ISMSC 2007 - Università degli Studi di Pavia

Self-assembly of N,C-linked peptidocalix[4]arenes
L. Baldini, G. Faimani, A. Casnati, F. Sansone, R. Ungaro
Dipartimento di Chimica Organica e Industriale, Università di Parma, via Usberti 17/a, 43100
Parma, Italy (laura.baldini@unipr.it)
In living organisms, peptides and amino acids play a fundamental role in many processes
controlled by molecular recognition, such as cell recognition or enzymatic catalysis. Thanks to
their ability to form weak interactions that are highly selective and efficient they are involved in
the formation of several self-assembled structures such as -helices, -sheets and nanotubes.
With the aim of developing artificial receptors able to mimic the molecular recognition
mechanisms of biological systems, we synthesized the first example of a calixarene amino acid
(1)[1] and optimized the reactions for its insertion in a pseudopeptide sequence.
The resulting peptidocalixarenes (e.g. 2) are self-complementary (the N-linked arm is
complementary to the C-linked arm and viceversa) in terms of hydrogen bonding donor and
acceptor groups. As a consequence, in apolar solutions they self-assemble in dimeric capsulelike
structures held together by hydrogen bonds between the CO and NH groups (e.g. 3).[1]
In order to evaluate the scope of these self-assembling systems and to further characterize the
structure of the self-assembled capsules, we synthesized new members of this N,C-linked
peptidocalixarene family. The correlation of the self-assembling properties of the new
compounds with their structure, together with 1D and 2D NMR studies allowed us to shed more
light on the geometry of the hydrogen bonding motif and on the factors that control the selfassembly
process.
N
H 2
HO
O OH
O
1
HO
O
CbzHN
O
HN
NH
O
HO
O OH
O
2
O
O
HN
NH
O
O
self-assembly
O
O
O
N
H
O
N
H
O
O
H
N
H
N
O
H
N
O
HO
O
O OH
HO O OH O
[1] F. Sansone, L. Baldini, A. Casnati, E. Chierici, G. Faimani, F. Ugozzoli and R. Ungaro, J.
Am. Chem. Soc. 126, 6204-6205 (2004).
3
O
N
H
O
H
N
H
N
O
O
H
N
O
H
N
PSA 7
O
O
O
Acyclic pyrrole-based anion receptors: Design, synthesis, and anion
binding properties
Jonathan L. Sessler † , Natalie M. Barkey † , G. Dan Pantos ‡ , Vince M. Lynch †
† Univeristy of Texas at Austin, 1 University Station A5300, Austin, TX 78712
‡ Univeristy of Cambridge, Cambridge CB2 1EW, UK
Anions have a wide range of importance both in chemical, as well as biological, systems;
thus, the design and synthesis of novel receptors with the ability to selectively recognize or bind
a specific class of anions is a rapidly developing field of supramolecular chemistry. 1,2
A series of novel, acyclic pyrrole-based anion receptors have recently been designed and
synthesized in the Sessler group (Figure 1). These systems, which are based on pyridine 2,6dicarboxamides,
bind nitrite and carboxylate anions with good selectivity in dichloroethane
solution and are also capable of binding cyanide anions weakly. Control systems, incorporating
a benzene-1,3-dicarboxamide spacer, or those wherein the connectivity of the amide linkage is
“reversed,” either failed to act as effective anion receptors or displayed very different
selectivities. Such observations provide support for the notion that small perturbations in the
structure of these receptors can lead to drastic changes in their anion-binding properties. 3
Efforts to attach these systems, as well as other oligopyrrolic anion receptors, to
cellulose-mediated solid support structures are underway and will be presented as appropriate.
O
O
O
N
H
HN
N NH HN
O
O
O
O
O O O
O
O
H
N HN
N NH HN
O
O
O O
O
O O O
O
O
H
N
NH
O
O
O
HN
O HN
O
O O O
O
H
N N
H
O
O
O O
DPPic DPPic II DPIPh RA DPPic
Figure 1: Novel anion receptors relevant to this presentation. 3
N N H
O HN
O
O
O O
PSA 8
[1] Camiolo, S; Gale, P; Hursthouse, M.B.; Light, M.E. Org. Biomol. Chem. 2003, 741
[2] Sessler, J.L.; Camiolo, S.; Gale, P.A. Coord. Chem. Rev. 2003, 17
[3] Sessler, J.L.; Barkey, N.M.; Pantos, G.D.; Lynch, V.M. N. J. Chem. 2007. Published on web.