Architectural chemistry: Synthesis of topologically diverse macromulticycles by sequential multiple multicomponent macrocyclizations

Article abstract of DOI:10.1021/ja809005k

How can conformationally restricted polyvalent molecules be accessed rapidly? A sequential approach involving two multiple multicomponent macrocyclizations including bifunctional building blocks (MiBs) with up to five Ugi-four-component reactions (Ugi-4CR

Full text of DOI:10.1021/ja809005k

Published on Web 02/20/2009
Architectural Chemistry: Synthesis of Topologically Diverse
Macromulticycles by Sequential Multiple Multicomponent
Macrocyclizations
Daniel G. Rivera†,‡ and Ludger A. Wessjohann*,†
Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3,
D-06120 Halle/Saale, Germany, and Center for Natural Products Study, Faculty of Chemistry,
UniVersity of HaVana, 10400 HaVana, Cuba
Received November 17, 2008; E-mail: wessjohann@ipb-halle.de
Abstract: How can conformationally restricted polyvalent molecules be accessed rapidly? A sequential
approach involving two multiple multicomponent macrocyclizations including bifunctional building blocks
(MiBs) with up to five Ugi-four-component reactions (Ugi-4CR) has been developed to produce nonsymmetric
macromulticycles. Topologically diverse structures, such as nonsymmetric cryptands and clam- and igloo-
shaped macromulticycles were obtained in reaction sequences that comprise the incorporation of up to 13
building blocks by forming 20 new bonds without purification of intermediates. Cryptands were produced
by a sequential-MiB procedure in which the Ugi-type functional groups of the second MiB are attached to
the peptoid backbones from the first multicomponent macrocyclization. These macrobicycles show two
completely new features; i.e., three different tether chains can be obtained in one pot, and tertiary amide
bonds are used as bridgeheads. Alternatively, the same reaction sequence, i.e., MiB/deprotection/MiB,
can be used to produce clam-shaped macrobicycles, demonstrated with a tetrafunctional cholanic steroid
as a hinge moiety. Macrotetracycles endowed with igloo-type topologies are accessible by an advanced
protocol featuring consecutive double and 3-fold Ugi-4CR-based macrocyclizations. Other building blocks
than cholanic steroids employed include aryl, heterocyclic, polyether, and other recognition motifs. The
examples given are a first-generation demonstration of an “architectural chemistry” that allows to construct
three-dimensional multimotif covalent molecular “buildings” of unprecedented complexity by design.
recognition due to their potential as encapsulating molecules.1
Other compounds presenting more complex and unconventional
Introduction
The design and facile synthesis of macrocyclic compounds
endowed with diverse topologies and functional domains is of
dominant importance for the development of supramolecular
chemistry and in some areas of nanotechnology and catalysis.
Like supramolecular chemistry, bottom-up nanotechnology is
based on the chemist’s ability to construct large functional
molecules from simple building blocks. Desirable are methods
that allow moving away from the now common homooligomers,
random self-assembly, or noncovalent networks toward the
plannable construction of three-dimensional molecules of high
complexity with covalent (and noncovalent) bonds formed in
predefined manner. Ideally, the topological and functional
possibilities of such molecules should besin principlescom-
parable (but not identical) to those achieved by proteins.
Architectural chemistry has the goal to devise design rules and
synthesis tools for the fast and efficient assembly of complex
three-dimensional molecules at will and from simple building
blocks, similar to building planning and construction.
topologies, such as interlocked and knotted molecules, have
recently proved their potential as prototypical molecular de-
vices.2 Indeed, the advent of real applications for all these
macrocycles has been only possible due to the progress in
templated and nontemplated macrocyclization strategies leading
to them.1,3
Recently, we have described the development of a novel
synthetic methodology for the one-pot assembly of complex,
nonrepetitive macrocycles.4 The approach relies on the perfor-
mance of multiple multicomponent macrocyclizations including
bifunctional building blocks (MiBs). Although several multi-
component reactions (MCRs) in principle work,4b the main focus
was on the use of the Ugi-four-component reaction (Ugi-4CR)
due to the tremendous capability of this process to generate
molecular complexity and diversity. In addition, this methodol-
(1) (a) Schneider, H.-J.; Yatsimirsky, A. Principles and Methods in
Supramolecular Chemistry; Wiley: Chichester, 2000. (b) Cram, D. J.;
Cram, M. J. Container Molecules and Their Guests; The Royal Society
of Chemistry: Cambridge, 1994. (c) Lehn, J.-M. Supramolecular
Chemistry: Concepts and PerspectiVes; Wiley-VCH: Weinheim, 1995.
(d) Vo¨gtle, F. Supramolecular Chemistry: An Introduction; Wiley &
Sons: New York, 1993.
(2) (a) Felder, T. Schalley, C. A. Artificial Rotary Motors Based on
Rotaxanes. In Highlights in Bioorganic Chemistry; Wennemers, H.,
Schmuck, C., Eds.; Wiley-VCH: Weinheim, 2004; p 256. (b) Balsani,
V.; Venturi, N.; Credi, A. Molecular deVices and machines: A journey
into the nanoworld; Wiley-VCH: Weinheim, 2003.
A variety of synthetic receptors, such as cryptands, cyclo-
phanes, and cages, are early examples of rather simple mostly
homo-oligomeric structures. They nevertheless demonstrated
their applicability in coordination chemistry and molecular
† Leibniz Institute of Plant Biochemistry.
‡ University of Havana.
9
10.1021/ja809005k CCC: $40.75
2009 American Chemical Society
J. AM. CHEM. SOC. 2009, 131, 3721–3732 3721

A R T I C L E S
Rivera and Wessjohann
ogy has proven to be suitable for the rapid construction of more
challenging, peptidic macrobicycles such as cryptands, cryp-
tophanes, and steroid-based cages.5
of producing genuine nonsymmetric cryptands8 and other types
of macromulticycles presenting hybrid peptidomimetic skeletons
with varied molecular topologies. Such complex frameworks
may include additional recognition or functional motifs (e.g.,
aromatic, heterocyclic, cholanic steroids, hydrogen bonding, etc.)
to address the encapsulation capability of selected guests or for
external binding domains suitable for supramolecular self-
assembly. Herein we report on the sequential use of Ugi-MiB
procedures to assemble nonsymmetric, peptoid-containing mac-
romulticycles featuring cryptand-like as well as clam- and igloo-
shaped architectures.
Cryptands are synthetic receptors capable of binding either
ions or neutral molecules depending on the features of the
macrobicyclic cavity.6 In general, these and other macromul-
ticycles are endowed with improved binding and inclusion
properties compared to their macrocyclic analogues.1 Most
cryptands (e.g., benzene- and tren-bridgeheaded ones) are based
on C3-symmetric building blocks.1,6 This feature renders their
cores symmetric as a whole and makes it difficult to achieve
selective recognition, for example of chiral guests, as well as
further differentiation of the tether chains. Another important
type of multicyclic receptors includes the so-called laterally
nonsymmetric cryptands.7 These are macrobicycles wherein the
two bridgehead atoms are connected by one tether different from
the other two bridging chains. The examples of this type reported
in the literature are endowed with a typical dissymmetry arising
from a symmetry plane running through the unlike tether.7 Also,
the peptidic macrobicycles obtained in our previous work5
present either a C3-symmetry or symmetry plane owing to the
3-fold character of the macrocyclization protocol as well as the
symmetric nature of the trifunctional building blocks.
Results and Discussion
Scheme 1 is a schematic representation of the synthetic
planning devised to implement two consecutive double Ugi-
4CR-based macrocyclizations. Thus, cryptand and clam-type
macrobicycles can be produced by performing a first MiB
approach, followed by deprotection of further Ugi-reactive
functional groups appended, and a subsequent MiB that may
be or not of the same type as the former. Cryptands can be
obtained when the functional groups taking part in the second
macrocyclization are attached to the peptoid backbones resulting
from the first MiB. In this case, the bridgehead cores of the
final cryptands are tertiary amide bonds included in the peptoid
skeletons arising from the first double Ugi-4CR-based macro-
cyclization (see Scheme 1A, cf. also Scheme 2). This structural
feature is not found in any other type of macrobicyclic receptor
and should influence the complexation properties of these unique
macrobicyclic architectures.
Likewise, clam-shaped macrobicyclic compounds can be
produced by utilizing tetrafunctional steroidal scaffolds by the
same reaction sequence, i.e., MiB/deprotection/MiB (Scheme
1B, cf. also Scheme 4). The concave shape of cholanic scaffolds
enables the precise geometrical positioning of each pair of Ugi-
type functionalities to achieve the varied clam-type topologies.
These are suitable to host two different guests in a defined
proximity range to study their interaction. Of course, the clam
design requires that two of the four functional groups originally
positioned on the steroidal moiety remain protected during the
first MiB process.
Very few types of ring-closing reactions are usually employed
in supramolecular chemistry for the production of macrocyclic
receptors.1-3,6 This represents a marked limitation with regard
to the structural diversity that is required for, e.g., screening of
recognition and catalytic properties. Hence, most multiple
macrocyclization protocols used in this field are based on the
formation of imine and amide bonds by reaction of primary
polyamines with aldehyhes and acyl chlorides (or active esters),
respectively.1-3,6 Another procedure widely used for the
construction of synthetic receptors is the Richman-Atkins
approach,9 which involves the nucleophilic substitution of
dihalides or their analogous tosylates and mesylates with
disulfonylamides or diols in the presence of a base. All these
procedures, besides serving as the ring-closing reaction, also
incorporate binding functionalities into the final macrocyclic
receptor. A different case is the ring-closing metathesis, which
In view of an increasing interest in three-dimensional large
molecules as well as in chiral recognition through encapsulation
processes, we set out to develop an alternative approach capable
(3) For reviews on templated and nontemplated macrocyclization strate-
gies, see:(a) Zhang, W.; Moore, J. S. Angew. Chem., Int. Ed. 2006,
45, 4416–4439. (b) Laughrey, Z. R.; Gibb, B. C. Top. Curr. Chem.
2005, 249, 67–125. (c) Arico´, F.; Badjic, J. D.; Cantrill, S. J.; Flood,
A. H.; Leung, K. C.-F.; Liu, Y.; Stoddart, J. F. Top. Curr. Chem.
2005, 249, 203–269. (d) Dietrich-Buchecker, C.; Colasson, B. X.;
Sauvage, J.-P. Top. Curr. Chem. 2005, 249, 261–283. (e) Wessjohann,
L. A.; Ruijter, E. Top. Curr. Chem. 2005, 243, 137–184. (f) Schalley,
C. A.; Wielandt, T.; Bruggemann, J.; Vo¨gtle, F. Top. Curr. Chem.
2004, 248, 141–200. (g) Vilar, R. Angew. Chem., Int. Ed. 2003, 42,
1460–1477. (h) Rowan, S. J.; Cantrill, S. J.; Cousin, G. R. L.; Sanders,
J. K. M.; Stoddart, J. F. Angew. Chem., Int. Ed. 2002, 41, 898–952.
(i) Gerbeleu, N. V.; Arion, V. B.; Burgess, J. Template Synthesis of
Macrocyclic Compounds; Wiley-VCH: Weinheim, 1999. (j) Seel, C.;
Vo¨gtle, F. Angew. Chem., Int. Ed. 1992, 31, 528–549.
(4) (a) Rivera, D. G.; Vercillo, O. E.; Wessjohann, L. A. Org. Biomol.
Chem. 2008, 6, 1787–1795. (b) Leo´n, F.; Rivera, D. G.; Wessjohann,
L. A. J. Org. Chem. 2008, 73, 1762–1767. (c) Michalik, D.; Schaks,
A.; Wessjohann, L. A. Eur. J. Org. Chem. 2007, 14, 9–157. (d)
Wessjohann, L. A.; Rivera, D. G.; Coll, F. J. Org. Chem. 2006, 71,
7521–7526. (e) Wessjohann, L. A.; Voigt, B.; Rivera, D. G. Angew.
Chem., Int. Ed. 2005, 44, 4785–4790. (f) Wessjohann, L. A.; Ruijter,
E. Mol. DiVersity 2005, 9, 159–169. (g) Wessjohann, L. A.; Rivera,
D. G.; Vercillo, E. O. Chem. ReV. 2009, 109, 796–814.
(5) (a) Rivera, D. G.; Wessjohann, L. A. J. Am. Chem. Soc. 2006, 128,
7122–7123. (b) Rivera, D. G.; Vercillo, O. E.; Wessjohann, L. A.
Synlett 2007, 308, 312. (c) Wessjohann, L. A.; Rivera, D. G.; Leo´n,
F. Org. Lett. 2007, 9, 4733–4736.
(6) For reviews on cryptand chemistry, see ref 1 and: (a) Amendola, V.;
Bonizzoni, M.; Esteban-Go´mez, D.; Fabbrizzi, L.; Licchelli, M.;
Sanceno´n, F.; Taglietti, A. Coord. Chem. ReV. 2006, 250, 1451–1470.
(b) Bowman-James, K. Acc. Chem. Res. 2005, 38, 671–678. (c)
McKee, V.; Nelson, J.; Town, R. M. Chem. Soc. ReV. 2003, 32, 309–
325. (d) Amendola, V.; Fabbrizzi, L.; Mangano, C.; Pallavacini, P.;
Poggi, A.; Taglietti, A. Coord. Chem. ReV. 2001, 219-221, 821–837.
(e) Llinares, J. M.; Powell, D.; Bowman-James, K. Coord. Chem. ReV.
2003, 240, 57–75. (f) Lehn, J.-M. Pure Appl. Chem. 1980, 52, 2442–
2459. (g) Lehn, J.-M. Pure Appl. Chem. 1978, 52, 871–892.
(7) (a) Koshabek, R.; Gleiter, R.; Rominger, F. Eur. J. Inorg. Chem. 2006,
60, 9–620. (b) Rey, D.; Bharadwaj, P. K. Eur. J. Inorg. Chem. 2006,
177, 1–1776. (c) Huang, F.; Slebodnick, C.; Switeck, K. A.; Gibson,
H. W. Chem. Commun. 2006, 1929, 1931. (d) Mukhopadhyay, P.;
Sarkar, B.; Bharadwaj, P. K.; Na¨ttinen, K.; Rissanen, K. Inorg. Chem.
2003, 42, 4955–4960. (e) Sarkar, B.; Mukhopadhyay, P.; Bharadwaj,
P. K. Coord. Chem. ReV. 2003, 236, 1–13. (f) Plenio, H.; El-Desoky,
H.; Heinze, J. Chem. Ber. 1993, 126, 2403–2408.
(8) For selected examples of cryptands being really nonsymmetric, see:
(a) To¨nsoff, C.; Merz, K.; Bucher, G. Org. Biomol. Chem. 2005, 3,
303–308. (b) Esteban, D.; Ban˜obre, D.; de Blas, A.; Rodr´ıguez-Blas,
T.; Bastida, R.; Mac´ıas, A.; Rodr´ıguez, A.; Fenton, D. E.; Adams,
H.; Mah´ıa, J. Eur. J. Inorg. Chem. 2000, 144, 5–1456. (c) Kranemann,
C.; Eilbracht, P. Eur. J. Org. Chem. 2000, 236, 7–2377.
(9) Richman, E. J.; Atkins, T. J. J. Am. Chem. Soc. 1974, 96, 2268–2270.
9
3722 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009

Synthesis of Topologically Diverse Macromulticycles
A R T I C L E S
Scheme 1. Approach Towards Topologically Diverse Macrobicycles Based on Two Sequential Ugi-MiBs of the Same Bifunctional
Combinationa
a See text for details; PG ) Protective Group; A: Cryptands; B: Clams.
has been widely employed as the final bond-forming reaction
in the synthesis of interlocked molecules, but it does not
introduce a dominant recognition motif.3b-d
remarkable when considering the great amount of readily
available bifunctional building blocks containing Ugi-reactive
functional groups. MiB approaches including dialdehyde build-
ing blocks have not been included in the present work as they
can lead to the formation of stereoisomers and thus cause
analytical complications. For the same reason, paraformaldehyde
was employed as an oxo-component, although other aliphatic
aldehydes usually give better yields. The resulting partially
N-substituted oligoglycine moieties (i.e., peptoids) in the
cryptand cores have no stereocenters, and thus single isomers
result.
As depicted in Scheme 2, one of the building blocks taking
part in the first Ugi-MiB must contain a protected, or initially
unreactive, Ugi-reactive functional group to be subsequently
activated for the next macrocyclization. The formation of several
amide bonds during the sequential MiBs is one of the key
features for any potential application of Ugi-based multimac-
rocycles in supramolecular chemistry. Amide-containing mac-
robicycles are one of the most exploited types of receptors due
to their remarkable binding capability toward a variety of
guests.1,3j,6b,11 Moreover, the presence of both substituted and
nonsubstituted amides alongside the macromulticyclic scaffold
opens up possibilities either for the coordination of cations and
anions or for the recognition of neutral guests based on hydrogen
bonding.11
The MiB methodology was developed to accomplish several
tasks in one step, e.g., to serve as multiple and simultaneous
ring-closing reactions of polyfunctional building blocks and to
incorporate several binding motifs with impressively low
synthetic effort.4,5 As demonstrated in this paper, the sequential
MiBs allow a remarkable increment of skeletal diversity of
macromulticyclic scaffolds by simply tuning the nature of the
building blocks and the combination of reacting functional
groups employed in each MiB. All MiB-deprotection-MiB
protocols can be performed in one pot, i.e., without the necessity
to isolate the intermediate macrocycle in protected or deprotected
form. Ugi-4CRs can be performed in a wide variety of solvents
and in the presence of, e.g., water (as used for protective group
hydrolysis), mineral or Lewis acids, salts, or air.
Scheme 2 summarizes three different combinations of con-
secutive MiBs from all the possible permutations accessible by
this sequential procedure. Because of the four components taking
part in the Ugi-4CR10 (i.e., a primary amine, an oxo compound,
a carboxylic acid, and an isocyanide), six different combinations
of bifunctional building blocks are possible: (i) diacid/diamine,
(ii) diacid/diisocyanide, (iii) diacid/dialdehyde, (iv) diisocyanide/
diamine, (v) diisocyanide/dialdehyde, and (vi) diamine/dialde-
hyde.4 Accordingly, up to 36 dissimilar macrobicycles can be
produced just by repeating two macrocyclization steps in a
sequential manner. Indeed, the synthetic scope with regard to
the accessible diversity of nonsymmetric cryptands is truly
(11) For reviews on amide-based receptors, see: (a) Gibson, S. E.; Lecci,
C. Angew. Chem., Int. Ed. 2006, 45, 1364–1377. (b) Kang, S. O.;
Hossain, M. A.; Bowman-James, K. Coord. Chem. ReV. 2006, 250,
3038–3052. (c) Davis, A. P.; James, T. D. Carbohydrate receptors. In
Functional Synthetic Receptors; Schrader, T., Hamilton, A. D., Eds.;
Wiley-VCH: Weinheim, 2005; pp 45-109. (d) Bondy, C. R.; Loeb,
S. J. Coord. Chem. ReV. 2003, 240, 77–99. (e) Beer, P. D.; Gale, P. A.
Angew. Chem., Int. Ed. 2001, 40, 486–516.
(10) (a) Do¨mling, A. Chem. ReV. 2006, 106, 17–89. (b) Multicomponent
Reactions; Zhu, J., Bienyame´, H., Eds.; Wiley-VCH: Weinheim, 2005.
(c) Do¨mling, A.; Ugi, I. Angew. Chem., Int. Ed. 2000, 39, 3168–3210.
9
J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009 3723

A R T I C L E S
Rivera and Wessjohann
Scheme 2. Synthesis of Nonsymmetric Cryptands by Two Sequential Double Ugi-4CR-Based Macrocyclizations: (A) Diacid/
Diisonitrile-Diacid/Diisonitrile Combination; (B) Diacid/Diisonitrile-Diamine/Diisonitrile; (C) Diamine/Diisonitrile-Diamine/Diacid, With Further
Orthogonally Protected Diamine Available
Rather than covering all possible combinations, our aim is
to demonstrate the significant molecular complexity that can
be reached in a very simple reaction sequence which involves
a “sandwich” of two macrocyclizations and a simple deprotec-
tion step. All macrocyclization reactions were performed under
pseudo-high-dilution conditions, implemented by slowly adding
the bifunctional building blocks to a stirred solution of the other
components. These experimental conditions have been previ-
ously standardized to give high macrocyclization yields (up to
ca. 80%, usually ca. 45-55%) even in the absence of any
template,4 albeit such high yields may require reaction times
as long as 5-7 days. Templating can give even higher yields
and faster reaction without pseudo-high-dilution.5c In addition
to the desired macrocycles, typical Ugi-MiBs also may furnish
certain amounts of uncyclized product,4c which if required can
be easily removed together with any excess of a monofuncional
component by flash chromatography or by consecutive acidic
and basic washings. Following this protocol, the first-generation
macrocycles were not purified by chromatography for detailed
characterization but only identified by ESI-MS, then deprotected,
and the resulting crude intermediates were subjected to the next
double Ugi-4CR-based macrocyclization. Hence, the yields
given in Schemes 2, 4, and 5 refer to the overall process and
can be considered as excellent regarding the great structural
complexity and the high number of bonds formed during the
sequences. For example, 16 bonds are formed in the reactions
of scheme 2 including two macrocyclizations. The simplicity
and reliability of protection/deprotection processes available for
the Ugi-reactive amino, carboxylic acid, and oxo functionalities,
mainly as carbamate, ester, or ketal, respectively, contribute to
the success of the sequential MiB approaches. In this regard,
the more challenging combination that involves an isocyanide
functionality not reacting during the first MiB to be later
activated for the second one may be regarded as a future option.
This appears possible due to the known differential reactivity
of, e.g., aliphatic isocyanides versus aromatic ones,4c or simply
by forming the isocyanide group from its precursor (i.e., amine
or formamide) once the first-generation macrocycle has been
produced.
The examples shown in Scheme 2 illustrate the production
of large cryptands by using diacids, diisocyanides, and diamines
containing a wide variety of recognition motifs, e.g., steroidal,
aromatic, polyether, and heterocyclic ones. Cryptand 5 was
obtained by a sequential diacid/diisocyanide-diacid/diisocya-
nide combination which takes advantage of the bifunctional
character of R-amino acids. Glycine tert-butyl ester hydrochlo-
ride was used as the amino component to provide, after cleavage
of the ester groups, the two carboxylic functionalities required
9
3724 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009

Synthesis of Topologically Diverse Macromulticycles
A R T I C L E S
Scheme 3. Synthesis of Tetrafunctional Cholanic Building Blocks
for the second MiB. Mild or orthogonal deprotection procedures
are important to not affect either the formed peptoid backbones
or other groups within the first-generation macrocycles. For
example, partial hydrolysis of the hemisuccinate moiety has been
noticed in analogues of macrocycle 8 during the deprotection
of methyl ester groups attached to the peptoid backbone.
Therefore, as outlined in Scheme 2b, protected amines rather
than esters were chosen in this sequence to avoid partial
destruction of the macrocyclic intermediate. Variation 2b
illustrates the successful use of a monoprotected diamine to
accomplish a sequential diacid/diisocyanide-diamine/diisocya-
nide combination. Cryptand 9 was produced via simple hydro-
genolysis of the Cbz-protecting groups in intermediate 8
followed by the second MiB, thereby featuring a perfect
orthogonality among all reaction steps.
Both C- and N-protected R-amino acids are well behaved as
either an amino or acid component, respectively, in single
MiBs.4,5 The sequential MiB procedure shown in Scheme 2c
may be considered especially interesting. It features a diamine/
diisocyanide-diamine/diacid combination which employs the
orthogonally biprotected R-amino acid L-lysine. The polyfunc-
tional character of lysine allows that, for example, the final
cryptand 13 may still behave as an intermediate for a third-
generation MiB considering the presence of the additionally
appended amino groups protected as carbamates.
As illustrated in Figure 1, due to the presence of three
different tether chains in cryptands 5, 9, and 13, a pair of
(enantiomeric) topological stereoisomers can appear for each
structure. Since the bridgeheads are planar tertiary amides
(peptoids), this does not coincide with a bridgehead stereocenter
like in carbon bridgeheads. Additionally, in compounds 9 and
13, one or more of the tether building blocks is chiral itself
(i.e., the cholanic steroid and L-lysine), and the two possible
topo-stereomers would be topological diastereomers and not
enantiomers. Interestingly, HPLC and NMR analyses of com-
pounds 9 and 13 (1H NMR spectra recorded at room and higher
temperatures) do not show evidence of diastereomeric mixtures
but of only a single isomer (see the Supporting Information),
which may be reasoned by rapid peptoid bridgehead s-cis/s-
trans conversions or through the preferential stabilization
orsunlikelysformation of one diastereomer. Alternatively, the
chiroptical activity of these compounds was studied by circular
dichroism (CD).
Figure 2 shows the CD spectra of cryptands 5, 9, and 13, all
revealing the occurrence of a single stereoisomer for this type
of macrobicycles. It must be noted that cryptands 9 and 13
contain a chiral moiety in the tether chain (9) or in the periphery
(13), while in cryptand 5 the three tethers and all appendages
are achiral, so it is a typical dissymmetric structure. The curves
observed in the CD spectra of compounds 9 and 13 exhibit
multiple Cotton effects that demonstrate their chiroptical activi-
ties.12 Thus, the CD spectrum of compound 9 displays a positive
couplet with the maximum at 240 nm and two negative couplets
with minima at 210 and 266 nm. Likewise, the CD spectrum
of compound 13 shows a negative couplet with the minimum
at 238 nm and a positive one with the maximum at 260 nm.
However, the CD spectrum of compound 5 lacks any positive
or negative Cotton effect over 200 nm. This result indicates
that this type of macrobicyclic scaffold does not exhibit
chiroptical activity derived either from the nfπ* or πfπ*
transitions. The presence of aromatic and carbonyl groups in
the structure of 5 advises that, in the case of the existence of a
Cotton effect derived from the topological chirality, the couplets
should appear in the region over 200 nm.12 Therefore, the lack
of any positive or negative couplet suggests either the absence
of topological chirality in this type of skeleton or its impos-
sibility to be detected by CD spectroscopy. This means that
interconversion between rotamers does not comprise the oc-
currence of topological stereoisomers. In contrast to this, the
Cotton effects observed for cryptands 9 and 13 arise from the
(12) Nakanishi, K.; Berova, N.; Woody, R. W. Circular Dichroism; Wiley-
VCH: Weinheim, 1994.
9
J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009 3725

A R T I C L E S
Rivera and Wessjohann
Scheme 4. Synthesis of Clam-Shaped Macrobicycles by Sequential Double Ugi-4CR-Based Macrocyclizations: (a) Diacid/Diisonitrile-Diacid/
Diisonitrile; (b) Diacid/Diisonitrile-Diacid/Diamine; (c) Diacid/Diamine-Diamine/Diacid, With Further Orthogonally Protected Tetraacid
Availablea
a Please note that for 25 and 27 the substituents at the central steroid attachment points are pointing into the concave R-side but that for clarity the
macrocyclic rings are drawn at opposite sides of the steroid hinge (“open clam”).
central chirality of the steroidal and the lysine moieties, which
make the cryptands chiral themselves.
As shown in Scheme 3, the cholanic derivatives 14 and 17,
previously obtained from cholic acid,4d were functionalized to
produce the tetracarboxylic acids 16 and 19 with two of their
carboxylic groups protected as methyl esters. In this and all
further approaches involving cholanic building blocks, the oxime
bond formation from ketosteroids was preferred for the instal-
lation of carboxylic functionalities as the connection point of
the steroidal nucleus. This choice is based on two arguments,
the resistance of this junction to ester cleavage under basic
Steroid-based macrocycles have proven their efficiency as
supramolecular receptors for a wide variety of guests, ranging
from anions to biomolecules like carbohydrates and peptides.13
An important reason for their common use is the intrinsic
preorganization and rigidity, which usually leads to excellent
(and sometimes unexpected) macrocyclization results compared
to other, more flexible building blocks.13,14 In addition, the
concave shape of cholanic steroids enables the creation of
topologically interesting molecules such as the clam-shaped
macrobicycles presented in Scheme 3. These latter macrobi-
cycles are endowed with two (not interlocked) macrocyclic rings
joined at the steroidal nucleus (cf. Scheme 1).
(14) For selected reports on cholane-based macrocycles, see refs 4, 5, and:
(a) Whitmarsh, S. D.; Redmond, A. P.; Sgarlata, V.; Davis, A. P. Chem.
Commun. 2008, 366, 9–3671. (b) Feigel, M.; Ladberg, R.; Engels, S.;
Herbst-Irmer, R.; Fro¨hlich, R. Angew. Chem., Int. Ed. 2006, 45, 5698–
5702. (c) Feigel, M.; Ladberg, R.; Winter, M.; Bla¨ser, D.; Boese, R.
Eur. J. Org. Chem. 2006, 371-377. (d) Sisson, A. L.; Clare, J. P.;
Davis, A. P. Chem. Commun. 2005, 5263, 5265. (e) Babu, P.; Maitra,
U. Proc. Indian Acad. Sci. (Chem. Sci.) 2003, 115, 607–612. (f)
Virtanen, E.; Koivukorpi, J.; Tamminen, J.; Ma¨ntta¨ri, P.; Kolehmainen,
E. J. Organomet. Chem. 2003, 668, 43–50. (g) Dias, J. R.; Pascal,
R. A.; Morrill, J.; Holder, A. J.; Gao, H.; Barnes, C. J. Am. Chem.
Soc. 2002, 124, 4647–4652. (h) Albert, D.; Feigel, M.; Benet-Buchholz,
J.; Boese, R. Angew. Chem., Int. Ed. 1998, 37, 2727–2729.
(13) For reviews on the use of steroids in molecular recognition, see: (a)
Davis, A. P. Molecules 2007, 12, 2106–2122. (b) Davis, A. P. Coord.
Chem. ReV. 2006, 250, 2939–2951. (c) Virtanen, E.; Kolehmainen,
E. Eur. J. Org. Chem. 2004, 338, 5–3399. (d) Davis, A. P.; Joss, J.-
B. Coord. Chem. ReV. 2003, 240, 143–156. (e) Tamminen, J.;
Kolehmainen, E. Molecules 2001, 6, 21–46. (f) Wallimann, P.; Marti,
T.; Fu¨rer, A.; Diederich, F. Chem. ReV. 1997, 97, 1567–1608.
9
3726 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009

Synthesis of Topologically Diverse Macromulticycles
A R T I C L E S
Scheme 5. Synthesis of Igloo-Shaped Macrotetracycles by Sequential Double and Threefold Ugi-4CR-Based Macrocyclizations: (a, b)
Diacid/Diisonitrile-Triacid/Triisonitrile; (c) Diacid/Diamine-Triacid/Triisonitrile Combinations
conditions and the difficulty to incorporate other types of
functionalized arms (e.g., succinate) through acylation of the
axial hydroxyl groups at positions 7 and 12. Another possibility
to obtain tetrafunctional steroidal scaffolds is the introduction
of amino groups directly attached to the steroidal nucleus and
not as functionalized arms. For example, the steroidal azide 20,
synthesized according to a procedure reported by Davis and
co-workers,15 is amenable for executing alternative combinations
to those allowed by the steroidal tetracarboxylic acids. Thus,
compound 20 was reduced to the corresponding amine, followed
by protection as carbamate and consecutive PCC oxidation of
hydroxyl 7R to furnish the intermediate 21. Finally, cleavage
of the methyl ester at C-24 and condensation of the ketone with
O-(carboxymethyl)hydroxylamine afforded the diacid 22 in 55%
overall yield from 20. Although oximes in theory can react in
Figure 1. Pair of possible topological stereoisomers derived from the
asymmetry of the macrobicycles.
(15) Barry, J. F.; Davis, A. P.; Pe´rez-Paya´n, M. N. Tetrahedron Lett. 1999,
40, 2849–2852.
9
J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009 3727

A R T I C L E S
Rivera and Wessjohann
Figure 2. CD spectra of cryptands 5, 9, and 13 in methanol.
Ugi-4CRs, this potential side reaction is much too slow to
compete with the standard components used for the macrocy-
clizations.
A similar approach including bifunctional building blocks has
recently been employed for the construction of tetracyclic
receptors for (oligo)saccharides, albeit relying on typical peptide
coupling protocols.16 The use of this simple sequential procedure
to assemble complex functional receptors foresees important
applications for novel macromulticycles, which should be more
readily accessible by multiple Ugi-4CRs, and with even more
intrinsic complexity if necessary.
A more demanding extension of the sequential MiB approach
is the combination with Ugi-4CR-based macrocyclizations of
higher multiplicity.17 Some examples are illustrated in Scheme
5 with the synthesis of macrotetracyclic skeletons featuring
igloo-shaped structures. These extremely complex architectures
were assembled by the combination of double4 and 3-fold5a Ugi-
4CR-based macrocyclizations. The whole process occurs through
incorporation of 13 building blocks, forming 20 new bonds in
a very efficient reaction sequence to give cages of a defined
constitution and with almost any desired degree of complexity
within the tethers or on the appendages.
The use of C-protected L-alanine as the amino component in
a first double Ugi-4CR-based macrocyclization featuring a
diacid/diisocyanide combination led to the macrocyclic inter-
mediates 32 and 36 (Scheme 5a,b). These were subjected to a
mild cleavage of the ester groups to afford, upon acidification,
the corresponding tricarboxylic acids. These triple Ugi-reactive
macrocycles were employed in the assembly of macrotetracycles
34 and 37 by 3-fold Ugi-4CR-based macrocyclizations.
A slightly different route was used for the synthesis of
macrotetracycle 40 (Scheme 5c). This cage target was also
achieved by sequential double and 3-fold Ugi-4CR-based
macrocyclizations, though with the first MiB featuring a diacid/
diamine combination that utilizes methyl isocyanoacetate as the
isonitrile component. Accordingly, the macrocyclic intermediate
39 was generated in a triester form, which was consecutively
Scheme 4 illustrates three examples of steroid-based clams
achieved by sequential MiBs. Compound 16 was reacted in a
consecutive diacid/diisocyanide-diacid/diisocyanide combina-
tion to yield macrobicycle 25, which contains two rims including
two similar but different aryl moieties and fully endocyclic
peptoid backbones. The very similar, but at the same time
distinct diisocyanides 7 and 23, were employed to allow NMR
differentiation of the two rims in further structural and binding
studies (see 1H NMR spectrum in the Supporting Information).
On the other hand, macrobicycle 27 was produced by a diacid/
diisocyanide-diacid/diamine combination, thereby affording a
hybrid structure wherein one of the two rims contains partially
exocyclic peptoid moieties. It is noteworthy that both types of
macrobicycles, i.e., cryptands and clams, were obtained by
incorporation of the same type of building blocks, e.g., steroidal,
aryl, and piperidine moieties, into the final macrobicyclic cores.
However, their dissimilar topologies arise from the different
principles applied to the same synthetic planning, i.e., the
cryptands by creating the bridgehead cores during the first MiB
and the clams by employing a previously functionalized
framework to which the two macrocyclic rings lay appended.
The example shown in Scheme 4c is remarkable considering
its potential toward metal ion or ion pair recognition. Macro-
bicycle 30 was synthesized from steroid 22 by a consecutive
diacid/diamine-diamine/diacid combination including the poly-
ether diamine 28 and diacid 1. This double polyether clam
structure comprises all its peptoid backbones partially exocyclic,
also containing four carboxylates suitably located for follow
up MiBssor metal ion binding. Compounds such as clam 30
and cryptand 13 perfectly show the potential of the sequential
MiB approach toward even more complex multicycles, as they
allow extending the sequential principle to further stages. This
prospect may lead to new generations of amide-based polycyclic
receptors due to the easy performance of the sequential MiBs
and the high accessibility of Ugi-type tri- and tetrafunctional
building blocks.
(16) (a) Klein, E.; Ferrand, Y.; Auty, E. K.; Davis, A. P. Chem. Commun.
2007, 2390, 2392. (b) Ferrand, Y.; Crump, M. P.; Davis, A. P. Science
2007, 318, 619–622.
(17) For a preliminary account on parts of the tetramacrocyclic work, see
ref 5a.
9
3728 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009

Synthesis of Topologically Diverse Macromulticycles
A R T I C L E S
subjected to deprotection and 3-fold Ugi-4CR-based macrocy-
clization to afford compound 40 in 29% overall yield, i.e., with
some 95% yield for each bond formed, including three mac-
rocyclizations.
In a more general way, we termed such a design (cf.
“blueprint”) and three-dimensional construction of covalent
molecular buildings like, e.g., the igloos, “architectural chem-
istry”. In architectural chemistry, the chemical building blocks
(cf. ”stones“, “prefab elements“) are covalently and usually
multiply connected by a limited reaction set orslike heresonly
one reliable reaction (“bolts“ or ”mortar”) that is repeatedly
applied to give the designed three-dimensional structure.
Through their covalent bonds such structures differ from
supramolecular assemblies or metal-organic-frameworks (MOFs).
Also they can be absolutely nonrepetitve and irregular with
respect to the building blocks, but nevertheless they have a
defined sequence/3D-arrangement and thus constitution, to some
extent comparable to (disulfide bridged) proteins that are
basically also covalently bound molecules, nonhomooligomeric
but linked by repetitve application of the same reaction(s), and
which eventually form 3D structures.
The macrotetracycles illustrate the potential of multiple MCRs
as a tool in architectural chemistry. The Ugi-MiBs allow
combining the various possibilities inherent to MCRs to generate
topological diversity by sequential processes of varied multiplic-
ity. The Ugi reaction is an easy, fast, and reliable rivet for the
rapid assembly of complex structures. A second requisite for
success is access to a set of structurally varied building blocks
with multiple functionalization sites (e.g., the steroidal diacids
31, 35, and 38). The combination of bi- or multifunctional
building blocks with an easy, efficient, and forgiving reaction
lays the foundation for a second round, then going into the third
dimension of structural diversity (i.e., topological).
Conclusions
Topologically diverse macromulticycles were produced by
some selected examples of the many possible combinations
allowed by the sequential use of multiple multicomponent
macrocyclizations. The examples shown involve two multiple
Ugi-4CR-based macrocyclizations that are performed according
to typical macrocyclization protocols. A mild, ideally quantita-
tive deprotection step is required before the second MiB is
performed. A very high level of structural complexity can be
reached due to the multicomponent nature of the two macro-
cyclization steps, which in addition allow the formation of
several bonds per single operation. Usually no purification of
intermediates is needed to achieve a good overall result. In
several cases, the whole reaction sequence can be performed in
one pot, but for new reactions the isolation of a crucial
intermediate is advised for control purposes.
The scope of this methodology to assemble further types of
large 3D structures, less or even more complex, in a combina-
torial, parallel, or designed way is immense. Compounds devised
from such molecular construction chemistry (“architectural
chemistry”, v.i.) can find applications in nanotechnology,
complex biological interactions that require multiple binding
domains,18 or as highly selective supramolecular receptors,
especially when considering: (i) the huge amount of readily
available building blocks that can be used and (ii) the fast and
efficient generation of structural diversity that is achieved in a
very short reaction sequence. The building blocks to be
incorporated into the final macromulticycles may have various
binding elements and shapes, rigidity, or functions that will
allow us to create topologically even better defined, more
diverse, or multifunctional molecules in the future. The now
possible (spatial) differentiation of several binding domains
(differential tethers, bridgeheads, or appendages) within one
molecule, as is available from a multiple MCR architectural
chemistry approach, can have a remarkable influence on the
specificity and selectivity of binding profiles, internally, e.g.,
for chiral guests, or externally for forming predefined supramo-
lecular networks. We believe that the approach presented here
opens new perspectives, not only for the synthesis and applica-
tions of macromulticycles which are well established in
coordination chemistry, molecular recognition, and catalysis but
also as a basis for the planned construction of very large but at
the same time unique molecular ensembles of a nonrepetitve
(nonsymmetrical) nature.
Experimental Section
General. Melting points are uncorrected. 1H NMR and 13C NMR
spectra were recorded at 399.94 and 100.57 MHz, respectively.
Chemical shifts (δ) are reported in ppm relative to the TMS (1H)
and to the solvent signal (13C). High-resolution ESI mass spectra
were obtained from a Fourier transform ion cyclotron resonance
(FT-ICR) mass spectrometer, an RF-only hexapole ion guide and
an external electrospray ion source. Flash column chromatography
was carried out using silica gel (0.015-0.040 µm), and analytical
thin layer chromatography (TLC) was performed using silica gel
aluminum sheets. All commercially available chemicals were used
without further purification. Diacid 6 was obtained from cholic acid
as described in ref 19. Diacids 14, 17, 31, 35, and 38 were obtained
as described in ref 4d. Diisocyanide 7 was obtained as described
in ref 4c, and diisocyanide 2 and triisocyanide 33 were obtained as
described in ref 5a. Azide 20 was prepared following the procedure
described in ref 15.
General Procedure A: Ugi-4CR-based macrocyclizations
of a diacid and a diisocyanide: A solution of the amine (1.0 mmol)
and paraformaldehyde (1.0 mmol) in MeOH (100 mL) was stirred
for 1 h at room temperature. Two solutions, one of the diacid (0.5
mmol) and another one of the diisocyanide (0.5 mmol), in 20 mL
of MeOH each were simultaneously and slowly added to the
reaction mixture using syringe pumps (flow rate 0.5 mL h-1). After
addition was completed, the reaction mixture was stirred for 8 h
and concentrated under reduced pressure to give a crude product,
which was redissolved in 100 mL of CHCl3. The organic phase
was washed sequentially with aqueous 10% HCl (2 × 50 mL),
aqueous 10% NaHCO3 (2 × 50 mL), and brine (50 mL) and then
dried over anhydrous Na2SO4 and concentrated under reduced
pressure.
General Procedure B: Ugi-4CR-based macrocyclizations of
a diacid and a diamine: A solution of the diamine (0.5 mmol)
and paraformaldehyde (1.0 mmol) in MeOH (150 mL) was stirred
for 1 h at room temperature. Two solutions, one of the diacid (0.5
mmol) and one of the isocyanide (1.0 mmol), in 20 mL of MeOH
each were simultaneously, but slowly, added to the reaction mixture
using syringe pumps (flow rate 0.5 mL h-1). After addition was
completed, the reaction mixture was stirred for 8 h and concentrated
under reduced pressure to give a crude product, which was
redissolved in 100 mL of CHCl3. The organic phase was washed
sequentially with aqueous 10% HCl (2 × 50 mL), aqueous 10%
NaHCO3 (2 × 50 mL), and brine (50 mL) and then dried over
anhydrous Na2SO4 and concentrated under reduced pressure.
(18) Driggers, E. M.; Hale, S. P.; Lee, J.; Terrett, N. K. Nat. ReV. 2008, 7,
(19) Batta, A. K.; Aggarwal, S. K.; Salen, G.; Shefer, S. J. Lipid Res. 1991,
32, 977–983.
608–624.
9
J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009 3729

A R T I C L E S
Rivera and Wessjohann
General Procedure C. Ugi-4CR-based macrocyclizations of
a diisocyanide and a diamine: A solution of the diamine (0.5
mmol) and paraformaldehyde (1.0 mmol) in MeOH (150 mL) was
stirred for 1 h at room temperature. The acid (1.0 mmol) was then
added and the stirring continued for 30 min. A solution of the
diisocyanide (0.5 mmol) in MeOH (20 mL) was slowly added to
the reaction mixture using a syringe pump (flow rate 0.5 mL h-1).
After addition was completed, the reaction mixture was stirred for
8 h and concentrated under reduced pressure to give a crude product,
which was redissolved in 100 mL of CHCl3. The organic phase
was washed sequentially with aqueous 10% HCl (2 × 50 mL),
aqueous 10% NaHCO3 (2 × 50 mL), and brine (50 mL) and then
dried over anhydrous Na2SO4 and concentrated under reduced
pressure.
128.5, 128.0, 127.8, 121.9, 121.3, 120.2, 119.8, 118.7, 118.1, 75.0,
72.3, 67.7, 66.5, 66.4, 57.2, 52.5, 52.3, 51.2, 46.3, 46.1, 42.6, 42.2,
41.6, 41.2, 39.4, 34.9, 34.6, 34.2, 31.2, 30.3, 29.0, 28.2, 27.0, 26.5,
26.2, 23.0, 22.5, 22.3, 21.2, 17.5, 14.7, 12.8. HRMS (ESI-FT-ICR)
m/z: 1211.6369 [M + Na]+; calcd. for C65H88NaO13N8: 1211.6368.
Cryptand 13: Diamine 10 (100 mg, 0.5 mmol), diisocyanide 7
(110 mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0 mmol), and
Nε-Cbz-NR-Boc-L-lysine (380 mg, 1.0 mmol) were reacted according
to macrocyclization procedure C to give the macrocycle 11
(identified by ESI-MS). The resulting product was dissolved in dry
EtOH (90 mL), and 10% Pd(C) (250 mg) was added. The mixture
was treated successively with hydrogen and vacuum and finally
stirred under a hydrogen atmosphere for 48 h. The catalyst was
removed by filtration, and the resulting solution was evaporated
under reduced pressure. The resulting crude diamine, diacid 12 (84
mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0 mmol), and tert-
butylisocyanide (0.115 mL, 1.0 mmol) were reacted according to
macrocyclization procedure B. Flash column chromatography
purification (CH2Cl2/MeOH/Et3N 20:1:0.2) afforded cryptand 13
(200 mg, 31% from 10) as a pale yellow solid. Rf ) 0.64 (CH2Cl2/
MeOH/Et3N 10:1:0.1). mp (from MeOH): 221-222 °C. IR (KBr,
cm-1): 3317, 3064, 3032, 2935, 2870, 1703, 1697, 1693, 1633,
1497, 1248, 1211, 1168. 1H NMR (CDCl3): δ ) 9.76 (s, 1H, NH);
8.58 (s, 1H, NH); 7.66 (d, 2H, J ) 8.6 Hz, Ar); 7.57 (d, 2H, J )
8.4 Hz, Ar); 7.48 (d, 2H, J ) 7.4 Hz, Ar); 7.29 (t, 1H, J ) 7.7 Hz,
Ar); 6.94 (d, 2H, J ) 8.8 Hz, Ar); 6.87 (d, 2H, J ) 8.8 Hz, Ar);
5.48 (s, 1H, NH); 5.29 (s, 1H, NH); 4.95-4.89 (m, 2H); 4.60-4.56
(m, 2H); 4.43-4.38 (m, 4H); 4.27-4.24 (m, 2H); 1.43 (s, 9H,
(CH3)3C); 1.41 (s, 9H, (CH3)3C); 1.37 (s, 9H, (CH3)3C); 1.35 (s,
9H, (CH3)3C). 13C NMR (CDCl3): δ ) 173.8, 172.9, 172.6, 168.3,
168.0, 166.9, 156.3, 153.3, 153.1, 133.9, 134.7, 132.9, 130.5, 122.3,
121.7, 120.5, 120.1, 80.5, 80.3, 55.6, 55.4, 53.6, 52.2, 51.5, 50.6,
50.6, 40.0, 31.8, 29.6, 28.9, 28.5, 28.4, 28.2, 28.0, 22.6, 14.2. HRMS
(ESI-FT-ICR) m/z: 1294.7561 [M + H]+; calcd. for C67H100O13N13:
1294.7568.
Macrobicycle 25: Steroidal diacid 16 (324 mg, 0.5 mmol),
diisocyanide 23 (109 mg, 0.5 mmol), paraformaldehyde (30 mg,
1.0 mmol), and iso-propylamine (0.085 mL, 1.0 mmol) were reacted
according to macrocyclization procedure A to give the macrocycle
24 (identified by ESI-MS). The crude product was dissolved in THF/
H2O (2:1, 100 mL), and LiOH (210 mg, 5.0 mmol) was added at
0 °C. The mixture was stirred at 0 °C for 6 h and then acidified
with aq. 10% NaHSO4 to pH 3. The resulting phases were separated,
and the aqueous phase was additionally extracted with EtOAc (2
× 100 mL). The combined organic phases were dried over
anhydrous Na2SO4 and concentrated under reduced pressure. The
resulting crude diacid, diisocyanide 7 (110 mg, 0.5 mmol),
paraformaldehyde (30 mg, 1.0 mmol), and iso-propylamine (0.085
mL, 1.0 mmol) were reacted according to macrocyclization
procedure A. Flash column chromatography purification (CH2Cl2/
MeOH 20:1) afforded the macrobicycle 25 (202 mg, 30% from
16). Rf ) 0.47 (CH2Cl2/MeOH 10:1). mp (from MeOH): 286-288
°C. IR (KBr, cm-1): 3126, 3064, 2974, 1711, 1702, 1698, 1677,
1665, 1633, 1511, 1498, 1208. 1H NMR (CDCl3): δ ) 9.40 (br. s,
1H, NH); 9.25 (br. s, 1H, NH); 8.98 (br. s, 1H, NH); 8.86 (m, 1H,
NH); 7.54-7.50 (m, 4H, Ar); 7.35-7.31 (m, 4H, Ar); 7.10 (m,
4H, Ar); 6.86-6.78 (m, 4H, Ar); 4.91 (m, 2H); 4.87 (m, 2H); 4.69
(m, 2H); 4.64 (m, 2H); 4.55-4.51 (m, 4H); 4.38-4.33 (m, 4H);
4.02-3.89 (m, 4H); 1.30-1.25 (m, 24H); 1.13 (s, 3H, H-19); 0.93
(s, 3H, H-18); 0.89 (d, 3H, J ) 5.9 Hz, H-21). 13C NMR (CDCl3):
δ ) 176.5, 171.2, 169.3, 168.6, 168.0, 167.9, 159.2, 156.2, 155.5,
138.4, 135.7, 134.9, 134.4, 129.4, 129.0, 128.6, 121.1, 120.3, 121.1,
119.3, 72.0, 70.4, 69.6, 55.3, 50.6, 49.8, 47.9, 46.9, 46.7, 45.6, 42.2,
42.0, 40.8, 38.9, 36.7, 36.2, 33.4, 33.3, 32.8, 28.4, 27.9, 25.9, 22.5,
21.5, 21.2, 20.9, 20.4, 18.6, 12.0. HRMS (ESI-FT-ICR) m/z:
1344.7373 [M + H]+; calcd. for C75H98N11O12: 1344.7390.
Macrobicycle 27: Steroidal diacid 19 (324 mg, 0.5 mmol),
diisocyanide 7 (110 mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0
mmol), and iso-propylamine (0.085 mL, 1.0 mmol) were reacted
Cryptand 5: Diacid 1 (111 mg, 0.5 mmol), diisocyanide 2 (78
mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0 mmol), glycine tert-
butyl ester hydrochloride (167 mg, 1.0 mmol), and Et3N (0.14 mL,
1.0 mmol) were reacted according to macrocyclization procedure
A to give the macrocycle 3 (identified by ESI-MS). The crude
product was dissolved in dry CH2Cl2 (20 mL) followed by
trifluoroacetic acid (TFA, 10 mL) at 0 °C. The reaction mixture
was stirred at room temperature for 4 h, and the volatiles were
evaporated under reduced pressure. TFA was removed completely
by repetitive addition and evaporation of further CH2Cl2. The
resulting crude diacid, diisocyanide 4 (110 mg, 0.5 mmol),
paraformaldehyde (30 mg, 1.0 mmol), and iso-propylamine (0.085
mL, 1.0 mmol) were reacted according to macrocyclization
procedure A. Flash column chromatography purification (CH2Cl2/
MeOH 10:1) afforded cryptand 5 (167 mg, 36% from 1) as a white
solid. Rf ) 0.43 (CH2Cl2/MeOH/Et3N 5:1:0.1). mp (from EtOAc):
176-178 °C. IR (KBr): 3336, 2976, 2930, 1698, 1692, 1679, 1653,
1
1540, 1249, 1166. H NMR (CD3OD): δ ) 7.39 (d, 1H, J ) 8.0
Hz, Ar); 7.32-7.27 (m, 2H, Ar); 7.24 (d, 1H, J ) 8.1 Hz, Ar);
4.50-4.44 (m, 4H); 4.42 (m, 4H); 4.33-4.26 (m, 4H); 4.21-4.19
(m, 4H); 4.15-4.10 (m, 4H); 4.08 (m, 1H); 4.03 (m, 1H);
3.91-3.82 (m, 4H); 3.72-3.65 (m, 4H); 3.60-3.48 (m, 8H);
3.24-3.19 (m, 4H); 4.50-4.44 (m, 4H); 3.07-2.99 (m, 4H);
1.94-1.83 (m, 4H); 1.27 (d, 6H, J ) 6.1 Hz); 1.26 (d, 6H, J ) 6.2
Hz). 13C NMR (CD3OD): δ ) 174.4, 174.2, 173.3, 172.0, 171.7,
171.4, 170.5, 169.5, 139.2, 138.5, 129.2, 128.8, 127.9, 127.8, 72.2,
71.9, 71.6, 71.3, 70.6, 70.5, 70.3, 69.6, 69.3, 55.9, 55.5, 55.2, 54.7,
54.0, 52.5, 52.1, 51.8, 50.5, 45.8, 43.8, 43.3, 43.1, 37.1, 36.6, 25.9,
25.7, 25.6, 21.0, 20.9, 20.8. HRMS (ESI-FT-ICR) m/z: 915.5307
[M + H]+; calcd. for C44H71O11N10: 915.5298.
Cryptand 9: Steroidal diacid 6 (254 mg, 0.5 mmol), diisocyanide
7 (110 mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0 mmol), and
mono-Cbz-ethylenediamine (97 mg, 1.0 mmol) were reacted
according to macrocyclization procedure A to give the macrocycle
8 (identified by ESI-MS). The resulting product was dissolved in
dry EtOH (100 mL), and 10% Pd(C) (200 mg) was added. The
reaction mixture was treated successively with hydrogen and
vacuum and finally stirred under hydrogen atmosphere for 48 h.
The catalyst was removed by filtration, and the resulting solution
was evaporated under reduced pressure. The resulting crude
diamine, diisocyanide 2 (78 mg, 0.5 mmol), paraformaldehyde (30
mg, 1.0 mmol), and acetic acid (0.055 mL, 1.0 mmol) were reacted
according to macrocyclization procedure C. Flash column chro-
matography purification (CH2Cl2/MeOH 18:1) afforded cryptand
9 (160 mg, 27% from 6) as a white solid. Rf ) 0.56 (CH2Cl2/MeOH
10:1). mp (from CH2Cl2/n-hexane): 247-250 °C. IR (KBr, cm-1):
3521, 3334, 3087, 3064, 2924, 1728, 1716, 1698, 1684, 1666, 1641,
1506, 1251, 1206, 1168, 1157. 1H NMR (CDCl3): δ ) 9.72 (br. s,
1H, NH); 9.47 (br. s, 1H, NH); 7.52 (d, 2H, J ) 8.4 Hz, Ar); 7.44
(d, 2H, J ) 8.4 Hz, Ar); 7.19 (m, 4H, Ar); 6.88 (m, 4H, Ar); 6.69
(m, 1H, NH); 6.48 (m, 1H, NH); 4.52 (m, 1H); 4.37 (d, 4H, J )
6.6 Hz); 4.19-4.12 (m, 8H); 3.83 (m, 1H); 3.75 (m, 1H); 2.02 (s,
6H); 1.17 (s, 3H, H-19); 1.02 (d, 3H, J ) 6.4 Hz, H-21); 0.85 (s,
3H, H-18). 13C NMR (CDCl3): δ ) 174.9, 172.0, 171.4, 170.3,
169.7, 167.1, 166.8, 154.5, 153.8, 137.5, 136.4, 133.2, 132.8, 128.7,
9
3730 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009

Synthesis of Topologically Diverse Macromulticycles
A R T I C L E S
according to macrocyclization procedure A to give the macrocycle
26 (identified by ESI-MS). The crude product was dissolved in THF/
H2O (2:1, 100 mL), and LiOH (210 mg, 5.0 mmol) was added at
0 °C. The reaction mixture was stirred at 0 °C for 6 h and then
acidified with aq. 10% NaHSO4 to pH 3. The layers were separated,
and the aqueous phase was additionally extracted with EtOAc (2
× 100 mL). The combined organic phases were dried over
anhydrous Na2SO4 and concentrated under reduced pressure. The
resulting crude diacid, diamine 10 (100 mg, 0.5 mmol), paraform-
aldehyde (30 mg, 1.0 mmol), and tert-butylisocyanide (0.115 mL,
1.0 mmol) were reacted according to macrocyclization procedure
B. Flash column chromatography purification (CH2Cl2/MeOH 15:
1) afforded the macrobicycle 27 (178 mg, 26% from 19). Rf )
0.35 (CH2Cl2/MeOH 5:1). mp (from EtOAc/CH2Cl2): 232-233 °C.
IR (KBr, cm-1): 3434, 3337, 2938, 2872, 1738, 1733, 1696, 1684,
1675, 1653, 1540. 1H NMR (CDCl3): δ ) 7.45 (m, 1H, NH); 7.42
(d, 2H, J ) 8.8 Hz, Ar); 7.38 (d, 2H, J ) 8.4 Hz, Ar); 6.92 (m,
1H, NH); 6.85 (d, 2H, J ) 9.2 Hz, Ar); 6.81 (d, 2H, J ) 8.8 Hz,
Ar); 6.62 (s, 1H, NH); 6.19 (s, 1H, NH); 4.88-4.82 (m, 4H); 4.61
(m, 2H); 4.42 (m, 2H); 4.30-4.21 (m, 4H); 4.02 (m, 2H);
3.64-3.59 (m, 2H); 3.53-3.49 (m, 2H); 3.37-3.33 (m, 2H); 1.31
(s, 18H, 2 × (CH3)3C); 1.28-1.26 (m, 12H, 2 × (CH3)2CH); 0.98
(d, 3H, J ) 6.6 Hz, H-21); 0.91 (s, 3H, H-19); 0.77 (s, 3H, H-18).
13C NMR (CDCl3): δ ) 174.8, 172.2, 171.0, 170.4, 168.9, 168.4,
168.1, 167.8, 166.0, 163.0, 162.8, 155.0, 154.2, 133.6, 133.4, 121.2,
120.5, 119.6, 119.3, 72.6, 71.1, 67.8, 56.7, 54.4, 53.3, 53.9, 52.0,
51.7, 51.5, 50.7, 46.6, 42.6, 41.5, 40.6, 40.0, 35.5, 34.3, 33.6, 32.0,
31.6, 30.1, 28.5, 27.8, 27.4, 26.7, 26.4, 26.1, 24.3, 24.0, 23.4, 23.1,
22.0, 20.9, 20.7, 20.6, 18.7, 12.0. HRMS (ESI-FT-ICR) m/z:
1374.8557 [M + H]+; calcd. for C74H112N13O12: 1374.8553.
Macrobicycle 30: Steroidal diacid 22 (340 mg, 0.5 mmol),
diamine 28 (74 mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0
mmol), and methyl isocyanoacetate (0.12 mL, 1.0 mmol) were
reacted according to macrocyclization procedure B to give the
macrocycle 29 (identified by ESI-MS). The crude product was
dissolved in dry CH2Cl2 (20 mL), and trifluoroacetic acid (TFA,
12 mL) was added to the solution at 0 °C. The reaction mixture
was stirred at 0 °C for 1 h and at room temperature for 4 h. The
solvent was evaporated under reduced pressure and the TFA
removed by addition and evaporation of further CH2Cl2. The
resulting trifluoroacetate salt was dissolved in CH2Cl2 (200 mL)
and washed with sat. aq. NaHCO3 (3 × 60 mL). The organic layer
was examined for the absence of TFA by ESI-MS and then dried
over anh. Na2SO4 and concentrated under reduced pressure. The
resulting crude diamine, diacid 1 (111 mg, 0.5 mmol), paraform-
aldehyde (30 mg, 1.0 mmol), and methyl isocyanoacetate (0.12 mL,
1.0 mmol) were reacted according to macrocyclization procedure
B. Flash column chromatography purification (CH2Cl2/MeOH 20:
1) afforded the macrobicycle 30 (185 mg, 28% from 22). Rf )
0.29 (CH2Cl2/MeOH 10:1). mp (from CH2Cl2): 183-185 °C. IR
(KBr, cm-1): 3427, 3345, 2946, 1734, 1730, 1707, 1703, 1692,
was dissolved in THF/H2O (2:1, 60 mL), and LiOH (158 mg, 2.5
mmol) was added at 0 °C. The mixture was stirred at 0 °C for 6 h
and then acidified with aq. 10% NaHSO4 to pH 3. The resulting
phases were separated, and the aqueous phase was additionally
extracted with EtOAc (2 × 80 mL). The combined organic phases
were dried over anhydrous Na2SO4 and concentrated under reduced
pressure. The resulting crude triacid, triisocyanide 33 (88 mg, 0.5
mmol), paraformaldehyde (45 mg, 1.5 mmol), and iso-propylamine
(0.125 mL, 1.5 mmol) were reacted according to macrocyclization
procedure A. Flash column chromatography purification (CH2Cl2/
MeOH 20:1) afforded 34 (169 mg, 26% from 31) as a light yellow
solid. Rf ) 0.54 (CH2Cl2/MeOH 10:1). mp (from EtOAc): 213-217
1
°C. H NMR (CDCl3): δ ) 7.35-7.32 (m, 4H, Ar); 6.32 (m, 1H,
NH); 6.28 (m, 1H, NH); 5.72 (m, 1H, NH); 5.69 (m, 1H, NH);
4.64 (m, 2H); 4.61 (m, 2H); 4.30-4.02 (m, 14H); 3.54 (m, 1H);
1.24-1.16 (m, 18H, 2 × (CH3)2CH); 1.13 (s, 3H, H-19); 0.92 (s,
3H, H-18); 0.91 (d, 3H, J ) 6.6 Hz, H-21). 13C NMR (CDCl3): δ
) 171.9, 171.3, 170.8, 170.4, 169.8, 166.2, 161.6, 156.1, 136.5,
128.5, 128.3, 71.5, 70.9, 70.8, 54.8, 54.6, 54.4, 53.9, 50.6, 47.3,
45.4, 43.4, 43.1, 42.5, 42.3, 40.8, 40.6, 37.5, 37.4, 37.1, 35.4, 32.6,
31.9, 30.7, 29.6, 28.8, 26.2, 22.1, 22.0, 19.8, 16.1, 12.6. HRMS
(ESI-FT-ICR) m/z: 1298.7839 [M + H]+; calcd. for C67H104O13N13
1298.7837.
Macrotetracycle 37: Diacid 35 (283 mg, 0.5 mmol), diisocya-
nide 7 (110 mg, 0.5 mmol), paraformaldehyde (30 mg, 1 mmol),
L-alanine methyl ester hydrochloride (139 mg, 1 mmol), and Et3N
(0.14 mL, 2 mmol) were reacted according to macrocyclization
procedure A. The resulting macrocycle 36 (identified by ESI-MS)
was dissolved in THF/H2O (2:1, 60 mL), and LiOH (158 mg, 2.5
mmol) was added at 0 °C. The mixture was stirred at 0 °C for 6 h
and then acidified with aq. 10% NaHSO4 to pH 3. The resulting
phases were separated, and the aqueous phase was additionally
extracted with EtOAc (2 × 80 mL). The combined organic phases
were dried over anhydrous Na2SO4 and concentrated under reduced
pressure. The resulting crude triacid, triisocyanide 33 (88 mg, 0.5
mmol), paraformaldehyde (45 mg, 1.5 mmol), and iso-propylamine
(0.125 mL, 1.5 mmol) were reacted according to macrocyclization
procedure A. Flash column chromatography purification (CH2Cl2/
MeOH 22:1) afforded 37 (149 mg, 22% from 35) as a pale yellow
solid. Rf ) 0.48 (CH2Cl2/MeOH 10:1). mp (from MeOH): 241-244
°C. 1H NMR (CDCl3): δ ) 8.65 (m, 1H, NH); 8.61 (m, 1H, NH);
7.42 (d, 2H, J ) 8.8 Hz, Ar); 7.38 (d, 2H, J ) 8.4 Hz, Ar); 7.04
(m, 1H, NH); 6.85 (d, 2H, J ) 9.2 Hz, Ar); 6.81 (d, 2H, J ) 8.8
Hz, Ar); 6.56 (m, 1H, NH); 6.49 (m, 1H, NH); 1.26-1.18 (m, 18H,
3 × (CH3)2CH); 1.12 (d, 3H, J ) 6.4 Hz, H-21); 1.02 (s, 3H, H-19);
0.92 (s, 3H, H-18). 13C NMR (CDCl3): δ ) 171.9, 171.0, 170.4,
169.8, 168.7, 168.1, 167.8, 166.1, 165.2, 162.8, 155.1, 154.0, 133.5,
133.3, 121.1, 120.8, 119.8, 119.2, 72.6, 71.1, 67.8, 55.0, 54.9, 54.6,
54.3, 52.8, 52.5, 52.1, 51.2, 50.5, 49.6, 49.1, 48.7, 47.5, 45.8, 44.4,
44.0, 42.1, 39.1, 37.0, 35.6, 34.2, 33.8, 31.6, 30.5, 29.2, 27.4, 26.9,
23.4, 22.1, 21.8, 21.7, 21.4, 20.9, 20.6, 20.4, 19.2, 12.3. HRMS
(ESI-FT-ICR) m/z: 1362.7819 [M + H]+; calcd. for C71H104O16N13
1362.7813.
1
1678, 1232, 1205, 1191, 1176. H NMR (CDCl3): δ ) 6.55 (s,
1H, NH); 6.42 (s, 1H, NH); 6.24 (s, 1H, NH); 6.12 (s, 1H, NH);
4.50 (m, 2H); 4.37 (m, 2H); 4.28 (m, 2H); 4.13 (m, 2H); 3.99 (m,
1H); 3.90-3.82 (m, 4H); 3.72 (s, 3H, CH3O); 3.70 (s, 3H, CH3O);
3.66 (s, 6H, CH3O); 3.56 (br. m, 1H); 3.46-3.37 (m, 4H); 3.29
(m, 4H); 3.15 (m, 2H); 3.08 (m, 2H); 1.15 (s, 3H, H-19); 1.03 (d,
3H, J ) 5.8 Hz, H-21); 0.92 (s, 3H, H-18). 13C NMR (CDCl3): δ
) 174.5, 173.2, 172.1, 168.4, 166.7, 166.0, 165.8, 74.2, 72.5, 70.1,
69.7, 68.4, 63.2, 62.9, 60.7, 59.5, 57.4, 56.8, 53.1, 51.8, 50.7, 49.1,
47.8, 46.2, 44.0, 42.9, 42.7, 40.9, 40.7, 40.3, 37.1, 36.4, 35.8, 35.3,
32.0, 31.6, 28.7, 26.9, 26.3, 24.4, 22.1, 21.3, 20.1, 18.8, 18.7, 12.1.
HRMS (ESI-FT-ICR) m/z: 1314.6332 [M + H]+; calcd. for
C60H93NaN9O22: 1314.6338.
Macrotetracycle 34: Diacid 31 (283 mg, 0.5 mmol), diisocya-
nide 2 (78 mg, 0.5 mmol), paraformaldehyde (30 mg, 1 mmol),
L-alanine methyl ester hydrochloride (139 mg, 1 mmol), and Et3N
(0.14 mL, 1 mmol) were reacted according to macrocyclization
procedure A. The resulting macrocycle 32 (identified by ESI-MS)
Macrotetracycle 40: Diacid 38 (283 mg, 0.5 mmol), diamine
28 (74 mg, 0.5 mmol), paraformaldehyde (30 mg, 1.0 mmol), and
methyl isocyanoacetate (0.12 mL, 1.0 mmol) were reacted according
to macrocyclization procedure B. The resulting macrocycle 39
(identified by ESI-MS) was dissolved in THF/H2O (2:1, 50 mL),
and LiOH (158 mg, 2.5 mmol) was added at 0 °C. The mixture
was stirred at 0 °C for 6 h and then acidified with aq. 10% NaHSO4
to pH 3. The resulting phases were separated, and the aqueous phase
was additionally extracted with EtOAc (2 × 80 mL). The combined
organic phases were dried over anhydrous Na2SO4 and concentrated
under reduced pressure. The resulting crude triacid, triisocyanide
33 (88 mg, 0.5 mmol), paraformaldehyde (45 mg, 1.5 mmol), and
iso-propylamine (0.125 mL, 1.5 mmol) were reacted according to
macrocyclization procedure A. Flash column chromatography
purification (CH2Cl2/MeOH 18:1) afforded 40 (186 mg, 29% from
38) as a pale yellow solid. Rf ) 0.23 (CH2Cl2/MeOH 10:1). mp
(from EtOAc): 217-219 °C. 1H NMR (CDCl3): δ ) 7.68 (m, 1H,
9
J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009 3731

A R T I C L E S
Rivera and Wessjohann
NH); 7.14 (m, 1H, NH); 6.53 (m, 1H, NH); 5.01-4.91 (m, 2H);
4.84-4.76 (m, 2H); 4.71-4.64 (m, 2H); 4.61-4.53 (m, 2H);
4.32-4.25 (m, 2H); 4.22-3.98 (m, 8H); 3.98 (m, 1H); 3.62-3.56
(m, 4H); 1.29-1.24 (m, 12H, 2 × (CH3)2CH); 1.22 (m, 6H, 2 ×
(CH3)2CH); 1.13 (s, 3H, H-19); 1.07 (d, 3H, J ) 6.1 Hz, H-21);
0.91 (s, 3H, H-18). 13C NMR (CDCl3): δ ) 171.5, 171.2, 170.3,
170.8, 170.4, 170.3, 169.8, 168.6, 168.4, 167.7, 166.3, 165.7, 70.6,
70.3, 68.8, 61.5, 59.9, 54.6, 52.8, 52.3, 51.9, 51.1, 50.9, 50.7, 49.8,
48.7, 48.5, 48.4, 45.6, 44.3, 44.1, 43.9, 42.1, 41.9, 41.7, 40.8, 40.3,
40.1, 39.7, 39.2, 38.1, 42.1, 37.0, 36.2, 36.1, 35.7, 35.6, 34.9, 34.6,
34.5, 33.7, 31.3, 30.6, 30.5, 29.8, 28.7, 28.1, 27.6, 25.6, 25.2, 22.7,
22.4, 21.8, 21.7, 21.6, 21.4, 20.9, 20.8, 20.6, 18.1. HRMS (ESI-
FT-ICR) m/z: 1304.7597 [M + Na]+; calcd. for C63H103O15N13Na
1304.7594.
Acknowledgment. We are grateful to Dr. Andrea Porzel and
Dr. Ju¨rgen Schmidt for NMR and HRMS (ESI-FT-ICR) measure-
ments, respectively. We gratefully acknowledge financial support
by the Deutsche Forschungsgemeinschaft (Grant programs: GRK-
894) and Land Sachsen-Anhalt (HWP).
Supporting Information Available: Experimental procedures
for the preparation of building blocks. NMR and HRMS spectra
of final compounds and intermediates. This material is available
free of charge via the Internet at http://pubs.acs.org.
JA809005K
9
3732 J. AM. CHEM. SOC. VOL. 131, NO. 10, 2009