Application of the 'direct amide cyclization' to peptides containing an anthranilic acid residue

Article abstract of DOI:10.1002/hlca.200590135

The 2,2-disubstituted 2H-azirin-3-amines 7a-7c were used as amino acid synthons to prepare linear peptides derived from anthranilic acid. These linear peptides, which contain α,α-disubstituted α-amino acids, were synthesized by using the 'azirine/oxazolon

Full text of DOI:10.1002/hlca.200590135

Helvetica Chimica Acta Vol. 88 (2005)
1711
Application of the −Direct Amide Cyclization× to Peptides Containing an
Anthranilic Acid Residue
by Irena Philipova1), Anthony Linden, and Heinz Heimgartner*
Organisch-chemisches Institut der Universit‰t Z¸rich, Winterthurerstrasse 190, CH-8057 Z¸rich
Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthday
The 2,2-disubstituted 2H-azirin-3-amines 7a 7c were used as amino acid synthons to prepare linear
peptides derived from anthranilic acid. These linear peptides, which contain a,a-disubstituted a-amino acids,
were synthesized by using the −azirine/oxazolone method× (Schemes 2 5) and were subjected to the acid-
catalyzed −direct amide cyclization×. Unfortunately, all attempts to isolate the ten-membered cyclotripeptides, by
starting with different precursors, failed. Instead of the expected cyclotripeptides, the corresponding 1,3a,7-
triazabenz[e]azulene-3,6-diones 12 and 17 (Schemes 2 and 3) were obtained in up to 44% yield. Most likely,
these products were formed by a transannular ring contraction of the desired products, followed by dehydration.
In the case of the linear precursor 24, the 20-membered cyclodimer 25 was formed in 50% yield, together with
traces of the 1,3a,7-triazabenz[e]azulene-3,6-dione 27 and the completely unexpected quinazolinone 26
(Scheme 5). In the cases of the linear precursors 30 and 34, no ring closure was observed under the conditions of
the −direct amide cyclization×, which indicates the limitations of this method.
Introduction. Non-proteinogenic amino acids and their peptides are of significant
interest with respect to their biological activity. For example, a,a-disubstituted a-amino
acids considerably restrict the conformational freedom of peptides because of the
presence of the tetrasubstituted C(a)-atom. Therefore, the incorporation of one or
several a,a-disubstituted a-amino acids is a common method for introducing rigidity
into the peptide backbone. One procedure for the introduction of such amino acids into
peptides is the so-called −azirine/oxazolone method×, in which 2,2-disubstituted 2H-
azirin-3-amines are used as amino acid synthons [1]. This strategy has been employed
widely in the synthesis of linear oligopeptides [2 9], peptaibols [10 13], and
endothiopeptides [14][15]. A further application is the synthesis of conformationally
restricted cyclic depsipeptides [16 20] and cyclic peptides [17][21 24] by using a
combination of the −azirine/oxazolone method× and the so-called −direct amide
cyclization×. The concept of this cyclization method is outlined in Scheme 1:
condensation of a carboxylic acid, bearing a nucleophilic group, with a 2H-azirin-3-
amine 1 leads to the corresponding diamide of type 2, which, on treatment with dry HCl
gas, affords the corresponding 1,3-oxazol-5(4H)-one 3. Under the acidic conditions, this
intermediate can be attacked by an external nucleophile to produce 4 via ring opening.
In the absence of an external nucleophile, suitable substrates are able to undergo an
intramolecular nucleophilic attack and yield the ring-enlarged product of type 5 [17].
1
)
Postdoctoral stay at the University of Z¸rich, 2000 2002; present address: Institute of Organic Chemistry,
Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 9, 1113 Sofia, Bulgaria.
¹ 2005 Verlag Helvetica Chimica Acta AG, Z¸rich

1712
Helvetica Chimica Acta Vol. 88 (2005)
Scheme 1
Natural cyclic peptides have been studied extensively in recent years, and the
synthesis of cyclopeptide analogues continues to be of great interest [25][26].
Stabilization of specific backbone conformations in such peptides by the incorporation
of fragments with restricted molecular freedom has become a focus of increasing
attention [27]. Conformationally restricted structures can be obtained by using
nonpeptidal fragments of low conformational flexibility [28]. For example, the
presence of an ortho-aminobenzoyl (anthraniloyl) moiety should decrease the
molecular flexibility as a result of the rigid aromatic skeleton. A few examples of
cyclic peptides with an anthranilic acid (Ant) residue are known [29][30]. Two such
peptides, which contain 5-methylanthranilic acid (MeAnt), i.e., cyclo(Phe-MeAnt-
Glyn) (n ˆ 4 and 6, resp.) have been synthesized to study their hydrolysis with a-
chymotrypsin [30]. With the aim of investigating the influence of the nonpeptidal
amino acids, two cyclic peptides, cyclo(Ant-Gly)2 and cyclo(Ant-Gly)3, have been
prepared [29]. The synthesis and conformation of ten-membered cyclotripeptides
containing a b-amino acid have also been studied extensively [31 35]. They have been
obtained by incorporating the b-amino acid residue into a diketopiperazine via ring
enlargement [35][36] or by cyclization of the linear precursor via the −active ester
method× [31][34][37]. b-Alanine and anthranilic acid derivatives have been used as the
N-terminal residue, since they represent two extreme cases of high and low conforma-
tional flexibility. Natural peptides containing an anthranilic acid, the so-called
−cycloaspeptides×, are very rare, although some, such as actinomycin D from
Streptomyces sp. [38], viridic acid from Penicillium viridicatum [39], and cyclo-
aspeptides A C from the fungus Aspergillus sp. NE-45 [40] were reported some years
ago. Two new linear peptides with a C-terminal anthranilic acid residue, dictyonamides
A and B, have been isolated from a marine-derived fungus recently [41].
As part of our continuing investigation of the synthesis and the conformation of
cyclic peptides and depsipeptides with conformationally restricted amino or hydroxy
acids [19 24], we started to examine such peptides containing anthranilic acid and its
derivatives [18][42]. As the combination of the −azirine/oxazolone method× with the
−direct amide cyclization× proved to be an excellent preparative route to cyclic

Helvetica Chimica Acta Vol. 88 (2005)
1713
depsipeptides and peptides, these methods should be used for the synthesis of
analogues of −cycloaspeptides×. Here, we present the results concerning the −direct
amide cyclization× of linear peptide precursors containing a N-terminal anthranilic acid.
Results and Discussion. The linear peptide precursors were designed with 2-
aminobenzoic acid (anthranilic acid, Ant) as the N-terminus of the chain. The peptides
were prepared via the so-called −azirine/oxazolone method× [1] by using the 2H-azirin-
3-amines 7a c. In contrast to the classical methods for the synthesis of peptides
containing a,a-disubstituted a-amino acids [43][44], the −azirine/oxazolone method×
does not require additional reagents, and the coupling reaction is performed under mild
conditions, where no side-products are formed. This simplifies the purification of the
products considerably.
The linear tripeptide 11 was prepared straightforwardly by the standard procedure
according to Scheme 2. The reaction of Z-protected anthranilic acid (6) [18] with 7a in
dry MeCN at room temperature led to the corresponding diamide 8 in 87% yield. The
selective hydrolysis of the C-terminal amide group was performed under standard
conditions with 3n HCl/THF 1:1 at room temperature [3] and yielded the
corresponding carboxylic acid 9 in nearly quantitative yield. The latter compound
was coupled with another unit of 7a to give the N-protected tripeptide 10 in 74% yield.
Deprotection of the amino group by hydrogenolysis (Pd/C in MeOH) led to compound
11, which was subjected to the reaction conditions of the −direct amide cyclization×: a
weak stream of dry HCl gas was bubbled through a suspension of the linear peptide 11
in toluene at 1008. Toluene was chosen as the solvent because of the low solubility of 11,
which assured a low concentration of the oxazolone intermediate 3 formed in the
course of the reaction (Scheme 1). This high dilution of the reactive intermediate
provides the optimum condition for the intramolecular ring closure, i.e., the formation
of the cyclic monomer is favored over the formation of oligomers [19]. The reaction of
11 with dry HCl gas was complete within 10 min and provided the heterobicyclic
compound 12, but not the desired 10-membered cyclopeptide A (Scheme 2). After
chromatographic purification, 12 was isolated in 44% yield. Its formation obviously
proceeds via the desired A as an intermediate, followed by a transannular ring
contraction and the elimination of H2O. Analogous transannular cyclizations of
anthranilic acid derivatives have been observed previously [18][31][43]. The formation
of 12 confirms the tendency of peptides, which contain the rigid anthranilic acid
residue, to undergo transannular reactions. In the ten-membered rings, this contraction
is favored due to the flattening effect of the fused benzene ring. Compound 12 was
isolated as a colorless solid and its structure was established by NMR, IR, and mass
spectra, and, finally, single crystals of 12 were grown successfully from CH2Cl2/Et2O,
and its structure was established by X-ray crystallography (Fig. 1).
The NH group of molecule 12 forms an intermolecular H-bond with the amide
O(3)-atom of a neighboring molecule. This interaction links the molecules into dimeric
units, which are situated about a center of inversion and have a graph-set motif [46] of
R22(8).
With the aim of exploiting a different pathway for the preparation of the ten-
membered cyclopeptide A, we synthesized the tripeptide ester 13 by treatment of 10
with BBr3 in CH2Cl2 and addition of MeOH [47] (Scheme 2). Then, 13 was heated in

1714
Helvetica Chimica Acta Vol. 88 (2005)
Scheme 2
toluene according to the cyclization conditions reported by Aguilar and Meyers [48],
but even after heating the solution under reflux for 2 days, only the starting material
was recovered.
As a second example, we prepared the linear tripeptide 16 as a precursor of a ten-
membered cyclic peptide containing the a,a-disubstituted a-amino acid 1-amino-
cyclopentane carboxylic acid (cPent) and glycine (Scheme 3). The presence of the
latter should increase the flexibility of the peptide chain. The coupling of 6 with
commercially available methyl glycinate hydrochloride was performed by using the
coupling reagent O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluorobo-
rate (TBTU) in MeCN in the presence of 1-hydroxybenzotriazole (HOBt) and EtN(i-
Pr)2. After chromatographic workup, the dipeptide 14 was obtained in 88% yield. The
deprotection of both the carboxy and amino group in a one-pot reaction was carried out

Helvetica Chimica Acta Vol. 88 (2005)
1715
Fig. 1. ORTEP Plot [45] of the molecular structure of 12 (arbitrary numbering of the atoms; displacement
ellipsoids with 50% probability)
with BBr3 (1m solution in CH2Cl2) [47]. The crude dipeptide 15 was used for the next
step without purification: the reaction with 7a in THF yielded the tripeptide 16. When
the latter was subjected to the cyclization conditions reported above, only the
heterobicyclic compound 17 could be isolated after chromatographic workup. The
structure of 17 was established by spectroscopic methods, and after crystallization from
CH2Cl2/Et2O, it was confirmed by X-ray crystallography (Fig. 2).
Scheme 3

1716
Helvetica Chimica Acta Vol. 88 (2005)
Fig. 2. ORTEP Plot [45] of the molecular structure of 17 (arbitrary numbering of the atoms; displacement
ellipsoids with 50% probability)
The H-bonding pattern of 17 is quite different to that of 12. The NH group forms an
intermolecular H-bond with N(2) of the heterocyclic five-membered ring of a
neighboring molecule. This latter molecule is related to the original one by a center
of inversion, so that centrosymmetric dimeric units with a graph-set motif of R22(10) are
formed.
The attempt to transform 14 into the corresponding N-protected carboxylic acid by
saponification (1n NaOH/MeOH 9 :4, 70 h) led to 2,4-dioxoquinazoline-3-acetic acid
(18) in quantitative yield (Scheme 4). After a shorter reaction time (30 min) and
treatment with a 0.3 :2 mixture of 1n NaOH/MeOH, the corresponding methyl 2,4-
dioxoquinazoline-3-acetate was obtained in 79% yield. The reaction of 18 with 7a gave
the quinazoline dipeptide amide 19 (78% yield), which, on treatment of its suspension
in toluene with HCl gas and aqueous workup, yielded the dipeptide acid 20 (72%).
After crystallization from MeOH/Et2O/CH2Cl2, the structure of the latter was again
established by X-ray crystallography (Fig. 3).
Scheme 4

Helvetica Chimica Acta Vol. 88 (2005)
1717
Fig. 3. ORTEP Plot [45] of the molecular structure of one of the two symmetry-independent molecules of 20
(arbitrary numbering of the atoms; displacement ellipsoids with 50% probability; the solvent molecule is not
shown)
The asymmetric unit contains two symmetry-independent molecules of 20 plus one
MeOH molecule. The independent molecules of 20 differ significantly in their
conformations as a result of a twist of ca. 308 about the C(9)ÀC(10) bond. The OH
group in molecule A forms an intermolecular H-bond with the O(15)-atom of
molecule B. Instead of the OH group in molecule B forming a similar intermolecular
H-bond with the corresponding O-atom in a different molecule A, this interaction
actually involves a route via the O-atom of the MeOH molecule, which accepts one H-
bond and then donates another H-bond to complete the link. The combination of these
interactions links the molecules into extended chains composed of the sequence
ÁÁÁ A ÁÁÁ B ÁÁÁ MeOH ÁÁÁ A' ÁÁÁ B' ÁÁÁ MeOH' ÁÁÁ . These chains run parallel to the [100]
direction and have a ternary graph-set motif [46] of C33(22). The chain amide H-atom in
molecule A forms an intermolecular H-bond with the O-atom of the corresponding
amide group in molecule B, and this amide group in molecule B forms a similar H-bond
with a different molecule A, thus building extended chains composed of the sequence
ÁÁÁ A ÁÁÁ B ÁÁÁA' ÁÁÁ B' ÁÁÁ , and which run parallel to the [100] direction and have a binary
graph set motif of C22(8). The ring amide H-atom in molecule A forms an
intermolecular H-bond to the ring carbonyl O-atom that is adjacent to the aromatic
ring of molecule B, while molecule B has a similar interaction with a different
molecule A. These interactions form extended chains composed of the sequence
ÁÁÁ A ÁÁÁ B ÁÁÁA''ÁÁÁ B'' ÁÁÁ , and which run parallel to the [010] direction and have a binary
graph-set motif of C22(12). The combination of all the interactions links all moieties in
the structure into two-dimensional networks which lie parallel to the (110) plane.

1718
Helvetica Chimica Acta Vol. 88 (2005)
Similar to the synthesis of 8, the reaction of 6 with aminoazirine 7b in dry MeCN
led to the corresponding diamide 21 (Scheme 5). Acidic hydrolysis gave the
corresponding carboxylic acid 22, which was further coupled with 7a to yield the
tripeptide 23. Removal of the protecting group by hydrogenolysis gave the linear
precursor 24, which was subjected to the conditions of the −direct amide cyclization×
(HCl gas in toluene at 1008). The results were quite different from our expectations and
somewhat surprising. The desired cyclic peptide of type A could not be obtained, but
three products have been isolated instead, i.e., the dimer 25 of the desired ten-
Scheme 5

Helvetica Chimica Acta Vol. 88 (2005)
1719
membered cyclic peptide (50% yield), an unexpected product recognized as the
quinazolinone 26 (32%), and traces of the transannular-ring-contraction product 27.
The formation of the cyclodimer 25 is obviously a result of an intermolecular
reaction of the oxazolone intermediate of type 3 (see, e.g., [19][20]), which is probably
influenced by the concentration and the conformational flexibility of the peptide
backbone, which may vary considerably in different peptides. The structure of 25 was
1
deduced on the basis of 1D- and 2D-NMR spectra: the assignment of the H and 13C
signals was achieved using HSQC and HMBC techniques. To determine the molecular
mass of the cyclic peptide, the soft-ionization technique ESI-MS was employed and
‡
indicated the base peak at m/z 783 ([M ‡ Na] ), which corresponds to the 20-
membered cyclodimer 25. Finally, the structure of 25 was established by X-ray
crystallography (Fig. 4). As only one very poor-quality crystal of 25 could be isolated,
the crystallographic data do not permit precise bond lengths and angles to be
determined. However, the data were good enough for the structure of the dimer to be
recognized. It is worth mentioning that the two benzyl groups are cis oriented. The
corresponding trans isomer could not be detected despite of the fact that racemic 7b
was used for the synthesis.
Fig. 4. ORTEP Plot [45] of the molecular structure of 25 (arbitrary numbering of the atoms; displacement
ellipsoids with 50% probability; H-atoms, except amide H-atoms, omitted for clarity)
The amide N(7)ÀH and N(17)ÀH form intramolecular H-bonds with the amide
O(20)- and O(10)-atoms, respectively, that are on the other side of the macrocycle, two
peptide units further around. Each of these interactions has the graph-set motif of
S(10). N(1)ÀH and N(11)ÀH form intermolecular H-bonds with amide O(16')- and
O(6'')-atoms, respectively, from two different neighboring molecules. Each of these
interactions independently links the molecules into extended chains, which run parallel
to the [001] direction and have a graph-set motif of C(8). In this way, two H-bonds

1720
Helvetica Chimica Acta Vol. 88 (2005)
bridge adjacent peptide molecules, with the sense of the N(1)ÀH ¥¥¥ O and N(11)ÀH ¥¥¥
O progression being in opposite directions. No reasonable H-bond acceptor could be
located for N(4)ÀH and N(17)ÀH, but the acceptors may be part of the omitted
solvent molecules (see Exper. Part).
The formation of compound 26 is very surprising, and we are not able to give a
reasonable explanation at this time. The structure of 26 was elucidated by means of its
NMR and IR spectra and confirmed by X-ray crystallography (Fig. 5). Compound 26
crystallized in a polar, non-centrosymmetric space group, but one, which dictates that
the crystals are racemic. There are two symmetry-independent molecules of 26 plus
one CH2Cl2 molecule in the asymmetric unit. Both molecules of 26 have similar
conformations. The most-significant difference is in the orientation of the benzyl
substituent, which, in molecule B, is pivoted about the C(42)ÀC(58) bond by ca. 308
with respect to the orientation of the corresponding group in molecule A. The five-
membered ring of molecule A is disordered with one atom of the ring occupying two
positions. The terminal NH group of each molecule forms an intramolecular H-bond
with the O-atom of the bicyclic ring system. This creates a ten-membered loop with a
graph-set motif [46] of S(10) and corresponds with the normal intramolecular
interactions seen for peptides with b-turns. The NH group in the center of molecule A
Fig. 5. ORTEP Plot [45] of the molecular structure of 26 (arbitrary numbering of the atoms; displacement
ellipsoids with 50% probability)

Helvetica Chimica Acta Vol. 88 (2005)
1721
forms an intermolecular H-bond with the amide O-atom at the Ph end of a neighboring
molecule B. The latter molecule, in turn, has an identical intermolecular interaction
with another molecule A. These interactions link the peptide molecules into extended
ÁÁÁ A ÁÁÁ B ÁÁÁA ÁÁÁ B ÁÁÁ chains, which run parallel to the [À110] direction and have a
binary graph set motif of C22(10).
Finally, the traces of compound 27 were successfully crystallized from CH2Cl2/Et2O/
hexane and its structure, which is analogous to that of 12 and 17, was established by
X-ray crystallography (Fig. 6).
Fig. 6. ORTEP Plot [45] of the molecular structure of 27 (arbitrary numbering of the atoms; displacement
ellipsoids with 50% probability)
As a result of the described reactions, the conditions of the −direct amide
cyclization× proved not to be suitable for the formation of ten-membered −cyclo-
aspeptides×. Therefore, it was of interest to test the application of this method to a
corresponding tetrapeptide precursor, which should lead to the 13-membered cyclo-
peptide. Tetrapeptide 31 was synthesized according to Scheme 6: the coupling reaction
of carboxylic acid 9 with methyl glycinate hydrochloride in the presence of TBTU,
HOBt, and EtN(i-Pr)2 gave the tripeptide methyl ester 28 in 98% yield, which was then
hydrolyzed with 1n NaOH in MeOH to yield the corresponding carboxylic acid 29. The
coupling of the latter with another unit of 7a afforded the tetrapeptide amide 30 in 93%
yield, which, after deprotection of the amino group by hydrogenolysis, gave 31. All
attempts to cyclize this tetrapeptide by treatment of its suspension with HCl gas failed.
Only a mixture of inseparable decomposition products was obtained. This result

1722
Helvetica Chimica Acta Vol. 88 (2005)
parallels the observation of a similar decomposition of tetrapeptide derivatives under
these conditions [18].
Scheme 6
Finally, a tripeptide derivative of type 36 was prepared (Scheme 7). Condensation
of Z-protected alanine with methyl anthranilate under standard conditions with [(1H-
benzotriazol-1-yl)oxy]tris(pyrrolidino)-phosphonium hexafluorophosphate (PyBOP)
and EtN(i-Pr)2 led to the corresponding amide 32, and saponification of the ester group
with 1n NaOH in MeOH yielded the acid 33 [49]. The latter compound was coupled
with 2H-azirin-3-amine 7c to give the N-protected tripeptide 34. Deprotection of the
amino group by hydrogenolysis led to the compound 35, which was subjected to the
cyclization conditions. Unfortunately the −direct amide cyclization×, as depicted in
Scheme 1, failed to give the desired cyclopeptide. This is most likely due to a complete
protonation of the primary amino group of 35 under the acidic conditions needed for
this cyclization. Hydrolytic ring opening of the initially formed 1,3-oxazol-5(4H)-one
intermediate with MeOH during workup explains the formation of the isolated methyl
ester 36. With this ester in hand, we were able to try the cyclization in refluxing toluene
according to [48], but even after heating for several days, only the starting material was
recovered.
Conclusions. We have shown that the −azirine/oxazolone method× is a convenient
preparative route for the synthesis of peptides containing a,a-disubstituted a-amino
acids and anthranilic acid. Unfortunately, attempts to prepare the corresponding ten-
membered cyclic peptide by the −direct amide cyclization× have so far been
unsuccessful. In the case of peptides 11 and 16, the tricyclic products 12 and 17 were

Helvetica Chimica Acta Vol. 88 (2005)
1723
Scheme 7
obtained as major products. Obviously, the initially formed cyclic peptides, under acidic
conditions, undergo a transannular ring closure, which is followed by elimination of
H2O. On the other hand, the −direct amide cyclization× of 24 gave the cyclodimer 25,
i.e., a 20-membered cyclohexapeptide. In all cases, the expected formation of the 1,3-
oxazol-5(4H)-one intermediate of type 3 takes place, and the aniline NH2 group acts as
a nucleophile. Finally, in the case of 35, oxazolone formation is proven by the isolation
of the ester 36. The NH2 group of alanine, in contrast, undergoes neither an intra- nor
an intermolecular nucleophilic addition, as it is completely protonated under the
chosen conditions.
As a conclusion, the −direct amide cyclization×, which has been shown to be a
superior method for the preparation of cyclodepsipeptides containing a,a-disubstituted
a-amino acids, is not suitable for the synthesis of ten-membered −cycloaspeptides×.
We thank the analytical services of our institute for NMR and mass spectra and elemental analyses, Miss J.
Cavegn for her assistance with the determination of the crystal structures, and the Dr. Helmut Legerlotz-
Foundation and F. Hoffmann-La Roche AG, Basel, for financial support.
Experimental Part
1. General. Solvents were purified by standard procedures. Thin layer chromatography (TLC): aluminium
sheets coated with silica gel Merck 60 F254. Column chromatography (CC): silica gel (0.040 0.063 mm, Merck
60). M.p.: B¸chi B-540 apparatus; uncorrected. IR Spectra: Perkin-Elmer 1600 Series FT-IR spectrometer; in

1724
Helvetica Chimica Acta Vol. 88 (2005)
KBr; absorptions in cmÀ1. NMR Spectra: Bruker ARX-300 spectrometer (1H: 300 MHz, 13C: 75.5 MHz); in
CDCl3; chemical shifts d [ppm] refer to residual CHCl3 (7.27 ppm, 1H) and to CDCl3 (77.0 ppm, 13C); coupling
constants J in Hz; the multiplicity of the 13C signals was deduced from DEPT spectra. MS: Finnigan MAT-SSQ-
700 (CI) and Finnigan MAT-TSQ-700 (ESI) spectrometer; m/z (rel.%). The following 2H-azirin-3-amines were
used: N-methyl-N-phenyl-1-azaspiro[2.4]hept-1-en-2-amine (7a) [50], 2-benzyl-N,N,2-trimethyl-2H-azirin-3-
amine (7b) [51], and N,N,2,2-tetramethyl-2H-azirin-3-amine (7c) [52].
General Procedure 1 (GP 1): Azirine Coupling. To a soln. of an N-protected amino acid or peptide acid in
the given solvent, the 2H-azirin-3-amine (7) was added at 08, and the mixture was stirred under N2 at r.t. After
completion of the reaction (TLC), the soln. was concentrated in vacuo, and the residue was purified by CC
(SiO2).
General Procedure 2 (GP 2): Selective Hydrolysis of the Terminal Amide Group. The C- and N-protected
peptide was dissolved in THF/6n HCl 1 :1 (n/n, ca. 5 ml/mmol) at 08, and the soln. was stirred at r.t. until
completion of the reaction (TLC). Then, the solvent was evaporated, CH2Cl2 and H2O were added, and the
layers were separated. The aq. layer was washed with Et2O, and the combined org. layer was dried (MgSO4) and
concentrated. The product was pure enough (> 90%) to be used in the next step without further purification.
General Procedure 3 (GP 3): Hydrolysis of the Methyl Ester. To a soln. of the C- and N-protected peptide in
MeOH, 1n NaOH was added. The mixture was stirred until completion of the reaction (TLC). Then, 1n HCl was
added to the mixture to adjust pH to 2 3. The solvent was evaporated, CH2Cl2 and H2O were added, and the
layers were separated. The aq. layer was washed with Et2O, and the combined org. layer was dried (MgSO4) and
concentrated in vacuo.
General Procedure 4 (GP 4): Hydrogenolysis of the Z-Protecting Group. To a soln. of the C- and N-
protected peptide in MeOH, 10% Pd/C was added at 08, and the mixture was stirred at r.t. under H2 until
completion of the reaction (TLC). Then, the soln. was filtered over a Celite pad, the solvent was evaporated, and
the resulting residue was purified by CC (SiO2).
General Procedure 5 (GP 5): Peptide Coupling. To a soln. of an N-protected amino acid, EtN(i-Pr)2
(2 equiv.), O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU, 1 equiv.), and 1-
hydroxy-1H-benzotriazole (HOBt, 1 equiv.) in MeCN or CH2Cl2 was added 1.1 equiv. of the amino acid ester.
The mixture was stirred at r.t. until the starting material was completely consumed (TLC). Then, the soln. was
concentrated in vacuo and the crude product purified by CC (SiO2).
General Procedure 6 (GP 6): Direct Amide Cyclization. A stirred suspension of the peptide in dry toluene
was warmed to 1008 under N2. A stream of dry HCl gas was slowly passed through the suspension at this temp.
for ca. 10 min, followed by a stream of N2 for 30 min to remove the remaining HCl. The solvent was evaporated
and the residue partitioned between H2O and CH2Cl2. The org. layer was dried (MgSO4) and evaporated. The
crude product was purified by CC (SiO2).
2. Dispiro[cyclopentane-1,2'(4'H)-[1H]imidazo[1,2-a][1,4]benzodiazepine-4',1''-cyclopentane]-1',6'(5'H)-
dione (12). 2.1. Benzyl (2-{[(1-{[(Methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]carbonyl}phenyl)carba-
mate (8). According to GP 1, with Z-protected anthranilic acid (6) (0.400 g, 1.470 mmol) in MeCN (4 ml), 7a
(0.353 g, 1.760 mmol) in MeCN (2 ml); reaction time 22 h. The obtained precipitate was collected by filtration,
washed with hexane, and dried in vacuo: 0.665 g of crude 8. Recrystallization from EtOH gave 0.603 g (87%) of
8. Colorless microcrystals. M.p. 202.3 202.88. IR: 3320m, 3267s, 3060w, 2965w, 1733s, 1635s, 1594s, 1520s, 1445s,
1
1386m, 1320m, 1207s, 1041m, 764m. H-NMR: 10.73 (br. s, NH); 8 .35 (d, J ˆ 8.4, 1 arom. H); 7.45 7.29 (m, 6
arom. H); 7.11 7.02 (m, 5 arom. H); 6.83 6.63 (m, 2 arom. H); 5.21 (s, PhCH2); 3.24 (s, MeN); 2.64 2.55,
1.90 1.74, 1.68 1.56 (3 m, (CH2)4). 13C-NMR: 172.1, 167.9, 153.7 (3s, 3 CO); 144.6, 140.1, 136.3 (3s, 3 arom. C);
132.7, 129.4, 128.5, 128.3, 128.2, 127.3, 126.9, 126.4, 121.4, 120.0 (10d, 14 arom. CH); 119.0 (s, 1 arom. C); 67.7 (s,
‡
(CH2)4C); 66.8( t, PhCH2); 40.7 (q, MeN); 39.5, 24.7 (2t, (CH2)4). ESI-MS: 494 (95, [M ‡ Na] ), 472 (13, [M ‡
‡
1] ), 365 (100). Anal. calc. for C28H29N3O4 (471.56): C 71.32, H 6.20, N 8.91; found: C 71.06, H 6.25, N 8.93.
2.2. 1-[(2-{[(Benzyloxy)carbonyl]amino}benzoyl)amino]cyclopentanecarboxylic Acid (9). According to
GP 2, hydrolysis of 8 (0.300 g, 0.636 mmol) led to 0.237 g (98%) of 9. Colorless powder. M.p. 195.6 196.48. IR:
3326m, 2963m, 2875w, 1701s, 1642s, 1600m, 1588s, 1524s, 1447s, 1280m, 1244s, 1216s, 1039s, 976w, 918m, 754m.
1H-NMR ((D6)DMSO): 12.30 (br. s, COOH); 10.62, 8.80 (2s, 2 NH); 8.19 (dd, J ˆ 8.4, 0.9, 1 arom. H); 7.76 (dd,
J ˆ 7.9, 1.4, 1 arom. H); 7.53 7.34 (m, 6 arom. H); 7.14 7.08( m, 1 arom. H); 5.16 (s, PhCH2); 2.51 2.48, 2.11
2.04 (2m, (CH2)4). 13C-NMR ((D6)DMSO): 175.0, 168.4, 152.6 (3s, 3 CO); 138.7, 136.2 (2s, 2 arom. C); 132.0,
128.7, 128.3, 127.9, 121.6 (5d, 8arom. CH); 120.0 ( s, 1 arom. C); 118.3 (d, 1 arom. CH); 66.0 (t, PhCH2); 65.6 (s,
‡
(CH2)4C); 36.2, 24.1 (2t, (CH2)4). ESI-MS: 405 (100, [M ‡ Na] ).
2.3. Benzyl (2-{[(1-{[(1-{[(Methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]carbonyl}cyclopentyl)ami-
no]carbonyl}phenyl)carbamate (10). According to GP 1, with 9 (0.480 g, 1.255 mmol) in THF (12 ml), 7a

Helvetica Chimica Acta Vol. 88 (2005)
1725
(0.276 g, 1.380 mmol) in THF (4 ml); reaction time 28 h. CC (CH2Cl2/MeOH 200 :1 to 60 :1) yielded 0.542 g
(74%) of 10. Colorless powder. M.p. 241.5 241.98. IR: 3310m, 2954m, 2870w, 1739s, 1655s, 1632s, 1589s, 1525s,
1448s, 1383m, 1323w, 1280w, 1243w, 1211s, 1104w, 1044m, 1028w. 1H-NMR (CDCl3/CD3OD): 10.00 (br. s, NH);
8.32 (d, J ˆ 8.4, 1 arom. H); 7.53 7.31 (m, 8arom. H); 7.08 7.01 ( m, 5 arom. H); 5.20 (s, PhCH2); 3.18( s, MeN);
2.15 2.02, 1.97 1.89, 1.68 1.65, 1.54 1.51 (4m, 2 (CH2)4). 13C-NMR (CDCl3/CD3OD): 172.6, 170.3, 153.6 (3s,
4 CO); 145.0, 139.7, 136.1 (3s, 3 arom. C); 133.2, 128.9, 128.7, 128.6, 127.4, 127.2, 122.3 (7d, 13 arom. CH); 120.6
(s, 1 arom. C); 120.4 (d, 1 arom. CH); 68.9, 67.5 (2s, 2 (CH2)4C); 67.2 (t, PhCH2); 41.0 (q, MeN); 38.5, 36.1, 23.9,
‡
23.8(4 t, 2 (CH2)4). ESI-MS: 605 (100, [M ‡ Na] ). Anal. calc. for C34H38N4O5 (582.71): C 70.08, H 6.57, N 9.61;
found: C 69.90, H 6.64, N 9.58.
2.4. 2-Amino-N-(1-{[(1-{[(methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]carbonyl}cyclopentyl)benz-
amide (11). According to GP 4, hydrogenolysis of 10 (0.240 g, 0.412 mmol) in MeOH (30 ml); reaction time
3 h. Evaporation yielded 0.182 g (98%) of 11. Colorless powder. M.p. 281.5 282.18. IR: 3490m, 3333s, 2953m,
2870m, 1657s, 1632s, 1610m, 1583s, 1492s, 1451s, 1382m, 1299m, 1266s. 1H-NMR ((D6)DMSO): 7.83 (s, 1 NH);
7.56 (d, J ˆ 6.6, 2 arom. H); 7.35 7.30 (m, 2 arom. H); 7.20 7.11 (m, 3 arom. H, NH); 6.67 (dd, J ˆ 8.2, 0.8, 1
arom. H); 6.52 (td-like, J ˆ 7.9, 7.0, 0.9, 1 arom. H); 6.20 (s, NH2); 3.23 (s, MeN); 2.19 2.08, 2.92 1.88, 1.65 1.52
(3m, 2 (CH2)4). 13C-NMR ((D6)DMSO): 172.7, 172.3, 169.1 (3s, 3 CO); 149.3, 145.4 (2s, 2 arom. C); 131.6, 128.9,
128.4, 126.7, 125.7, 116.1 (6d, 8arom. CH); 115.1 ( s, 1 arom. C); 114.3 (d, 1 arom. CH); 66.5, 66.2 (2s, 2 (CH2)4C);
‡
38.8 (q, MeN); 36.2, 35.7, 23.7 (3t, 2 (CH2)4). CI-MS: 449 (18, [M ‡ 1] ), 342 (100).
2.5. Compound 12. According to GP 6, with 11 (0.040 g, 0.089 mmol), in toluene (30 ml), at 1008; reaction
time 10 min. CC (CH2Cl2/MeOH 180 :1) yielded 0.012 g (44%) of 12. Colorless crystals. M.p. 224.1 225.38. IR:
3285w, 3178s, 3065m, 2961s, 2929s, 2878m, 1743s, 1661s, 1636s, 1600s, 1489m, 1460s, 1393s, 1358s, 1333s, 1271m,
1163m, 1062m, 1005w, 950w, 8 91w, 8 03w, 779m, 750m. 1H-NMR: 7.92 (dd, J ˆ 7.8, 1.5, 1 arom. H); 7.71 (dd, J ˆ
8.2, 1.0, 1 arom. H); 7.59 (td-like, J ˆ 8.2, 7.4, 1.1, 1 arom. H); 6.65 (s, NH); 2.11 1.65 (m, 2 (CH2)4). 13C-NMR:
184.4 (s, CN2); 168.7, 161.9 (2s, 2 CO); 132.5 (d, 1 arom. CH); 132.0 (s, 1 arom. C); 131.1 (d, 1 arom. CH); 127.8( s,
1 arom. C); 126.9, 123.3 (2d, 2 arom. CH); 61.6 (s, 2 (CH2)4C); 38.1, 37.6, 37.2, 36.8, 26.2, 24.6, 23.2 (7t, 2 (CH2)4).
‡
ESI-MS: 324 (100, [M ‡ 1] ).
Recrystallization from CH2Cl2/Et2O yielded crystals of 12 suitable for X-ray crystal-structure determi-
nation.
3. Methyl 1-[({1-[(2-Aminobenzoyl)amino]cyclopentyl}carbonyl)amino]cyclopentanecarboxylate (13).
General Procedure 7 (GP 7): The soln. of 10 (0.150 g, 0.257 mmol) in CH2Cl2 (20 ml) was cooled to À 108
and BBr3 (4 ml, 1m in CH2Cl2, 4.0 mmol) was added dropwise while stirring. Stirring was continued at À 108 for
1 h and at 258 for 2 h. The reaction was terminated by careful, dropwise addition of MeOH (20 ml). The solvents
were evaporated, and the residue was partitioned between H2O and CH2Cl2. The org. layer was dried (MgSO4)
and evaporated. The crude product was purified by CC (SiO2, CH2Cl2/MeOH 60 :1 to 30 :1): 0.054 g (66%) of
13. Colorless powder. M.p. 174.6 175.38. IR: 3441m, 3377s, 3302s, 3030w, 2958s, 2874m, 1723s, 1654s, 1617s,
1596s, 1523s, 1452m, 1302m, 1252m, 1160w, 1133w, 1070w, 1029w. 1H-NMR: 7.46 (br. s, 2 NH); 7.24 7.12 (m, 2
arom. H); 6.63 6.56 (m, 2 arom. H); 6.25 (s, NH2); 3.61 (s, MeO); 2.37 2.30, 2.15 2.08, 2.01 1.86, 1.76 1.66
(4m, 2 (CH2)4). 13C-NMR: 174.6, 173.2, 169.9 (3s, 3 CO); 148.6 (s, 1 arom. C); 132.6, 127.2, 117.4, 116.7 (4d, 4
arom. CH); 115.9 (s, 1 arom. C); 67.8, 65.8 (2s, 2 (CH2)4C); 52.2 (q, MeO); 37.0, 36.6, 24.4, 24.0 (4t, 2 (CH2)4).
‡
‡
ESI-MS: 412 (100, [M ‡ K] ), 374 (71, [M ‡ 1] ).
4. 4',5'-Dihydrospiro[cyclopentane-1,2'(6'H)-[1H]imidazo[1,2-a][1,4]benzodiazepine]-1',6'-dione (17). 4.1.
Methyl [(2-{[(Benzyloxy)carbonyl]amino}benzoyl)amino]acetate (14). According to GP 5, with 6 (0.200 g,
0.737 mmol), methyl glycinate hydrochloride (0.110 g, 0.737 mmol), HOBt (0.100 g, 0.737 mmol), TBTU
(0.236 g, 0.737 mmol), EtN(i-Pr)2 (0.26 ml, 1.474 mmol), and MeCN (8ml); reaction time 4 h. CC (CH 2Cl2/
MeOH 250 :1) gave 0.222 g (88%) of 14. Colorless powder. M.p. 89.7 90.08. IR: 3420s, 3157m, 3039w, 2953m,
1738s, 1641s, 1591s, 1537s, 1455s, 1407s, 1374s, 1331m, 1283s, 1207s, 1127m, 1084w, 1045m, 1028w, 1000w, 909w,
855w, 8 29w, 754m, 697m. 1H-NMR: 10.42 (s, NH); 8.40 (dd, J ˆ 8.4, 0.9, 1 arom. H); 7.54 7.31 (m, 7 arom. H);
7.04 (td-like, J ˆ 8.6, 7.6, 1.1, 1 arom. H); 6.68 (s, NH); 5.20 (s, PhCH2); 4.20 (d, J ˆ 5.0, CH2CO); 3.81 (s, MeO).
13C-NMR: 170.1, 168.8, 153.5 (3s, 3 CO); 140.0, 136.2 (2s, 2 arom. C); 133.0, 128.5, 128.2, 128.1, 126.8, 121.9, 120.0
‡
(7d, 9 arom. CH); 66.8( t, PhCH2); 52.6 (q, MeO); 41.6 (t, CH2CO). CI-MS: 360 (27, [M ‡ NH4] ), 343 (100,
‡
[M ‡ 1] ), 299 (15), 254 (52). Anal. calc. for C18H18N2O5 (342.36): C 63.15, H 5.30, N 8.18; found: C 63.08, H
5.30, N 8.16.
4.2. 2-Amino-N-{2-[(1-{[(methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]-2-oxoethyl}benzamide
(16). According to GP 7, with 14 (0.340 g, 0.993 mmol) in CH2Cl2 (15 ml), BBr3 (12 ml, 1m in CH2Cl2,
12 mmol). The reaction was terminated by addition of H2O (50 ml). The crude N-(2-aminobenzoyl)glycine (15)
was used for the next step without further purification: according to GP 1, with 15 (0.072 g, 0.404 mmol) in THF

1726
Helvetica Chimica Acta Vol. 88 (2005)
(10 ml), 7a (0.121 g, 0.606 mmol) in THF (4 ml); reaction time 48h. CC (CH 2Cl2/MeOH 60 :1) gave 0.090 g
(57%) of 16. Colorless powder. M.p. 206.7 207.98. IR: 3480m, 3376m, 3317m, 3290m, 1683s, 1638s, 1611s, 1592s,
1518s, 1495m, 1444w, 1380m, 1315w, 1253m, 1155w, 1025w, 8 91w, 749w, 708w. 1H-NMR ((D6)DMSO): 8.20 8.10
(m, 1 NH); 7.65 7.55 (br. s, 1 NH); 7.51 6.90 (m, 7 arom. H); 6.72 6.69 (d-like, 1 arom. H); 6.55 6.48( t-like, 1
arom. H); 6.35 (s, NH2); 3.55 (m, CH2CO); 3.13 (s, MeN); 2.30 2.15, 1.80 1.49 (2m, (CH2)4). 13C-NMR
(CDCl3/CD3DO): 176.1, 173.0, 171.5 (3s, 3 CO); 151.5, 148.3 (2s, 2 arom. C); 135.7, 132.4, 130.8, 130.6, 129.8,
120.4, 119.9 (7d, 9 arom. CH); 118.3 (s, 1 arom. C); 70.2 (s, (CH2)4C); 45.7 (t, CH2CO); 43.6 (q, MeN); 41.7, 27.3
‡
(2t, (CH2)4). ESI-MS: 417 (100, [M ‡ Na] ), 288 (23).
4.3. Compound 17. According to GP 6, with 16 (0.075 g, 0.190 mmol), in toluene (60 ml), 1008; reaction
time 10 min. CC (CH2Cl2/MeOH 150 :1 to 50 :1) yielded 0.010 g (20%) of 17. Colorless crystals. M.p. 268.5
269.88. IR: 3442w, 3190s, 3099s, 2960m, 2923m, 1729s, 1662s, 1599s, 1573s, 1484m, 1461s, 1430m, 1389s, 1333s,
1298w, 1270m, 1231m, 1158m, 1083s, 1058m, 1019m, 957m, 8 77w, 790m, 764m. 1H-NMR ((D6)DMSO): 9.03 (t,
J ˆ 5.7, 1 NH); 8.07 (td, J ˆ 7.6, 1.0, 1 arom. H); 7.96 7.88 (m, 2 arom. H); 7.75 7.66 (m, 1 arom. H); 4.41 4.14
(m, CH2NH); 2.15 2.04 (m, (CH2)4). 13C-NMR ((D6)DMSO): 182.8 (s, CN2); 167.6, 158.6 (2s, 2 CO); 131.7,
130.9, 126.7, 123.0 (4d, 4 arom. CH); 131.0, 127.7 (2s, 2 arom. C); 77.5 (s, (CH2)4C); 39.2, 25.2 (2t, (CH2)4); 37.0 (t,
‡
CH2NH). ESI-MS: 270 (100, [M ‡ 1] ).
Recrystallization from CH2Cl2/Et2O yielded crystals of 17 suitable for X-ray crystal-structure determi-
nation.
5. Synthesis of 1-{[(1,4-Dihydro-2,4-dioxo-2H-quinazolin-3-yl)acetyl]amino}-N-methyl-N-phenylcyclopen-
tanecarboxamide (19). 5.1. 1,4-Dihydro-2,4-dioxoquinazoline-3(2H)-acetic Acid (18). According to GP 3, with
14 (0.100 g, 0.290 mmol) in MeOH (2 ml) and 0.3 ml 1n NaOH; reaction time 30 min. CC (CH2Cl2/MeOH
300 :1) gave 0.054 g (79%) of methyl 1,4-dihydro-2,4-dioxoquinazoline-3(2H)-acetate. 1H-NMR ((D6)DMSO):
11.61 (s, NH); 7.95 (dd, J ˆ 7.7, 1.4, 1 arom. H); 7.71 (td, J ˆ 7.8, 1.5, 1 arom. H); 7.30 7.15 (m, 2 arom. H); 4.67 (s,
CH2); 3.68( s, MeO). 13C-NMR ((D6)DMSO): 168.6, 162.3, 150.5 (3s, 3 CO); 139.0 (s, 1 arom. C); 135.2, 127.9,
‡
123.0, 115.0 (4d, 4 arom. CH); 113.7 (s, 1 arom. C); 52.2 (q, MeO); 41.3 (t, CH2). ESI-MS: 257 (100, [M ‡ Na] ).
According to GP 3, 14 (0.115 g, 0.336 mmol) in MeOH (4 ml) was treated with 9 ml of 1n NaOH; reaction
time 70 h: 0.073 g (99%) of 18. 1H-NMR ((D6)DMSO): 13.0 (br. s, COOH); 11.56 (s, NH); 7.94 (dd, J ˆ 8.3, 1.4,
1 arom. H); 7.70 (td, J ˆ 7.4, 1.5, 1 arom. H); 7.27 7.21 (m, 2 arom. H); 4.56 (s, CH2). 13C-NMR: 169.2, 161.5,
149.8(3 s, 3 CO); 139.3 (s, 1 arom. C); 135.3, 127.3, 122.7, 115.2 (4d, 4 arom. CH); 113.3 (s, 1 arom. C); 41.3 (t,
CH2).
5.2. Compound 19. According to GP 1, with 18 (0.073 g, 0.332 mmol) in THF (8ml), 7a (0.068g,
0.341 mmol) in THF (2 ml); reaction time 98h. CC (CH 2Cl2/MeOH 100 :1 to 50 :1) gave 0.105 g (78%) of 19.
White powder. M.p. 263.7 264.38. IR: 3340s, 3058m, 2934m, 2866m, 1721s, 1669s, 1635s, 1594m, 1537m, 1494s,
1
1455s, 1431m, 1367m, 1335m, 1278m, 1252m, 1139m, 977w, 723w. H-NMR ((D6)DMSO): 11.41 (s, NH); 7.94
(dd, J ˆ 8.3, 1.5, 1 arom. H); 7.85 (br. s, 1 NH); 7.68( td, J ˆ 8.2, 1.5, 1 arom. H); 7.41 7.20 (m, 7 arom. H); 4.26 (s,
CH2CO); 3.13 (s, MeN); 2.25 2.09, 1.74 1.68, 1.60 1.58 (3m, (CH2)4). 13C-NMR ((D6)DMSO): 173.0, 166.3,
162.6, 150.6 (4s, 4 CO); 139.0 (s, 1 arom. C); 134.8, 129.0, 127.5, 127.0, 122.6, 114.7 (6d, 9 arom. CH); 113.7 (s, 1
arom. C); 66.8( s, (CH2)4C); 42.2 (t, CH2CO); 40.0 (q, MeN); 38.1, 23.9 (2t, (CH2)4); 1 arom. C not found. CI-
‡
MS: 421 (42, [M ‡ 1] ), 314 (100). Anal. calc. for C23H24N4O4 (420.47): C 65.70, H 5.75, N 13.32; found: C 65.49,
H 5.74, N 13.10.
5.3. 1-{[(1,4-Dihydro-2,4-dioxo-2H-quinazolin-3-yl)acetyl]amino}cyclopentanecarboxylate (20). According
to GP 6, with 19 (0.100 g, 0.238mmol) in toluene (40 ml), 100 8; reaction time 30 min: 0.057 g (72%) of 20.
White powder. M.p. 234.9 235.38. IR: 3600m, 3359m, 3267m, 2962m, 1720s, 1700s, 1652s, 1537s, 1494s, 1449s,
1419s, 1406m, 1347m, 1324m, 1267s, 1184w, 1160w, 1135m, 1071w, 1031w, 98 3m, 78 5m, 761m, 749m, 68 9m.
1H-NMR ((D6)DMSO): 12.1 (br. s, COOH); 11.41 (s, NH); 8.36 (s, NH); 7.92 (d-like, J ˆ 7.2, 1 arom. H); 7.67 (t-
like, J ˆ 8.2, 1 arom. H); 7.21 (t-like, J ˆ 7.7, 2 arom. H); 4.49 (s, CH2CO); 2.08 2.02, 1.99 1.82, 1.66 1.65 (3 m,
(CH2)4). 13C-NMR ((D6)DMSO): 174.9, 166.2, 161.2, 149.8(4 s, 4 CO); 139.3 (s, 1 arom. C); 134.9, 127.3, 122.4,
115.0 (4d, 4 arom. CH); 113.5 (s, 1 arom. C); 64.9 (s, (CH2)4C); 42.0 (t, CH2CO); 36.2, 23.9 (2t, (CH2)4). CI-MS:
‡
332 (67), 349 (100, [M ‡ NH3] ).
Recrystallization from MeOH/Et2O/CH2Cl2 yielded crystals of 20 suitable for X-ray crystal-structure
determination.
6. Cyclization of 2-[(2-Aminobenzoyl)amino]-2-methyl-N-(1-{[(methyl)(phenyl)amino]carbonyl}cyclo-
pentyl)-3-phenyl-propanamide (24). 6.1. Benzyl [2-({[2-(Dimethylamino)-1-methyl-2-oxo-1-(phenylmethyl)-
ethyl]amino}carbonyl)phenyl]carbamate (21). According to GP 1, with 6 (0.500 g, 1.843 mmol) in MeCN
(6 ml), 7b (0.416 g, 2.110 mmol) in MeCN (4 ml); reaction time 48h. The crude product was filtered, washed
with cold hexane/Et2O 1:1, and dried in vacuo: 0.695 g (82%) of 21. Colorless powder. M.p. 211.5 212.48. IR:

Helvetica Chimica Acta Vol. 88 (2005)
1727
3281m, 3102w, 3066w, 3036w, 3098w, 2957w, 1733s, 1620s, 1587s, 1524s, 1450s, 1391m, 1374m, 1328m, 1306w,
1278m, 1221s, 1104m, 1090s, 1041s, 1029m, 8 95m, 8 49w, 768m, 758m, 739w, 706w. 1H-NMR: 10.57 (s, NH); 8.36
(dd, J ˆ 8.5; 1.0, 1 arom. H); 7.46 7.30 (m, 6 arom. H); 7.28 7.17 ( m, 4 arom. H); 7.03 7.00 (m, 2 arom. H); 6.92
(td, J ˆ 8.0, 1.2, 1 arom. H); 5.23, 5.18 (AB, J ˆ 12.0, PhCH2O); 3.73, 3.35 (AB, J ˆ 14.1, PhCH2C); 3.11 (s,
Me2N); 1.80 (s, MeC). 13C-NMR: 171.9, 167.6, 153.7 (3s, 3 CO); 139.9, 136.4 (2s, 2 arom. C); 132.5, 129.9, 128.5,
128.4, 128.3 (5d, 10 arom. CH); 128.2 (s, 1 arom. C); 127.1, 126.7, 122.0 (3d, 3 arom. CH); 120.4 (s, 1 arom. C);
120.0 (d, 1 arom. CH); 66.7 (t, PhCH2O); 61.1 (s, MeC); 40.1 (t, PhCH2); 38.5 (q, Me2N); 22.7 (q, Me). CI-MS:
‡
460 (3, [M ‡ 1] ), 415 (33), 308(20), 307 (100). Anal. calc. for C 27H29N3O4 (459.55): C 70.57, H 6.36, N, 9.14;
found: C 70.06, H 6.43, N 9.04.
6.2. 2-[(2-{[(Benzyloxy)carbonyl]amino}benzoyl)amino]-2-methyl-3-phenylpropanoic Acid (22). Accord-
ing to GP 2, hydrolysis of 21 (0.580 g, 1.260 mmol) led to 0.506 g (93%) of 22. Colorless powder. M.p. 101.5
101.98. IR: 3283w, 3064m, 3032m, 2943w, 1736s, 1648s, 1589s, 1524s, 1449s, 1375w, 1318w, 1280w, 1216m, 1109w,
1093w, 1043m, 1029w, 8 8 w4, 8 47w, 754m, 700m. 1H-NMR: 10.34 (s, NH); 8 .35 (d, J ˆ 8.4, 1 arom. H); 7.46 7.10
(m, 12 arom. H); 6.94 (td, J ˆ 8.4, 1.1, 1 arom. H); 6.69 (s, NH); 5.21 (s, PhCH2O); 3.57, 3.37 (AB, J ˆ 13.6,
PhCH2C); 1.76 (s, Me). 13C-NMR: 178.6, 168.6, 153.8 (3s, 3 CO); 139.7, 136.3, 135.7 (3s, 3 arom. C); 132.8, 130.0,
128.6, 128.5, 128.3, 128.2, 127.3, 126.8, 122.1, 120.2 (10d, 14 arom. CH); 66.9 (t, PhCH2O); 61.3 (s, PhCH2C); 41.0
‡
(t, PhCH2C); 23.3 (q, Me); 1 arom. C could not be detected. CI-MS: 450 (10, [M ‡ NH4] ), 434 (28), 433 (100,
‡
[M ‡ 1] ), 415 (26), 281 (48).
6.3. Benzyl {2-[({1-Methyl-2-[(1-{[(methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]-2-oxo-1-(phenyl-
ethyl)ethyl}amino)carbonyl]phenyl}carbamate (23). According to GP 1, with 22 (0.470 g, 1.087 mmol) in THF
(10 ml), 7a (0.240 g, 1.196 mmol) in THF (5 ml); reaction time 72 h. The crude product was filtered, washed with
cold hexane/Et2O 1 :1, and dried in vacuo: 0.544 g (79%) of 23. Colorless powder. M.p. 205.4 206.88. IR: 3316s,
3063m, 3031m, 2954m, 2872m, 1733s, 1660s, 1632s, 1589s, 1525s, 1449s, 1375s, 1323s, 1279s, 1214s, 1135m, 1105m,
1093m, 1042s, 1029m, 98 6m, 8 8 w5, 8 51w, 756s, 702s. 1H-NMR: 10.03 (s, NH); 8 .36 (d, J ˆ 8.3, 1 arom. H); 7.54
7.19 (m, 12 arom. H); 7.08 6.97 ( m, 2 arom. H); 6.86 6.85 (m, 4 arom. H); 6.57, 5.94 (2s, 2 NH); 5.22 (s,
PhCH2O); 3.66, 2.86 (AB, J ˆ 13.8, PhCH2C); 3.18( s, MeN); 2.36 2.26, 1.79 1.72, 1.66 1.63 (3m, (CH2)4); 1.47
(s, Me). 13C-NMR: 172.2, 172.0, 169.9, 153.4 (4s, 4 CO); 144.9, 139.8, 136.1, 135.6 (4s, 4 arom. C); 133.2, 130.8,
128.7, 128.65, 128.6, 128.5, 127.4, 127.3, 126.9, 126.7, 122.1, 120.4 (12d, 19 arom. CH); 120.5 (s, 1 arom. C); 67.7 (s,
PhCH2C); 67.0 (t, PhCH2O); 62.3 (s, (CH2)4C); 41.5 (t, PhCH2C); 40.9 (q, MeN); 38.8, 38.5, 24.1, 24.0 (4t,
‡
(CH2)4); 23.6 (q, Me). ESI-MS: 655 (100, [M ‡ Na] ). Anal. calc. for C38H40N4O5 (632.77): C 72.13, H 6.37, N
8.85; found: C 72.46, H 6.43, N 8.68.
6.4. Compound 24. According to GP 4, hydrogenolysis of 23 (0.250 g, 0.395 mmol) in MeOH (30 ml)
yielded 0.190 g (96%) of 24. Colorless powder. M.p. 218.1 218.58. IR: 3468m, 3348s, 3058w, 3026w, 2959m,
2870w, 1659s, 1635s, 1593w, 1577m, 1523s, 1493s, 1452m, 1371m, 1327w, 1263m, 1234w, 1160w, 1095m, 1026w,
985w, 799w, 745m, 700m. 1H-NMR ((D6)DMSO): 7.88, 7.56 (2s, 2 NH); 7.38 7.32, 7.24 7.11 (2 m, 12 arom. H);
6.70 (dd, J ˆ 8.2, 0.7, 1 arom. H); 6.48 (td, J ˆ 7.9, 0.9, 1 arom. H); 6.21 (s, NH2); 3.61, 3.08( AB, J ˆ 13.5, PhCH2);
3.28( s, MeN); 2.34 2.28, 2.16 2.09, 2.05 1.95, 1.61 1.54 (4m, (CH2)4); 1.35 (s, Me). 13C-NMR ((D6)DMSO):
173.1, 172.4, 168.7 (3s, 3 CO); 149.2, 145.6, 137.4 (3s, 3 arom. C); 131.5, 130.4, 128.5, 127.6, 126.7, 126.0, 125.7,
116.0 (8d, 13 arom. CH); 115.5 (s, 1 arom. C); 114.4 (d, 1 arom. CH); 66.4 (s, PhCH2C); 59.2 (s, (CH2)4C); 38.9
‡
(q, MeN); 38.7 (t, PhCH2); 36.3, 36.1, 24.2, 23.9 (4t, (CH2)4); 21.1 (q, Me). ESI-MS: 521 (100, [M ‡ Na] ), 391
(40).
6.5. cis-10',22'-Dibenzyl-10',22'-dimethyl-10',11',22',23'-tetrahydro-6'H,8'H-dispiro[cyclopentane-1,7'-diben-
zo[h,r][1,4,7,11,14,17]hexaazacycloicosine-19',1''-cyclopentane]-6',9',12',18',21',24'(5'H,17'H,20'H)-hexone (25),
1-{[2-Methyl-1-oxo-2-(4-oxoquinazolin-3(4H)-yl)-3-phenylpropyl]amino}-N-phenylcyclopentanecarboxamide
(26), and 4'-Benzyl-4',5'-dihydro-4'-methylspiro[cyclopentane-1,2'(6'H)-[1H]imidazo[1,2-a][1,4]benzodiaze-
pine]-1',6'-dione (27). According to GP 6, with 24 (0.193 g, 0.388 mmol), in toluene (120 ml), 1008; reaction
time 3 min. CC (CH2Cl2/MeOH 150 :1 to 50 :1) yielded 0.075 g (50%) of 25, 0.065 g (32%) of 26, and traces of
27.
Data of 25: Colorless microcrystals. M.p. 2708 (decomp.). IR: 3364m, 3031w, 2940m, 2926s, 2855m, 1681s,
1651s, 1603m, 1583m, 1523s, 1444s, 1371w, 1268s, 1170w, 1127w, 905w, 749m, 708w. 1H-NMR ((D6)DMSO,
360 K): 9.80 (s, 2 NH); 7.91 (d, J ˆ 8.1, 2 arom. H); 7.72 (s, 2 NH); 7.64 (s, 2 NH); 7.46 7.37 (m, 4 arom. H);
7.25 7.10 (m, 12 arom. H); 3.82, 3.12 (AB, J ˆ 13.3, 2 PhCH2); 2.26 2.21, 2.09 2.01, 1.72 1.63 (3m, 2 (CH2)4);
1.32 (s, 2 Me). 13C-NMR ((D6)DMSO): 173.6, 173.5, 167.3 (3s, 6 CO); 137.0, 136.1 (2s, 6 arom. C); 130.6, 130.0,
127.8, 126.3, 124.0 (5d, 18arom. CH); 67.4 ( s, 2 (CH2)4)C); 60.0 (s, 2 PhCH2C); 38.7 (t, 2 PhCH2); 35.9, 23.8(2 t,
‡
2 (CH2)4); 22.6 (q, 2 Me). ESI-MS: 783 (100, [M ‡ Na] ), 511 (33), 419 (17), 392 (29).

1728
Helvetica Chimica Acta Vol. 88 (2005)
Recrystallization from THF/toluene/MeOH/CH2Cl2 yielded crystals of 25 suitable for X-ray crystal-
structure determination.
Data of 26: Colorless crystals. M.p. 2808 (decomp.). IR: 3448w, 3296m, 2950w, 1683s, 1665s, 1651s, 1603w,
1583m, 1520s, 1446m, 1363w, 1272m, 1167w, 1128w, 748m, 705m. 1H-NMR: 9.17 (s, PhNHCO); 8.30 8.27 (m, 1
arom. H); 7.86 7.80 (m, 2 arom. H); 7.78 7.73 ( m, 2 arom. H); 7.65 7.62 (m, 1 arom. H); 7.53 7.47 (m, 1 arom.
H); 7.45 (s, NH); 7.31 7.21 (m, 1 arom. H); 7.16 6.99 (m, 4 arom. H); 6.76 6.72 (m, 2 arom. H); 5.77 (s,
NˆCH); 3.88, 3.17 (AB, J ˆ 13.5, PhCH2); 2.52 2.45, 2.31 2.22, 2.03 1.95, 1.85 1.75 (4m, (CH2)4); 1.70 (s,
Me). 13C-NMR: 171.9, 171.3, 162.4 (3s, 3 CO); 147.6 (s, 1 arom. C); 142.9 (d, NˆCH); 138.9 (s, 1 arom. C); 135.2
(d, 1 arom. CH); 134.2 (s, 1 arom. C); 130.3, 128.6, 127.9, 127.7, 127.6, 127.0, 123.8 (7d, 12 arom. CH); 121.7 (s, 1
arom. C); 120.5 (d, 1 arom. CH); 68.4 (s, (CH2)4C); 66.2 (s, PhCH2C); 38.7 (t, PhCH2); 38.4, 37.5, 24.7, 24.6 (4t,
(CH2)4); 23.0 (q, Me).
Recrystallization from Et2O/CH2Cl2 yielded crystals of 26 suitable for X-ray crystal-structure determi-
nation.
Data of 27. Recrystallization from CH2Cl2/Et2O/hexane yielded a crystal of 27 suitable for X-ray crystal-
structure determination.
7. Synthesis of 2-Amino-N-{1-[({2-[(1-{[(methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]-2-oxoethyl}-
amino)carbonyl]cyclopentyl}benzamide (31). 7.1. Methyl [({1-[(2-{[(Benzyloxy)carbonyl]amino}benzoyl)ami-
no]cyclopentyl}carbonyl)amino]acetate (28). According to GP 5, with 9 (0.160 g, 0.418mmol), methyl glycinate
hydrochloride (0.063 g, 0.502 mmol), TBTU (0.134 g, 0.418mmol), HOBt (0.057 g, 0.418mmol), EtN(i-Pr)
2
(0.14 ml, 0.837 mmol), and CH2Cl2 (10 ml); reaction time 2 h. CC (CH2Cl2/MeOH 300 :1) gave 0.186 g (98%) of
28. Colorless powder. M.p. 176.7 177.48. IR: 3366s, 3313s, 3275s, 3066m, 2955s, 2874w, 1754s, 1738s, 1666s, 1627s,
1600s, 1586s, 1538s, 1511s, 1449s, 1300m, 1206s, 1179m, 1046s, 1057m, 771w, 700w. 1H-NMR: 10.42 (s, NH); 8 .35
(dd, J ˆ 8.7, 0.7, 1 arom. H); 7.46 7.31 (m, 7 arom. H); 7.08( t, J ˆ 5.1, NH); 7.03 6.98( m, 1 arom. H); 6.66 (s,
NH); 5.18( s, PhCH2); 4.00 (d, J ˆ 5.3, CH2CO); 3.66 (s, MeO); 2.44 2.35, 2.12 2.03, 1.88 1.69 (3m, (CH2)4).
13C-NMR: 173.8, 170.3, 169.3, 153.6 (4s, 4 CO); 139.9, 136.2 (2s, 2 arom. C); 132.9, 128.5, 128.2, 126.8, 122.0, 120.0
(6d, 9 arom. CH); 119.8( s, 1 arom. C); 67.9 (s, (CH2)4C); 66.8( t, PhCH2); 52.2 (q, MeO); 41.5 (t, CH2CO); 36.9,
‡
24.2 (2t, (CH2)4). ESI-MS: 476 (100, [M ‡ Na] ). Anal. calc. for C24H27N3O6 (453.48): C 63.57, H 6.00, N 9.26;
found: C 63.78, H 5.91, N 9.18.
7.2. [({1-[(2-{[(Benzyloxy)carbonyl]amino}benzoyl)amino]cyclopentyl}carbonyl)amino]acetic Acid (29).
According to GP 3, with 28 (0.186 g, 0.410 mmol) in MeOH (10 ml) and 1n NaOH (2.05 ml, 2.05 mmol);
reaction time 90 h: 0.134 g (74%) of 26. Colorless powder. M.p. 203.2 203.88. IR: 3300s, 3035w, 2961m, 2874m,
1736s, 1657s, 1628s, 158 8s, 1521s, 1449s, 1304w, 1281w, 1244s, 1214s, 1108w, 1038m, 914w, 765w, 754w, 699m. 1H-NMR
((D6)DMSO): 12.36 (br. s, OH); 10.55, 8.61 (2s, 2 NH); 8.09 (dd, J ˆ 8.3, 0.9, 1 arom. H); 7.88 7.83 (m, 2 arom.
H); 7.51 7.32 (m, 5 arom. H, NH); 7.14 7.09 (m, 1 arom. H); 5.15 (s, PhCH2); 3.71 (d, J ˆ 4.4, CH2CO); 2.21
2.17, 2.04 1.99, 1.66 1.50 (3m, (CH2)4). 13C-NMR ((D6)DMSO): 177.2, 176.7, 171.0, 155.8(4 s, 4 CO); 138.0,
137.2 (2s, 2 arom. C); 133.4, 129.7, 129.5, 129.1 (4d, 7 arom. CH); 125.2 (s, 1 arom. C); 125.1, 122.7 (2d, 2 arom.
‡
CH); 68.9 (s, (CH2)4C); 68.2 (t, PhCH2); 45.1 (t, CH2CO); 37.9, 25.5 (2t, (CH2)4). ESI-MS: 462 (100, [M ‡ Na] ).
7.3. Benzyl {2-[({1-[({2-[(1-{[(Methyl)(phenyl)amino]carbonyl}cyclopentyl)amino]-2-oxoethyl}amino)-
carbonyl]cyclopentyl}amino)carbonyl]phenyl}carbamate (30). According to GP 1, with 29 (0.127 g,
0.289 mmol) in THF (8 ml), 7a (0.06 g, 0.300 mmol) in THF (2 ml); reaction time 90 h. CC (CH2Cl2/MeOH
200 :1 to 20 :1) gave 0.172 g (93%) of 30. Colorless powder. M.p. 214.5 215.38. IR: 3392m, 3335s, 3035w, 2952m,
2875w, 1728s, 1678s, 1655s, 1633s, 1594s, 1533s, 1453s, 1374m, 1328m, 1281m, 1244m, 1219s, 1106m, 1044m,
1028w, 98 5w, 954w, 8 49w. 1H-NMR: 10.34 (s, 1 NH); 8.41 (d, J ˆ 8.4, 1 arom. H); 7.66 (d, J ˆ 7.9, 1 arom. H); 7.52
(td, J ˆ 8.5, 1.2, 1 arom. H); 7.42 7.30 (m, 6 arom. H); 7.18 6.87 ( m, 5 arom. H, NH); 6.41 (br. s, NH); 5.20 (s,
PhCH2); 3.51 3.43 (m, CH2CO); 3.10 (s, MeN); 2.26 2.04, 1.97 1.85, 1.81 1.69, 1.62 1.52 (4m, 2 (CH2)4).
13C-NMR: 173.6, 172.6, 169.7, 168.3, 153.5 (5s, 5 CO); 144.8, 139.9, 135.8 (3s, 3 arom. C); 132.2, 129.0, 128.5,
128.4, 127.5, 126.9, 126.7, 122.0, 119.8 (9d, 14 arom. CH); 118.9 (s, 1 arom. C); 67.4, 67.2 (2s, 2 (CH2)4C); 67.0 (t,
‡
PhCH2); 43.5 (t, CH2CO); 40.4 (q, MeN); 38.4, 37.1, 24.2, 24.0 (3t, 2 (CH2)4). ESI-MS: 662 (100, [M ‡ Na] ).
7.4. Compound 31. According to GP 4, hydrogenolysis of 30 (0.163 g, 0.255 mmol) in MeOH (10 ml);
reaction time 24 h. CC (AcOEt/hexane 2 :1) yielded 0.091 g (71%) of 31. Colorless powder. M.p. 158.2 159.58.
IR: 3448m, 3332s, 2956s, 2873m, 1636s, 1592s, 1525s, 1495s, 1450m, 1372m, 1260m, 750m, 703m. 1H-NMR
((D6)DMSO): 8.33 (s, 1 NH); 7.65 (dd, J ˆ 7.9, 1.2, 1 arom. H); 7.27 7.06 (m, 6 arom. H, NH); 6.71 6.69 (m, 1
arom. H); 6.59 6.54 (m, 1 arom. H); 6.21 (s, NH2); 3.40 3.37 (m, CH2CO); 3.07 (s, MeN); 2.21 2.12, 1.83
1.79, 1.65 1.63, 1.54 1.53 (4m, 2 (CH2)4). 13C-NMR ((D6)DMSO): 175.3, 173.5, 170.8, 169.2 (4s, 4 CO); 148.9,
144.9 (2s, 2 arom. C); 133.1, 129.5, 128.3, 127.4, 126.9, 117.6, 117.0 (7d, 9 arom. CH); 116.0 (s, 1 arom. C); 67.6, 67.3
‡
(2s, 2 (CH2)4C); 43.3 (t, CH2CO); 40.6 (q, MeN); 38.6, 37.4, 24.7, 24.5 (4t, 2 (CH2)4). ESI-MS: 528(100, [ M‡ Na] ).

Helvetica Chimica Acta Vol. 88 (2005)
1729
All attempts to cyclize 31 under the conditions of the −direct amide cyclization× failed, and only
decomposition was observed.
8. Synthesis of Methyl 2-[({2-[(2-Amino-1-oxopropyl)amino]phenyl}carbonyl)amino]-2-methylpropanoate
(36). 8.1. Methyl 2-[(1-Oxo-2-{[(benzyloxy)carbonyl]amino}propyl)amino]benzoate (32). Methyl anthranilate
(0.300 g, 1.98mmol), Z-alanine (0.4386 g, 2.18mmol), and [(1 H-benzotriazol-1-yl)oxy]tris(pyrrolidino)-
phosphonium hexafluorophosphate (PyBOP) (1.13 g, 2.18mmol) were dissolved in CH 2Cl2 (20 ml). At r.t.,
EtN(i-Pr)2 (0.75 ml, 4.35 mmol) was added, and the mixture was stirred for 24 h. Then, the solvent was
evaporated in vacuo, and the product was purified by CC (CH2Cl2/MeOH 500 :1 to 250 :1): 0.433 g (61%) of 32.
1H-NMR: 11.50 (s, NH); 8.69 (dd, J ˆ 8.5, 1.5, 1 arom. H); 8.03 (dd, J ˆ 8.0, 1.6, 1 arom. H); 7.57 7.52 (m, 1
arom. H); 7.37 7.26 (m, 5 arom. H); 7.10 (td, J ˆ 8.2, 1.2, 1 arom. H); 5.47 (br. s, NH); 5.16 (s, PhCH2); 4.47
4.43 (m, MeCH); 3.89 (s, MeO); 1.53 (d, J ˆ 7.1, MeCH). 13C-NMR: 171.2, 171.0, 168.4 (3s, 3 CO); 140.9 (s, 1
arom. C); 134.5, 130.8, 128.4, 128.0 (4d, 7 arom. CH); 126.9 (s, 1 arom. C); 122.8, 120.3 (2d, 2 arom. CH); 115.3
(s, 1 arom. C); 67.0 (t, PhCH2); 52.2 (q, MeO); 51.8( d, MeCH); 18.9 (q, MeCH).
8.2. 2-[(1-Oxo-2-{[(benzyloxy)carbonyl]amino}propyl)amino]benzoic Acid (33). According to GP 3, with
32 (0.359 g, 1.008mmol) in MeOH (12 ml) and 1 n NaOH (2 ml, 2 mmol); reaction time 24 h: 0.233 g (68%) of
33. 1H-NMR ((D6)DMSO): 11.70 (s, NH); 8.61 (d, J ˆ 8.4, 1 arom. H); 8.03 7.94 (m, 2 arom. H); 7.63 7.58( m,
1 arom. H); 7.39 7.21 (m, 4 arom. H); 7.17 (td, J ˆ 8.3, 1.2, 1 arom. H); 5.12, 5.03 (AB, J ˆ 12.7, PhCH2); 4.18
4.09 (m, MeCH); 1.36 (d, J ˆ 7.3, MeCH). 13C-NMR ((D6)DMSO): 171.7, 169.2, 156.0 (3s, 3 CO); 140.6, 136.8
(2s, 2 arom. C); 134.0, 131.0, 128.2, 127.6, 127.5, 122.6, 119.4 (7d, 9 arom. CH); 116.1 (s, 1 arom. C); 65.6 (t,
PhCH2); 51.9 (d, MeCH); 17.2 (q, MeCH).
8.3. Benzyl N-(2-{[2-({[2-(Dimethylamino)-1,1-dimethyl-2-oxoethyl]amino}carbonyl)phenyl]amino}-1-
methyl-2-oxoethyl)carbamate (34). According to GP 1, with 33 (0.250 g, 0.730 mmol) in THF (15 ml), 7c
(0.080 g, 0.730 mmol) in THF (5 ml); reaction time 48 h. CC (CH2Cl2/MeOH 200 :1 to 150 :1) gave 0.195 g
(59%) of 34. Colorless powder. M.p. 165.8 166.5 8. IR: 3299m, 3064w, 2936w, 1723s, 1710s, 1665s, 1649s, 1622s,
1587m, 1515s, 1447s, 1406m, 1389m, 1326w, 1298m, 1245s, 1174w, 1119m, 1069m, 915w, 909w, 756m, 701w.
1H-NMR: 11.60 (s, 1 NH); 8.54 (dd, J ˆ 8.5, 0.9, 1 arom. H); 7.96 (s, 1 NH); 7.54 (dd, J ˆ 7.9, 1.4, 1 arom. H); 7.43
(td, J ˆ 8.5, 1.4, 1 arom. H); 7.36 7.31 (m, 5 arom. H); 7.07 (td, J ˆ 8.5, 1.1, 1 arom. H); 5.59 5.57 (m, 1 NH);
5.17, 5.09 (AB, J ˆ 6.7, PhCH2); 4.41 (t, J ˆ 6.7, MeCH); 3.08( s, Me2N); 1.78, 1.76 (2s, Me2C); 1.49 (d, J ˆ 7.0,
MeCH). 13C-NMR: 173.1, 171.1, 167.2, 155.7 (4s, 4 CO); 139.2, 136.4 (2s, 2 arom. C); 132.4, 128.4, 128.0, 126.8,
123.1, 121.4 (6d, 9 arom. CH); 121.0 (s, 1 arom. C); 66.8( t, PhCH2); 57.4 (s, Me2C); 51.7 (d, MeCH); 38.3 (q,
‡
‡
Me2N); 24.0, 23.9 (2q, Me2C); 19.3 (q, MeCH). ESI-MS: 477 (21, [M ‡ Na] ), 455 (100, [M ‡ 1] ), 410 (78), 348
(30), 281 (19).
8.4. 2-[(2-Amino-1-oxopropyl)amino]-N-[2-(dimethylamino)-1,1-dimethyl-2-oxoethyl]benzamide (35).
According to GP 4, hydrogenolysis of 34 (0.190 g, 0.418mmol) in MeOH (15 ml); reaction time 2 h: 0.110 g
(82%) of 35. Colorless powder. M.p. 205.1 206.48. IR: 3276s, 2985m, 2932m, 1627s, 1583s, 1513s, 1446s, 1393s,
1363m, 1320m, 1289m, 1206m, 1119s, 1055w, 948w, 904w, 794w, 759m, 706w. 1H-NMR: 11.60 (s, 1 NH); 8.58 (d, J ˆ
8.2, 1 arom. H); 7.76 (s, 1 NH); 7.53 7.43 (m, 2 arom. H); 7.08( t, J ˆ 7.4, 1 arom. H); 3.65 3.63 (m, MeCH); 3.10
(s, Me2N); 1.79 (s, Me2C); 1.43 (d, J ˆ 6.7, MeCH). 13C-NMR: 175.2, 173.1, 167.6 (3s, 3 CO); 137.9 (s, 1 arom. C);
131.9, 127.1, 123.1 (3d, 3 arom. CH); 122.1 (s, 1 arom. C); 121.4 (d, 1 arom. CH); 57.0 (s, Me2C); 51.3 (d, MeCH);
‡
‡
37.9 (q, Me2N); 24.8( q, Me2C); 21.0 (q, MeCH). ESI-MS: 343 (100, [M ‡ Na] ), 321 (34, [M ‡ 1] ), 276 (22).
8.5. Compound 36. According to GP 6, with 35 (0.100 g, 0.312 mmol), in toluene (100 ml), 1008; reaction
time 10 min. CC (CH2Cl2/MeOH 150 :1) yielded 0.027 g (28%) of 36. White powder. M.p. 154.9 156.08. IR:
3402w, 3300m, 3062w, 2986m, 2933w, 1740s, 1660s, 1643s, 1598m, 1580m, 1507s, 1444s, 1387m, 1327m, 1292m,
1270m, 1221w, 1194w, 1152s, 1002w, 923w, 792w, 756m. 1H-NMR: 11.36 (s, 1 NH); 8.55 (d, J ˆ 8.1, 1 arom. H);
7.51 7.43 (m, 2 arom. H); 7.08( td, J ˆ 8.1, 1.0, 1 arom. H); 6.78 (s, 1 NH); 3.78( s, MeO); 3.64 3.59 (m, MeCH);
1.67 (s, Me2C); 1.41 (d, J ˆ 6.96, MeCH). 13C-NMR: 175.1, 174.9, 168.3 (3s, 3 CO); 138.5 (s, 1 arom. C); 132.2,
126.8, 122.9 (3d, 3 arom. CH); 122.4 (s, 1 arom. C); 121.7 (d, 1 arom. CH); 57.0 (s, Me2C); 52.8( q, MeO); 52.0 (d,
‡
‡
MeCH); 24.7 (q, Me2C); 21.7 (q, MeCH). CI-MS: 309 (18, [M ‡ 2] ), 308(100, [ M ‡ 1] ), 191 (5).
9. X-Ray Crystal-Structure Determinations of Compounds 12, 17, 20, 25, 26, and 27 (see Tables 1 and 2 and
Figs. 1 6)2). All measurements were performed on a Nonius KappaCCD area-detector diffractometer [53] by
2
)
CCDC-265726 265731 contain the supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax: ‡ 44-(0)1223-336033; e-mail: depos-
it@ccdc.cam.ac.uk)).

1730
Helvetica Chimica Acta Vol. 88 (2005)
using graphite-monochromated MoKa radiation (l 0.71073 ä) and an Oxford Cryosystems Cryostream-700
cooler. Data reduction was performed with HKL Denzo and Scalepack [54]. The intensities were corrected for
Lorentz and polarization effects. In the case of 26, an absorption correction based on the multi-scan method [55]
was applied. The data collection and refinement parameters are given in Tables 1 and 2, and views of the
molecules are shown in Figs. 1 6. Each structure was solved by direct methods using SIR92 [56], which revealed
the positions of all non-H-atoms. The non-H-atoms were refined anisotropically.
Table 1. Crystallographic Data of Compounds 12, 17, 20, and 27
12
1720
27
Crystallized from
CH2Cl2/Et2O
C19H21N3O2
323.39
CH2Cl2/Et2O
C15H15N3O2
269.30
MeOH/Et2O/CH2Cl2 CH2Cl2/Et2O/hexane
2C16H17N3O5 ¥ CH3OH C23H23N3O2
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
Crystal dimensions [mm]
Temperature [K]
Crystal system
Space group
]
694.69
373.45
colorless, prism colorless, prism colorless, prism
colorless, plate
0.07 Â 0.20 Â 0.20
160(1)
0.22 Â 0.25 Â 0.40 0.10 Â 0.15 Â 0.25 0.05 Â 0.12 Â 0.12
160(1)
160(1)
monoclinic
P21/c
160(1)
triclinic
triclinic
P1
monoclinic
P21/c
≈
≈
P1
Z
2
4
2
4
Reflections for cell
determination
2q range for cell
determination [8]
3800
4039
3973
3608
2
60
4
60
4
44
4 50
Unit cell parameters
a [ä]
6.1782(1)
9.2220(2)
14.7542(3)
102.685(1)
91.494(1)
97.7754(9)
811.22(3)
1.324
10.8624(2)
7.5537(1)
15.9813(3)
90
101.4916(9)
90
1285.00(4)
1.392
0.0951
f and w
60
9.1119(3)
13.5302(6)
13.9245(7)
89.080(2)
90.123(2)
72.749(2)
1639.2(1)
1.407
17.4548 (5)
7.0316 (2)
17.0160 (4)
90
116.345 (1)
90
1871.55 (9)
1.325
0.0860
b [ä]
c [ä]
a [8]
b [8]
g [8]
V [ä3]
Dx [g cmÀ3
]
m(MoKa) [mmÀ1
Scan type
]
0.0876
f and w
55
0.107
f and w
44
f and w
50
2q(max) [8]
Total reflections measured
Symmetry-independent
reflections
13837
3686
37521
3773
29317
3990
26714
3324
Reflections with I > 2s(I)
Reflections used in refinement
32482797
32482797
21818 460
0.0490
0.0665
0.010
2935
2935
2527
2527
Parameters refined
Final R(F)
wR(F)
6
258
0.0480
0.0486
0.007
0.0775
0.0783
0.013
0.0446
0.0461
0.005
Weighting parameter [p]a)
Goodness-of-fit
3.266
2.635
2.910
2.475
Secondary extinction coefficient 0.000004(2)
0.0000018(5)
0.0006
0.0000013(5)
0.0001
0.24; À 0.20
0.0000015(3)
0.0004
0.25; À 0.21
Final Dmax/s
D1 (max; min) [e äÀ3
0.0003
]
0.38; À 0.280.32;
À 0.29
a) wÀ1 ˆ s2(Fo) ‡ (pFo)2.
In the case of 26, the asymmetric unit contains two molecules of the peptide plus one molecule of CH2Cl2.
The five-membered ring of one peptide molecule is disordered. Two equally occupied positions were defined for
one CH2 group of the ring. Bond-length restraints were applied to all bonds involving the disordered atoms.

Helvetica Chimica Acta Vol. 88 (2005)
1731
Table 2. Crystallographic Data of Compounds 25 and 26
25
26
Crystallized from
THF/toluene/MeOH/CH2Cl2
C46H50N6O6 ¥ CH3OH ¥ H2O
832.99
colorless, needle
0.02 Â 0.07 Â 0.30
160(1)
Et2O/CH2Cl2
2C30H30N4O3 ¥ CH2Cl2
1074.1
colorless, prism
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
Crystal dimensions [mm]
Temperature [K]
]
0.07 Â 0.17 Â 0.25
160(1)
Crystal system
Space group
triclinic
P1
monoclinic
Cc
≈
Z
2
4
Reflections for cell determination
709894939
2q range for cell determination [8]
4
50
4 50
Unit-cell parameters a [ä]
11.456(1)
11.948(2)
16.975(3)
76.962(8)
87.559(9)
77.471(6)
2209.6(5)
1.252
17.7319(2)
15.3756(2)
21.5283(3)
90
109.7593(7)
90
5523.9(1)
1.291
0.177
b [ä]
c [ä]
a [8]
b [8]
g [8]
V [ä3]
Dx [g cmÀ3
]
m(Mo Ka) [mmÀ1
Scan type
]
0.0862
f and w
50
f and w
50
2q(max) [8]
Transmission factors (min; max)
Total reflections measured
Symmetry-independent reflections
Reflections with I > 2s(I)
Reflections used in refinement
Parameters refined
0.914; 0.991
40211
9586
8323
9579
27387
7656
3339
7656
526
705
Final R(F) (I > 2s(I) reflections)
wR(F2) (all indep4t9. reflections)
Weighting parameters [a; b]a)
Goodness-of-fit
0.137
0.0365
0.3780.08
0.1666; 3.34
1.032
0.0361; 1.8544
1.062
Secondary extinction coefficient
Final Dmax/s
0.034(5)
0.001
0.44; À 0.37
0.001
0.18; À 0.37
D1 (max; min) [e äÀ3
]
a) wÀ1 ˆ s2(F2o ) ‡ (aP)2 ‡ bP where P ˆ (Fo2 ‡ 2F2c )/3.
The crystal of 20 was very weakly diffracting and the results are of low precision. The asymmetric unit
contains two molecules of the peptide plus one molecule of MeOH.
In the case of 25, only one very poor crystal could be isolated, which was weakly diffracting and gave broad
reflection profiles. The structure unambiguously reveals the nature of the peptide molecule, but the geometric
parameters are very imprecise. The asymmetric unit contains one molecule of the peptide plus a region, which is
presumably occupied by solvent molecules. It was not possible to model the solvent, or even find sensible
residual electron-density peaks representing the solvent atoms. Therefore, the contribution of the solvent
molecules to the intensity data was removed by using the SQUEEZE [57] routine of the PLATON [58]
program. Omission of the solvent molecules leaves one cavity of 323 ä3 per unit cell. The number of electrons
contributing to each void in the structure was calculated by the SQUEEZE routine to be ca. 52 e. Allowing for
two MeOH and two H2O molecules per cavity and unit cell yields 56 e and this was used in the subsequent
calculation of the empirical formula, formula weight, density, linear absorption coefficient and F(000). The

1732
Helvetica Chimica Acta Vol. 88 (2005)
nature of the solvent is purely an assumption used to approximate the correct values for the parameters just
described, but would be consistent with the solvent from which the crystals were obtained and the positions of
the residual electron-density peaks observed in the void.
The amide H-atoms in 17 and 27, as well as the OH and MeO H-atoms in 20, were placed in the positions
indicated by difference electron-density maps and, except for the OH H-atom of one peptide molecule of 20,
their positions were allowed to refine together with individual isotropic displacement parameters. All of the
remaining H-atoms in the structures were placed in geometrically calculated positions and refined using a riding
model, where each H-atom was assigned a fixed isotropic displacement parameter with a value equal to 1.2 Ueq
of its parent atom (1.5 Ueq for the Me groups in 25 and 26).
For 12, 17, 20, and 27, each structure was refined on F using full-matrix least-squares procedures, which
minimized the function Sw(j Fo jÀj Fc j )2. The refinement of the structures of 25 and 26 was carried out on F2 by
minimizing the corresponding function based on F2. Corrections for secondary extinction were applied, except
for 26. Compound 26 has crystallized in a polar, non-centrosymmetric space group, but one which dictates that
the crystals are racemic. The absolute structure was confirmed by refinement of the absolute-structure
parameter [59], which yielded a value of À 0.03(4). Neutral-atom-scattering factors for non-H-atoms were
taken from [60a], and the scattering factors for H-atoms were taken from [61]. Anomalous dispersion effects
were included in Fc [62]; the values for f' and f'' were those of [60b]. The values of the mass-attenuation
coefficients are those of [60c]. The calculations for 25 and 26 were performed by using the SHELXL97 program
[63], while those for the remaining structures were carried out by using the teXsan crystallographic software
package [64].
REFERENCES
[1] H. Heimgartner, Angew. Chem., Int. Ed. 1991, 30, 238.
[2] D. Obrecht, H. Heimgartner, Helv. Chim. Acta 1981, 64, 482; D. Obrecht, H. Heimgartner, Helv. Chim.
Acta 1987, 70, 102.
[3] P. Wipf, H. Heimgartner, Helv. Chim. Acta 1986, 69, 1153; P. Wipf, H. Heimgartner, Helv. Chim. Acta 1987,
70, 354; P. Wipf, H. Heimgartner, Helv. Chim. Acta 1988, 71, 258.
[4] M. Sahebi, P. Wipf, H. Heimgartner, Tetrahedron 1989, 45, 2999.
[5] J. M. Villalgordo, H. Heimgartner, Tetrahedron 1993, 49, 7215.
[6] C. B. Bucher, A. Linden, H. Heimgartner, Helv. Chim. Acta 1995, 78, 935; C. B. Bucher, H. Heimgartner,
Helv. Chim. Acta 1996, 79, 1903.
[7] G. Suter, S. A. Stoykova, A. Linden, H. Heimgartner, Helv. Chim. Acta 2000, 83, 2961.
[8] R. A. Breitenmoser, T. R. Hirt, R. T. N. Luykx, H. Heimgartner, Helv. Chim. Acta 2001, 84, 972.
[9] K. A. Brun, A. Linden, H. Heimgartner, Helv. Chim. Acta 2002, 85, 3422.
[10] P. Wipf, H. Heimgartner, Helv. Chim. Acta 1990, 73, 13.
[11] W. Altherr, Ph.D. Thesis, University of Z¸rich, 1994.
[12] R. Luykx, C. B. Bucher, A. Linden, H. Heimgartner, Helv. Chim. Acta 1996, 79, 527; R. T. N. Luykx, A.
Linden, H. Heimgartner, Helv. Chim. Acta 2003, 86, 4093.
[13] N. Pradeille, H. Heimgartner, J. Pept. Sci. 2003, 9, 826.
[14] J. Lehmann, A. Linden, H. Heimgartner, Tetrahedron 1998, 54, 8721; J. Lehmann, A. Linden, H.
Heimgartner, Helv. Chim. Acta 1999, 82, 888; J. Lehmann, A. Linden, H. Heimgartner, Tetrahedron 1999,
55, 5359; J. Lehmann, H. Heimgartner, Helv. Chim. Acta 1999, 82, 1899.
[15] R. A. Breitenmoser, H. Heimgartner, Helv. Chim. Acta 2001, 84, 768.
[16] D. Obrecht, H. Heimgartner, Helv. Chim. Acta 1984, 67, 526; D. Obrecht, H. Heimgartner, Helv. Chim.
Acta 1990, 73, 221.
[17] H. Heimgartner, F. S. Arnhold, S. P. Fritschii, K. N. Koch, J. E. F. Magirius, A. Linden, J. Heterocycl. Chem.
1999, 36, 1539.
[18] J. M. Villalgordo, H. Heimgartner, Helv. Chim. Acta 1997, 80, 748.
[19] K. N. Koch, A. Linden, H. Heimgartner, Helv. Chim. Acta 2000, 83, 233; K. N. Koch, H. Heimgartner, Helv.
Chim. Acta 2000, 83, 1881; K. N. Koch, A. Linden, H. Heimgartner, Tetrahedron 2001, 57, 2311.
[20] B. Iliev, A. Linden, H, Heimgartner, Helv. Chim. Acta 2003, 86, 3215.
[21] I. Dannecker-Dˆrig, Ph.D. Thesis, University of Z¸rich, 1995.
[22] F. S. Arnhold, Ph.D. Thesis, University of Z¸rich, 1997.
[23] T. Jeremic, A. Linden, H. Heimgartner, Chem. Biodiv. 2004, 1, 1730; T. Jeremic, A. Linden, H.
Heimgartner, Helv. Chim. Acta 2004, 87, 3056.

Helvetica Chimica Acta Vol. 88 (2005)
1733
[24] T. Jeremic, A. Linden, K. Moehle, H. Heimgartner, Tetrahedron 2005, 61, 1871.
[25] J. N. Lambert, J. P. Mitchell, K. D. Roberts, J. Chem. Soc., Perkin Trans. 1 2001, 471.
[26] F. Cardenas, J. M. Caba, M. Feliz, P. Lloyd-Williams, E. Giralt, J. Org. Chem. 2003, 68, 9554.
[27] K. Sato, U. Nagai, J. Chem. Soc., Perkin Trans. 1 1986, 1231 and refs. cit. therein.
[28] M. Feigel, J. Am. Chem. Soc. 1986, 108, 18 1.
[29] M. Feigel, G. Lugert, Liebigs. Ann. Chem. 1989, 1089.
[30] J. P. Mazaleyrat, M. Wakselman, Int. J. Pept. Protein Res. 1987, 30, 622.
[31] F. Pinnen, G. Zanotti, G. Lucente, Tetrahedron Lett. 1984, 25, 5201.
[32] F. Pinnen, A. Di Muro, G. Zanotti, G. Lucente, Int. J. Pept. Protein Res. 1987, 30, 388.
[33] S. Cerrini, F. Gavuzzo, G. Lucente, F. Pinnen, Int. J. Pept. Protein Res. 1988, 31, 447.
[34] S. Cerrini, F. Gavuzzo, G. Lucente, F. Pinnen, G. Zanotti, Int. J. Pept. Protein Res. 1989, 34, 6.
[35] S. Cerrini, F. Gavuzzo, G. Lucente, G. Luisi, F. Pinnen, L. Radics, Int. J. Pept. Protein Res. 1991, 38, 289.
[36] A. Calcagni, M. Kajtar-Predy, G. Lucente, G. Luisi, F. Pinnen, L. Radics, D. Rossi, Int. J. Pept. Protein Res.
1993, 42, 8 4.
[37] G. Zanotti, F. Pinnen, G. Lucente, S. Cerrini, E. Gavuzzo, F. Mazza, Int. J. Pept. Protein Res. 1983, 22, 410.
[38] H. Brockmann, Ann. N. Y. Acad. Sci. 1960, 323.
[39] C. W. Holzapfel, J. M. Koekemoer, M. S. Van Dyk, S. Afr. J. Chem. 1986, 39, 75.
[40] R. Kobayashi, Y. Samejima, S. Nakajima, K. Kawai, S. Udagawa, Chem. Pharm. Bull. 1987, 36, 1347.
[41] K. Komatsu, H. Shigemori, J. Kobayashi, J. Org. Chem. 2001, 66, 6189.
[42] T. Jeremic, Diploma Thesis, University of Z¸rich, 1999.
[43] B. Liberek, J. Zarebski, in −Peptide 1980×, Ed. K. Brunfeldt, Scriptor, Copenhagen, 1981, p. 236.
[44] J. M. Humphrey, A. R. Chamberlin, Chem. Rev. 1997, 97, 2243.
[45] C. K. Johnson, −ORTEP II, Report ORNL-5138×, Oak Ridge National Laboratory, Oak Ridge, Tennessee,
1976.
[46] J. Bernstein, R. E. Davis, L. Shimoni, N.-L. Chang, Angew. Chem., Int. Ed. 1995, 34, 1555.
[47] A. M. Felix, J. Org. Chem. 1974, 39, 1427.
[48] E. Aguilar, A. I. Meyers, Tetrahedron Lett. 1994, 35, 2477.
[49] A. Witt, J. Bergman, J. Org. Chem. 2001, 66, 2784.
[50] M. Sahebi, Diploma Thesis, University of Z¸rich, 1987.
[51] P. Wipf, Ph.D. Thesis, University of Z¸rich, 1987.
[52] M. Rens, L. Ghosez, Tetrahedron Lett. 1970, 3765.
[53] R. Hooft, KappaCCD COLLECT Software, Nonius BV, Delft, The Netherlands, 1999.
[54] Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307.
[55] R. H. Blessing, Acta Crystallogr., Sect. A 1995, 51, 33.
[56] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl.
Crystallogr. 1994, 27, 435.
[57] P. van der Sluis, A. L. Spek, Acta Crystallogr., Sect. A 1990, 46, 194.
[58] A. L. Spek, PLATON, Program for the Analysis of Molecular Geometry, University of Utrecht, The
Netherlands, 2005.
[59] a) H. D. Flack, G. Bernardinelli, Acta Crystallogr., Sect A 1999, 55, 908; b) H. D. Flack, G. Bernardinelli, J.
Appl. Crystallogr. 2000, 33, 1143.
[60] a) E. N. Maslen, A. G. Fox, M. A. O×Keefe, in −International Tables for Crystallography×, Ed. A. J. C.
Wilson, Kluwer Academic Publishers, Dordrecht, 1992, Vol. C, Table 6.1.1.1, p. 477 486; b) D. C. Creagh,
W. J. McAuley, in −International Tables for Crystallography×, Ed. A. J. C. Wilson, Kluwer Academic
Publishers, Dordrecht, 1992, Vol. C, Table 4.2.6.8, p. 219 222; c) D. C. Creagh, J. H. Hubbell, in
−International Tables for Crystallography×, Ed. A. J. C. Wilson, Kluwer Academic Publishers, Dordrecht,
1992, Vol. C, Table 4.2.4.3, p. 200 206.
[61] R. F. Stewart, E. R. Davidson, W. T. Simpson, J. Chem. Phys. 1965, 42, 3175.
[62] J. A. Ibers, W. C. Hamilton, Acta Crystallogr. 1964, 17, 78 1.
[63] G. M. Sheldrick, SHELXL97, Program for the Refinement of Crystal Structures, University of Gˆttingen,
Germany, 1997.
[64] teXsan: Single Crystal Structure Analysis Software, Version 1.10, Molecular Structure Corporation, The
Woodlands, Texas, 1999.
Received March 11, 2005