Diversity oriented synthesis of a vinblastine-templated library of 7-aryl-octahydroazonino[5,4-b]indoles via a three-component reaction

Article abstract of DOI:10.1021/co300122n

A vinblastine-templated library of 7-aryl-octahydroazonino[5,4-b]indoles was prepared by a three-component reaction from indolizino[8,7-b]indoles, chloroformates, and activated arenes via a chloroformate mediated fragmentation of the indolizinoindole nucleus followed by insertion of an activated arene. In addition to N3-carbamoyl-7-aryl-octahydroazonino[5,4-b]indoles prepared in one step, a wide range of N3-substituted substrates were synthesized in one pot via the derivatization of a versatile N3-H-azonino[5,4-b]indole intermediate generated in situ by application of the same strategy. A subset of 308 compounds out of a virtual library of 3216, representing 13 different chemotypes, was prepared by high throughput solution-phase synthesis and subsequently purified by mass-triggered high performance liquid chromatography (HPLC). A total of 188 compounds with a minimum purity of 80% by UV_{214 nm} and 85% by evaporative light scattering detection (ELSD) was isolated for primary screening.

Full text of DOI:10.1021/co300122n

Research Article
pubs.acs.org/acscombsci
Diversity Oriented Synthesis of a Vinblastine-Templated
Library of 7‑Aryl-Octahydroazonino[5,4‑b]indoles via a
Three-Component Reaction
Demosthenes Fokas,*,† Mira Kaselj,‡ Yuko Isome,§ and Zhimin Wang∥
Department of Chemistry, ArQule Inc, 19 Presidential Way, Woburn, Massachusetts 01801, United States
S
* Supporting Information
ABSTRACT: A vinblastine-templated library of 7-aryl-octa-
hydroazonino[5,4-b]indoles was prepared by a three-component
reaction from indolizino[8,7-b]indoles, chloroformates, and
activated arenes via a chloroformate mediated fragmentation of
the indolizinoindole nucleus followed by insertion of an activated
arene. In addition to N3-carbamoyl-7-aryl-octahydroazonino-
[5,4-b]indoles prepared in one step, a wide range of N3-substituted
substrates were synthesized in one pot via the derivatization of a
versatile N3−H-azonino[5,4-b]indole intermediate generated in situ by application of the same strategy. A subset of 308 compounds
out of a virtual library of 3216, representing 13 different chemotypes, was prepared by high throughput solution-phase synthesis and
subsequently purified by mass-triggered high performance liquid chromatography (HPLC). A total of 188 compounds with a
minimum purity of 80% by UV214 nm and 85% by evaporative light scattering detection (ELSD) was isolated for primary screening.
KEYWORDS: 7-aryl-octahydroazonino[5,4-b]indole, indolizino[8,7-b]indole, chloroformate, arene, three-component reaction
INTRODUCTION
■
The design and synthesis of screening libraries for the generation
of new leads constitutes an integral part of the drug discovery
process since the advent of combinatorial chemistry.1 Natural
products have achieved an unrivaled success rate in generating
lead structures for drug discovery because of their inherent
complexity and high density of functional and pharmacophoric
groups.2−4 They cover diversity and chemistry space not yet
readily available from synthetic drug-like libraries and continue
to inspire the design of novel natural product-like libraries by
diversity oriented synthesis (DOS) strategies.5−9 Natural
product-like molecules could populate chemical space occupied
by bioactive natural products and lead to the discovery of novel
modulators of protein−protein interactions as well as chemical
probes for dissecting dynamic signaling pathways.10,11
In the search for natural product-like screening libraries, we
turned our attention to the design of structurally diverse azonino-
[5,4-b]indoles as new simplified vinblastine analogues. Vinblas-
tine and vincristine were among the earliest clinically active
antimitotic agents identified to inhibit tubulin polymerization by
binding β-tubulin at the Vinca alkaloid site.12,13 They are widely
used as antitumor drugs, and research toward the discovery of
new analogues of vinblastine and vincristine is ongoing.14−17
Inspired by early model studies on vinblastine’s hypothetical
mechanism of action,18 we surmised that a series of octahydro-
azonino[5,4-b]indoles (I) with an activated aryl group at the
C7 carbon center might exhibit some of vinblastine’s structural
features required for cytotoxic activity and lead to a series of new
truncated vinblastine analogues (Figure 1). Access to a diverse
set of the target compounds would involve the intermediacy of
Figure 1. 7-Aryl-octahydroazonino[5,4-b]indoles from β-THC scaffolds.
7-aryl-octahydroazonino[5,4-b]indole II, containing an activated
aryl group at the C7 carbon center as well as a secondary N3
nitrogen center. Compound II would in turn result from the
fragmentation of tertiary amine III.
Received: October 9, 2012
Revised: December 6, 2012
Published: December 13, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of 7-Aryl-octahydroazonino[5,4-b]indoles via a Three-Component Reaction
Aiming to develop a strategy amenable to high throughput
solution-phase synthesis of the target compounds, we turned our
attention to the chloroformate mediated fragmentation19−21 of
indolizino[8,7-b]indole III (R1 = H, CO2Me). Herein, we wish to
report the results of our studies pertaining to the solution-phase
synthesis of a diverse library of 7-aryl-octahydroazonino[5,4-b]indoles
with general structure I, resulting from the chloroformate mediated
fragmentation of indolizinoindole III (R1 = H, CO2Me) accom-
panied by insertion of an activated arene to the newly generated
azonino nucleus.
fragmentation of 1{1} and 1{2}. Indeed, treatment of 1{1} with a
chloroformate, in the presence of 3,4,5-trimethoxylphenol, gave
phenol adduct 4. However, spirolactone 5, instead of azonine
ester 4 (R1 = CO2Me), was formed from scaffold 1{2} under the
same reaction conditions.23 Attempts to generate compound 4
(R1 = CO2Me) were not fruitful and spirolactone 5 was obtained
as the sole product, presumably via an intramolecular lactonization
reaction between the C7 carboxymethyl group and the neighbor-
ing phenolic hydroxyl.29 Both aromatic and aliphatic chlorofor-
mates induced azonine ring formation equally well.
Given the limited number of available m-dialkylaminoanisoles,
the use of N-substituted-4-(3-methoxyphenyl)piperazines seemed
a viable alternative since they could exhibit similar reactivity and
furthermore introduce additional diversity based on the substitu-
tion pattern of the secondary piperazine nitrogen. However, the
limited reactivity of N-alkyl substrates,30 coupled with the limited
availability of N-acyl and N-sulfonyl-4-(3-methoxyphenyl)-
piperazines, led us to explore the use of N-Boc-4-(3-methoxy-
phenyl)piperazine instead (Scheme 2). The presence of the N-Boc
carbamate group would reduce the basicity of the piperazine
nitrogen and thus prevent its competitive side reaction with the
chloroformate reagent during the fragmentation of the indolizino-
indole nucleus. In addition, subsequent cleavage of the N-Boc
carbamate group would enable the introduction of additional
diversity at the secondary piperazine nitrogen through a wide
range of capping reagents.
RESULTS AND DISCUSSION
■
Library Design. On the basis of prior studies,22,23 we realized
that a series of structurally diverse N3-carbamoyl-7-aryloctahy-
droazonino[5,4-b]indoles with general structures 2−4 could
result in one step from indolizino[8,7-b]indole 1{1,2}, chloroformates
and the corresponding activated arenes, that is, m-dimethylamino-
anisole, indoles, and 3,4,5-trimethoxyphenol (Scheme 1). Treatment
of indolizinoindole 1{1,2} with a chloroformate would induce
cleavage of the C1−N2 bond in the β-THC nucleus, providing a
transient iminium ion which could then be trapped by an
activated arene to produce the corresponding azoninoindole.
The participation of activated anilines in the chloroformate
mediated fragmentation of indolizinoindoles has been described
in the past.24,25 Thus, combination of 1{1,2} with m-dimethyl-
aminoanisole and a chloroformate in dichloroethane (DCE),
upon stirring at room temperature, resulted in the formation of
N-carbamoyl-azonino[5,4-b]indole 2.26 Activated arenes such as
indoles and oxygenated aromatics were also found to participate
in this fragmentation/insertion chemistry.23 Indolizinoindoles
1{1}27 and 1{2}28 underwent a chloroformate induced facile ring
expansion with indoles in DCE to produce the corresponding
bis-indole alkaloids with general structure 3. A number of indoles
with various substitution patterns were shown to be reactive, with
the alkylation occurring exclusively at the β-indolic carbon. Of a
series of oxygenated aromatics tested, 3,4,5-trimethoxylphenol
was that found to insert to the azonino nucleus during the
Indeed, indolizinoindoles 1{1} and 1{2} underwent a similar
insertion reaction with N-Boc-4-(3-methoxyphenyl)piperazine31
to afford octahydroazonino[5,4-b]indole 6 (Scheme 2). Sub-
sequent cleavage of the N-Boc group with HCl in dioxane re-
sulted in piperazine 7, a versatile intermediate for the synthesis of
several chemotypes. For example, treatment of crude piperazine
7 with acid chlorides, in the presence of an excess of Hunig’s base
̈
at room temperature, afforded a set of amides 8. Similarly,
reaction of 7 with sulfonyl chlorides under the same reaction
conditions gave sulfonamides 9. Also, piperazine 7 underwent a
reductive amination with aldehydes in the presence of NMe4BH-
(OAc)3 to produce N-alkylated piperazines 10.32
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a
Scheme 2. Entry to Azonino[5,4-b]indoles Containing a 4-(3-Methoxyphenyl)piperazine Moiety at C7
a
Reagents and conditions: (a) 4 N HCl in dioxane, DCE, rt, 3 h; (b) R3COCl (1 equiv), NiPr2Et (9 equiv), CH3CN, rt, 16 h; (c) R3SO2Cl (1 equiv),
NiPr2Et (7.5 equiv), CH3CN, rt, 16 h; (d) R3CHO (1 equiv), NMe4BH(OAc)3 (2.5 equiv), DCE, rt, 15 h.
Scheme 3. Access to a Diverse Set of N3-Substituted-7-aryl-octahydroazonino[5,4-b]indoles via the in Situ Derivatization of a
a
Secondary Azonine
a
Reagents and conditions: (a) ACE-Cl (1.1 equiv), ArH (1 equiv), DCE, rt, 12 h; (b) MeOH, 50 °C, 3 h; (c) Epoxide (1 equiv), NiPr2Et (5 equiv),
MeOH, 55 °C, 8 h; (d) R2COCl (1 equiv), NiPr2Et (7.5 equiv), CH3CN, rt, 16 h; (e) R2SO2Cl (1 equiv), NiPr2Et (7.5 equiv), CH3CN, rt, 16 h.
The strategies described in Schemes 1 and 2 provide access to
a diverse set of N3-carbamoyl-7-aryl-octahydroazonino[5,4-b]-
indoles in one pot. Although enrichment of diversity at the C7-
carbon center is achieved through the insertion of different
activated arenes, the diversity at the newly generated azonine N3-
center is limited to the carbamate group. Therefore, access to a
structurally diverse set of octahydroazonino[5,4-b]indoles
should be attained via the derivatization of the secondary azonine
nitrogen and shouldrequire the intermediacy of the corresponding
N3−H-azonino[5,4-b]indole. Considering the rather harsh con-
ditions required for the cleavage of nonactivated alkyl or aryl
carbamates, access was necessary to a carbamate intermediate
which could be cleaved to the requisite secondary azonine in a high
throughput synthesis platform under mild conditions. Among
several activated carbamate groups which could be readily cleaved,
α-chloroethylcarbamate33 seemed to constitute an attractive
candidate since it could be cleaved by heating in MeOH.
Indolizinoindoles 1{1} and 1{2} underwent a facile ring expansion
as well with α-chloroethylchloroformate (ACE-Cl), in the pre-
sence of m-dimethylaminoanisole and indoles, to produce the
corresponding α-chloroethylcarbamates 11 and 12 respectively
(Scheme 3). Subsequent cleavage of the labile carbamates 11 and
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Figure 2. cLogP plot versus MW profile of a set of 160 compounds selected for synthesis.
12 under heating inMeOHat50°C for 3 h, producedthe requisite
N3−H-azonino[5,4-b]indoles 13 and 14, respectively.34 Azonines
13 and 14 could subsequently be derivatized in situ, without
having to be isolated, and result in a diverse set of N3-substituted-
7-aryl-octahydroazonino[5,4-b]indoles. Thus, treatment of crude
mainly by cherry-picking38 of the virtual library. A subset of 308
compounds was selected for synthesis from a potential virtual
library of 3216 octahydroazoninoindoles (Table 1). These com-
pounds were then purified on an in-house high throughput
purification platform by reverse phase high performance liquid
chromatography (HPLC) with mass-triggered fraction collec-
tion,39,40 quantified by weight, and characterized by LC/MS to
establish the purity and identity of each collected compound.
The overall passing rate of the library was 61%, and 188 good
compounds were isolated for primary screening assays according
to our purity and quantity criteria (quantity ≥5 μmol, purity:
UV214 nm ≥80% and ELSD ≥ 85%). Compounds that did not
fulfill the purity and quantity criteria were immediately culled.
Representative compounds from the library are illustrated in
Figure 4. Numbers in parentheses indicate the isolated yield in
μmol, the UV214 nm and the evaporative light scattering detection
(ELSD) purity of samples isolated after high throughput HPLC
purification, respectively. More details regarding the purity and
quantity of all compounds synthesized, as well as the synthesis
layout of the chemotypes described, can be found in the
Supporting Information section. A few samples were randomly
selected from each chemotype subset for evaluation by 1H NMR
and 13C NMR to confirm their structures and purities.41
A passing rate >50% was observed for the majority of chemo-
types synthesized, as shown in Table 1, except for azoninoindoles
16, 18, and 20 which were produced with a passing rate <40%.
The low passing rate for these chemotypes is not surprising and
may be attributed to the instability of the intermediate azonine
14 (R1 = H), as it was observed in the early library design process.
Although a high passing rate was observed for the synthesis of
chemotypes 9 and 10, their average recovery was rather low pre-
sumably because of incomplete derivatization of the intermediate
piperazine 7.
13 with epoxides in MeOH and an excess of Hunig’s base,
̈
produced aminoalcohols 15. Reaction of 13 with a series of acid
chlorides as well as sulfonyl chlorides in the presence of an excess
of Hunig’s base, produced amides 17 and sulfonamides 19,
̈
respectively.35 Likewise, elaboration of azonine 14 under the same
reaction conditions afforded azonino[5,4-b]indoles16, 18, and 20.
Indolylazonines with general structure 14 (R1 = H) were
found to be unstable, and they gradually decomposed at room
temperature. They were acid sensitive and decomposed to
indolizinoindole 1{1}.23 Decomposition was observed even
when samples were dissolved in CDCl3, presumably by traces of
HCl present in the solvent. Therefore, immediate derivatization
of azonine 14 was necessary.
Library Synthesis. On the basis of the chemistry depicted in
Schemes 1, 2, and 3, the synthesis of a diverse library of 7-aryl-
octahydroazonino[5,4-b]indoles, consisting of 13 different
chemotypes, utilized indolizinoindoles 1{1,2}, m-dimethylami-
noanisole, 3,4,5-trimethoxyphenol, N-Boc-4-(3-methoxyphenyl)-
piperazine, and a set of commercially available indoles, chloro-
formates, acid chlorides, sulfonyl chlorides, aldehydes, and epoxides.
Given that the design of these octahydroazonino[5,4-b]indoles is
based on a large natural product, it was expected that the overall
library profile would not comply with Lipinski’s36 rule of five criteria.
Indeed, reagent selection according to the rule of five criteria was
rather limited because of prevalent molecular weight and clogP
violations observed in a large portion of the library (Figure 2).
Therefore, chemsets of 10 chloroformates, 23 indoles, 25 acid
chlorides, 25 sulfonyl chlorides, 18 aldehydes, and 12 epoxides
were selected from a larger pool of commercially available
reagents, based on diversity criteria, using an integrated ArQule
library design tool (Figure 3).37
CONCLUSIONS
■
We have designed and prepared by solution-phase synthesis a
vinblastine-templated library of 7-aryl-octahydroazino[5,4-b]-
indoles, constisting of 13 different chemotypes. The chemistry
Library synthesis was performed on 100 μmol scale with a
small set of compounds being produced for each chemotype,
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Figure 3. Chemsets of commercially available monomers used in library synthesis.
described here contains all the attributes of a multicomponent
reaction42−44 resulting in diverse natural product-like structures
in an efficient and convergent manner. In addition, it illustrates
an example of diversity oriented synthesis of natural product-like
molecules encompassing elements of appendage and functional
diversity.45,46 Furthermore, entry to spirolactone chemotype 5
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Table 1. Library Results Per Azonino[5,4-b]indole Chemotype Synthesis
a
b
c
d
chemotype
virtual library size
produced
isolated
quantity (μmol)
purity UV214/ELSD (%)
passing rate (%)
2
20
460
10
20
24
10
20
43
23
24
24
24
24
24
24
24
308
17
17
6
50.3
36.4
36.9
27.2
27
95/100
97/100
99/100
92/98
85
71
60
70
54
67
79
71
38
75
17
79
38
3
4
7
20
14
23
16
19
17
9
8
500
250
180
24
95/99
9
9.8
96/100
98/100
95/100
94/100
92/100
90/100
99/100
93/100
10
8.9
e
15
36.7
23.9
36
e
16
552
25
17
18
4
18
575
25
27.6
27.3
15.4
19
19
9
20
575
3216
f
f
f
total
188
27.9
95/99.8
61
a
b
Isolated compounds after HPLC purification meeting the purity/quantity criteria. Average recovery per chemotype set isolated based on 100 μmol
c
d
e
scale reactions. Average purity per chemotype set isolated. Percentage of the library that passed the purity/quantity culling criteria. Aminoalcohol
derivatives from optically active epoxides were isolated as a mixture of diastereomers. Overall library recovery, purity, and passing rate.
f
represents an example of skeletal diversity47 where a new scaffold
can be generated within the same library. Results of our studies,
including biological data, will be reported in due course.
Compound 3{17}. 300 MHz H NMR (CDCl3) δ 7.50 (d,
1 H, J = 7.6 Hz), 7.40−6.99 (m, 9 H), 4.05 (t, 1 H, J = 6.1 Hz),
3.96 (m, 1 H), 3.76 (s, 3 H), 3.72 (s, 3 H), 3.1 (br s, 5 H), 2.62 (br
s, 1 H), 1.62 (m, 6 H), 0.94 (t, 3 H, J = 7.3 Hz). MS (ES+) m/z for
C29H33N3O4: calcd, 487.25; found, 488.31 (M+H).
1
EXPERIMENTAL PROCEDURES
■
Compound 4{4}. 300 MHz 1H NMR (CDCl3, as a mixture of
rotamers) δ 7.75 (br s, 1 H), 7.48 (d, 1 H, J = 7.0 Hz), 7.26−7.06
(m, 3 H), 6.39 (s, 0.7 H), 6.30 (s, 0.3 H), 5.20 (dd, 0.7 H, J = 5.3,
13.2 Hz), 5.12 (dd, 0.3 H, J = 4.4, 13.1 Hz), 4.18−4.0 (m, 2 H),
3.96 (s, 2 H), 3.88 (d, 3 H), 3.79 (d, 6 H), 3.73 (s, 1 H), 3.39
(t, 0.7 H, J = 12, 14.9 Hz), 3.24 (t, 0.3 H, J = 11.7, 14.1 Hz), 3.04
(m, 1 H), 2.81−2.60 (m, 2 H), 1.85−1.62 (m, 2 H), 1.35 (m, 1 H),
1.05 (q, 1 H, J = 12, 13.5 Hz). 75.4 MHz 13C NMR (CDCl3, as a
mixture of rotamers) δ 158.1, 157.3, 152.7, 152.0, 150.4, 149.9,
138.4, 138.3, 135.4, 129.0, 128.2, 127.8, 125.3, 120.8, 118.6,
117.5, 117.4, 116.1, 115.6, 112.2, 111.7, 110.6, 97.5, 97.0, 61.4,
60.9, 55.9, 52.8, 52.7, 51.0, 50.1, 49.6, 49.2, 31.9, 31.5, 31.3, 24.7,
23.7, 22.4, 21.4. MS (ES+) m/z for C25H30N2O6: calcd, 454.21;
found, 455.25 (M+H).
Synthesis of Azonino[5,4-b]indoles 7. A solution of crude
carbamate 6 (∼100 μmol) in DCE, prepared according to the
general method, was treated with 500 μL (2 mmol) of a solution
of 4 N HCl in dioxane. The reaction mixture was shaken at room
temperature for 3 h and then concentrated to afford the crude
product. The samples were dissolved in 500 μL of DMSO and
subsequently purified by mass-triggered reverse phase prep-HPLC.
Compound 7{11}. 300 MHz 1H NMR (CDCl3, as a mixture of
rotamers) δ 9.40 (br s, 1 H), 7.45 (d, 1 H, J = 7.0 Hz), 7.28−7.06
(m, 4 H), 6.43 (t, 2 H, J = 6.4 Hz), 4.60−4.30 (br s, 1 H), 4.03 (m,
2 H), 3.75 (m, 6 H), 3.16 (s, 6 H), 3.04 (s, 6 H), 2.55 (s, 4 H),
1.62 (q, 4 H, J = 7.0 Hz), 0.93 (q, 3 H, J = 6.7 Hz). 100.6 MHz 13C
NMR (CDCl3, as a mixture of rotamers) δ 157.0, 151.7, 134.5,
129.0, 128.2, 125.3, 121.8, 119.0, 118.0, 117.9, 110.7, 107.7,
100.6, 66.9, 66.7, 55.5, 52.4, 49.3, 49.2, 47.6, 47.2, 46.7, 45.9, 45.4,
26.3, 25.8, 23.1, 22.4, 10.6, 10.5. MS (ES+) m/z for C31H40N4O5:
calcd, 548.30; found, 549.50 (M+H).
General Experimental Procedure for the Synthesis of
N3-Carbamoyl Azonino[5,4-b]indoles (2, 3, 4, 6, 11, 12).
Stock solutions of indolizinoindoles 1{1,2} (0.1 M), chloro-
formates (0.5 M), and activated arenes (0.5 M) were prepared
in anhydrous DCE. Solutions of 1{1,2} (1000 μL, 100 μmol),
arene (200 μL, 100 μmol) and chloroformate (220 μL, 110 μmol)
were subsequently dispensed to a round-bottom two-drum vial in
a 24 well plate. The reaction mixture was shaken at room tem-
perature overnight and then concentrated under vacuum to
generate the crudeproduct. Thesamples ofchemotypes2, 3, and 4
were dissolved in 500 μL of DMSO and subsequently purified by
mass-triggered reverse phase prep-HPLC.
Compound 2{11}. 300 MHz 1H NMR (CDCl3, as a mixture of
rotamers) δ 7.45 (d, 1 H, J = 7.6 Hz), 7.29 (m, 1 H), 7.15−7.06
(m, 3 H), 6.32 (br s, 2 H), 4.02 (m, 2 H), 3.75 (d, 3 H), 3.63
(s, 3 H), 3.32−2.60 (m, 8 H), 2.92 (s, 6 H), 1.62 (q, 4 H, J = 6.7,
7.0 Hz), 0.88 (q, 3 H, J = 6.4, 7.3 Hz). 75.4 MHz 13C NMR
(CDCl3, as a mixture of rotamers) δ 157.1, 157.0, 156.3, 150.9,
134.5, 133.0, 129.0, 128.2, 125.3, 121.6, 118.8, 117.9, 117.8,
110.5, 104.3, 96.8, 66.8, 66.7, 55.4, 52.3, 47.6, 47.3, 46.7, 45.9,
41.0, 26.3, 25.8, 23.1, 22.4, 10.6, 10.5. MS (ES+) m/z for
C29H37N3O5: calcd, 507.27; found, 508.39 (M+H).
Compound 3{7}. 300 MHz 1H NMR (CDCl3, as a mixture of
rotamers) δ 8.20 (s, 1 H), 7.65 (s, 1 H), 7.60 (d, 1 H, J = 6.4 Hz),
7.36−6.88 (m, 11 H), 6.98 (d, 1 H, J = 7.9 Hz), 6.91 (t, 1 H, J =
7.9 Hz), 4.83 (m, 1 H), 4.32 (m, 2 H), 3.54 (m, 1 H), 3.32−3.12
(dddd, 1 H, J = 4.7, 15.8 Hz), 3.06−2.83 (m, 2 H), 2.60−2.07
(m, 2 H), 1.48 (d, 1 H, J = 13.2 Hz), 1.21 (m, 1 H). 75.4 MHz 13C
NMR (CDCl3, as a mixture of rotamers) δ 156.0, 155.0, 151.7,
151.6, 137.7, 137.3, 136.8, 135.8, 129.5, 129.4, 129.3, 128.7,
128.6, 128.4, 127.3, 127.2, 125.53, 125.5, 125.4, 122.7, 122.6,
122.2, 122.1, 121.3, 120.8, 120.6, 120.0, 119.9, 119.8, 119.5,
119.3, 118.6, 118.5, 117.9, 117.7, 112.6, 111.8, 111.3, 111.1,
110.9, 110.8, 51.4, 50.5, 49.9, 49.8, 33.6, 32.8, 32.7, 24.6, 24.3,
24.2, 22.4, 21.7. MS (ES+) m/z for C29H27N3O2: calcd, 449.21;
found, 450.29 (M+H).
Synthesis of Azonino[5,4-b]indoles 8 and 9. Crude
piperazine 7, resulting from the deprotection of crude carbamate
6 prepared on 100 μmol scale, was dissolved in CH3CN (1 mL)
and in 1 mL (0.75 mmol) of a 0.75 M solution of Hunig’s base in
CH3CN. Addition of 440 μL (110 μmol) of a 0.25 M solution of
acid chloride or sulfonyl chloride in CH3CN followed, and the
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Figure 4. Representative library members isolated after HPLC purification.
reaction mixture was then shaken at room temperature over-
night. The solvent was removed under vacuum, and the resulting
residue was dissolved in 2 mL of DCE, followed by a liquid−
liquid extraction workup on an automated station with 2 mL of
H2O. The organic layer was transferred to clean collection vials
and then concentrated to afford the crude product. The samples
were dissolved in 500 μL of DMSO and subsequently purified by
mass-triggered reverse phase prep-HPLC.
151.2, 151.1, 137.6, 137.3, 135.4, 129.0, 128.3, 128.2, 128.0,
127.3, 125.3, 124.1, 124.0, 120.8, 118.9, 117.6, 117.5, 112.2,
111.6, 110.4, 108.5, 101.2, 101.1, 55.7, 55.6, 52.5, 50.3, 50.2, 50.0,
49.8, 49.5, 49.0, 48.5, 45.7, 42.0, 41.4, 41.0, 36.6, 35.8, 31.3, 31.2,
25.8, 25.0, 24.5, 23.8, 22.7, 21.4. MS (ES+) m/z for C32H42N4O4:
calcd, 546.32; found, 547.36 (M+H).
Synthesis of Azonino[5,4-b]indoles 10. 500 μL (125 μmol)
of a 0.25 M solution of aldehyde in DCE-DMF (4:1) and 1200 μL
(300 μmol) of a 0.25 M solution of Me4NBH(OAc)3 in DCE were
added to a suspension of crude piperazine 7 (∼100 μmol) in 0.5 mL
of DCE. The reaction mixture was shaken at room temperature
overnight and a liquid−liquid extraction workup was conducted on
an automated station with 2.5 mL of 10% aqueous NH4OH. The
organic layer was transferred to a clean collection vials and then
concentrated to afford the crude product. The resulting residues
Compound 8{12}. 300 MHz 1H NMR (CDCl3, as a mixture of
rotamers) δ 8.10 (s, 0.5 H), 7.92 (s, 0.5 H), 7.50 (d, 1 H, J = 3.5
Hz), 7.26−7.17 (m, 2 H), 7.08 (m, 2 H), 6.52 (dd, 1 H, J = 1.8,
8.2 Hz), 6.45 (d, 1 H, J = 10.5 Hz), 4.64 (m, 1 H), 3.97 (m, 2 H),
3.83 (s, 1 H), 3.81 (s, 2 H), 3.78 (s, 2 H), 3.73 (s, 1 H), 3.64
(s, 3 H), 3.40−2.80 (m, 10 H), 2.43−2.05 (m, 2 H), 2.0−1.77
(m, 2 H), 1.42−1.25 (m, 2 H), 1.0 (d, 6 H). 75.4 MHz 13C NMR
(CDCl3, as a mixture of rotamers) δ 171.0, 157.9, 157.5, 156.9,
55
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ACS Combinatorial Science
Research Article
were dissolved in 500 μL of dimethylsulfoxide (DMSO) and sub-
sequently purified by mass-triggered reverse phase prep-HPLC.
Synthesis of N3-hydroxyalkylazonines 15 and 16. The
crude α-chloroethylcarbamates 11 and 12 (∼100 μmol),
prepared according to the general method, were dissolved in
1 mL of MeOH and heated at 50 °C for 3 h. The methanol
solution was cooled down at room temperature and then treated
with 100 μL (0.57 mmol) of neat Hunig’s base and 700 μL of a
0.15 M solution of epoxide in MeOH (105 μmol). The reaction
mixture was heated at 55 °C for 8 h and then concentrated. The
resulting residue was subsequently dissolved in 2 mL of DCE
followed by a liquid−liquid extraction workup on an automated
station with 2 mL of saturated aqueous NH4Cl. The organic layer
was transferred to clean collection vials and then concentrated to
afford the crude product. The samples were dissolved in 500 μL
of DMSO and subsequently purified by mass-triggered reverse
phase prep-HPLC.
MS (ES+) m/z for C26H33N3O2: calcd, 419.26; found, 420.31
(M+H).
Compound 18{8}. 300 MHz 1H NMR (CDCl3, as a mixture
of rotamers) δ 8.45 (s, 1 H), 8.26 (s, 0.5 H), 7.64−7.41 (m, 2 H),
7.27 (m, 1 H), 7.20−6.93 (m, 4 H), 6.82 (m, 1 H), 4.62 (m, 1 H),
4.45 (m, 1 H), 4.15 (m, 0.3 H), 3.90 (t, 0.7 H, J = 13.2, 14.6 Hz),
3.55−3.10 (m, 2 H), 3.0 (m, 1 H), 2.70 (t, 1 H, J = 10.8 Hz), 2.55
(m, 1 H), 2.32−2.05 (m, 2 H), 1.80 (dd, 1 H, J = 2.3, 7.0 Hz),
1.50 (br d, 1 H, J = 13.5 Hz), 1.25 (br s, 1 H), 1.06 (d, 3 H), 1.03
(d, 6 H). MS (ES+) m/z for C28H32ClN3O: calcd, 461.22; found,
462.24 (M+H).
Compound 19{20}. 300 MHz 1H NMR (CDCl3, as a mixture
of rotamers) δ 8.26 (s, 0.7 H), 8.14 (s, 0.3 H), 7.78 (d, 2 H, J =
8.5 Hz), 7.50 (d, 2 H, J = 8.5 Hz), 7.40 (d, 1 H, J = 7.6 Hz), 7.30−
7.12 (m, 2 H), 7.05 (m, 2 H), 6.78 (s, 0.3 H), 6.73 (d, 0.3 H, J =
8.2 Hz), 6.34 (d, 0.7 H, J = 8.5 Hz), 6.30 (s, 0.7 H), 5.54 (dd,
0.3 H, J = 3.8, 12.9 Hz), 5.14 (dd, 0.7 H, J = 4.4, 12.9 Hz), 3.86 (s,
2 H), 3.80 (s, 1 H), 3.60 (m, 2 H), 3.40 (m, 1 H), 3.24 (m, 1 H),
2.94 (s, 6 H), 2.87 (m, 2 H), 2.60 (m, 1 H), 1.98 (m, 1 H), 1.43−
1.25 (m, 2 H). MS (ES+) m/z for C29H32ClN3O3S: calcd, 537.19;
found 537.97 (M+H).
Compound 15{13}. 300 MHz 1H NMR (CDCl3) δ 8.85−8.45
(br s, 1 H), 7.45 (d, 1 H, J = 7.3 Hz), 7.26−7.05 (m, 4 H), 6.23 (s,
2 H), 3.79 (s, 3 H), 3.69 (s, 3 H), 3.30−3.0 (m, 6 H), 2.94 (s,
6 H), 2.80−2.37 (m, 6 H), 1.15 (s, 6 H). MS (ES+) m/z for
C29H39N3O4: calcd, 493.29; found, 494.23 (M+H).
ASSOCIATED CONTENT
* Supporting Information
1
■
Compound 16{1}. 300 MHz H NMR (CDCl3) δ 8.12 (s,
S
1 H), 7.54 (s, 1 H), 7.52 (s, 1 H), 7.34 (d, 1 H, J = 8.2 Hz), 7.27−
7.02 (m, 6 H), 6.93 (t, 1 H, J = 7.9 Hz), 5.46 (t, 1 H, J = 8.2 Hz),
3.20−2.94 (m, 3 H), 2.88−2.72 (m, 4 H), 2.60 (d, 1 H, J = 13.8
Hz), 2.27 (m, 2 H), 1.39 (m, 2 H), 1.24 (s, 3 H), 1.20 (s, 3 H).
100.6 MHz 13C NMR (CDCl3) δ 137.6, 136.6, 135.4, 129.0,
128.7, 128.2, 127.1, 122.4, 120.8, 120.5, 119.7, 119.6, 118.8,
117.6, 110.9, 110.5, 73.0, 70.7, 59.9, 34.3, 33.5, 28.6, 28.4, 26.3,
24.9. MS (ES+) m/z for C26H31N3O: calcd, 401.25; found,
402.19 (M+H).
General methods and purification conditions. Copies of 1H and
13C NMR spectra (PDF) of compounds 2{11}, 2{16}, 2{18},
3{5}, 4{1}, 4{8}, 3{7}, 3{17}, 4{4}, 7{11}, 8{12}, 8{32}, 8{33},
8{39}, 13 (R1 = H), 13 (R1 = CO2Me), 15{13}, 15{23}, 16{1},
16{12}, 17{15}, 18{8}, 19{9}, 19{12}, and 19{20}. Copies of
1H NMR spectra (PDF) of compounds 2{11}, 3{7}, 4{4},
7{11}, 8{12}, and 19{20} recorded at 55 °C. Tables reporting
the purity and quantity of all 308 compounds synthesized as well
as the synthesis layout of each chemotype, are also included.
Copies of LC/MS chromatograms (PDF) of the aforementioned
compounds and other library members are also provided. This
material is available free of charge via the Internet at http://pubs.
acs.org.
Compound 16{12}. 300 MHz 1H NMR (CDCl3, as a mixture
of diastereomers) δ 8.11 (s, 1 H), 7.56 (s, 1 H), 7.52 (d, 1 H, J =
7.3 Hz), 7.31−6.80 (m, 12 H), 5.38 (br s, 1 H), 4.45 (s, 2 H), 4.0
(br s, 1 H), 3.59−3.42 (m, 2 H), 3.35−2.95 (m, 4 H), 2.72 (s,
4 H), 2.47 (s, 3 H), 2.20 (s, 2 H), 1.36 (m, 2 H). MS (ES+) m/z
for C33H37N3O2: calcd, 507.29; found, 508.12 (M+H).
AUTHOR INFORMATION
Corresponding Author
*E-mail: dfokas@cc.uoi.gr.
■
Synthesis of Azonino[5,4-b]indoles 17−18 and 19−20.
The crude α-chloroethylcarbamates 11 and 12 (∼100 μmol),
prepared according to the general method, were dissolved in
1 mL of MeOH and heated at 50 °C for 3 h. The solvent was
concentrated, and the resulting residue was dissolved in 1 mL
(0.75 mmol) of a 0.75 M solution of Hunig’s base in CH3CN,
followed by the addition of 500 μL (125 μmol) of a 0.25 M
solution of acid chloride or sulfonyl chloride in CH3CN. The
reaction mixture was stirred at room temperature overnight and
then concentrated under vacuum. The resulting residue was
dissolved in 2 mL of DCE followed by a liquid−liquid extraction
workup on an automated station with 2 mL of H2O. The organic
layer was transferred to clean collection vials and then con-
centrated to afford the crude product. The samples were dis-
solved in 500 μL of DMSO and subsequently purified by mass-
triggered reverse phase prep-HPLC.
Present Addresses
†Department of Materials Science and Engineering, University of
Ioannina, Ioannina 45110, Greece.
‡Galapagos Research Institute Ltd., Prilaz baruna Filipovica
́
29,
Zagreb, HR-10000, Croatia.
§Novartis Institutes for BioMedical Research, Inc., 250
Massachusetts Avenue 2C-184, Cambridge, MA 02139, U.S.A.
∥Suli Group Shanghai R&D, Building 1#, Libing Road 306,
Zhangjian Hi-Tech Park, Shanghai 201203, China.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Compound 17{15}. 300 MHz 1H NMR (CDCl3, as a mixture
of rotamers) δ 8.10 (s, 0.7 H), 7.87 (s, 0.3 H), 7.52 (m, 1 H), 7.22
(m, 2 H), 7.10 (s, 2 H), 6.73 (s, 0.3 H), 6.40 (t, 2 H, J = 7.3,
8.2 Hz), 4.62 (dd, 0.7 H, J = 4.4, 13.8 Hz), 4.53 (dd, 0.3 H, J = 3.8,
12.9 Hz), 4.28 (dd, 0.7 H, J = 5.3, 13.2 Hz), 4.05 (m, 0.3 H), 3.80
(d, 3 H), 3.72 (t, 1 H, J = 12.0 Hz), 3.42−3.12 (m, 2 H), 3.05 (m,
1 H), 2.90 (s, 6 H), 2.75 (t, 1 H, J = 12.0 Hz), 2.55 (m, 3 H), 1.85
(m, 1 H), 1.52 (m, 1 H), 1.25 (m, 1 H), 1.15 (t, 3 H, J = 7.3 Hz).
The authors thank ArQule’s Analytical Department for the
purification and mass spectra analysis of the compounds
described in the manuscript.
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piperazine. Similarly, LC/MS on crude reaction mixture as well as
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(34) For the synthesis, isolation, and characterization of azonines 14
(R1 = H, CO2Me), see reference 23. Azonines 13 were prepared
accordingly and isolated in 61% (R1 = H) and 53% (R1 = CO2Me) yield,
respectively. Compound 13 (R1 = H): 1H NMR (300 MHz, CD3OD): δ
7.51 (d, 1 H, J = 7.6 Hz), 7.34 (s, 1 H), 7.32−7.18 (m, 3 H), 7.04 (m, 2
H), 4.73 (dd, 1 H, J = 12. 6, 3.2 Hz), 3.98 (s, 3 H), 3.62−2.90 (m, 6 H),
3.25 (s, 6 H), 2.56 (q, 1 H, J = 12.3 Hz), 2.18 (m, 1 H), 2.12−1.84 (m, 2
H). 13C NMR (75.4 MHz, CD3OD): δ 157.9, 142.5, 136.5, 136.0, 134.4,
129.4, 129.3, 127.8, 121.7, 119.2, 117.2, 110.8, 107.8, 103.6, 55.7, 47.4,
46.0, 45.0, 38.7, 29.2, 25.9, 21.1. MS (ES+) m/z for C23H29N3O: calcd,
1
363.23; found, 364.22 (M+H). Compound 13 (R1 = CO2Me): H
NMR (300 MHz, CD3OD): δ 7.89 (s, 1 H), 7.51 (d, 1 H, J = 7.6 Hz),
7.40 (s, 1 H,), 7.37 (s, 1 H), 7.24−7.05 (m, 3 H), 3.94 (s, 3 H), 3.70 (s, 3
H), 3.56−3.34 (m, 3 H), 3.29 (s, 6 H), 3.26−3.05 (m, 4 H), 2.64 (br d, 1
H, J = 14.6 Hz), 1.83 (br s, 2 H). 13C NMR (75.4 MHz, CD3OD):δ
172.2, 156.5, 142.0, 134.6, 131.2, 129.6, 128.8, 126.5, 121.0, 118.0, 115.9,
109.9, 108.5, 103.2, 76.8, 54.4, 53.8, 50.6, 44.4, 43.9, 28.5, 21.4, 20.3. MS
(ES+) m/z for C25H31N3O3: calcd, 421.23; found, 422.17 (M+H).
(35) LC/MS on crude reaction mixture as well as postpurification
samples showed that chemotypes 15, 17, and 19 (R = H), resulting from
scaffold 1{1}, contain a small amount (5−10%) of a regioisomeric
product which might presumably be generated from the alkylation of m-
dimethylaminoanisole para to the OMe group.
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(41) Most of the N3-carbamate and amide analogues exhibited
1
complex H and 13C NMR spectra due to the presence of rotamers.
However, when the 1H NMR spectra of certain compounds were
recorded at 55 °C, peak coalescence of some protons was observed
leading to higher resolution spectra. This is presumably due to the
disruption of rotamers at an increased temperature. For more details, see
the Supporting Information section.
́
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