Solid-phase synthesis and chemical properties of 2-(2-Amino/ hydroxyethyl)-l-aryl-3,4-dihydropyrazino[l, 2b]indazol-2-iums

Article abstract of DOI:10.1021/cc9001422

Amino alcohols, diamines, benzenesulfonyl chlorides, and bromoketones were used to prepare polymersupported 2-(2-(2-(amino/hydroxyl)ethy].amino)emyl)-3- benzoyl-2H-indazoles. Acid-mediated release yielded 2-((amino/hydroxy].)ethy].)- l-aryl-3,4-dihydropyr

Full text of DOI:10.1021/cc9001422

168
J. Comb. Chem. 2010, 12, 168–175
Solid-Phase Synthesis and Chemical Properties of 2-(2-Amino/
hydroxyethyl)-1-aryl-3,4-dihydropyrazino[1, 2-b]indazol-2-iums
Jan Kocˇ´ı and Viktor Krchnˇa´k*
Department of Chemistry and Biochemistry, 251 Nieuwland Science Center, UniVersity of Notre Dame,
Notre Dame, Indiana 46556
ReceiVed September 3, 2009
Amino alcohols, diamines, benzenesulfonyl chlorides, and bromoketones were used to prepare polymer-
supported 2-(2-(2-(amino/hydroxyl)ethylamino)ethyl)-3-benzoyl-2H-indazoles. Acid-mediated release yielded
2-((amino/hydroxyl)ethyl)-1-aryl-3,4-dihydropyrazino[1,2-b]indazole-2-iums. In neutral pH, iminiums spon-
taneously cyclized to complex fused heterocycles 3,6,9,10-tetraazatetracyclo[7.7.0.02,6.011,16]hexadeca-
11,13,15-trienes, 3-oxa-6,9,10-triazatetracyclo[7.7.0.02,6.011,16]hexadeca-11,13,15-trienes, and 3,7,10,11-
tetraazatetracyclo[8.7.0.02,7.012,17]heptadeca-12,14,16-trienes. Transformations were carried out under mild
conditions and tolerated diverse substitution patterns.
Introduction
Iminium salts were applied in combinatorial solid-phase
syntheses. Polymer-supported syntheses of bi-, tri-, and
tetracyclic derivatives of 1-acyl-3-oxopiperazines employed
tandem N-acyliminium ion cyclization-nucleophilic addition
as the ring-forming process.15 Polymer-supported synthesis
with the aromatic aza Diels-Alder reaction via iminium-
initiated cyclization provided an efficient approach to produce
(pyrido-fused) tetrahydroquinoline.16,17 A novel strategy of
the Pictet-Spengler reaction provided for the synthesis of
triazabenzoazulenes.18 Various ring systems with a pyrro-
lidino-lactam core were prepared by intramolecular [3 + 2]
azomethine ylide cycloaddition via iminium intermediates.
These syntheses were carried out in solid phase, as well as
in solution.19
As part of our ongoing research on solid-phase synthesis
of heterocyclic compounds and the generation of combina-
torial libraries for drug discovery, we recently developed a
novel synthetic route to indazoles.1 N-alkylation of polymer-
supported 2-nitrobenzenesulfonyl (2-Nos)-activated/protected
amines by bromoketones (a variant of the Fukuyama
method2) provided R-sulfonylamino ketones. Treatment of
these 2-Nos derivatives with DBU led to tandem carbon-
carbon followed by nitrogen-nitrogen bond formation to
produce indazole oxides of excellent purity (Scheme 1). The
target indazoles contained a carbonyl functional group
attached to the side-chain of the substituent in position 2 of
the indazole ring. The carbonyl group enabled subsequent
transformations of indazoles and formation of a fused
pyrazine ring via an intramolecular nucleophile located on
the R1 side-chain, providing a route for pyrazino[1,2-
b]indazole synthesis.3
Herein, we extend our chemistry to indazole derivatives
with a secondary, rather than primary, amino group in the
ꢀ-position with respect to the sulfonamide. After TFA-
mediated cleavage from the resin, these resin-bound inter-
mediates yielded iminium trifluoroacetes. The presence of a
nucleophile on the side-chain of the amino group enabled
ring closure in neutral pH and formation of complex fused
heterocycles.
Results and Discussion
To investigate the outcome of the iminium-forming
reaction, we synthesized the resin-bound precursor using
diethylenetriamine, 2-nitrobenzenesulfonyl chlorides, and
bromoketones. The commercially available diethylenetri-
amine was immobilized to Wang resin via a carbamate
linkage using carbonyldiimidazole (CDI) activation to pro-
vide resin 1 (Scheme 2). The reaction occurred exclusively
through the primary amino group; there was no need to
distinguish between primary amino groups due to the
symmetrical nature of diethylenetriamine. A large excess of
diethylenetriamine essentially eliminated the potential cross-
linking reaction (reaction of the amino group of already
immobilized diethylenetriamine). Resin 1 was used for the
synthesis of the model indazole derivatives.
Synthesis Using Dual 2-Nos Protecting Groups. To
enable the selective alkylation of the primary group of resin
1, we protected/activated both amino groups with a 2-ni-
trobenzenesulfonyl (2-Nos) group (LC purity of crude 2 was
>90%). The secondary amino group was protected against
subsequent reaction with bromoketones and the 2-Nos-
activated primary amino group facilitated N-monoalkylation
Iminium ions are well-established powerful intermediates
used in many chemical transformations.4-7 The wide ap-
plicability of the iminium intermediate is documented
through their use in the construction of complex hetero-
cycles8-10 including polycyclic alkaloids.11-14 Among the
various methods for iminium ion synthesis, the condensation
of secondary amines with aldehydes (ketones) is regarded
as one of the most versatile procedures.
* Corresponding author. Phone: (574) 631-5113. E-mail: vkrchnak@
nd.edu.
10.1021/cc9001422  2010 American Chemical Society
Published on Web 12/04/2009

Solid-Phase Synthesis
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1 169
Scheme 1. Synthesis of Indazoles and Pyrazino[1,2-b]indazoles
Scheme 2. Synthesis of 1,2-Substituted-3,4-dihydropyrazino[1,2-b]indazole-2-ium 6-Oxides using 2-Nos Protecting Groupsa
a Reagents and conditions: (i) CDI, pyridine, DCM, rt, 3 h, then diethylenetriamine, DCM, rt, 16 h; (ii) 2-nitrobenzenesulfonyl chlorides, lutidine, DCM,
rt, 16 h; (iii) bromoketones, DIEA, DMF, rt, 16 h; (iv) DBU, DMF, rt, 30 min; (v) 2-mercaptoethanol, DBU, DMF, rt, 5 min; (vi) methanesulfonyl chloride,
TEA, DCM, 16 h; (vii) 50% TFA, DCM, rt, 1 h.
(Scheme 2). Reaction with four 2-nitrobenzenesylfonyl
chlorides containing both electron-donating and electron-
withdrawing groups (H, CF3, NO2, and OMe, Table 1)
yielded the sulfonamides 2. The reaction outcome was
monitored by LCMS analysis of a sample released from the
resin using 50% TFA in dichloromethane (DCM) cleavage
cocktail.
the effect of substitution on the aromatic ring. The reaction
was carried out in DMF in the presence of a tertiary base.1
All four 2-nosyl derivatives yielded the expected products
3. However, LC analysis of the 2,4-diNO2 derivatives 3(3,1),
3(3,2), and 3(3,6) showed a complex mixture. The next step,
DBU-mediated cyclization of alkylated sulfonamides 3 to
indazole-6-oxides 4, was carried out in DMF. Only the 4(1,2),
4(1,3), and 4(1,6) derivatives were obtained in high purity
(∼95%) and the purity of the crude derivatives (4(2,1), 4(2,2)
Alkylation of resin 2 was carried out with four bromoke-
tones (4-Me, 4-OMe, 4-Cl, and 4-CF3, Table 1) to assess

170 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1
Kocˇ´ı and Krchnˇa´k
Scheme 4. Equilibrium Iminium-Amino Ketone
Table 1. Selection of 2-Nitrobenzenesulfonyl Chlorides and
Bromoketones
BB no.
R1
R2
1
2
3
4
5
6
H
CF3
NO2
OMe
4-Me
4-OMe
4-Cl
4-CN
3,5-diCl-4-NH2
4-CF3
Scheme 3. Equilibrium Iminium-Imidazolidine
Table 2. Relative Contents of Amino-ketones as a Function of
Substitutiona
R1/R2
CN
Me
Cl
OMe
diCl-NH2
H
CF3
NO2
5%
3%
3%
5%
8%
5%
9%
ND
6%
ND
14%
9%
30%
21%
16%
a ND ) not determined.
An analogous pH-dependent equilibrium between iminium
ions and the corresponding cyclic products has previously
been reported, for example, between 3,4-dihydroisoquino-
linium21 and 1-(2-hydroxyethyl)-2,3,4,5-tetrahydropyridinium
cations.22
and 4(2,3)) was still acceptable (80%). The cyclization of
the 4(4,1), 4(4,3), and 4(4,6) derivatives was characterized
by very low conversion and the crude product was ac-
companied by several impurities. The cleavage of the
2-nitrobenzenesulfonyl groups was carried out with 2-mer-
captoethanol and DBU in DMF.2 The 2-NO2 and 2-NO2-4-
CF3 derivatives provided products 7 with acceptable purity
(80%). Cleavage of the 2-NO2-4-OCH3-benzenesulfonyl
group was not successful, probably because of the presence
of the electron-donating methoxy group. Compounds that
provided acceptable purity were deoxygenated using meth-
anesulfonyl chloride in the presence of triethylamine (TEA)20
to provide resin-bound parent heterocycles 6.
Hydrolysis of Iminiums. An LCMS analysis of the
products highlighted the tendency of iminiums to hydrolyze
in aqueous solutions (Scheme 4). The LC traces revealed
the presence of two components, the iminiums 7 (or 8) and
the keto-amines 11 (or 12). The relative ratio of the keto-
amine was dependent on the substitution pattern on both
aromatic rings (Table 2). The ratio was significantly influ-
enced by the R2 substitution with a clear preference for the
open form with increasing electron-donating character of the
substituent. The electron-donating character of the 4-OMe
and 3,5-diCl-4-NH2 groups increased the electron density
on the carbonyl group, and caused the hydrated form to be
less prone to cyclization. The effect of substitution on the
indazole ring was less profound. In a few cases, the
difference of retention times of both components was too
small to reliably integrate the individual peaks, and therefore,
the ratio was not determined. The NMR spectra (collected
in anhydrous d6 DMSO) did not indicate the presence of
any hydrolyzed components.
Although synthesis of resins 5 using the 2-Nos protection/
activation strategy was not generally applicable for prepara-
tion of compounds with diverse side-chains, it provided
straightforward access to compounds with electron-neutral
and electron-withdrawing substituents and allowed for full
characterization and structure determination of model
compounds.
Equilibrium Iminium-Imidazolidine Derivatives. All
compounds were cleaved from the resin 6 with a TFA-
containing cleavage cocktail, and the crude products were
isolated as trifluoroacetates. The crude compounds were
purified by semipreparative reversed-phase HPLC using a
gradient elution with two different aqueous buffers, acidic
0.1% TFA and neutral ammonium acetate. There were
The hydrolysis of structurally unrelated iminium interme-
diates was reviewed23 and also exploited for preparative
purposes.24,25
Synthesis using Pht and Boc Protecting Groups. Al-
though synthesis of resins 5 using a dual 2-Nos protection/
activation strategy was straightforward, it was not generally
applicable and did not allow for the synthesis of target
compounds with a diverse side-chain group profile. Encour-
aged by the smooth transition of iminium intermediates to
complex fused heterocycles, we altered the protection
strategy and prepared the resin-bound triamine 1 using
orthogonal protection, which enabled the use of building
blocks with diverse substituents.
To differentiate between the primary and secondary amino
groups on resin 1, we protected the primary amino group
with a phthaloyl (Pht) group and the secondary amino group
by a Boc-protecting group (Scheme 5). We have shown that
a Pht group can be introduced under very mild conditions
1
remarkable differences in the H and 13C spectra of com-
pounds purified using the two different buffers.
The structures of the compounds were determined by 1D
1H and 13C NMR with 2D homo- (COSY) and heteronuclear
1H-13C (HETCOR, gHMBC) experiments. Signals of all
carbons with directly attached protons were assigned using
the HETCOR spectra. gHMBC spectra were used to analyze
connectivities. The compounds purified in 0.1% aqueous
TFA corresponded to iminium ions 7 and 8 (Scheme 3),
whereas compounds purified in aqueous ammonium acetate
cyclized to complex fused heterocycles 9 and 10. All spectra
and interpretations are included in the Supporting Informa-
tion.

Solid-Phase Synthesis
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1 171
Scheme 5. Synthesis using Pht and Boc Protecting Groupsa
a Reagents and conditions: (i) CDI, pyridine, DCM, rt, 3 h, then diethylenetriamine, DCM, rt, 16 h; (ii) N-hydroxyphthalimide, DMF, rt, 16 h; (iii) Boc2O,
pyridine, DCM, rt, 2 h; (iv) hydrazine monohydrate, MeOH/THF (1:1), rt, 4 h; (v) 2-nitrobenzenesulfonyl chloride, lutidine, DCM, rt, 16 h; (vi) bromoketone,
DIEA, DMF, rt, 16 h; (vii) DBU, DMF, rt, 30 min; (viii) 50% TFA/DCM, rt, 1 h; (ix) MsCl, TEA, DCM, 30 min at 0°C, then rt, 16 h; (x) Ac2O, acetonitrile,
2 h.
using N-hydroxyphthalimide in DMF.26 The reaction of resin
1 containing both the primary and secondary amino groups
with N-hydroxyphthalimide yielded the protected amine resin
13. Quantification of this on-resin protection reaction was
confirmed by reaction of resin 13 with Fmoc-OSu and
subsequent analysis of a cleaved sample. No double Fmoc-
ylated compound was detected in the LC traces. The reaction
of resin 13 with (Boc)2O was accomplished in 2 h in the
presence of pyridine as a base in DCM to produce resin 14.
The completion of reactions was again verified by treatment
with Fmoc-OSu. The absence of the Fmoc-derivative in a
cleaved sample confirmed the complete reaction with
(Boc)2O. The Pht group was cleaved by a hydrazine
monohydrate solution with a 50% methanol/THF mixture.
The best results were obtained with 2 M hydrazine hydrate
and a reaction time of 4 h.
The resin-bound primary amine 15 was then reacted with
2-nitrobenzenesylfonyl chlorides and the sulfonamides 16
were alkylated with bromoketones to yield the corresponding
sulfonamide ketones 17. The intermediates 17 were cyclized
to indazole 6-oxide 18, the resin was split, and one part was
deoxygenated using methanesulfonyl chloride and TEA in
DCM.20 Removal of the Boc protecting group with concur-
rent cleavage from the resin in 50% TFA/DCM yielded target
compounds 7 and 8.
(2-NO2, 2,4-diNO2, 2-NO2-4-CF3) and five bromoketones;
the set of bromoketones used for optimization (4-OMe,
4-CF3, 4-Cl) was expanded by 4-CN and 3,5-diCl-4-NH2
derivatives. We eliminated compounds having the same
substituent on both aromatic rings (e.g., compound 7(2,6)
was not made). At the polymer-supported indazoles 6-oxide
18 stage, the resins were split and one-half was deoxygenated
using methanesulfonyl chloride in the presence of TEA1 to
provide parent heterocycles 8 after cleavage from the resin.
The rate of deoxygenation was substitution-dependent; target
compounds without substitution on the indazole (R1 ) H)
were quantitatively deoxygenated after overnight treatment,
with the exception of the R2 ) CN derivative. Deoxygenation
of compounds with R1 ) CF3 and R1 ) NO2 was repeated
to complete the reaction. The compounds with the most
electron-withdrawing groups on both rings (R1 ) NO2 and
R2 ) CN) required a substantially extended reaction time
of 4 days. Synthetic data are listed in Table 3.
The target compound 7(1,1) was further derivatized in
solution by acylation of the amino group by acetanhydride
(Scheme 5). The product 19 was isolated, purified in
methanol with an 0.1% aqueous TFA gradient, and fully
1
characterized. The presence of the amide proton in the H
NMR spectrum provided further evidence for the iminium
structure.
This protection strategy was compatible with the diverse
substitution pattern on both the 2-nitrobenzenesulfonyl
chlorides and bromoketones and enabled the efficient syn-
thesis of a small combinatorial array of target compounds
(Table 1). We used three 2-nitrobenzenesulfonyl chlorides
Combinatorial Synthesis of Triamines. The orthogonal
Pht/Boc protection strategy proved to be the preferred route
for the synthesis of target compounds with diverse side-
chains on both aromatic rings. However, the use of dieth-
ylenetriamine prevented the introduction of side-chain func-

172 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1
Table 3. Analytical Data on Synthesized Compounds
Kocˇ´ı and Krchnˇa´k
resin underwent a Mitsunobu reaction with N-(2-hydroxy-
ethyl)phthalimide (resin 27). The Nos group was cleaved,
and the amine resin was protected with Boc2O. The Pht group
was cleaved by hydrazine hydrate, and the amine resin was
reacted with 2-Nos-Cl to yield resin 28. Target compounds
were obtained after finishing the reaction sequence described
for the preparation of compounds 7 and 8.
compound R1
R2
MS ESI+ puritya(%) yieldb(%)
7(1,1)
7(1,2)
7(1,3)
7(1,4)
7(1,5)
7(2,1)
7(2,2)
7(2,3)
7(2,4)
7(2,5)
7(3,1)
7(3,2)
7(3,3)
7(3,4)
7(3,5)
8(1,1)
8(1,2)
8(2,2)
8(2,3)
8(2,4)
8(3,3)
8(3,4)
8(3,5)
10(1,2)
10(1,3)
10(1,4)
10(1,5)
10(2,5)
10(3,2)
19(1,1)
29(1,1)
29(1,3)
29(1,4)
30(1,4)
34(1,1)
34(1,3)
40(1,2)
40(1,3)
40(1,4)
H
H
H
H
H
4-Me
4-OMe
4-Cl
4-CN
321
337
341
332
390
389
405
409
400
458
366
382
386
377
435
305
321
389
393
384
370
361
419
321
325
316
374
442
366
344
322
342
333
317
335
355
427
430
422
89
86
91
65
89
95
95
84
88
95
93
96
90
89
92
89
96
94
81
84
81
67
84
96
90
76
86
92
87
94
91
85
78
85
81
87
98
97
54
23
81
59
28
99
82
55
59
63
99
33
64
59
55
78
56
76
97
56
49
31
41
43
69
35
11
45
68
73
53
64
67
47
63
57
63
68
83
19
3,5-di-Cl-4-NH2
CF3 4-Me
CF3 4-OMe
CF3 4-Cl
CF3 4-CN
CF3 3,5-di-Cl-4-NH2
NO2 4-Me
NO2 4-OMe
NO2 4-Cl
NO2 4-CN
NO2 3,5-di-Cl-4-NH2
H
H
CF3 4-OMe
CF3 4-Cl
CF3 4-CN
NO2 4-Cl
NO2 4-CN
Synthesis of 2-(3-Aminopropyl)-1-aryl-3,4-dihydropy-
razino[1,2-b]indazole-2-ium 6-oxides 34. The expanded ring
analogs of compounds 7 and 8 were prepared by reacting
CDI-activated Wang resin with 1-aminopropanol (Scheme
8). The alcohol resin 31 was converted to a mesyl derivative
by reaction with methanesulfonyl chloride. The resin-bound
unsymmetrical triamine 32 was obtained after reaction with
ethylenediamine. The reaction sequence was finished using
the previously described protocol and products 34 were
obtained after TFA-mediated cleavage from the resin.
4-Me
4-OMe
Synthesis of 4-Carbamoyl-Benzyl Derivatives 40. All
compounds described so far contained a nucleophile (amino
or hydroxyl group) that facilitated ring closure of iminiums
to produce fused five or six-membered rings. We also
prepared 4-carbamoyl derivatives 40 (Scheme 9) that elimi-
nated the nucleophile from the side-chain. Briefly, Rink
amide resin was acylated with 4-(Fmoc-aminomethyl)benzoic
acid (resin 35). The Fmoc group was cleaved and the amine
resin was reacted with 2-Nos-Cl to generate sulfonamide
resin 36. N-alkylation with N-(2-hydroxyethyl)phthalimide
under Mitsunobu conditions yielded resin 37. At this stage,
the 2-Nos group was cleaved and the secondary amine was
reacted with Boc2O in the presence of pyridine to afford the
protected amine 38. After cleavage of the phthalimide group,
the resin 39 was reacted with 2-Nos-Cl. Alkylation with three
bromoketones (4-MeO, 4-Cl, and 4-CN) proceeded smoothly.
After cyclization to indazoles and cleavage from resins, the
LC-MS analyses of final products indicated iminium/amino
ketone equilibriums of 86%/11%, 71%/25%, and 66%/31%
for the 4-OMe, 4-Cl, and 4-CN derivatives, respectively.
NO2 3,5-di-Cl-4-NH2
H
H
H
H
4-OMe
4-Cl
4-CN
3,5-di-Cl-NH2
CF3 3,5-di-Cl-4-NH2
NO2 4-OMe
H
H
H
H
H
H
H
H
H
H
4-Me
4-Me
4-Cl
4-CN
4-CN
4-Me
4-Cl
4-OMe
4-Cl
4-CN
a Purity of crude product; b Yield after purification.
tional groups on the triamine and limited the substitution
pattern of the products. In addition, it did not allow for the
modification of the substituent attached to the secondary
amine. Thus, as a next step in the development of these
syntheses, we prepared amine resins from two building
blocks while maintaining the same protection strategy. Two
different scenarios were tested and successfully applied for
the synthesis.
Route A (Scheme 6) involved the immobilization of an
amino alcohol using CDI-activated Wang resin. The alcohol
resin was converted to mesylate 22 using methanesulfonyl
chloride and reacted with ethylenediamine to yield amine
resin 23. An alternative route B involved reaction of immo-
bilized amine with 2-Nos-Cl (resin 24) and Mitsunobu
reaction with the ꢀ-amino alcohol protected by the Pht group
(resin 25).
All library compounds were submitted for evaluation of
biological activities to High Throughput Screening in the
Molecular Libraries Probe Production Centers Network. The
results are available in PubChem (http://pubchem.ncbi.nlm.
nih.gov/).
Conclusion
Efficient solid-phase synthesis of complex fused hetero-
cyclic systems was developed using amino alcohols, di-
amines, benzenesulfonyl chlorides, and bromoketones. Syn-
theses tolerated a wide range of substitution patterns on
building blocks, and all reactions were carried out under mild
conditions. Acid-mediated cleavage of resin-bound indazole
precursors yielded 1,2-substituted 3,4-dihydropyrazino[1,2-
b]indazole-2-ium trifluoroacetates that spontaneously cyclized
to complex fused heterocycles including 3,6,9,10-tetra-
azatetracyclo[7.7.0.02,6.011,16]hexadeca-11,13,15-trienes, 3-oxa-
6,9,10-triazatetracyclo[7.7.0.02,6.011,16]hexadeca-11,13,15-
These routes were used to prepare compounds that enabled
iminium-mediated cyclization with different ring sizes
(hexahydro-pyrimidine and oxazolidine in addition to im-
idazolidine), as well as compounds that did not contain an
internal nucleophile amenable to reaction with the iminium
(4-carbamoyl-benzyl).
Synthesis of Oxazolidine Derivatives 30. Wang resin was
activated via trichloroacetmimidate27 (Scheme 7) and reacted
with Fmoc-ethanolamine (resin 26). The Fmoc group was
cleaved, and the amine resin reacted with 2-Nos-Cl. The Nos

Solid-Phase Synthesis
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1 173
Scheme 6. Combinatorial Assembly of Amine Resins
Scheme 7. Synthesis of Oxazolidine Derivativesa
a Reagents and conditions: (i) trichloroacetonitrile, DBU, DCM, 0 °C to rt, DCM wash, then Fmoc-ethanolamine, BF3 · Et2O, anhydrous THF, rt, 30 min;
(ii) piperidine, DMF, rt, 20 min; (iii) 2-nitrobenzenesulfonyl chloride, lutidine, DCM, rt, 16 h; (iv) N-(2-hydroxyethyl)phthalimide, DIAD, anhydrous THF,
5 h; (v) mercaptoethanol, DBU, DMF, rt, 30 min; (vi) Boc2O, pyridine, DCM, rt, 2 h; (vii) hydrazine monohydrate, MeOH/THF (1:1), rt, 4 h; (viii) cf.,
Scheme 5, reactions vi to viii; (ix) MsCl, TEA, DCM, 30 min at 0°C, then rt, 16 h.
Scheme 8. Synthesis of Hexahydro-pyrimidine Derivativesa
a Reagents and conditions: (i) CDI, pyridine, DCM, rt, 3 h, then 1-aminopropanol, DCM, rt, 16 h; (ii) mesyl chloride, pyridine, 1 h; (iii) ethylenediamine,
DMSO, 2 days; (iv) N-hydroxyphthalimide, DMF, rt, 16 h; (v) Boc2O, pyridine, DCM, rt, 2 h; (vi) hydrazine monohydrate, MeOH/THF (1:1), rt, 4 h; (vii)
2-nitrobenzenesulfonyl chloride, lutidine, DCM, rt, 16 h, (viii) cf., Scheme 5, reactions vi-viii.
trienes, and 3,7,10,11-tetraazatetracyclo[8.7.0.02,7.012,17]hepta-
deca-12,14,16-trienes.
Experimental Procedures. Reaction with CDI and
Diethylenetriamine (Resin 1). Wang resin, 1 g, was swollen
in DCM. A solution of CDI (5 mmol, 810 mg) and pyridine
(5 mmol, 400 µL) in 10 mL of DCM was added, and the
slurry was shaken for 3 h. The resin was washed 3× with
DCM, and a solution of diethylenetriamine (5 mmol, 540
µL) in 10 mL of DCM was added. The resin slurry was
shaken for 16 h and washed 3× with DCM.
Experimental Section
Solid-phase syntheses were carried out using a manually
operated Domino Block synthesizer28 (www.torviq.com) in
disposable polypropylene reaction vessels. Commercially
available solvents, resins, and reagents were used. The Rink
resin (100-200 mesh, 1% DVB, 0.75 mmol/g), aminometh-
yl resin (100-200 mesh, 1% DVB, 0.9 mmol/g) and Wang
resin (100-200 mesh, 1% DVB, 1.0 mmol/g) were obtained
from Advanced ChemTech (Louisville, KY, www.peptide.
com). The swelling of resins in DCM was measured before
syntheses, and those with swollen volumes greater than 7
mL/g of dry resin were used.29 All reactions were carried
out at ambient temperature (21 °C) unless otherwise stated.
Reaction with N-Hydroxyphthalimide (Resins 13).
Resin 1, 1 g, was washed 3× with DCM and 3× DMF, and
a solution of N-hydroxyphthalimide (10 mmol, 1.63 g) in
10 mL of DMF was added to the resin. The reaction slurry
was shaken for 16 h. The resin was washed with 5× DMF
and 3× DCM.
Reaction with Boc2O (Resins 14). Resin 13, 1 g, was
washed 3× with DCM. A solution of Boc2O (5 mmol, 1.1 g)

174 Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1
Scheme 9. Synthesis of 4-Carbamoyl-benzyl Derivatives 40a
Kocˇ´ı and Krchnˇa´k
a Reagents and conditions: (i) 50% piperidine, DMF, 15 min; (ii) 4-(Fmoc-aminomethyl)-benzoic acid, HOBt, DIC, DCM/DMF (1:1), 16; (iii)
2-nitrobenzenesulfonyl chloride, lutidine, DCM, 16 h; (iv) N-(2-hydroxyethyl)phthalimide, PPh3, DIAD, 0 °C, 30 min then rt, 16 h; (v) 2-mercaptoethanol,
DBU, DMF, 5 min; (vi) Boc2O, pyridine, DCM, 2 h; (vii) hydrazine monohydrate, MeOH/THF (1:1), rt, 4 h; (viii) cf. Scheme 5, reactions vi-viii.
and pyridine (5 mmol, 400 µL) in 10 mL of DCM was added
to the resin, and reaction slurry was shaken for 2 h. The
resin was washed 3× with DCM.
DCM, washed 3× with DMF, and treated with 50%
piperidine in DMF for 15 min. After it was washed 3× with
DMF and 3× with DCM, a solution of 4-(Fmoc-aminom-
ethyl)benzoic acid (3 mmol, 1.12 g), HOBt (3 mmol, 405
mg), and DIC (3 mmol, 463 µL) in 10 mL of DCM/DMF
(1:1) was added to syringe and the slurry was shaken for
16 h. The resin was washed 5× with DMF and 5× with
DCM.
Reaction with Hydrazine Monohydrate (Resins 15).
Resin 14, 1 g, was washed 3× with DCM and 3× with THF.
A solution of hydrazine monohydrate (41.2 mmol, 2 mL) in
10 mL MeOH/THF (1:1) was added to the resin, and reaction
slurry was shaken for 6 h. The resin was washed with MeOH
(5×) and with DCM (3×).
Mitsunobu Reaction with N-(2-Hydroxyethyl)phthal-
imide (Resin 37). Resin 36, 1 g, was washed 3× with DCM
and 3× with anhydrous THF. A solution of N-(2-hydroxy-
ethyl)phthalimide (2.6 mmol, 480 mg) and PPh3 (2.5 mmol,
655 mg) in 10 mL of anhydrous THF was added to the
syringe and cooled in freezer over 30 min. Then DIAD (2.4
mmol, 480 µL) was added into syringe and shaken for 16 h.
The resin was washed 5× with THF and 5× with DCM.
Cleavage and Purification of Products. Resins with
target compounds, typically ∼250 mg, were treated with 50%
TFA/DCM for 1 h. TFA solution was collected; the resin
was washed with 50% TFA/DCM, 3× DCM, and the com-
bined extracts were evaporated by a stream of nitrogen and
purified by semipreparative HPLC.
Reaction with 2-Nos-Cl (Resin 16). Resin 15, 1 g, was
washed 3× with DCM. A solution of 2-Nos-Cl (3 mmol,
663 mg) and lutidine (3.3 mmol, 382 µL) in 10 mL of DCM
was added to the resin, and the reaction slurry was shaken
for 16 h. The resin was washed with 5× DCM.
Reaction with Bromoketone (Resins 17). Resin 16, 1 g,
was washed 3× with DCM and 3× with DMF. A solution
of 0.5 M bromoketone (5 mmol) and 1 M DIEA (10 mmol,
1.73 mL) in 10 mL of DMF was added. The resin slurry
was shaken for 16 h. The resin was washed 3× with DMF
and 5× DCM.
Cyclization to Indazole Oxides (Resins 18). Resin 17,
250 mg, was washed 3× with DCM and 3× with DMF. A
solution of 0.2 M DBU (1 mmol, 150 µL) in 5 mL of DMF
was added, and the resin slurry was shaken for 30 min. The
resin was washed 3× with DMF, 3× with MeOH, and 5×
with DCM.
Reaction with Acetic Anhydride (21). The compound
7(1,1) (0.07 mmol, 24.6 mg) was dissolved in acetonitrile
(2 mL) and acetic anhydride (2.3 mmol, 217 µL) was added,
and the reaction mixture was stirred for 3 h and evaporated
under reduced pressure. The crude product purified by
semipreparative HPLC (MeOH-0.1% aqueous TFA).
Deoxygenation of indazole oxides. Syringe with indazole
oxide resin 18, 250 mg, was washed 3× with DCM, and
0.7 M TEA (245 µL) in 2.5 mL of DCM was added. The
syringe was connected with the second syringe containing
0.5 M mesyl chloride (96 µL) in 2.5 mL of DCM. Connected
syringes were left in a freezer for 30 min, and then mesyl
chloride solution was drawn into the syringe with the resin.
The resin slurry was shaken for 16 h. Resin was washed
with 5× with DCM.
Acknowledgment. The work was supported by the
Department of Chemistry and Biochemistry, University of
Notre Dame, and the NIH (GM079576). We gratefully
appreciate the use of the NMR facility at the University of
Notre Dame.
Acylation of Rink Resin with 4-(Fmoc-aminomethyl)-
benzoic Acid (Resin 35). Rink resin, 1 g, was swollen in
Supporting Information Available. Details regarding
experimental procedures, spectroscopic data and NMR

Solid-Phase Synthesis
Journal of Combinatorial Chemistry, 2010 Vol. 12, No. 1 175
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spectra for new compounds are available free of charge via
the Internet at http://pubs.acs.org.
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