl derivatives and applied them in the synthesis of a

series of diacetylene-containing peptides via Pd-catalyzed

sp–sp cross-coupling reactions. These diacetylene–peptide

conjugates may be useful building blocks for the preparation

of non-natural oligopeptides. Thus, the diacetylene amphi-

philes 2 were synthesized which served as low molecular

weight model compounds for the previously reported, self-

assembling diacetylene macromonomers 1. The model com-

pounds were found to reliably self-assemble into b-sheet

secondary structures in apolar organic solvents if a minimum

SFM Imaging: Samples were analyzed in tapping mode using a Nano-

scope IIIa instrument operating at room temperature in air. Microfabri-

cated silicon nanoprobes with a resonating frequency of 300 kHz on aver-

age were used. Scan rates between 0.5 and 2 Hz were applied and the

image size was 512ꢃ512 pixels. Samples were prepared by spin-coating

À

number of five N H···O=C hydrogen bonds was present in

the molecule, and six such hydrogen bonds were required

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397

H. Frauenrath et al.

(3800 rpm) a solution of octadecylamine in chloroform (0.1 mgmL^À1

onto freshly cleaved HOPG. Dilute solutions of the macromolecules

were ultrasonicated for 30 min and left standing for 16 h, and then spin-

coated onto the amphiphile monolayer on HOPG.

)

AgNO₃(44 mg, 0.26 mmol) was added, and the reaction was monitored

by TLC. After 90 min, all starting material (R_f=0.6, CH₂Cl₂/MeOH 10:1)

was transformed into the silver acetylide (R_f=0, CH₂Cl₂/MeOH 10:1),

and KI (50 mg, 0.30 mmol) was added to the solution. The reaction mix-

ture was stirred overnight, and a fine yellow precipitate of AgI formed.

The solvents were removed in vacuo, the crude product was taken up in

chloroform, and the AgI was filtered off. The residue was dried and puri-

fied by column chromatography (silica gel, CHCl₃/MeOH 24:1) to yield

the title compound as a slightly yellow, light-sensitive solid (77 mg,

91%). R_f=0.6 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO):

d=0.91 (t, J=6.9 Hz, 3H, (CH₂)₁₁CH₃),), 1.2–1.6 (m, 26H, (CH₂)₁₀CH₃, 2

ꢂ

General synthetic procedures: Unless otherwise noted, all reactions were

carried out in dried Schlenk glassware in an inert N₂atmosphere. Sol-

vents were purchased as reagent grade and distilled prior to use. Ether,

toluene and THF were dried over sodium/benzophenone, CH₂Cl₂over

CaH₂, and acetone was dried using P₂O₅. The solvents were freshly dis-

tilled and stored over molecular sieves prior to use. N-Fmoc-l-alanine, l-

alanine tert-butyl ester hydrochloride, N-acetyl-l-alanine, propargyl

amine, propargyl bromide, propargyl alcohol, TMS-acetylene, and all

peptide coupling promoters were commercially obtained and used with-

out further purification.

CHCH₃), 2.20 (s, 1H, C CH), 3.26 (m, 2H, NHCH₂ACHTUNGTREN(UNG CH₂)₁₀CH₃), 4.26

(m, 1H, CHCH₃), 4.45 (m, 1H, CHCH₃), 4.77 (s, 2H, NHCO₂CH₂), 5.50

(brs, 1H, NH), 6.17 (brs, 1H, NH), 6.68 ppm (brs, 1H, NH); HRMS

(MALDI): m/z: calcd for C₂₄H₃₉N₃O₄Na: 456.2838; found: 456.2833

[M+Na]⁺.

General procedure for Sonogashira couplings (GP A): N-Propargyloxy-

carbonyl-l-alanine tert-butyl ester 7 (1 equiv), the iodoacetylene com-

pound (1.2 equiv) and diisopropylamine (4 equiv) were dissolved in dry

THF. The solution was degassed in three freeze-pump-thaw cycles. After

N-{6-[N’-(4-Methoxysuccinyl)amido]hexa-2,4-diynyl-1-oxycarbonyl}-l-

alanyl-l-alanine dodecylamide (2c): Following GP C, 13 (228 mg,

0.88 mmol) and 10b (297 mg, 0.88 mmol) were dissolved in a mixture of

dry CH₂Cl₂(30 mL) and dry DMF (5 mL). DIEA (0.46 g, 3.56 mmol) and

PyBOP (502 mg, 0.96 mmol) were added, and the solution was stirred at

room temperature overnight. The solvents were removed in vacuo. The

crude product was dissolved in a 1:1 mixture of THF (10 mL) and

MeOH (10 mL), and purified by precipitation in water (120 mL). The

precipitate was filtered off and dried in HV to yield the title compound

as a slightly brownish solid (0.36 g, 65%). R_f=0.3 (CH₂Cl₂/MeOH 10:1);

¹H NMR (300 MHz, [D₆]DMSO): d=0.86 (t, J=6.9 Hz, 3H,

(CH₂)₁₁CH₃), 1.1–1.5 (m, 26H, (CH₂)₁₀CH₃, 2CHCH₃), 2.39 (t, J=6.4 Hz,

2H, NHCOCH₂), 2.52 (t, J=6.4 Hz, 2H, CH₂CO₂Me), 3.03 (m, 2H,

covering the flask with aluminum foil and cooling to 08C, [PdCl₂ACTHNUTRGEN(UNG PPh₃)₂]

(2.0 mol%) and CuI (10 mol%) were added. The solution was stirred for

2 to 12 h, followed by the removal of the solvent. The crude product was

taken up in CH₂Cl₂followed by an aqueous workup, unless otherwise

noted. The organic phase was dried over MgSO₄, filtered, and concentrat-

ed in vacuo. The purification was carried out by column chromatography

(silica gel) to separate the desired product from homo- and self-coupling

side products.

General procedure for the cleavage of tert-butyl esters (GP B): The tert-

butyl ester derivatives 9 and 10 were dissolved in dry CH₂Cl₂. Then, a

large excess (ꢁ13 equiv) of trifluoroacetic acid (TFA) was added, and

the solution was stirred for 3 to 16 h. The reaction was monitored by

TLC. After completion of the reaction, the solvents were removed in

vacuo. The crude product was typically used in the next step without fur-

ther purification.

NHCH

G

1H, CHCH₃), 4.21 (m, 1H, CHCH₃), 4.74 (s, 2H, NHCO₂CH₂), 7.61 (d,

J=7.2 Hz, 1H, NH), 7.74 (m, 1H, NH), 7.93 (d, J=7.8 Hz, 1H, NH),

8.43 ppm (t, J=5.4 Hz, 1H, NH); HRMS (MALDI): m/z: calcd for

C₃₀H₄₈N₄O₇Na: 577.3595; found: 577.3588 [M+Na]⁺.

General procedure for PyBOP-promoted peptide couplings (GP C): The

carboxylic acid component was dissolved in a mixture of dry CH₂Cl₂and

dry DMF. The amine component (1 equiv) was added, as well as diiso-

propylethylamine (DIEA; 4 equiv). The resulting solution was cooled to

08C, and (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluoro-

phosphate (PyBOP; 1.05 equiv) was added in one portion. The cooling

bath was removed, and the reaction mixture was stirred at room temper-

ature for 3 to 16 h. The solvents were removed and the crude product

was purified by column chromatography, unless otherwise noted.

N-{6-[N’-(9-Fluorenylmethyloxycarbonyl-l-alanyl)amido]hexa-2,4-diynyl-

1-oxycarbonyl}-l-alanyl-l-alanine dodecylamide (2d): Following GP C,

13 (186 mg, 0.73 mmol) and 10 f (370 mg, 0.72 mmol) were dissolved in a

mixture of dry CH₂Cl₂(30 mL) and dry DMF (5 mL). DIEA (0.37 g,

2.86 mmol) and PyBOP (394 mg, 0.76 mmol) were added, and the solu-

tion was stirred at room temperature overnight. The solvents were re-

moved in vacuo. The crude product was dissolved in a 1:1 mixture of

THF (10 mL) and MeOH (10 mL), and purified by precipitation in water

(120 mL). The precipitate was filtered off and dried in HV to yield the

title compound as a slightly brown solid (0.43 g, 78%). R_f=0.4 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=0.82 (t, J=6.9 Hz,

3H, (CH₂)₁₁CH₃), 1.1–1.5 (m, 29H, (CH₂)₁₀CH₃, 3CHCH₃), 3.15 (m, 2H,

N-(5-Trimethylsilylpenta-2,4-diynyl-1-oxycarbonyl)-l-alanyl-l-alanine do-

decylamide (2a): Following GP C, 13 (148 mg, 0.58 mmol) and 10h

(150 mg, 0.56 mmol) were dissolved in a mixture of dry CH₂Cl₂(30 mL)

and dry DMF (5 mL). DIEA (0.30 g, 2.32 mmol) and PyBOP (1.06 g,

2.04 mmol) were added, and the solution was stirred at room tempera-

ture overnight. The solvents were removed in vacuo. The crude product

was dissolved in a 1:1 mixture of THF (5 mL) and MeOH (5 mL), and

purified by precipitation in water (120 mL). The precipitate was filtered

NHCH

G

2CHCH_3,fluorenyl CH), 4.2–4.4 (m, 3H, CHCH₃, Fmoc-CO₂CH₂), 4.65

(s, 2H, NHCO₂CH₂), 7.26 (t, J=7.2 Hz, 2H, aromatic H), 7.35 (t, J=

7.2 Hz, 2H, aromatic H), 7.5–7.8 (m, 3H, NH), 7.74 (m, 2H, aromatic

H), 7.85–7.95 (m, 3H, 2aromatic H, NH), 8.42 ppm (m, 1H, NH);

HRMS (MALDI): m/z: calcd for C₄₃H₅₇N₅O₇Na: 778.4156; found:

778.4150 [M+Na]⁺.

off and dried in HV to yield a slightly brown solid (240 mg, 84%). R_f

0.6 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=0.19 (s, 9H,

Si(CH₃)₃), 0.88 (t, J=6.6 Hz, 3H, (CH₂)₁₁CH₃), 1.25 (brs, 18H,

(CH₂)₉CH₃), 1.38 (d, J=6.9 Hz, 6H, 2 CHCH₃), 1.50 (m, 2H, CH₂-

(CH₂)₉CH₃), 3.24 (m, 2H, NHCH₂A(CH₂)₁₀CH₃), 4.26 (m, 1H, CHCH₃),

=

ACHTUNGTRENNUNG

Hexa-2,4-diynylene-1,6-bis(oxycarbonyl-l-alanyl-l-alanine dodecylamide)

(2e): Following GP C, 13 (513 mg, 2 mmol) and 11 (340 mg, 1 mmol)

were dissolved in a mixture of dry CH₂Cl₂(50 mL) and dry DMF (5 mL).

DIEA (0.65 g, 5 mmol) and PyBOP (1.06 g, 2.04 mmol) were added, and

the solution was stirred at room temperature overnight. The solvents

were removed in vacuo. The crude product was dissolved in a 1:1 mixture

of THF (10 mL) and MeOH (10 mL), and purified by precipitation in

water (200 mL). The precipitate was filtered off and dried in HV to yield

the title compound as a colorless solid (0.67 g, 82%). R_f=0.4 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=0.83 (t, J=6.9 Hz,

A

CHTUNGTRENNUNG

4.44 (m, 1H, CHCH₃), 4.74 (s, 2H, NHCO₂CH₂), 5.55 (d, J=7.5 Hz, 1H,

NH), 6.27 (m, 1H, NH), 6.78 ppm (d, J=7.2 Hz, 1H, NH); ¹³C NMR

(75 MHz, CDCl₃): d=À0.5 (Si

(2CHCH₃), 22.7, 26.9, 29.3, 29.3, 29.4, 29.6, 29.6, 31.9 (10 CH₂), 39.7

(NHCH₂A(CH₂)₁₀CH₃), 49.0, 50.8 (2CHCH₃), 53.1 (NHCO₂CH₂), 71.4,

ACTHGNUNERTN(UNG CH₃)₃), 14.1 ((CH₂)₁₁CH₃), 18.6, 19.0

CHTUNGTRENNUNG

71.7, 86.9, 88.2 (diacetylene C), 155.0 (carbamate C=O), 171.8 (amide C=

O), 172.0 ppm (amide C=O); elemental analysis calcd (%) for

C₂₇H₄₇N₃O₄Si: C 64.12, H 9.37, N 8.31; found: C 64.16, H 9.22, N 8.59;

HRMS (MALDI): m/z: calcd for C₂₇H₄₇N₃O₄SiNa: 528.3234; found:

528.3228 [M+Na]⁺.

6H, (CH₂)₁₁CH₃), 1.1–1.5 (m, 52H, 2

ACTHUGNNERTN(UNG CH₂)₁₀CH₃, 4CHCH₃), 2.9–3.1 (m,

4H, 2NHCH₂A(CH₂)₁₀CH₃), 4.0–4.1 (m, 2H, 2CHCH₃), 4.15–4.3 (m, 2H,

CTHUNGTRENNUNG

2CHCH₃), 4.74 (s, 4H, 2NHCO₂CH₂), 7.60 (d, J=7.5 Hz, 2H, NH), 7.7–

7.8 (m, 2H, NH), 7.90 ppm (d, J=7.5 Hz, 2H, NH); HRMS (MALDI):

m/z: calcd for C₄₄H₇₆N₆O₈Na: 839.5617; found: 839.5618 [M+Na]⁺.

N-(Penta-2,4-diynyl-1-oxycarbonyl)-l-alanyl-l-alanine

(2b): The TMS-protected derivative 2a (0.10 g, 0.22 mmol) was dissolved

in a mixture of MeOH (10 mL), EtOH (20 mL), and H₂O (2 mL).

dodecylamide

398

www.chemeurj.org

ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2009, 15, 388 – 404

Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

3-Iodo-N,N-bis(trimethylsilyl)propargylamine (3) and 3-iodopropargyl-

amine hydrochloride (4): Hexamethyldisilazane (HMDS, 9.68 g,

60 mmol) was dissolved in ether (30 mL) at 08C, and n-butyl lithium

(60 mmol, 1.6m solution in hexanes) was added slowly. The mixture was

allowed to reach room temperature and stirred for another 30 min. The

flask was covered with aluminum foil, the solution was cooled to À788C,

and propargyl bromide (3.57 g, 30 mmol) in dry ether (20 mL) was added

dropwise. The reaction mixture was allowed to reach room temperature

again and stirred for 2 h. Then, I₂(7.61 g, 30 mmol) was added at À788C,

and the reaction mixture was stirred at room temperature overnight. The

reaction was quenched by washing with saturated Na₂S₂O₃solution. The

organic phase was dried over MgSO₄, filtered, and concentrated in vacuo

at room temperature. Residual HMDS was distilled off the crude mixture

at 08C (4ꢃ10^À2mbar). The remaining crude 3-iodo-N,N-bis(trimethylsi-

lyl)propargylamine (3; 9.17 g, 80%), a slightly orange oil, was deprotect-

ed without further purification. For this purpose, acetyl chloride (7.85 g,

100 mmol) was dissolved in dry MeOH (25 mL) at 08C in order to gener-

ate anhydrous HCl in MeOH. The solution was stirred for 30 min at

room temperature and diluted with CH₂Cl₂(25 mL). The protected

amine derivative 3 (6.0 g, 18.4 mmol) was added at 08C, and a fine brown

precipitate formed instantaneously. The precipitate was filtered off and

dried in vacuo. 4 (3.21 g, 80%) was obtained as a slightly brown powder.

M.p. 168–1698C (decomposition); ¹H NMR (300 MHz, [D₆]DMSO): d=

3.79 (s, 2H, CH₂), 8.46 ppm (s, 3H, NH₃Cl); ¹³C NMR (75 MHz,

4.24 (m, 1H, fluorenyl-CH), 4.33 (d, J=6.9 Hz, 2H, Fmoc-CO₂CH₂), 7.34

(t, J=7.2 Hz, 2H, aromatic H), 7.43 (t, J=7.5 Hz, 2H, aromatic H), 7.70

(d, J=7.2 Hz, 2H, aromatic H), 7.80 (t, J=5.4 Hz, 1H, NH), 7.90 ppm

(d, J=7.5 Hz, 2H, aromatic H); ¹³C NMR (75 MHz, [D₆]DMSO): d=8.4

ꢂ

(C CI), 32.2 (NHCH₂), 47.1 (fluorenyl-CH), 66.2 (Fmoc-CO₂CH₂), 90.8

(CꢂCI), 120.6, 125.6, 127.6, 128.1, 141.2, 144.3 (aromatic C), 156.4 ppm

(carbamate C=O); elemental analysis calcd (%) for C₁₈H₁₄NO₂I: C 53.62,

H 3.50, N 3.47, I 31.47; found: C 53.78, H 3.60, N 3.47, I 31.47; HRMS

(EI): m/z: calcd for C₁₈H₁₄NO₂I: 403.0064; found: 403.0067 [M]⁺.

N-(5-Dimethylamino-1-naphthalenesulfonyl) 3-iodopropargylamide (5d):

Compound 4 (0.50 g, 2.3 mmol) was dissolved in a mixture of dry CH₂Cl₂

(20 mL) and DIEA (0.74 g, 5.8 mmol). The solution was cooled to 08C

and 5-dimethylamino-1-naphthalenesulfonyl chloride (0.68 g, 2.5 mmol)

was added. The mixture was stirred for 20 min at 08C. The reaction was

quenched by the addition of MeOH (10 mL). The resulting solution was

washed twice with water. The organic phase was dried over MgSO₄, fil-

tered, and concentrated in vacuo. The crude product was purified by

column chromatography (silica gel, CH₂Cl₂/MeOH 10:1) to yield the title

compound as a slightly brown powder (0.63 g, 57%). R_f= 0.7 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=2.85 (s, 6H, N-

AHCTNUGTREN(GNNU CH₃)₂), 3.86 (d, J=6 Hz, 2H, NHCH₂), 7.27 (d, J=7.2 Hz, 1H, aromatic

H), 7.62 (m, 2H, aromatic H), 8.15 (dd, J=7.2 Hz, 1.2 Hz, 1H, aromatic

H), 8.26 (d, J=8.7 Hz, 1H, aromatic H), 8.36 (t, J=6 Hz, 1H, amide

NH), 8.5 ppm (d, J=8.7 Hz, 1H, aromatic H); ¹³C NMR (75 MHz,

ꢂ

[D₆]DMSO): d=20.2 (C CI), 30.3 (CH₂), 84.9 ppm (C CI); HRMS (EI):

[D₆]DMSO): d=10.0 (CꢂCI), 34.0 (NHCH₂), 45.7 (N(CH₃)₂), 88.4 (Cꢂ

N

m/z: calcd for C₃H₄IN: 180.9384; found 180.9383 [MÀHCl]⁺.

CI), 115.5, 119.7, 124.0, 128.3, 129.2, 129.6, 129.7, 130.2, 136.4, 151.8 ppm

(aromatic C); elemental analysis calcd (%) for C₁₅H₁₅IN₂O₂S: C 43.49, H

3.65, N 6.76, O 7.72, S 7.74, I 30.63; found: C 43.66, H 3.52, N 6.70, O

7.76, S 7.56, I 30.80; HRMS (EI): m(z: calcd for C₁₅H₁₄IN₂O₂S: 412.9816;

found: 412.9816 [M+H]⁺.

N-(3-Iodoprop-2-ynyl)acetamide (5a): Compound 4 (3.0 g, 13.8 mmol)

was dissolved in a mixture of dry CH₂Cl₂(70 mL) and DIEA (8.91 g,

68.9 mmol). The reaction mixture was cooled to 08C, and acetic anhy-

dride (14.1 g, 138 mmol) was added via a syringe. The flask was covered

with aluminum foil, and the reaction mixture was stirred at room temper-

ature overnight. The solution was diluted with CH₂Cl₂, and the organic

phase was washed twice with saturated NaHCO₃solution and once with

saturated NaCl solution. The organic phase was dried over MgSO₄, fil-

tered, and concentrated in vacuo at room temperature in the dark. The

crude product was purified by column chromatography (silica gel,

CH₂Cl₂/MeOH 100:1) to yield the title compound as a slightly yellow

N-[N’-(9-Fluorenylmethyloxycarbonyl)-l-alanyl] 3-iodopropargylamide

(5e): DIEA (9.69 g, 75 mmol) was dissolved in a mixture of dry CH₂Cl₂

(60 mL) and dry DMF (20 mL). Compound 4 (3.26 g, 15 mmol) and N-

Fmoc-l-alanine (4.67 g, 15 mmol) were added. At 08C, PyBOP (8.32 g,

16 mmol) was added, and the solution was stirred overnight. After re-

moval of the solvent, the crystalline product was washed with CH₂Cl₂to

yield the title compound as colorless crystalline product (5.24 g, 74%).

crystalline solid (1.76 g, 57%). R_f

= 0.35 (CH₂Cl₂/MeOH 10:1); m.p.

104–1068C; ¹H NMR (300 MHz, CDCl₃): d=1.99 (s, 3H, CH₃), 4.16 (d,

J=5.1 Hz, 2H, CH₂), 6.29 ppm (brs, 1H, NH); ¹³C NMR (75 MHz,

CDCl₃): d=À0.1 (CꢂCI), 22.9 (CH₃), 31.1 (CH₂), 89.7 (CꢂCI),

170.0 ppm (amide C=O); elemental analysis calcd (%) for C₅H₆INO: C

26.93, H 2.71, N 6.28, I 56.90; found: C 26.76, H 2.62, N 6.12, I 56.99;

HRMS (EI): m/z: calcd for C₅H₆INO: 222.9489; found 222.9488 [M]⁺.

R_f

= 0.8 (CH₂Cl₂/MeOH 10:1); m.p. 189–1908C (decomposition);

¹H NMR (300 MHz, [D₆]DMSO): d=1.21 (d, J=7.2 Hz, 3H, CHCH₃),

4.0–4.1 (m, 3H, CH₂NH, fluorenyl CH), 4.2–4.4 (m, 3H, CHCH₃,

CO₂CH₂), 7.34 (t, J=7.2 Hz, 2H, aromatic H), 7.43 (t, J=7.2 Hz, 2H, ar-

omatic H), 7.55 (d, J=7.8 Hz, 1H, carbamate NH), 7.74 (t, J=6.0 Hz,

2H, aromatic H), 7.90 (d, J=7.5 Hz, 2H, aromatic H), 8.31 ppm (t, J=

13

ꢂ

5.3 Hz, 1H, amide NH); C NMR (75 MHz, [D₆]DMSO): d=8.4 (C

N-(4-Methoxysuccinyl) 3-iodopropargylamide (5b): Compound 4 (3.04 g,

14 mmol) was dissolved in a mixture of dry CH₂Cl₂(60 mL) and DIEA

(9.0 g, 70 mmol). The solution was cooled to 08C. Succinic acid mono-

methyl ester chloride (2.10 g, 14 mmol) was added dropwise, and the so-

lution was stirred overnight. After an acidic aqueous work-up, the organ-

ic solution was concentrated in vacuo. The crude product was purified by

column chromatography (silica gel, CH₂Cl₂/MeOH 50:1) to yield the title

compound as a colorless solid (2.96 g, 73%). R_f=0.5 (CH₂Cl₂/MeOH

10:1); m.p. 104–1058C; ¹H NMR (300 MHz, [D₆]DMSO): d=2.37 (t, J=

6.3 Hz, 2H, CH₂), 2.52 (t, J=6.3 Hz, 2H, CH₂), 3.58 (s, 3H, CH₃), 3.97

(d, J=5.4 Hz, 2H, CH₂N), 8.32 ppm (s, 1H, NH); ¹³C NMR (75 MHz,

CI), 18.6 (CHCH₃), 30.5 (CH₂N), 47.2 (fluorenyl CH), 50.4 (CHCH₃),

ꢂ

66.1 (CO₂CH₂), 90.4 (C CI), 120.6, 125.8, 127.6, 128.1, 141.2, 144.3 (aro-

matic C), 156.2 (carbamate C=O), 172.8 ppm (amide C=O); elemental

analysis calcd (%) for C₂₁H₁₉IN₂O₃: C 53.89, H 4.04, I 26.76, N 5.91;

found: C 52.89, H 4.34, I 26.57, N 5.77; HRMS (EI): m/z: calcd for

C₂₁H₁₉IN₂O₃: 474.0435; found: 474.0432 [M]⁺.

N-[N’-(9-Fluorenylmethyloxycarbonyl)glycyl] 3-iodopropargylamide (5 f):

DIEA (6.65 g, 45.0 mmol) was dissolved in a mixture of dry CH₂Cl₂

(30 mL) and dry DMF (10 mL). Compound 4 (1.96 g, 9.0 mmol) and

Fmoc-Gly-OH (2.68 g, 9.0 mmol) were added. At 08C, PyBOP (4.92 g,

9.45 mmol) was added, and the solution was stirred overnight. After re-

moval of the solvent, the crystalline product was washed with CH₂Cl₂to

yield the title compound as a colorless solid (3.35 g, 81%). R_f=0.8

(CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=3.62 (d, J=

ꢂ

[D₆]DMSO): d=8.1 (C CI), 29.0, 30.0, 30.2 (CH₂NH, CH₂CO₂Me,

ꢂ

NHCOCH₂), 51.8 (CH₃), 90.5 (C CI), 170.9, 173.2 ppm (2C=O); elemen-

tal analysis calcd (%) for C₈H₁₀INO₃: C 32.56, H 3.42, N 4.75, I 43.01;

found: C 32.77, H 3.40, N 4.62, I 42.84; HMRS (EI): m/z: calcd for

C₈H₁₀NO₃I: 294.9700; found: 294.9700 [M]⁺.

ꢂ

6.3 Hz, 2H, Gly-CH₂), 4.01 (d, J=5.4 Hz, 2H, C CCH₂NH), 4.2–4.4 (m,

3H, fluorenyl-CH, Fmoc-CO₂CH₂), 7.34 (t, J=7.2 Hz, 2H, aromatic H),

7.43 (t, J=7.2 Hz, 2H, aromatic H), 7.57 (t, J=6.0 Hz, 1H, NH), 7.73 (d,

J=7.2 Hz, 2H, aromatic H), 7.90 (d, J=7.2 Hz, 2H, aromatic H),

8.32 ppm (t, J=5.4 Hz, 1H, NH); ¹³C NMR (75 MHz, [D₆]DMSO): d=

N-(9-Fluorenylmethyloxycarbonyl) 3-iodopropargylamine (5c): Com-

pound 4 (2.90 g, 13.3 mmol) was dissolved in a mixture of dry CH₂Cl₂

(60 mL) and DIEA (9.10 g, 70.4 mmol). Fmoc-Cl (3.45 g, 13.3 mmol) was

added at 08C, and the solution was stirred at room temperature over-

night. The solvents were removed in vacuo, and the crude product was

recrystallized from CH₂Cl₂to yield the title compound as a colorless

solid (4.10 g, 76%). R_f= 0.7 (CH₂Cl₂/MeOH 10:1); m.p. 159–1608C;

¹H NMR (300 MHz, [D₆]DMSO): d=3.93 (d, J=5.4 Hz, 2H, NHCH₂),

ꢂ

8.4 (C CI), 30.3 (NHCH₂), 43.8 (Gly-CH₂), 47.1 (fluorenyl CH), 66.2

ꢂ

(Fmoc-CO₂CH₂), 90.4 (C CI), 120.6, 125.7, 127.6, 128.1, 141.2, 144.3 (ar-

omatic C), 157.0 (carbamate C=O), 169.4 ppm (amide C=O); elemental

analysis calcd (%) for C₂₀H₁₇N₂O₃I: C 52.19, H 3.72, N 6.09, O, 10.43, I

Chem. Eur. J. 2009, 15, 388 – 404

ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

399

H. Frauenrath et al.

27.57; found: C 52.20, H 3.78, N 6.00; HRMS (ESI): m/z: calcd for

C₂₀H₁₇N₂O₃I: 460.0279; found: 460.0281 [M]⁺.

chromatography (silica gel, CH₂Cl₂/MeOH 24:1). Compound 5j (2.25 g,

70%) was obtained as a yellowish oil. R_f=0.5 (CH₂Cl₂/MeOH 10:1);

¹H NMR (300 MHz, CDCl₃): d=3.28 (s, 3H, CH₃), 3.42–3.46 (m, 2H,

N-(N’-Acetyl-l-alanyl) 3-iodopropargylamide (5g): Compound 4 (1.66 g,

7.63 mmol) was dissolved in dry CH₂Cl₂(20 mL) and dry DMF (10 mL).

N-Acetyl-l-alanine (1.02 g, 7.63 mmol) and DIEA (4.92 g, 38.2 mmol)

were added. At 08C, PyBOP (3.98 g, 7.63 mmol) was added, and the solu-

tion was stirred overnight. The solvents were removed in vacuo, and the

purification was carried out by column chromatography (silica gel,

CH₂Cl₂/MeOH 24:1) to yield the title compound as a colorless crystalline

solid (1.80 g, 76%). R_f= 0.4 (CH₂Cl₂/MeOH 10:1); m.p. 173–1748C;

¹H NMR (300 MHz, [D₆]DMSO): d=1.15 (d, J=6.9 Hz, 3H, CHCH₃),

1.82 (s, 3H, C(O)CH₃), 3.96 (m, 2H, CH₂NH), 4.22 (m, 1H, CHCH₃),

8.03 (d, J=7.5 Hz, 1H, NH), 8.29 ppm (t, J=5.1 Hz, 1H, NH); ¹³C NMR

CH₂), 3.51–3.60 (m, 14H, CH₂), 4.24 ppm (s, 2H, CH₂-C C); ¹³C NMR

ꢂ

(75 MHz, CDCl₃): d=3.6 (CꢂCI), 59.0, 60.0, 69.2, 70.3, 70.4, 70.5, 70.5,

ꢂ

70.5, 70.5, 71.9 (O-CH₂, O-CH₃), 90.4 ppm (C CI); elemental analysis

calcd (%) for C₁₂H₂₁IO₅: C 38.72, H 5.69, I 34.10; found: C 38.82, H 5.47,

I 34.20.

N-Propargyloxycarbonyl-l-alanine tert-butyl ester (7): l-Alanine tert-

butyl ester hydrochloride (3.30 g, 18.15 mmol) was dissolved in dry

CH₂Cl₂(50 mL). TEA (3.86 g, 38.12 mmol) was added, which led to the

precipitation of its hydrochloride. The mixture was cooled to À788C, and

propargyl chloroformate (2.15 g, 18.15 mmol) was added dropwise. The

solution was stirred for 1 h at À788C and for 2 h at 08C before it was al-

lowed to warm up to room temperature. The organic phase was washed

with water and saturated NaCl solution, dried over MgSO₄, filtered, and

concentrated in vacuo. 7 (3.87 g, 93%) was obtained as a colorless oil,

and no further purification was necessary. R_f=0.7 (CH₂Cl₂/MeOH 10:1);

¹H NMR (300 MHz, CDCl₃): d=1.32 (d, J=7.2 Hz, 3H, CHCH₃), 1.41 (s,

ꢂ

(75 MHz, [D₆]DMSO): d=8.2 (C CI), 18.6 (CHCH₃), 23.0 (C(O)CH₃),

ꢂ

30.3 (CH₂NH), 48.4 (CHCH₃), 90.4 (C CI), 169.4, 172.6 ppm (amide C=

O); elemental analysis calcd (%) for C₈H₁₁IN₂O₂: C 32.67, H 3.77, I

43.15, N 9.53; found: C 32.86, H 3.83, I 43.01, N 9.50; HRMS (EI): m/z:

calcd for C₈H₁₁IN₂O₂: 293.9860; found: 293.9861 [M]⁺.

1-Iodo-2-trimethylsilylacetylene (5h): Trimethylsilylacetylene (1.96 g,

20.0 mmol) was dissolved in dry THF (25 mL). The solution was cooled

to À788C, and n-butyl lithium (1.6m in hexanes, 20.0 mmol) was added.

The reaction mixture was stirred for 10 min, allowed to warm up to 08C,

and stirred for another 10 min. Then, the temperature was, again, adjust-

ed to À788C, and I₂(5.08 g, 20.0 mmol) was added in one portion. The

flask was covered with aluminum foil, and the reaction mixture was

stirred at room temperature overnight. The solution was diluted with

CH₂Cl₂and washed with saturated Na₂S₂O₃solution as well as water. The

organic phase was dried over MgSO₄, filtered, and concentrated in vacuo.

Purification of the crude product was carried out by distillation (20 mbar,

708C), and 5h (3.60 g, 80%) was obtained as a colorless liquid. R_f=0.8

9H, CACHTUNGTRNE(NUG CH₃)₃), 2.44 (t, J=2.5 Hz, 1H, C CH), 4.18 (m, 1H, CHCH₃),

4.63 (m, 2H, NHCO₂CH₂), 5.6 ppm (d, J=6.6 Hz, 1H, NH); ¹³C NMR

(75 MHz, CDCl₃): d=18.6 (CHCH₃), 27.9 (C(CH₃)₃), 50.2 (CHCH₃), 52.4

(NHCO₂CH₂), 74.7 (C CH), 78.2 (C CH), 81.8 (C(CH₃)₃), 154.6 (carba-

AHCTUNGTRENNUNG

ꢂ

AHCTUNGTRENNUNG

mate C=O), 171.9 ppm (ester C=O); elemental analysis calcd (%) for

C₁₁H₁₇NO₄: C 58.14, H 7.54, N 6.16; found: C 57.85, H 7.50, N 6.14;

HRMS (EI): m/z: calcd for C₇H₉NO₃: 154.0499; found: 154.0501

[MÀC₄H₉O]⁺.

N-[6-(N’-Acetamido)hexa-2,4-diynyl-1-oxycarbonyl]-l-alanine tert-butyl

ester (8a): Following GP A, 7 (0.65 g, 2.86 mmol), 5a (0.8 g, 3.59 mmol),

and the catalysts were dissolved in dry THF (30 mL). The solution was

stirred overnight, and the solvents were removed in vacuo. After purifica-

tion by column chromatography (silica gel, CH₂Cl₂/MeOH 50:1 to 20:1),

8a (0.52 g, 56%) was obtained as a brownish solid. R_f=0.5 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=1.32 (d, J=7.2 Hz, 3H,

(CH₂Cl₂); ¹H NMR (300 MHz, CDCl₃): d=0.18 ppm (s, 9H, Si

ACHTUNGTRENNUNG

¹³C NMR (75 MHz, CDCl₃): d=À0.1 (Si

AHCTUNGTRENNUNG

ꢂ

(C CI).

3-Iodoprop-2-yn-1-ol (5i): Propargyl alcohol (16.0 g, 285.3 mmol) was dis-

solved in MeOH (400 mL). A solution of KOH (56.0 g, 1.0 mol) in H₂O

(100 mL) was prepared, cooled to 08C, and added to the reaction mix-

ture. I₂(63.5 g, 250 mmol) was added in one portion, and the solution

was stirred at room temperature overnight. The reaction mixture was

neutralized with 1m HCl and extracted with diethyl ether. The organic

phase was washed with saturated Na₂S₂O₃solution, dried over Na₂SO₄,

filtered, and concentrated in vacuo to yield the title compound as a color-

less solid (43.3 g, 83%). R_f=0.7 (CH₂Cl₂/MeOH 10:1); m.p. 42–438C;

CHCH₃), 1.41 (s, 9H, CACHTUNRGTNE(UNG CH₃)₃), 1.96 (s, 3H, C(O)CH₃), 4.05 (d, J=

5.4 Hz, 2H, CH₂NHAc), 4.15 (m, 1H, CHCH₃), 4.67 (m, 2H,

NHCO₂CH₂), 5.63 (d, J=7.5 Hz, 1H, NH), 6.76 ppm (m, 1H, NH);

¹³C NMR (75 MHz, CDCl₃): d=18.4 (CHCH₃), 22.7 (C(O)CH₃), 27.8 (C-

AHCTUNGTRENNUNG

(amide C=O), 171.9 ppm (ester C=O); HRMS (EI): m/z: calcd for

C₁₆H₂₂N₂O₅: 322.1524; found: 322.1523 [M]⁺.

¹H NMR (300 MHz, CDCl₃): d=2.04 (t, J=5.4 Hz, 1H, OH), 4.41 ppm

N-{6-[N’-(4-Methoxysuccinyl)amido]hexa-2,4-diynyl-1-oxycarbonyl}-l-

alanine tert-butyl ester (8b): Following GPA, 7 (0.58 g, 2.55 mmol), 5b

(0.92 g, 3.12 mmol) and the catalysts were dissolved in dry THF (30 mL).

The solution was stirred for 4 h, and the solvents were removed in vacuo.

After purification by column chromatography (silica gel, CH₂Cl₂/MeOH

13

ꢂ

(d, J=5.4 Hz, 2H, CH₂); C NMR (75 MHz, CDCl₃): d=2.8 (C CI),

ꢂ

52.6 (CH₂), 92.5 ppm (C CI); elemental analysis calcd (%) for C₃H₃IO:

C 19.80, H 1.66, I 69.74; found: C 19.85, H 1.64, I 69.77; HRMS (EI):

m/z: calcd for C₃H₃IO: 181.9233; found: 181.9236 [M]⁺.

1-{2’’’-{2’’-[2’-(2-Methoxyethoxy)ethoxy]ethoxy}ethoxy}-3-iodoprop-2-yne

(5j) and 1-{2’’’-{2’’-[2’-(2-methoxyethoxy)ethoxy]ethoxy}ethoxy}prop-2-

yne (6): In a thoroughly dried Schlenk flask, NaH (60% dispersion in

mineral oil, 0.40 g, 10.0 mmol) was mixed with THF (100 mL), and the

mixture was degassed in two freeze-pump-thaw cycles. Tetra(ethylene

glycol) monomethyl ether (2.08 g, 10.0 mmol) was added at 08C, forming

a suspension. The mixture was stirred for 30 min before propargyl bro-

mide (80% in toluene, 2.23 g, 15 mmol) was added. Stirring was contin-

ued overnight. The reaction mixture was concentrated in vacuo and

taken up in diethyl ether. The organic phase was washed with water,

dried over MgSO₄and concentrated. Thus, 6 (2.29 g, 93%) was obtained

as a yellow liquid, which was directly used in the following step without

further purification. For the iodination reaction, 6 (2.12 g, 8.61 mmol)

20:1), 6 f (0.55 g, 55%) was obtained as

(CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=1.33 (d, J=

7.2 Hz, 3H, CHCH₃), 1.41 (s, 9H, C(CH₃)₃), 2.48 (t, J=6.7 Hz, 2H,

NHCOCH₂), 2.62 (t, J=6.7 Hz, 2H, CH₂CO₂Me), 3.63 (s, 3H, OCH₃),

4.07 (d, J=5.4 Hz, 2H, CH₂NH), 4.16 (m, 1H, CHCH₃), 4.67 (s, 2H,

a brownish solid. R_f=0.4

AHCTUNGTRENNUNG

ꢂ

CO₂CH₂C C), 5.61 (d, J=7.5 Hz, 2H, NH), 6.71 ppm (t, J=5.1 Hz, 1H,

NH); ¹³C NMR (75 MHz, CDCl₃): d=18.4 (CHCH₃), 27.8 (C

(CH₃)₃),

29.1, 29.6, 30.4 (CH₂NH, CH₂CO₂Me, NHCOCH₂), 50.3 (CHCH₃), 51.8

(OCH₃), 52.8 (CO₂CH₂CꢂC), 66.7, 70.5, 72.4, 76.3 (diacetylene C), 81.9

(CACTHNURGTNEG(UN CH₃)₃), 154.7 (carbamate C=O), 171.4, 171.9, 173.3 ppm (2 ester C=O,

amide C=O); HRMS (EI): m/z: calcd for C₁₉H₂₆N₂O₇: 394.1735; found:

394.1733 [M]⁺.

N-{6-

ACHTUNGTRENNUNG

was dissolved in MeOH (50 mL).

A solution of KOH (1.45 g,

bonyl}-l-alanine tert-butyl ester (8c): Following GPA,

7

25.84 mmol) in H₂O (3 mL) was prepared, cooled to 08C, and added to

the reaction mixture. After 10 min, I₂(2.35 g, 9.25 mmol) was added in

one portion, and the solution was stirred at room temperature overnight.

The solvent was removed in vacuo, and the residue was taken up in 1m

HCl. The aqueous phase was extracted with CHCl₃. The organic phase

was washed with saturated Na₂S₂O₃solution, dried over Na₂SO₄, filtered,

and concentrated in vacuo. The crude product was purified by column

4.4 mmol), 5c (2.1 g, 5.3 mmol) and the catalysts were dissolved in dry

THF (50 mL). The solution was stirred for 3 h, and the solvents were re-

moved in vacuo. The crude product was purified by repeated column

chromatography (silica gel, CHCl₃/toluene 10:1) and preparative GPC

(CHCl₃). However, only mixtures of 8c and the homo- as well as hetero-

coupling side products were obtained, which were used in the next step

400

www.chemeurj.org

ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2009, 15, 388 – 404

Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

without further purification. R_f=0.75 (CH₂Cl₂/MeOH 10:1); HRMS (EI):

m/z: calcd for C₂₉H₃₀N₂O₆: 502.2098; found 502.2085 [M]⁺.

(1.4 g, 4.76 mmol), and the catalysts were dissolved in dry THF (30 mL).

The solution was stirred for 3 h, diluted with CH₂Cl₂, and subjected to an

acidic aqueous workup. The organic phase was dried over MgSO₄, fil-

tered, and concentrated in vacuo. The crude product was purified by

column chromatography (silica gel, CH₂Cl₂/MeOH 50:1 to 20:1) to yield

the title compound as colorless solid (0.80 g, 51%). R_f=0.5 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=1.32 (d, J=7.2 Hz, 3H,

N-{6-ACHTUNGTRENNUNG[N’-(5-Dimethylamino-1-naphthalenesulfonyl)amido]hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine tert-butyl ester (8d): Following GPA, 7

(0.18 g, 0.81 mol), 5d (0.46 g, 0.97 mmol) and the catalysts were dissolved

in THF (30 mL). The solution was stirred overnight, diluted with CHCl₃

(40 mL) and washed twice with saturated NaHCO₃solution. The organic

phase was dried over MgSO₄, filtered, and concentrated in vacuo. The

crude product was purified by column chromatography (silica gel, ethyl

acetate/hexane 1:3) to yield the title compound as a yellow powder

(0.20 g, 47%). R_f=0.5 (EtOAc/Hex 1:1); ¹H NMR (300 MHz,

CHCH₃), 1.33 (d, J=7.5 Hz, 3H, CHCH₃), 1.43 (s, 9H, CACHTNUGTRENUNG(CH₃)₃), 1.99 (s,

3H, C(O)CH₃), 4.07 (d, J=5.1 Hz, 2H, CH₂NH), 4.18 (m, 1H, CHCH₃),

4.58 (m, 1H, CHCH₃), 4.68 (m, 2H, NHCO₂CH₂), 5.77 (d, J=7.8 Hz,

1H, NH), 7.03 (d, J=7.8 Hz, 1H, NH), 7.68 ppm (m, 1H, NH); ¹³C NMR

(75 MHz, CDCl₃): d=18.2, 18.3 (2 CHCH₃), 23.0 (C(O)CH₃), 27.9 (C-

[D₆]DMSO): d=1.39 (d, J=7.2 Hz, 3H, CHCH₃), 1.48 (s, 9H, C

ACHTUGNRTNE(NUNG CH₃)₃),

AHCTUNGTRENNUNG

2.90 (s, 6H, N(CH₃)₂), 3.87 (d, J=6.3 Hz, 2H, NHCH₂), 4.24 (m, 1H,

ACHTUNGTRENNUNG

AHCTUNGTRENNUNG

CHCH₃), 4.62 (m, 2H, NHCO₂CH₂), 5.27 (brs, 1H, NH), 5.46 (m, 1H,

NH), 7.21 (d, J=7.5 Hz, 1H, aromatic H), 7.56 (m, 2H, aromatic H),

8.26 (m, 2H, aromatic H), 8.57 ppm (d, J=8.4 Hz, 1H, aromatic H);

170.6, 172.1, 172.6 ppm (2 amide C=O, ester C=O); HRMS (EI): m/z:

calcd for C₁₉H₂₇N₃O₆: 393.1895; found: 393.1896 [M]⁺.

¹³C NMR (75 MHz, [D₆]DMSO): d=18.8 (CHCH₃), 27.9 (C

A

N-(5-Trimethylsilylpenta-2,4-diynyl-1-oxycarbonyl)-l-alanine

tert-butyl

(NHCH₂), 45.4 (N

G

ester (8h): Following GPA, 7 (0.98 g, 4.41 mmol), 5h (1.22 g, 5.35 mmol),

and the catalysts were dissolved in dry THF (50 mL). The solution was

stirred overnight, diluted with CH₂Cl₂, and subjected to an acidic aque-

ous workup. The organic phase was dried over MgSO₄, filtered, and con-

centrated in vacuo. The crude product was purified by column chroma-

tography (silica gel, CH₂Cl₂). 8h (0.85 g, 61%) was obtained as an

orange oil. R_f=0.3 (CH₂Cl₂); ¹H NMR (300 MHz, CDCl₃): d=0.16 (s,

AHCTUNGTRENNUNG

129.7, 129.9, 129.9, 131.0, 134.1, 151.4 (aromatic C), 154.4 (carbamate C=

O), 171.9 ppm (ester C=O); elemental analysis calcd (%) for

C₂₆H₃₁N₃O₆S: C 60.80, H 6.08, N 8.18; found: C 59.69, H 5.90, N 7.97.

N-{6-{N’-[N’’-(9-Fluorenylmethyloxycarbonyl)-l-alanyl]amido}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine tert-butyl ester (8e): Following GPA, 7

(1.53 g, 6.73 mmol), 5e (3.80 g, 8.01 mmol), and the catalysts were dis-

solved in THF (80 mL). The solution was stirred for 3 h, diluted with

CH₂Cl₂, and subjected to an acidic aqueous workup. The organic phase

was dried over MgSO₄, filtered, and concentrated in vacuo. The crude

product was purified by column chromatography (silica gel, CH₂Cl₂/

MeOH 50:1) to yield the title compound as slightly brown crystals

(1.94 g, 50%). R_f=0.4 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz,

9H, SiACTHNUTRGENN(GU CH₃)₃), 1.34 (d, J=7.2 Hz, 3H, CHCH₃), 1.44 (s, 9H, CACHTUNGTRENNUNG(CH₃)₃),

4.20 (m, 1H, CHCH₃), 4.70 (m, 2H, NHCO₂CH₂), 5.45 ppm (d, J=

7.2 Hz, 1H, NH); ¹³C NMR (75 MHz, CDCl₃): d=À0.6 (Si

ACHTUGNTRNEN(UNG CH₃)₃), 18.8

(CHCH₃), 27.9 (CACTHNURTGNEUNG(CH₃)₃), 50.3 (CHCH₃), 52.8 (NHCO₂CH₂), 71.2, 72.0,

87.1, 87.9 (diacetylene C), 82.1 (CACHTUNTRGNEUNG(CH₃)₃), 154.5 (carbamate C=O),

171.9 ppm (ester C=O); elemental analysis calcd (%) for C₁₆H₂₅N₂O₄Si:

C 59.41, H 7.79, N 4.33; found: C 59.40, H 8.04, N 4.31; HRMS (EI):

m/z: calcd for C₁₆H₂₅NO₄Si: 323.1547; found: 323.1546 [M]⁺.

CDCl₃): d=1.36 (d, J=6.9 Hz, 6H, 2CHCH₃), 1.46 (s, 9H, CACTHNUTRGNEUNG(CH₃)₃),

4.11 (m, 2H, CH₂NH), 4.2–4.3 (m, 3H, Fmoc CO₂CH₂, fluorenyl CH),

N-(6-Hydroxyhexa-2,4-diynyl-1-oxycarbonyl)-l-alanine tert-butyl ester

(8i): Following GPA, 7 (1.02 g, 4.49 mmol), 5i (0.98 g, 5.39 mmol), and

the catalysts were dissolved in dry THF (30 mL). The solution was stirred

for 4 h, diluted with CH₂Cl₂, and subjected to an acidic aqueous workup.

The organic phase was dried over MgSO₄, filtered, and concentrated in

vacuo. The crude product was purified by column chromatography (silica

gel, CH₂Cl₂/MeOH 24:1) to yield the title compound as a yellowish oil

(0.74 g, 59%). R_f=0.4 (CH₂Cl₂/MeOH 24:1); ¹H NMR (300 MHz,

ꢂ

4.4–4.5 (m, 2H, 2 CHCH₃), 4.69 (m, 2H, OCH₂C C), 5.44 (d, J=6.6 Hz,

2H, NH), 6.62 (s, 1H, NH), 7.29 (dt, J=1.2 Hz, 7.5 Hz, 2H, aromatic H),

7.39 (t, J=7.5 Hz, 2H, aromatic H), 7.57 (d, J=7.5 Hz, 2H, aromatic H),

7.75 ppm (d, J=7.5 Hz, 2H, aromatic H); ¹³C NMR (75 MHz, CDCl₃):

d=18.5, 18.8 (2 CHCH₃), 28.0 (C

CH), 50.3 (2 CHCH₃), 52.9 (CO₂CH₂C C), 67.1, 67.4, 70.5, 72.7, 75.6 (di-

acetylene C, CO₂CH₂), 82.1 (C(CH₃)₃), 120.0, 125.0, 127.1, 127.8, 141.3,

ACHTNUGTERN(NUGN CH₃)₃), 29.8 (CH₂NH), 47.2 (fluorenyl

ꢂ

AHCTUNGTRENNUNG

143.7 (aromatic C), 154.5, 156.1 (2 carbamate C=O), 172.0, 172.1 ppm

(amide and ester C=O); elemental analysis calcd (%) for C₃₂H₃₅N₃O₇: C

67.00, H 6.15, N 7.33; found: C 66.72, H 6.19, N 7.08; HRMS (MALDI):

m/z: calcd for C₃₂H₃₅N₃O₇Na: 596.2367; found: 596.2367 [M+Na]⁺.

CDCl₃): d=1.32 (d, J=7.2 Hz, 3H, CHCH₃), 1.41 (s, 9H, CACHTUNGETRNNU(G CH₃)₃), 3.34

(s, 1H, OH), 4.16 (m, 1H, CHCH₃), 4.26 (s, 2H, CH₂OH), 4.71 (m, 2H,

NHCO₂CH₂), 5.64 ppm (d, J=7.5 Hz, 1H, NH); ¹³C NMR (75 MHz,

CDCl₃): d=18.6 (CHCH₃), 27.9 (C

(CH₂OH), 53.0 (NHCO₂CH₂), 69.1, 70.5, 73.4, 78.3 (diacetylene C), 82.2

(C(CH₃)₃), 154.8 (carbamate C=O), 172.1 ppm (ester C=O); elemental

ACHTNUGTRNEN(NUG CH₃)₃), 50.3 (CHCH₃), 51.0

N-{6-{N’-[N’’-(9-Fluorenylmethyloxycarbonyl)glycyl]amido}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine tert-butyl ester (8 f): Following GPA, 7

(0.45 g, 2.0 mmol), 5 f (1.10 g, 2.4 mmol) and the catalysts were dissolved

in dry THF (30 mL). The solution was stirred for 3 h, diluted with

CH₂Cl₂, and subjected to an acidic aqueous workup. The organic phase

was dried over MgSO₄, filtered, and concentrated in vacuo. The crude

product was purified by column chromatography (silica gel, CH₂Cl₂/

MeOH 20:1) to yield the title compound as a slightly brown solid (0.68 g,

61%). R_f=0.4 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=

AHCTUNGTRENNUNG

analysis calcd (%) for C₁₄H₁₉NO₅: C 59.78, H 6.81, N 4.98; found: C

59.98, H 6.89, N 5.12; HRMS (EI): m/z: calcd for C₁₄H₁₉NO₅: 281.1258;

found: 281.1258 [M]⁺.

N-{6-{2’’’-{2’’-[2’-(2-Methoxyethoxy)ethoxy]ethoxy}ethoxy}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine tert-butyl ester (8j): Following GPA, 7

(0.31 g, 1.32 mmol), 5j (0.60 g, 1.61 mmol), and the catalysts were dis-

solved in dry THF (25 mL). The solution was stirred overnight, and the

solvents were removed in vacuo. The purification was carried out by

column chromatography (silica gel, CH₂Cl₂/MeOH 24:1) to yield the title

compound as a yellowish oil (0.29 g, 45%). R_f=0.5 (CH₂Cl₂/MeOH

10:1); ¹H NMR (300 MHz, CDCl₃): d=1.30 (d, J=7.2 Hz, 3H, CHCH₃),

1.39 (d, J=7.2 Hz, 3H, CHCH₃), 1.49 (s, 9H, CACTHNURGTNEG(UN CH₃)₃), 3.90 (s, 2H, Gly-

CH₂), 4.14 (m, 2H, CꢂCCH₂NH), 4.2–4.3 (m, 2H, CHCH₃, fluorenyl-

CH), 4.48 (d, J=6.9 Hz, 2H, Fmoc-CO₂CH₂), 4.73 (s, 2H,

NHCO₂CH₂CꢂC), 5.65 (s, 1H, NH), 6.59 (s, 1H, NH), 7.33 (t, J=

7.2 Hz, 2H, aromatic H), 7.42 (t, J=7.2 Hz, 2H, aromatic H), 7.61 (d, J=

7.2 Hz, 2H, aromatic H), 7.78 ppm (d, J=7.2 Hz, 2H, aromatic H);

1.39 (s, 9H, CACHTNUTRGNEG(UN CH₃)₃), 3.30 (s, 3H, OCH₃), 3.47 (m, 2H, CH₂O), 3.55–

3.65 (m, 14H, CH₂O), 4.14 (m, 1H, CHCH₃), 4.19 (s, 2H, C₄CH₂O), 4.66

(m, 2H, NHCO₂CH₂), 5.50 ppm (d, J=7.5 Hz, 1H, NH); ¹³C NMR

¹³C NMR (75 MHz, CDCl₃): d=18.5 (CHCH₃), 27.9 (C

ACTHNUGTRNEUGN(CH₃)₃), 29.6

ꢂ

(NHCH₂C C), 47.1 (fluorenyl-CH), 50.4 (Gly-CH₂), 52.9 (CHCH₃), 53.6

(NHCO₂CH₂), 67.0 (Fmoc-CO₂CH₂), 67.1, 70.6, 72.8, 76.1 (diacetylene

(75 MHz, CDCl₃): d=18.7 (CHCH₃), 27.9 (C

(NHCO₂CH₂), 58.8 (OCH₃), 58.9 (CH₂O), 69.3, 70.2–70.5, 73.4, 76.0 (6

CH₂O, diacetylene C), 82.0 (C(CH₃)₃), 154.5 (carbamate C=O),

ACHTNUGTRNEN(NUG CH₃)₃), 50.3 (CHCH₃), 52.8

C), 82.0 (C(CH₃)₃), 120.0, 125.1, 127.1, 127.7, 141.3, 143.8 (aromatic C),

G

ACHTUNGTRENNUNG

154.8 (carbamate C=O), 156.9 (carbamate C=O), 169.6 (amide C=O),

172.2 ppm (ester C=O); HRMS (ESI): m/z: calcd for C₃₁H₃₃N₃O₇Na:

582.2211; found: 582.2210 [M+Na]⁺.

171.9 ppm (ester C=O); HRMS (EI): m/z: calcd for C₁₆H₂₈NO₇: 370.1861;

found: 370.1861 [MÀC₅H₉O₂]⁺.

Hexa-2,4-diynylene-1,6-bis(oxycarbonyl-l-alanine tert-butyl ester) (9): A

solution of CuCl (0.96 g, 9.7 mmol) and TMEDA (1.2 g, 10 mmol) in ace-

tone (20 mL) was added to a solution of 7 (2 g, 8.8 mmol) in acetone

N-{6-[N’-(N’’-Acetyl-l-alanyl)amido]hexa-2,4-diynyl-1-oxycarbonyl}-l-

alanine tert-butyl ester (8g): Following GPA, 7 (0.90 g, 3.96 mmol), 5g

Chem. Eur. J. 2009, 15, 388 – 404

ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

401

H. Frauenrath et al.

(60 mL), and the resulting green mixture was stirred for 5 h at room tem-

perature with dry air bubbling through the reaction mixture. The solution

was diluted with acetone and filtered through a pad of silica gel. After

evaporation of the solvent, the residue was taken up in CH₂Cl₂and

washed twice with water. The organic phase was dried over MgSO₄, fil-

tered, and concentrated in vacuo. Column chromatography afforded 9

(1.28 g, 64%) as a yellow oil which slowly crystallized. R_f=0.7 (CH₂Cl₂/

MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=1.31 (d, J=7.2 Hz, 6H, 2

128.4, 129.2, 129.3, 129.5, 130.0, 136.1, 150.7 (aromatic C), 155.2 (carba-

mate C=O), 174.6 ppm (acid C=O).

N-{6-{N’-[N’’-(9-Fluorenylmethyloxycarbonyl)-l-alanyl]amido}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine (10e): Following GP B, 8e (0.52 g,

0.9 mmol) was dissolved in dry CH₂Cl₂(20 mL), a large excess of TFA

was added, and the solution was stirred overnight. 10e (0.59 g, 100%)

was obtained as a brownish, crystalline product. A further purification

was not necessary before the next step. R_f=0.1 (CH₂Cl₂/MeOH 10:1);

¹H NMR (300 MHz, [D₆]DMSO): d=1.1–1.4 (m, 6H, 2 CHCH₃), 3.9–4.1

(m, 4H, 2CHCH₃, CH₂NH), 4.2–4.4 (m, 3H, Fmoc-CO₂CH₂, fluorenyl

CH), 4.76 (s, 2H, CO₂CH₂CꢂC), 7.32 (t, J=7.2 Hz, 2H, aromatic H),

7.43 (t, J=7.2 Hz, 2H, aromatic H), 7.57 (d, J=7.5 Hz, 1H, NH), 7.7–7.8

(m, 3H, aromatic H, NH), 7.89 (d, J=7.5 Hz, 2H, aromatic H), 8.43 ppm

(m, 1H, NH); ¹³C NMR (75 MHz, [D₆]DMSO): d=17.5, 18.5 (2 CCH₃),

29.2 (CH₂NH), 47.1 (fluorenyl CH), 49.8, 50.4 (2 CHCH₃), 52.4

(CO₂CH₂CꢂC), 65.77, 66.12, 70.08, 74.31, 78.64 (diacetylene C, Fmoc-

CO₂CH₂), 120.6, 125.8, 127.5, 128.1, 141.2, 144.4 (aromatic C), 155.3,

156.2 (2 carbamate C=O), 172.9 (amide C=O), 174.6 ppm (acid C=O);

HRMS (MALDI): m/z: calcd for C₂₈H₂₇N₃O₇: 518.1922; found: 518.1922

[M]⁺.

CHCH₃), 1.40 (s, 18H, 2 C

2 NHCO₂CH₂), 5.59 ppm (d, J=7.5 Hz, 2H, 2 NH); ¹³C NMR (75 MHz,

CDCl₃): d=18.6 (2 CHCH₃), 27.9 (2 C(CH₃)₃), 50.3 (2 CHCH₃), 52.7 (2

NHCO₂CH₂), 70.2, 74.0 (diacetylene C), 81.9 (2 C(CH₃)₃), 154.5 (2 carba-

ACHTNUGTERN(NUGN CH₃)₃), 4.16 (m, 2H, 2 CHCH₃), 4.67 (m, 4H,

AHCTUNGTRENNUNG

mate C=O), 171.9 ppm (2 ester C=O); elemental analysis calcd (%) for

C₂₂H₃₂N₂O₈: C 58.40, H 7.13, N 6.19; found: C 58.42, H 7.2, N 6.13;

HRMS (EI): m/z: calcd for C₂₂H₃₂N₂O₈: 452.2153; found: 452.2195 [M]⁺.

N-[6-(N’-Acetamido)hexa-2,4-diynyl-1-oxycarbonyl]-l-alanine (10a): Fol-

lowing GP B, 8a (0.86 g, 2.67 mmol) was dissolved in dry CH₂Cl₂

(10 mL), a large excess of TFA was added and the solution was stirred

overnight. 10a (0.71 g, 100%) was obtained as a brown amorphous prod-

uct, and no further purification was carried out before the next step. R_f=

0.1 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, CDCl₃): d=1.40 (d, J=

7.2 Hz, 3H, CHCH₃), 2.00 (s, 3H, C(O)CH₃), 4.06 (d, J=5.1 Hz, 2H,

CH₂NHAc), 4.26 (m, 1H, CHCH₃), 4.68 (s, 2H, NHCO₂CH₂), 5.77 (d,

J=7.5 Hz, 1H, NH), 7.00 (m, 1H, NH), 8.82 ppm (brs, 1H, COOH);

¹³C NMR (75 MHz, CDCl₃): d=18.4 (CHCH₃), 22.6 (C(O)CH₃), 29.7

(CH₂NHAc), 49.7 (CHCH₃), 52.9 (NHCO₂CH₂), 67.0, 70.5, 72.6, 76.0 (di-

acetylene C), 154.8 (carbamate C=O), 170.9 (amide C=O), 174.9 ppm

(acid C=O).

N-{6-{N’-[N’’-(9-Fluorenylmethyloxycarbonyl)glycyl]amido}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine (10 f): Following GP B, 8 f (0.4 g,

0.71 mmol) was dissolved in dry CH₂Cl₂(20 mL), a large excess of TFA

was added, and the solution was stirred overnight. The crude product

was dried in HV and purified by column chromatography (silica gel,

CH₂Cl₂/MeOH/TFA 199:10:1). 10 f (0.33 g, 92%) was obtained as a

brown solid. R_f=0.1 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz,

[D₆]DMSO): d=1.25 (d, J=7.2 Hz, 3H, CHCH₃), 3.64 (s, 2H, Gly-CH₂),

4.03 (d, J=5.1 Hz, 2H, NHCH₂CꢂC), 4.11 (m, 1H, CHCH₃), 4.2–4.3 (m,

3H, fluorenyl-CH, Fmoc-CO₂CH₂), 4.76 (s, 2H, NHCO₂CH₂), 7.34 (t, J=

7.5 Hz, 2H, aromatic H), 7.43 (t, J=7.5 Hz, 2H, aromatic H), 7.59 (t, J=

6.0 Hz, 1H, NH), 7.73 (d, J=7.5 Hz, 2H, aromatic H), 7.90 (d, J=7.5 Hz,

2H, aromatic H), 8.42 ppm (t, J=5.4 Hz, 1H, NH); ¹³C NMR (75 MHz,

[D₆]DMSO): d=17.5 (CHCH₃), 29.0 (NHCH₂CꢂC), 47.1 (fluorenyl-

CH), 49.8 (CHCH₃), 52.4 (CO₂CH₂CꢂC), 55.3 (Gly-CH₂), 66.2 (Fmoc-

CO₂CH₂), 65.7, 70.0, 74.3, 78.7 (diacetylene C), 120.6, 125.7, 127.5, 128.1,

141.2, 144.3 (aromatic C), 155.3, 157.0 (2carbamate C=O), 169.7 (amide

C=O), 174.6 ppm (acid C=O); HRMS (MALDI): m/z: calcd for

C₂₇H₂₅N₃O₇Na: 526.1585; found: 526.1588 [M+Na]⁺.

N-{6-[N’-(4-Methoxysuccinyl)amido]hexa-2,4-diynyl-1-oxycarbonyl}-l-

alanine (10b): Following GP B, 8b (0.32 g, 0.8 mmol) was dissolved in

dry CH₂Cl₂(10 mL), a large excess of TFA was added and the solution

was stirred overnight. 10b (0.34 g, 100%) was obtained as a brown amor-

phous product. A further purification was not necessary before the next

step. R_f=0.1 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO):

d=1.26 (d, J=7.2 Hz, 3H, CHCH₃), 2.39 (t, J=6.6 Hz, 2H, NHCOCH₂),

2.52 (t, J=6.6 Hz, 2H, CH₂CO₂Me), 3.58 (s, 3H, OCH₃), 3.9–4.0 (m, 3H,

CꢂCCH₂NH, CHCH₃), 4.75 (s, 2H, CꢂCCH₂O), 7.57 (d, J=7.5 Hz,

1H, NH), 8.43 ppm (t, J=5.4 Hz, 1H, NH); ¹³C NMR (75 MHz,

[D₆]DMSO): d=17.5 (CHCH₃), 29.0, 30.0 (CH₂NH, CH₂CO₂Me,

NHCOCH₂), 49.8 (CHCH₃), 51.7 (OCH₃), 52.4 (CO₂CH₂CꢂC), 65.7,

70.0, 74.2, 78.7 (diacetylene C), 155.3 (carbamate C=O), 171.2, 173.2,

174.6 ppm (ester C=O, amide C=O, acid C=O).

N-{6-[N’-(N’’-Acetyl-l-alanyl)amido]hexa-2,4-diynyl-1-oxycarbonyl}-l-

alanine (10g): Following GP B, 8g (0.16 g, 0.40 mmol) was dissolved in

dry CH₂Cl₂(20 mL), a large excess of TFA was added, and the solution

was stirred for 5 h. 10g (0.13 g, 100%) was obtained as a brownish solid.

A further purification was not necessary before the next step. R_f=0.1

(CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=1.18 (d, J=

7.2 Hz, 3H, CHCH₃), 1.27 (d, J=7.2 Hz, 3H, CHCH₃), 1.84 (s, 3H,

C(O)CH₃), 3.9–4.1 (m, 3H, CH₂NH, CHCH₃), 4.23 (m, 1H, CHCH₃),

4.75 (s, 2H, NHCO₂CH₂), 7.76 (d, J=7.5 Hz, 1H, NH), 8.08 (d, J=

7.2 Hz, 1H, NH), 8.40 ppm (m, 1H, NH); ¹³C NMR (75 MHz,

[D₆]DMSO): d=17.5, 18.5 (2 CHCH₃), 23.0 (C(O)CH₃), 29.1 (CH₂NH),

48.4, 49.7 (2 CHCH₃), 52.4 (NHCO₂CH₂), 65.7, 70.1, 74.3, 78.7 (diacety-

lene C), 155.3 (carbamate C=O), 169.5, 172.8 (2 amide C=O), 174.6 ppm

(acid C=O).

N-{6-ACHTUNGTRENNUNG[N’-(9-Fluorenylmethyloxycarbonyl)amino]hexa-2,4-diynyl-1-oxycar-

bonyl}-l-alanine (10c): Following GP B, 8c (1.8 g, impure) was dissolved

in dry CH₂Cl₂(20 mL), a large excess of TFA was added, and the solution

was stirred overnight. The crude product was purified by column chroma-

tography (silica gel, CH₂Cl₂/MeOH 10:1) to yield the title compound as a

nearly colorless solid (1.0 g, 62%). R_f=0.1 (CH₂Cl₂/MeOH 10:1);

¹H NMR (300 MHz, [D₆]DMSO): d=1.28 (d, J=7.5 Hz, 3H, CHCH₃),

3.95 (d, J=5.7 Hz, 2H, NHCH₂), 4.02 (m, 1H, CHCH₃), 4.24 (t, J=

6.3 Hz, 1H, fluorenyl CH), 4.36 (d, J=6.9 Hz, 2H, Fmoc-CO₂CH₂), 4.77

(m, 2H, NHCO₂CH₂), 7.34 (t, J=7.2 Hz, 2H, aromatic H), 7.43 (t, J=

7.5 Hz, 2H, aromatic H), 7.70 (d, J=7.5 Hz, 2H, aromatic H), 7.76 (d,

J=7.5 Hz, 1H, NH), 7.8–8.0 ppm (m, 3H, 2 aromatic H, NH).

N-(5-Trimethylsilylpenta-2,4-diynyl-1-oxycarbonyl)-l-alanine (10h): Fol-

lowing GP B, 8h (0.85 g, 2.6 mmol) was dissolved in dry CH₂Cl₂(20 mL),

a large excess of TFA was added, and the solution was stirred overnight.

10h (0.70 g, 100%) was obtained as a brown amorphous product, and no

further purification was carried out before the next step. R_f=0.15

(CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=0.19 (s, 9H,

N-{6-ACHTUNGTRENNUNG[N’-(5-Dimethylamino-1-naphthalenesulfonyl)amido]hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine (10d): Following GP B, 8d (0.14 g,

0.27 mmol) was dissolved in CH₂Cl₂(10 mL), a large excess of TFA was

added, and the solution was stirred overnight. 10d (0.11 g, 90%) was ob-

tained as a dark amorphous substance. A further purification was not

necessary before the next step. R_f=0.3 (CH₂Cl₂/MeOH 10:1); ¹H NMR

(300 MHz, [D₆]DMSO): d=1.27 (d, J=7.5 Hz, 3H, CHCH₃), 2.90 (s, 6H,

SiACHTNURTGNEUG(N CH₃)₃), 1.27 (d, J=7.2 Hz, 3H, CHCH₃), 4.01 (m, 1H, CHCH₃), 4.76

(s, 2H, NHCO₂CH₂), 7.74 (d, J=7.5 Hz, 1H, NH) 9.3 ppm (brs, 1H,

COOH); ¹³C NMR (75 MHz, [D₆]DMSO): d=À0.3 (Si

ACHTUGNTRNEN(UNG CH₃)₃), 17.5

NACHTUNGTRENNUNG(CH₃)₂), 3.90 (d, J=5.7 Hz, 2H, NHCH₂), 3.99 (m, 1H, CHCH₃), 4.66

(CHCH₃), 49.7 (CHCH₃), 52.3 (NHCO₂CH₂), 70.3, 74.8, 87.6, 88.3 (diace-

tylene C), 155.3 (carbamate C=O), 174.6 ppm (acid C=O); HRMS (EI):

m/z: calcd for C₁₂H₁₇NO₄Si: 267.0921; found: 267.0923 [M]⁺.

(m, 2H, NHCO₂CH₂), 7.35 (d, J=7.5 Hz, 1H, aromatic H), 7.65 (m, 2H,

aromatic H, NH), 7.74 (d, J=7.5 Hz, 1H, aromatic H), 8.17 (d, J=

6.9 Hz, 1H, aromatic H), 8.31 (d, J=8.7 Hz, 1H, aromatic H), 8.5–

8.6 ppm (m, 2H, aromatic H, NH); ¹³C NMR (75 MHz, [D₆]DMSO): d=

N-(6-Hydroxyhexa-2,4-diynyl-1-oxycarbonyl)-l-alanine (10i): Following

GP B, 8i (1.20 g, 4.27 mmol) was dissolved in dry CH₂Cl₂(20 mL), a

large excess of TFA was added, and the solution was stirred for 4 h. 10i

17.5 (CHCH₃), 32.7 (NHCH₂), 46.0 (N

ACHTNUGTRNEN(NUG CH₃)₂), 49.7 (CHCH₃), 52.3

(NHCO₂CH₂), 66.9, 69.5, 74.6, 76.7 (diacetylene C), 116.0, 120.2, 124.3,

402

www.chemeurj.org

ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2009, 15, 388 – 404

Diacetylene-Containing Peptide Building Blocks and Amphiphiles

FULL PAPER

(0.90 g, 92%) was obtained as a brownish amorphous product, and no

further purification was carried out before the next step. R_f=0.1

(CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz, [D₆]DMSO): d=1.27 (d, J=

7.2 Hz, 3H, CHCH₃), 3.18 (s, 1H, OH), 4.00 (m, 1H, CHCH₃), 4.18 (s,

2H, CH₂OH), 4.75 (s, 2H, NHCO₂CH₂), 7.72 ppm (d, J=7.5 Hz, 1H,

NH); ¹³C NMR (75 MHz, [D₆]DMSO): d=17.4 (CHCH₃), 49.0 (CHCH₃),

49.8 (CH₂OH), 52.4 (NHCO₂CH₂), 67.9, 70.0, 75.1, 81.1 (diacetylene C),

155.3 (carbamate C=O), 174.6 ppm (acid C=O).

CH₂), 39.1 (NHCH₂ACHTUGNTRENUN(G CH₂)₁₀CH₃), 50.7 (CHCH₃), 175.7 ppm (amide C=

O); HRMS (EI): calcd for C₁₅H₃₂N₂O: 256.2509; found: 256.2507 [M]⁺.

Acknowledgements

The authors would like to thank Professor Jꢁrgen P. Rabe and Dr. Niko-

lai Severin (Humboldt University Berlin, Germany) for their help with

SFM imaging, as well as Prof. A. Dieter Schlꢁter (ETH Zꢁrich, Switzer-

land) for his generous support. Funding from Fonds der Chemischen In-

dustrie (Fonds-Stipendium Eike Jahnke), ETH Zꢁrich (Projekt TH-20

07-1), Schweizerischer Nationalfonds (SNF-Projekt 200021–113509),

Deutscher Akademischer Austauschdienst (DAAD-Stipendien Jan Weiß,

Sonja Neuhaus) is gratefully acknowledged.

N-{6-{2’’’-{2’’-[2’-(2-Methoxyethoxy)ethoxy]ethoxy}ethoxy}hexa-2,4-

diynyl-1-oxycarbonyl}-l-alanine (10j): Following GP B, 8j (0.22 g,

0.47 mmol) was dissolved in dry CH₂Cl₂(20 mL), a large excess of TFA

was added, and the solution was stirred for 5 h. 10j (0.19 g, 99%) was ob-

tained as a brownish oil, and no further purification was carried out

before the next step. R_f=0.2 (CH₂Cl₂/MeOH 10:1); ¹H NMR (300 MHz,

CDCl₃): d=1.38 (d, J=6.9 Hz, 3H, CHCH₃), 3.33 (s, 3H, OCH₃), 3.52

(m, 2H, CH₂O), 3.6–3.7 (m, 14H, CH₂O), 4.22 (s, 2H, C₄CH₂O), 4.25 (m,

1H, CHCH₃), 4.75 (m, 2H, NHCO₂CH₂), 5.81 (d, J=4.2 Hz, 1H, NH),

8.4 ppm (s, 1H, COOH); ¹³C NMR (75 MHz, CDCl₃): d=18.5 (CHCH₃),

50.0 (CHCH₃), 52.9 (NHCO₂CH₂), 58.8, 58.9 (CH₂O), 69–71 (6 CH₂O, 2

diacetylene C), 73.5, 76.0 (diacetylene C), 154.8 (carbamate C=O),

176.5 ppm (acid C=O).

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1

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[D₆]DMSO): d=1.27 (d, J=7.2 Hz, 3H, CHCH₃), 4.00 (m, 1H, CHCH₃),

4.77 (s, 2H, CO₂CH₂), 7.76 ppm (d, J=7.8 Hz, 1H, NH); ¹³C NMR

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N-(9-Fluorenylmethyloxycarbonyl)-l-alanine dodecylamide (12): Follow-

ing GPA, dodecylamine (3.22 g, 17.37 mmol) and N-(9-fluorenylmethyl-

oxycarbonyl)-l-alanine (5.52 g, 17.73 mmol) were dissolved in a mixture

of dry CH₂Cl₂(90 mL) and dry DMF (30 mL). DIEA (6.7 g, 52.60 mmol)

and PyBOP (9.4 g, 18.07 mmol) were added, and the reaction mixture

was stirred overnight. The organic phase was washed with saturated

NaHCO₃solution, 1m HCl and saturated NaCl solution, dried over

MgSO₄, filtered, and concentrated in vacuo. The crude product was puri-

fied by column chromatography (silica gel, gradient from CH₂Cl₂/MeOH

24:1 to 10:1) to yield the title compound as a colorless solid (5.83 g,

81%). R_f=0.75 (CH₂Cl₂/MeOH 10:1); m.p. 136–1378C; ¹H NMR

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18H, (CH₂)₉CH₃), 1.38 (d, J=6.9 Hz, 3H, CHCH₃), 1.44 (t, J=6.6 Hz,

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2H, CHCH_3,fluorenyl CH), 4.37 (d, J=6.9 Hz, 2H, CO₂CH₂), 5.63 (d,

J=7.2 Hz, 1H, NH), 6.30 (brs, 1H, NH), 7.29 (t, J=7.5 Hz, 2H, aromatic

H), 7.39 (t, J=7.5 Hz, 2H, aromatic H), 7.57 (d, J=7.2 Hz, 2H, aromatic

H), 7.75 ppm (d, J=7.5 Hz, 2H, aromatic H); ¹³C NMR (75 MHz,

CDCl₃): d=14.1 ((CH₂)₁₁CH₃), 18.9 (CHCH₃), 22.7, 26.9, 29.3, 29.4, 29.5,

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Received: August 12, 2008

Published online: December 3, 2008

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Synthesis of diacetylene-containing peptide building blocks and amphiphiles, their self-assembly and topochemical polymerization in organic solvents

DOI: 10.1002/chem.200801668

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