Construction of 1,3,4-Oxadiazole and 1,3,4-Thiadiazole Library with a High Level of Skeletal Diversity Based on Branching Diversity-Oriented Synthesis on Solid-Phase Supports

Article abstract of DOI:10.1021/acscombsci.7b00174

An efficient solid-phase synthetic route for the construction of 1,3,4-oxadiazole and 1,3,4-thiadiazole libraries based on branching diversity-oriented synthesis (DOS) has been developed in this study. The core skeleton resins, 1,3,4-oxadiazole and 1,3,4-thiadiazole, were obtained through desulfurative and dehydrative cyclizations of thiosemicarbazide resin, respectively. Various functional groups have been introduced to the core skeleton resins, such as aryl, amine, amide, urea, thiourea, and an amino acid. Most of the libraries were purified by simple trituration without extraction or column chromatography after cleavage of the products from the solid-supported resin. As a result, we obtained high yields of pure 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives (total numbers = 128). Finally, we confirmed the drug-like properties of our library by calculation of physicochemical properties, displays of the skeletal diversities of the library in 3D-space, and occupation of a broad range of areas by their functional groups.

Full text of DOI:10.1021/acscombsci.7b00174

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Article
Construction of 1,3,4-Oxadiazole and 1,3,4-Thiadiazole
Library with a High Level of Skeletal Diversity based on
Branching Diversity-oriented Synthesis on Solid-phase
Ji-Eun Ha, Seung-Ju Yang, and Young-Dae Gong
ACS Comb. Sci., Just Accepted Manuscript • DOI: 10.1021/acscombsci.7b00174 • Publication Date (Web): 08 Jan 2018
Downloaded from http://pubs.acs.org on January 12, 2018
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Graphical Abstract
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Construction of 1,3,4-Oxadiazole and 1,3,4-Thiadiazole Library with a
High Level of Skeletal Diversity based on Branching Diversity-oriented
Synthesis on Solid-phase
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Ji-Eun Ha, Seung-Ju Yang, Young-Dae Gong*
Innovative Drug Library Research Center, Department of Chemistry, College of Science,
Dongguk University, 26, 3-ga, Pil-dong Jung-gu, Seoul 100-715, Korea
* Corresponding author. Tel. : +82-2-2260-3206, Fax : +82-2-2290-1349 ; e-mail: ydgong@dongguk.edu
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Page 2 of 46
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Construction of 1,3,4-Oxadiazole and 1,3,4-Thiadiazole Library with a High
Level of Skeletal Diversity based on Branching Diversity-oriented Synthesis on
Solid-phase
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Ji-Eun Ha, Seung-Ju Yang, Young-Dae Gong*
Innovative Drug Library Research Center, Department of Chemistry, College of Science,
Dongguk University, 26, 3-ga, Pil-dong Jung-gu, Seoul 100-715, Korea
Abstract: An efficient solid-phase synthetic route for the construction of 1,3,4-oxadiazole and 1,3,4-
thiadiazole libraries based on branching diversity-oriented synthesis (DOS) has been developed in this
study. The core skeleton resins, 1,3,4-oxadiazole and 1,3,4-thiadiazole, were obtained through
desulfurative and dehydrative cyclizations of thiosemicarbazide resin, respectively. Various functional
groups have been introduced to the core skeleton resins such as aryl, amine, amide, urea, thiourea, and
an amino acid. Most of the libraries were purified by simple trituration without extraction or column
chromatography after cleavage of the products from the solid-supported resin. As a result, we obtained
high yields of pure 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives (total numbers = 128). Finally,
we confirmed the drug-like properties of our library by calculation of physicochemical properties,
displays of the skeletal diversities of the library in 3D-space, and occupation of a broad range of areas
by their functional groups.
KEYWORDS: 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, Solid-phase, Diversity.
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Introduction
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Construction of a small-molecule library is one of the crucial challenges in the drug discovery
process.1 Of all the small molecules, heterocyclic compounds have played vital roles in the
development of potent therapeutic agents.2 This is because, in chemical biology, heterocyclic
modulators facilitate the elucidation of complex biological mechanisms.3 Along these lines, diversity-
oriented synthesis (DOS) emerged as a powerful tool to generate a library of heterocyclic compounds
in a time- and cost-efficient manner.4 As a part of the DOS strategy, the branching DOS strategy has
been spotlighted to generate discrete library sets of small heterocyclic compounds.5 Of these
heterocyclic compounds, 5-membered heterocyclic compounds have played pivotal roles;
approximately, 23% (n = 250) of the 1086 unique small molecules approved by the U.S. Food and
Drug Administration (FDA) belong to the class of 5-membered heterocyclic compounds.6 As 5-
membered heterocyclic compounds, 1,3,4-oxadiazoles and 1,3,4-thiadiazoles have been shown to
have numerous biological activities such as anti-inflammatory,7 antimicrobial,8 anticonvulsant,9
anticancer,10 and antihypertensive properties.11 Furthermore, 1,3,4-oxadiazole and 1,3,4-thiadiazole
core skeletons also have been used in liquid crystal,12 Organic Light Emitting Diodes (OLED),13 solar
cell,14 and agricultural chemistry.15
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H
H
N
O
F
O
N
H
N
S
O
S
F
S
N N
N
N
N
N N
H
OH
Fructose-1,6-biphosphatase Inhibitor20a
Anticonvulsant Activity20c
Antibacterial Activity20b
NH
O
H
CF3
H
N
NH
N
S
O
N
O
N N
N N
O
Cl
Human Helicase DDX3 Inhibitor20e
Phosphodiesterase-4 Inhibitor20d
Figure 1. Examples of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles with diverse functional groups and
pharmacological activities
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In addition, 1,3,4-oxadiazole and 1,3,4-thiadiazole have been used to replace peptide fragments to
increase the chemical stability and oral availability of a compound16a, 16c since heterocyclic compounds
have been considered as alternative structural motifs for peptide bonds, and there are many reports
about synthetic methodology and biological activities of peptide analogues equipped with heterocyclic
motifs.16
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For these reasons, these core skeletons have been targeted for synthesis by many organic chemists
and medicinal chemists using solution-phase synthesis17 and solid-phase methods.18 In this context,
we were interested in developing expedient synthesis of 1,3,4-oxadiazole and 1,3,4-thiadiazole via a
regioselective way from one versatile intermediate.19 As an extension of our previous work, we
focused on skeletal diversity of substituents of the phenyl group, adjacent to the 1,3,4-oxadiazole and
1,3,4-thiadiazole core skeletons, due to the fact that various kinds of functional groups at this position
could result in interesting biological activities (Figure 1).20 Thus, as a part of our ongoing project
aimed at construction of a small-molecule library,21 we have used solid-phase synthesis based on the
branching DOS strategy to construct 1,3,4-oxadiazole and 1,3,4-thiadiazole libraries with a high level
of skeletal diversity, containing aryl, amide, urea, thiourea, amine and peptide group as depicted in
Figure 2. Herein, we report our recent progress on this project.
H
H
N
H
H
H
N
N
H
O
O
S
N
N
R5, 6
R3
N
R3
R7
H
R2
R4
R4
Y
S
N
R3
N
N
N N
N
N
O
H
N
O
O
O
Y
Y = O or S
N
N
R3
O
R5, 6
N
N
N
N
H
O
H
Y = O or S
R1
R1
S
O
H
O
N
R3
O
S
N
N
H
N
N
N
NH
R1
N
N
H
H
O
N
N
N
H
N
H
O
R7
H
N
R8
H
H
S
O
R3
N
R3
N
N
N
N
H
R8
H
N
N
N
O
Peptide chains
O
O
R3
H
S
R3
N
Peptide chains
N
N
O
N
N
O
Figure 2. Schematic diagram to yield a myriad of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles based on
branching diversity-oriented synthesis
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Results and Discussion
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We prepared 1,3,4-oxadiazole and 1,3,4-thiadiazole core skeleton resins 4 and 5 using our previous
methodology19a (Scheme 1) in order to construct a structurally diversified 1,3,4-oxadiazole and 1,3,4-
thiadiazole library.
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Scheme 1. Synthesis of 1,3,4-oxadiazole and 1,3,4-thiadiazole resina
R1
O
Desulfurative
cyclization
N
N
N
H
R1 = meta-I (
4a
4b
)
) or meta-NO2 (
S
O
(a)
(b)
(c)
NO2
NH2
NCS
N
N N
R1
H
H H
2
1
3
Dehydrative
cyclization
O
S
N
NH2
=
O
N
N
H
P
P = Merrifield resin
5
a Reagents and conditions : (a) Et3N, CS2, p-TsCl, THF, rt, 19 h. (b) Et3N, THF, rt, 16 h. (c) For desulfurative cyclization,
EDC.HCl, DMSO, 60 oC, 16 h; For dehydrative cyclization, Et3N, p-TsCl, NMP, rt, 12 h.
The 4-benzyloxy-2-methoxybenzylamine (BOMBA) resin 1 was used as a starting material and
reacted with CS2 and p-TsCl in the presence of Et3N in tetrahydrofuran (THF) for 16 h to yield an
isothiocyanate-terminated resin 222 followed by a reaction with hydrazides to obtain a
thiosemicarbazide resin 3. The thiosemicarbazide resin 3 was successfully chemoselectively cyclized
to form 1,3,4-oxadiazole resin 4 and 1,3,4-thiadiazole resin 5 under conditions using EDC.HCl and p-
TsCl / Et3N, respectively. Next, with 1,3,4-oxadiazole resin 4 and 1,3,4-thiadiazole resin 5 in hand, we
synthesized numerous 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives via a branching pathway.
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Synthesis of 1,3,4-oxadiazole derivatives 8 and 9
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5
6
Scheme 2. N-Alkylation / acylation, and Suzuki coupling reaction for synthesis of 1,3,4-
7
8
oxadiazole derivatives 8 and 9
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H
O
O
N
N
10% TFA in DCM
1. Alkyl halides, tBuOK, DMF
R2
R2
R4
R4
N
N
N
N
, XPhos,
, 1,4-Dioxane : H
I
2. Boronic acids, Cs
2CO3
2,R4
2,R4
Pd
6
{R
8
{R
}
}
2O
2(dba)3
O
N
N
N
H
4a
, XPhos,
2CO3
1. Boronic acids, Cs
H
Pd
O
10% TFA in DCM
O
, 1,4-Dioxane : H
N
N
2O
2(dba)3
R3
R3
R4
R4
N
N
N
N
2. Acid chlorides, Pyridine
O
O
3,R4
3,R4
7
{R
9
}
}
{R
- Alkyl halides (R2
- Acid halides (R3
)
)
O
O
O
Cl
Br
O
Cl
Cl
I
Cl
2
3
1
1
2
3
- Boronic acids (R4
)
HO
OH
HO
OH
HO
OH
HO
OH
B
B
B
B
S
NO2
O
2
1
3
4
Table 1. Yields and purities of 1,3,4-oxadiazole 8 and 9a
R4
R4
1
2
3
4
1
2
3
4
H
N
H
O
O
N
O
R4
R4
R4
R4
N
N
N
N
17
(98)
17
13
13
(95)
36
(96)
37
(95)
28
(92)
23
(100)
(96)
(95)
8{1,R4}
9{1,R4}
H
N
H
O
O
N
O
R4
N
N
N
N
19
(97)
10
10
12
(97)
20
37
40
(100)
31
(100)
O
(97)
(100)
(92)
(100)
9{2,R4}
8{2,R4}
H
O
H
N
O
O
N
13
(95)
11
58
8
(96)
17
(86)
17
(81)
21
(68)
11
(80)
N
N
R4
N
N
(91)
(96)
8{3,R4}
9{3,R4}
a Yield (Purity); Yield is an obtained yield for six steps, and purity is checked by LC-MS at 254 nm.
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Before we carried out a Suzuki-coupling reaction on solid-phase, we conducted a model study in
solution-phase (Scheme S1 in Supporting Information). As a result, we set N-alkylation at an earlier
stage than the Suzuki-coupling reaction. Although a quantitative yield was seen in the solution phase,
NaH in THF gave a low conversion in the case of performing the N-alkylation reaction on solid phase.
Thus, we screened several reaction conditions (Entry 1 – 5 of Scheme S2 in Supporting Information).
Among these conditions, tBuOK in DMF gave good conversion (Entry 5 of Scheme 2 in Supporting
Information). After the alkylation reaction, we carried out a Suzuki-coupling reaction with boronic
acids in the presence of Pd2(dba)3, XPhos, and, Cs2CO3 in 1,4-dioxane and H2O (9:1, v/v), followed
by a cleavage reaction with 10% trifluoroacetic acid (TFA) in dichloromethane (DCM) to yield N-
alkyl-Suzuki-coupled 1,3,4-oxadiazole 8. The liquid chromatography-mass spectrometry (LC-MS)
result of the crude product mixture for 1,3,4-oxadiazole 8 is displayed in Figure S3(a) (of Supporting
Information), showing that our desired product was the major constituent of the mixture without
further purification. To purify the mixture, we used a short plug of silica with hexane/ethyl acetate,
then trituration with hexane and diethyl ether. The yields and purities of 1,3,4-oxadiazole 8 are
summarized in Table 1. Next, to afford N-acyl-Suzuki-coupled 1,3,4-oxadiazole 9, we introduced an
acyl moiety at the 2-amine-position, then Suzuki-coupled it with boronic acid. However, in this
synthetic sequence, the major product was obtained in the non-acylated product form (Scheme S3 in
Supporting Information). Thus, we first used various boronic acids for the Suzuki-coupling reaction,
and then introduced acid chlorides followed by a cleavage reaction with treatment of 10% TFA in
DCM at room temperature for 8 h. As a result, we obtained the desired N-acylated-Suzuki-coupled
1,3,4-oxadiazole 9 as a major product without further purification (Figure S3(b) in Supporting
Information). To purify the 1,3,4-oxadiazole 9, we triturated the crude product mixture with ethyl
acetate / diethyl ether. The yields and purities of 1,3,4-oxadiazole 9 are summarized in Table 1.
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Synthesis of 1,3,4-oxadiazole derivatives 12 and 1,3,4-thiadiazole derivatives 13
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Scheme 3. N-Acylation, and Urea formation for synthesis of 1,3,4-oxadiazole derivatives 12 and
7
8
1,3,4-thiadiazole derivatives 13
9
R5
10
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NH2
NO2
NH
O
NH
R5
N
1.
C O
H
X
X
1. Acid chlorides, Pyridine
X
Base, Solvents
N
N
N
O
.
N
N
N
2. SnCl2 2H
2O, DMF
N
2. 10% TFA in DCM
N N
R3
H
R3
X = O,
= S,
O
3,R5
12
13
X = O,
= S,
4b
5
3
X = O,
= S,
{R
3,R5
}
10
{R }
3
{R
}
11
{R }
- Acid chlorides (R3
- Isocyanate (R5
)
)
O
O
O
NCO
S
O
NCO
NCO
Cl
Cl
Cl
1
2
3
1
2
3
Table 2. Yields and purities of 1,3,4-oxadiazole 12 and 1,3,4-thiadiazole 13 a
R5
R5
1
2
3
1
2
3
H
H
N
N
H
N
O
O
O
O
H
N
S
R5
O
O
O
N
R5
N
N
N
H
N
N
H
13
39
57
(97)
12
(94)
20
(100)
19
(100)
(100)
(96)
12{1,R5}
13{1,R5}
H
H
N
N
H
N
O
H
N
S
R5
O
O
O
N
R5
N
N
N
H
38
46
58
16
(95)
11
(100)
20
(100)
N
N
H
O
O
(98)
(100)
(100)
12{2,R5}
13{2,R5}
H
H
N
N
H
N
O
H
N
S
R5
O
O
O
N
R5
N
N
N
H
34
33
18
13
(91)
22
(100)
32
(100)
N
N
H
S
S
(100)
(100)
(100)
12{3,R5}
a Yield (Purity); Yield is an obtained yield for seven steps, and purity is checked by LC-MS at 254 nm.
13{3,R5}
For urea formation, we used nitro-substituted 1,3,4-oxadiazole 4b and 1,3,4-thiadiazole 5. First, we
introduced an acyl group at the 2-amine position, then reduced the nitro group to an amine group using
SnCl2.2H2O in dimethylformamide (DMF) to yield the 1,3,4-oxadiazole resin 10 and the 1,3,4-
thiadiazole resin 11. To optimize the reaction condition for urea formation, we screened several solvent,
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base, and temperature conditions with phenyl isocyanate and 1,3,4-oxadiazole resin 10 (Entries 1 – 5
of Scheme S4 in Supporting Information). Among various conditions, pyridine in THF at 60 oC gave
a quantitative conversion (Entry 5 of Scheme S4 in Supporting Information). However, in the case of
benzyl and ethyl isocyanate, the conversion was decreased under this condition. Thus, we studied
reaction conditions, and found that 4-(dimethylamino)pyridine (DMAP) in DCM at 60 oC and room
temperature gave excellent conversion with benzyl isocyanate and ethyl isocyanate, respectively
(Entries 6 – 11 of Scheme S4 in Supporting Information). Next, we carried out the same reaction with
1,3,4-thiadiazole resin 11, and the reaction proceeded smoothly. The LC-MS result of the crude
product mixture for 1,3,4-oxadiazole 12 and 1,3,4-thiadiazole 13 is displayed in Figure S3(e), and (j)
of the Supporting Information. To purify 1,3,4-oxadiazole 12 and 1,3,4-thiadiazole 13, we triturated
the crude product mixture with diethyl ether / ethyl acetate / ethanol. Consequently, we obtained the
desired 1,3,4-oxadiazole 12 and 1,3,4-thiadiazole 13 in good yields and high purities (Table 2).
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60
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Page 10 of 46
Synthesis of 1,3,4-oxadiazole derivatives 14 and 1,3,4-thiadiazole derivatives 15
1
2
3
4
5
6
Scheme 4. N-Acylation, and Thiourea formation for synthesis of 1,3,4-oxadiazole derivatives 14
7
8
and 1,3,4-thiadiazole derivatives 15
9
R6
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
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57
58
59
60
NH2
NH
S
NH
1. R6 N C S
DMAP, CHCl3
H
X
X
N
N
O
N
N
2. 10% TFA in DCM
N N
R3
O
R3
X = O,
= S,
3,R6
14
15
X = O,
= S,
3
{R
}
10
11
{R }
3,R6
3
{R
}
{R }
- Acid chlorides (R3
- Isothiocyanate (R6
)
)
O
O
O
NCS
NCS
NCS
N
O2
O
NCS
S
O
Cl
Cl
Cl
F
4
1
2
3
1
2
3
Table 3. Yields and purities of 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 15 a
R6
R6
1
2
3
4
1
2
3
4
H
H
N
N
H
N
S
O
H
N
S
R6
O
O
N
R6
S
N
N
N
H
N
N
17
22
(94)
32
27
10
19
21
(94)
12
(92)
H
(100)
(100)
(100)
(95)
(88)
14{1,R6}
15{1,R6}
H
H
N
N
H
N
S
O
H
N
S
R6
O
O
N
H
R6
S
N
N
N
42
30
(93)
36
30
15
15
17
(100)
13
(91)
N
N
H
O
O
(100)
(100)
(100)
(100)
(100)
14{2,R6}
15{2,R6}
H
H
N
N
H
N
S
O
H
N
S
R6
O
O
N
H
R6
S
N
N
N
H
18
24
(92)
16
10
11
7
11
(100)
10
(90)
N
N
S
S
(100)
(100)
(100)
(100)
(100)
14{3,R6}
a Yield (Purity); Yield is an obtained yield for seven steps, and purity is checked by LC-MS at 254 nm.
15{3,R6}
For thiourea formation, we used nitro-substituted 1,3,4-oxadiazole 4b and 1,3,4-thiadiazole 5. First,
we introduced an acyl moiety at the 2-amine position, then reduced the nitro group to an amine group
using SnCl2.2H2O in DMF to yield the 1,3,4-oxadiazole resin 10 and the 1,3,4-thiadiazole resin 11. To
optimize the reaction conditions, we used diverse solvent and base conditions, with phenyl
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isothiocyanate and 1,3,4-oxadiazole resin 10 (Scheme S5 in Supporting Information). Among these
conditions, DMAP in CHCl3 at 60 oCshowed a high conversion (Entries 8 of Scheme S5 in Supporting
Information). The optimized reaction conditions also worked well in the case of 1,3,4-thiadiazole resin
11. The LC-MS spectra of the crude product mixture for 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 15
is shown in Figure S3 (f), and (k) of the Supporting Information. After thiourea formation, the resin
was treated with 10% TFA in DCM at room temperature for 8 h to cleavage 1,3,4-oxadiazole 14 and
1,3,4-thiadiazole 15 from polymer-supported resin, then a crude product mixture was purified by
trituration with diethyl ether / ethyl acetate/ ethanol. The yields and purities of 1,3,4-oxadiazole 14
and 1,3,4-thiadiazole 15 are summarized in Table 3.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
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50
51
52
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59
60
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Synthesis of 1,3,4-oxadiazole derivatives 16 and 1,3,4-thiadiazole derivatives 17
1
2
3
4
5
6
Scheme 5. N-Acylation, and Reductive amination for synthesis of 1,3,4-oxadiazole derivatives 16
7
8
and 1,3,4-thiadiazole derivatives 17
9
NH2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
R7
1. R7
CHO
AcOH, MeOH
NH
H
X
NaBH
X
3(CN), 1,2-DCE
N
N
O
N
N
2. 10% TFA in DCM
N N
R3
O
R3
X = O,
= S,
3,R7
16
17
X = O,
= S,
3
{R
}
10
{R }
3,R7
3
{R
}
11
{R }
- Acid halides (R3
- Aldehydes (R7
)
)
O
O
O
O
O
O
O
O
S
O
S
Cl
Cl
Cl
N
O2
O
N
1
2
3
1
5
2
3
4
Table 4. Yields and purities of 1,3,4-oxadiazole 16 and 1,3,4-thiadiazole 17 a
R7
R7
1
2
3
4
5
1
2
3
4
5
H
N
H
N
R7
O
H
N
S
O
O
N
H
R7
N
N
N
N
21
(88)
24
(93)
57
28
27
41
40
21
(92)
38
(92)
22
(90)
(100) (100)
(80)
(73)
(92)
16{1,R7}
17{1,R7}
H
N
H
O
N
R7
H
S
N
O
O
N
H
R7
N
N
26
(83)
22
(100)
54
24
28
41
47
N
N
34
(100)
54
36
O
O
(90)
(93)
(100) (100) (100)
(100)
(100)
16{2,R7}
17{2,R7}
H
N
H
O
N
R7
H
S
N
O
O
N
H
R7
N
N
21
(77)
20
(91)
19
18
15
32
11
N
N
29
(100)
53
23
S
S
(98)
(100) (100) (100) (100)
(100)
(100)
16{3,R7}
17{3,R7}
a Yield (Purity); Yield is an obtained yield for seven steps, and purity is checked by LC-MS at 254 nm.
Before we conducted reductive amination on solid-phase, we studied reaction conditions in solution-
phase (Scheme S6 in Supporting Information). From these studies in solution-phase, we confirmed
reaction conditions for reductive amination (benzaldehyde, acetic acid, NaBH3(CN), MeOH in 1,2-
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dichloroethane), and applied these conditions to solid-phase. For reductive amination, we used nitro-
substituted 1,3,4-oxadiazole 4b and 1,3,4-thiadiazole 5. First, we introduced an acyl moiety at the 2-
amine position, then reduced the nitro group to an amine group using SnCl2.2H2O in DMF to yield the
1,3,4-oxadiazole resin 10 and the 1,3,4-thiadiazole resin 11. In case of the solid-phase, the reaction
1
2
3
4
5
6
7
8
9
o
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
was conducted at 60 C without methanol due to a concern of low swelling of our lipophilic poly-
styrene resin in MeOH, resulting in moderate conversion (Entry 1 of Scheme S7 in Supporting
Information). Thus, for complete conversion, we used MeOH, and the reaction was mediated at room
temperature, resulting in good conversion (Entry 2 of Scheme S7 in Supporting Information). Next,
we carried out the same reaction with 1,3,4-thiadiazole resin 11, and the reaction proceeded well. The
LC-MS spectra of the crude product mixture for 1,3,4-oxadiazole 16 and 1,3,4-thiadiazole 17 are
shown in Figure S3 (d), and (i) of the Supporting Information. To purify 1,3,4-oxadiazole 16 and 1,3,4-
thiadiazole 17, we triturated the crude product mixture with diethyl ether / ethyl acetate / ethanol. The
yields and purities are summarized in Table 4.
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Synthesis of 1,3,4-oxadiazole derivatives 18 and 1,3,4-thiadiazole derivatives 19
1
2
3
4
5
6
Scheme 6. N-Acylation, and Amide coupling for synthesis of 1,3,4-oxadiazole derivatives 18 and
7
8
1,3,4-thiadiazole derivatives 19
9
NH2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
R8
O
NH
H
X
X
1. Acid chlorides, Pyridine, THF
2. 10% TFA in DCM
N
N
O
N
N
N N
R3
R3
X = O,
= S,
O
3,R8
18
19
X = O,
= S,
3
{R
3,R8
}
10
{R }
3
{R
}
11
{R }
- Acid chlorides (R3
- Acid chlorides (R8
)
)
O
O
O
O
O
O
S
S
O
O
Cl
Cl
Cl
Cl
Cl
Cl
1
2
3
3
1
2
Table 5. Yields and purities of 1,3,4-oxadiazole 18 and 1,3,4-thiadiazole 19 a
R8
R8
1
2
3
1
2
3
H
N
H
N
R8
R8
R8
O
O
H
N
S
O
O
O
N
H
R8
N
N
N
N
28
34
40
21
(98)
19
(97)
16
(92)
(100)
(98)
(100)
18{1,R8}
19{1,R8}
H
N
H
N
O
O
H
N
S
O
O
O
N
H
R8
N
N
33
36
(100)
39
(100)
21
(100)
9
(98)
14
(98)
N
N
O
O
(100)
18{2,R8}
19{2,R8}
H
N
H
O
O
H
N
S
N
O
O
O
N
H
R8
N
N
15
14
10
16
(98)
18
(97)
18
(98)
N
N
S
S
(98)
(98)
(98)
18{3,R8}
a Yield (Purity); Yield is an obtained yield for seven steps, and purity is checked by LC-MS at 254 nm.
19{3,R8}
For amide formation, we used nitro-substituted 1,3,4-oxadiazole 4b and 1,3,4-thiadiazole 5. First, we
introduced an acyl moiety at the 2-amine position, then reduced the nitro group to an amine group
using SnCl2.2H2O in DMF to yield the 1,3,4-oxadiazole resin 10 and the 1,3,4-thiadiazole resin 11.
1,3,4-oxadiazole 10 was reacted with benzoyl chloride in pyridine under neat condition (Entry 2 of
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Scheme S8 in Supporting Information). However, after the cleavage reaction using 10% TFAin DCM,
we obtained the desired 1,3,4-oxadiazole 18 in only moderate yield. Thus, to increase the yield, we
used pyridine as base and THF as solvent followed by cleavage with a treatment of 10% TFA in DCM
at room temperature for 8 h. As a result, the starting material was almost completely converted to the
desired product (Entry 1 of Scheme S8 in Supporting Information). With these reaction conditions in
hand, we used 1,3,4-thiadiazole resin 11, and the reaction proceeded well. The LC-MS spectra of the
crude product mixture for 1,3,4-oxadiazole 18 and 1,3,4-thiadiazole 19 showed high purity without
further purification (Figure S3 (c), and (h) in Supporting Information) and attenuated total reflection-
fourier transform infrared spectroscopy (ATR-FTIR) spectra showing the amide peaks for 1,3,4-
oxadiazole resin 10-acylation, and 1,3,4-thiadiazole resin 11-acylation are displayed in Figure S1 (d)
and S2 (d) of the Supporting information. To obtain our desired product, we triturated the crude
product mixture of 1,3,4-oxadiazole 18, and 1,3,4-thiadiazole 19 with diethyl ether / ethyl acetate /
ethanol. The yields and purities of 1,3,4-oxadiazole 18 and 1,3,4-thiadiazole 19 are summarized in the
Table 5.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
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59
60
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Synthesis of 1,3,4-oxadiazole derivatives 20 and 1,3,4-thiadiazole derivatives 21
1
2
3
4
5
6
Scheme 7. N-Acylation, and peptide coupling for synthesis of 1,3,4-oxadiazole derivatives 20 and
7
8
1,3,4-thiadiazole derivatives 21
9
NH2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
H
R9
S
N
H
H
N
X
O
1. Amino acid, DIC, HOBt, DMF
2. 10% piperidine in DMF
3. Ac-Gly-OH, DIC, HOBt, DMF
N
N
H
O
H
1. Fmoc Solid-phase peptide synthesis
2. Ac-Gly-OH, DIC, HOBt, DMF
O
O
N
N
H
X
N
N
X
H
N
H
O
N
N
O
N
H
O
N
N
O
3. 50% TFA in DCM
4. TFA in DCM
N
N
N
H
HO
O
O
9
9
20
X = O,
= S,
10
11
X = O,
= S,
20'
21'
{1,R }
X = O,
= S,
{1}
{1}
{1,R }
9
9
21
{1,R }
{1,R }
{
- Amino acids (R9
)
O
O
O
H
O
O
H
O
O
H
H
H
N
H
N
N
N
N
N
Fmoc
OH
OH
O
Fmoc
Fmoc
Fmoc
Fmoc
Fmoc
OH
OH
OH
OH
S
tert-butyl
tert-butyl
O
1
2
5
3
4
6
Table 6. Yields and purities of 1,3,4-oxadiazole 20 (20’) and 1,3,4-thiadiazole 21 (21’)a
R9
1
2
3
4
5
6
H
N
O
O
O
H
N
O
N
H
N
N
31
34
35
29
26
16
(100)
N
H
R9
O
(100)
(100)
(100)
(100)
(100)
20{1,R9}
R9
H
O
N
H
N
H
N
S
N
H
O
O
N
N
20
17
32
18
16
29
(100)
O
(100)
(100)
(100)
(100)
(100)
21{1,R9}
H
N
O
O
N
N
O
S
HN
NH
O
O
b
HN
HO
28
(100)
NH
O
O
HN
20’{1,1-4-3}
H
N
O
S
N
NH
N
O
O
HN
S
b
NH
O
OH
O
20
(90)
HN
NH
O
21’{1,1-4-3}
a Yield (Purity); Yield is an obtained yield for nine steps, and purity is checked by LC-MS at 254 nm.
b Yield is an obtained yield for thirteen steps.
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Finally, we tried to synthesize peptide-like derivatives equipped with 1,3,4-oxadiazole and 1,3,4-
thiadiazole motifs. To achieve this, we used nitro-substituted 1,3,4-oxadiazole 4b and 1,3,4-thiadiazole
5. We introduced an acyl moiety at the 2-amine position, then reduced the nitro group to an amine
group using SnCl2.2H2O in DMF to yield the 1,3,4-oxadiazole resin 10 and the 1,3,4-thiadiazole resin
11. We first introduced six kinds of amino acids at the amine position of 1,3,4-oxadiazole resin 10 and
1,3,4-thiadiazole resin 11 by using DIC, and HOBt in DMF, and then end-capped with acetic glycine
followed by treatment with TFA in DCM (the concentration of TFA solution was depend on the nature
of the protecting group: see the experimental section) to afford amino acid equipped 1,3,4-oxadiazole
20 and 1,3,4-thiadiazole 21 (Table 6). Most amino acids were introduced in good yields and high
purities. However, in the case of methionine (20{1,4} and 21{1,4}), the yields were low compared to
other amino acids (the yields are 6%, and 9% for 20{1,4}, and 21{1,4}, respectively). Thus, to increase
the yields, we used EDC.HCl instead of DIC, and obtained 20{1,4} and 21{1,4} in good yields. The
LC-MS spectra showed high purity after cleavage without further purification (Figure S3 (g), and (l)
in the Supporting Information). Next, we elongated the peptide chains using glycine, methionine, and
serine to afford 1,3,4-oxadiazole 20’ and 1,3,4-thiadiazole 21’ followed by treatment with 50% TFA
in DCM and purified crude product mixture by trituration with diethyl ether / THF. The yields and
purities are summarized in Table 6.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
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Displayed 3D structure, Polar surface area, and Physicochemical property of 1,3,4-oxadiazole
and 1,3,4-thiadiazole library
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Displayed 3D structure, and Polar surface area of 1,3,4-oxadiazole and 1,3,4-thiadiazole
derivatives
To measure structural diversity, we display each library aligned at the 1,3,4-oxadiazole or 1,3,4-
thiadiazole (Figure 3) and show polar surface area of representative 1,3,4-oxadiazole and 1,3,4-
thiadiazole analogues. As can be seen in Figure 3, the 12 kinds of libraries occupy distinct 3D spaces
with respect to their specific functional groups. In addition, these functional groups bring different
polar surface areas, which has been consider one of the key factors to interact with target proteins by
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non-covalent interaction, promising that each library set could have distinct biological activities.
1
2
3
4
5
6
Table 7. Physicochemical property of representative 1,3,4-oxadiazole and 1,3,4-thiadiazolea
7
8
9
Rotatable
bond
No
ALogP
MW
HBA
HBD
PSA (Å2)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
8{1,1}
9{1,1}
4.581
3.973
3.148
3.706
4.992
5.55
327.37
341.36
399.40
415.46
415.46
431.53
370.40
386.47
384.38
400.45
436.42
452.48
3
3
4
4
4
4
4
4
4
4
6
6
1
1
3
3
3
3
2
2
2
2
4
4
50.95
68.02
5
4
5
5
7
7
6
6
5
5
8
8
12{1,1}
13{1,1}
14{1,1}
15{1,1}
16{1,1}
17{1,1}
18{1,1}
19{1,1}
20{1,1}
21{1,1}
109.15
124.25
124.17
139.27
80.05
3.847
4.405
3.24
95.15
97.12
3.798
-0.305
0.253
112.22
155.32
170.42
MW: Molecular Weight; HBA: Hydrogen Bonding Acceptor; HBD: Hydrogen Bonding Donor; PSA: Polar Surface Area
a is calculated by Drug Discovery Studio 2016.
Next, to measure the orally available drug properties, we calculated the physicochemical properties of
representative 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives (Table 7). Lipinski’s Rule23 and
similar parameters have been used as a guide to achieve the ultimate goal of isolating an orally
bioavailable drug during the drug discovery process. In this context, most of the key parameters of our
12 kinds of 1,3,4-oxadiazole and 1,3,4-thiadiazole analogues fall within a range of those typically
predicted for orally bioavailable drugs. Compared with other analogues, the ALogP and PSA values
are very low and high, respectively, for 1.3.4-oxadiazole 20{1,1} and 1,3,4-thiadiazole 21{1,1}. This
is probably due to the hydrophilicity of the peptide moiety.
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Conclusion
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In conclusion, we have synthesized 128 1,3,4-oxadiazole and 1,3,4-thiadiazole analogues classified to
12 kinds of distinct library sets having aryl, urea, thiourea, amine, amide, and peptide chains on solid-
phase. In this synthetic procedure, most of the 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives are
purified by simple trituration after cleavage from the polymer supported resin - our protocols do not
require complex processes for purification such as extraction, and column chromatography facilitating
rapid library construction. Each library set occupies specific positions in 3D space based on their
functional groups and have distinct polar surface areas. Finally, we calculated the physicochemical
properties of representative analogues to probe their orally available drug properties. As a result, most
of the key parameters of the analogues fall within the acceptable range for oral drugs, thus enabling
us to explore and biologically evaluate each library set. We will use these libraries to evaluate
biological activities of these compounds in our future work.
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Experimental section
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General procedure for synthesis : All chemicals were reagent grade and used as purchased.
Reactions were monitored by ATR-FTIR. Flash column chromatography was carried out on silica gel
(230-400 mesh). 1H NMR and 13C NMR spectra were recorded in δ units relative to deuterated solvent
as an internal reference using a 500 MHz NMR instrument. Liquid chromatography tandem mass
spectrometry analysis was performed on an electro spray ionization (ESI) mass spectrometer with
photodiode-array detector (PDA) detection. High-resolution mass spectrometry spectra were obtained
using TOF LC/MS system.
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Representative procedure for the preparation of isothiocyanate-terminated resin 2
A mixture of BOMBA resin 1 (5.00 g, 5.80 mmol), and Et3N (5.86 g, 58.0 mmol) in THF (30.0 mL)
was added CS2 (2.65 g, 34.8 mmol) at 0 oC and then the mixture was shaken at room temperature for
3 h. The mixture was cooled down to 0 oC and then added p-TsCl (5.53 g, 29.0 mmol). The mixture
was shaken at room temperature for 15 h. The precipitate obtained by filteration of the mixture was
washed with THF, H2O, MeOH, and DCM and dried in a vacuum oven. This process made resin 2 as
a brown solid. Single-Bead ATR-FTIR : 2918, 2061(N=C=S), 1610, 1504, 1451, 1286, 1195, 1159,
1028, 817, 757 and 697 cm-1.
Representative procedure for the preparation of thiosemicarbazide resin 3-I
A mixture of isothiocyanate resin 2 (3 g, 3.18 mmol), and Et3N (0.97 g, 9.54 mmol) in THF (20 mL)
was added 3-iodobenzhydrazide (2.5 g, 9.54 mmol) and then the mixture was shaken at room
temperature for 16 h. The resin was filtered and washed several times with MeOH and DCM and then
dried in a vacuum oven. Resin 3-I was obtained as a yellow brown solid. Single-Bead ATR-FTIR :
Single-Bead ATR-FTIR: 3310(br), 2916, 1670(C〓O), 1610, 1450, 1194, 1157, 818, 733, 697 cm−1.
Representative procedure for the preparation of thiosemicarbazide resin 3-m-NO2
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A mixture of isothiocyanate resin 2 (3 g, 3.18 mmol), and Et3N (0.97 g, 9.54 mmol) in THF (20 mL)
was added 3-nitrobenzahydrazide (1.73 g, 9.54 mmol) and then the mixture was shaken at room
temperature for 16 h. The resin was filtered and washed several times with MeOH and DCM and then
dried in a vacuum oven. Resin 3-m-NO2 was obtained as a yellow brown solid. Single-Bead ATR-
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FTIR : 3310(br), 2918, 1670(C〓O), 1612, 1530, 1450, 1194, 1157, 816, 732, 697 cm−1.
Representative procedure for the preparation of 1,3,4-oxadiazole resin 4a
A mixture of thiosemicarbazide resin 3-I (3 g, 3.18 mmol) and EDC∙HCl (3.03 g, 15.9 mmol) in
DMSO (20 mL) was stirred at 60 oC for 16 h. The resin was filtered and washed several times with
MeOH, H2O and DCM and then dried in a vacuum oven. Resin 4a was obtained as a dark gold solid.
Single-Bead ATR-FTIR: 2918, 1610(C〓N), 1492, 1450, 1194, 1159, 817, 733, and 697 cm−1.
Representative procedure for the preparation of 1,3,4-oxadiazole resin 4b
A mixture of thiosemicarbazide resin 3-m-NO2 (3 g, 3.18 mmol) and EDC∙HCl (3.03 g, 15.9 mmol)
in DMSO (20 mL) was stirred at 60 oC for 16 h. The resin was filtered and washed several times with
MeOH, H2O and DCM and then dried in a vacuum oven. Resin 4b was obtained as a brown solid.
Single-Bead ATR-FTIR: 3023, 2919, 1612(C〓N), 1529, 1504, 1493, 1451, 1348, 1194, 1158, 817,
756, 730, and 698 cm−1.
Representative Procedure for 1,3,4-oxadiazole resin 6{1,1}
To a mixture of cyclized resin 4a (0.2 g, 0.21 mmol) in DMF (3 mL), t-BuOK (0.112 g, 1.1 mmol)
was added, and the reaction mixture was shaken for 1 h at room temperature. After 1 h benzyl chloride
(0.134 g, 1.1 mmol) was added, and the temperature was increased to 60 oC. The reaction mixture was
shaken for 16 h. The resin was filtered and washed successively with DCM, MeOH, H2O, MeOH (×2),
and DCM (×2), and dried under high vacuum. Resin 4a-alkylation was obtained as a dark orange
solid. Single-bead ATR-FTIR: 3022, 2019, 1600, 1490, 1449, 1280, 1250(C−N), 1196, 1159, and 895
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cm−1.
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Suzuki coupling reaction was carried out under inert atmosphere. To a suspension of resin 4a-
alkylation (200 mg, 0.21 mmol) in 1,4-dioxane (1.8 mL), Pd2(dba)3 (39 mg, 0.04 mmol), XPhos (41
mg, 0.08 mmol), phenylboronic acid (78 mg, 0.06 mmol), and Cs2CO3 (0.35 g, 1.06 mmol) dissolved
in H2O (0.2 mL) were added. The reaction mixture was shaken for 14 h at 110 oC and cooled to room
temperature. The resin was filtered and washed several times with MeOH, H2O and DCM, and dried
under high vacuum. Resin 6{1,1} was obtained as a dark black solid.
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Representative Procedure for the Preparation of 8{1,1}
A resin 6{1,1} (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:4, v/v, 2 mL) and
shaken for 8 h at 40 oC. The resin was filtered and then washed several times with DCM and MeOH,
and organic filtrate was collected and evaporated. The residue was dissolved in ethyl acetate, washed
with H2O, and neutralized to pH 7 with saturated aqueous NaHCO3 solution. The organic layer was
dried with anhydrous NaSO4 and evaporated. The crude mixture was purified by column
chromatography on silica gel (hexane/ethyl acetate) and triturated with hexane and diethyl ether (7:3,
v/v) affording 8{1,1} (17%, six-step overall yield). 1H NMR (500 MHz, DMSO-d6) δ 8.42 (t, J = 6.2
Hz, 1H), 8.02 (s, 1H), 7.81 (d, J = 8.9 Hz, 2H), 7.71 (d, J = 7.3 Hz, 2H), 7.63 (t, J = 7.8 Hz, 1H), 7.52
(t, J = 7.6 Hz, 2H), 7.44 (d, J = 7.3 Hz, 1H), 7.41 (d, J = 7.4 Hz, 2H), 7.36 (t, J = 7.6 Hz, 2H), 7.28 (t,
13
J = 7.2 Hz, 1H), 4.48 (d, J = 6.1 Hz, 2H); C NMR (126 MHz, Chloroform-d) δ 163.30, 159.20,
141.93, 140.04, 137.37, 129.34, 129.28, 128.89, 128.86, 128.02, 127.82, 127.80, 127.14, 124.89,
124.58, 124.47, 47.74; m.p. 153-158 oC; LC-MS (ESI): m/z = 328.2 [M + H]+; HRMS (ESI) calcd for
C21H17N3O [M + H]+ : 328.1444, found : 328.1439.
Representative procedure for the Preparation of 1,3,4-oxadiazole resin 7{1,1}
Suzuki coupling reaction was carried out under inert atmosphere. To a suspension of resin 4a (200 mg,
0.21 mmol) in 1,4-dioxane (1.8 mL), Pd2(dba)3 (39 mg, 0.04 mmol), XPhos (41 mg, 0.08 mmol),
phenylboronic acid (78 mg, 0.06 mmol), and Cs2CO3 (0.35 g, 1.06 mmol) dissolved in H2O (0.2 mL)
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were added. The reaction mixture was shaken for 14 h at 110 oC and cooled to room temperature. The
resin was filtered and washed several times with MeOH, H2O and DCM, and dried under high vacuum.
Resin 4a-Suzuki coupling was obtained as a dark black solid.
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To a suspension of resin 4a-Suzuki coupling (0.2 g, 0.21 mmol) in pyridine (2 mL), benzoyl chloride
(0.149 g, 1.06 mmol), and DMAP (cat. amount) were added successively. The reaction mixture was
shaken for 12 h at 60 oC. Resin 7{1,1} was filtered and washed successively with DCM, MeOH, H2O,
MeOH (×2), and DCM (×2), and dried under high vacuum. Resin 7{1,1} was obtained as a dark brown
solid. Single-bead ATR-FTIR: 3022, 2921, 1680(amide), 1600, 1575, 1504, 1449, 1265, 1195, 1022,
825 cm−1.
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Representative Procedure for the Preparation of 9{1,1}
A resin 7{1,1} (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:9, v/v, 2 mL)
and shaken for 6 h at room temperature. The resin was filtered and washed with DCM and MeOH (×3),
and organic filtrate was collected and evaporated. The crude mixture was purified by trituration with
diethyl ether and ethyl acetate (9:1, v/v) solvent mixture and dried under high vacuum. The resulting
product was beige color solid (36%, six-step overall yield). 1H NMR (500 MHz, Chloroform-d) δ 8.24
(s, 1H), 8.09 (d, J = 7.7 Hz, 2H), 7.99 (d, J = 7.6 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.77 (t, J = 7.3 Hz,
1H), 7.68 (t, J = 7.7 Hz, 1H), 7.63 (t, J = 9.3 Hz, 4H), 7.51 (t, J = 7.4 Hz, 2H), 7.46 – 7.42 (m, 1H);
13C NMR (126 MHz, Chloroform-d) δ 166.57, 161.40, 157.10, 143.27, 138.99, 135.80, 133.09, 130.41,
o
129.73, 129.31, 129.24, 128.92, 128.67, 127.23, 126.02, 125.86, 120.62; m.p. 180-190 C; LC-MS
(ESI): m/z = 342.2 [M + H]+; HRMS (ESI) calcd for C21H15N3O2 [M + H]+ : 342.1237, found :
342.1227.
Representative Procedure for the Preparation of resin 10{1}
To a suspension of resin 4b (0.2 g, 0.21 mmol) in pyridine (2 mL), benzoyl chloride (0.149 g, 1.06
mmol), and DMAP (cat. Amount) were added successively. The reaction mixture was shaken for 12 h
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at 60 oC. The resin was filtered and washed several times with DCM, MeOH, H2O, MeOH (×2), and
DCM (×2), and dried under high vacuum. Resin 4b-Acylation was obtained as a brown solid. Single-
bead ATR-FTIR: 2919, 1680(amide), 1529, 1506, 1492, 1450, 1348, 1195, 1159, 1113, 817, 735, 690
cm−1.
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And then, to a suspension of resin 4b-Acylation (0.2 g, 0.21 mmol) in DMF (2 mL), SnCl2∙2H2O
(0.24 g, 1.06 mmol) was added successively. The reaction mixture was shaken for 12 h at room
temperature. The resin was filtered and washed several times with DMF, MeOH, H2O, MeOH (×2),
and DCM (×2), and dried under high vacuum. Resin 10{1} was obtained as a brown solid. Single-
bead ATR-FTIR: 3220(br), 1680(amide), 1449, 1194, 1159, 1115, 818, 732, 697 cm−1.
Representative Procedure for the Preparation of resin 10-Urea
(1) In case of Phenyl isocyanate : A mixture of resin 10{1} (0.2 g, 0.21 mmol), and Pyridine (83
mg, 1.06 mmol) in THF (2 mL) was added phenyl isocyanate (126 mg, 1.06 mmol) and then
the mixture was shaken at 60 oC for 12 h. The resin was filtered and washed several times with
THF, MeOH, H2O, MeOH (×2), and DCM (×2), and dried under high vacuum. Resin 10{1,1}-
Urea was obtained as a brown solid.
(2) In case of Benzyl isocyanate : A mixture of resin 10{1} (0.2 g, 0.21 mmol), and DMAP (14
mg, 0.12 mmol) in DCM (2 mL) was added benzyl isocyanate (158 mg, 1.06 mmol) and then
the mixture was shaken at 60 oC for 12 h. The resin was filtered and washed several times with
DCM, MeOH, H2O, MeOH (×2), and DCM (×2), and dried under high vacuum. Resin
10{1,2}-Urea was obtained as a brown solid.
(3) In case of Ethyl isocyanate : A mixture of resin 10{1} (0.2 g, 0.21 mmol), and DMAP (14
mg, 0.12 mmol) in DCM (2 mL) was added ethyl isocyanate (75 mg, 1.06 mmol) and then the
mixture was shaken at room temperature for 12 h. The resin was filtered and washed several
times with DCM, MeOH, H2O, MeOH (×2), and DCM (×2), and dried under high vacuum.
Resin 10{1,3}-Urea was obtained as a brown solid.
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Representative Procedure for the Preparation of 12{1,1}
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A resin 10{1,1}-Urea (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:9, v/v, 2
mL) and shaken for 6 h at room temperature. The resin was filtered and washed with DCM and MeOH
(×3), and organic filtrate was collected and evaporated. The crude mixture was purified by trituration
with diethyl ether and ethyl acetate (9:1, v/v) solvent mixture and dried under high vacuum. The
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resulting product was beige color solid (12%, seven-step overall yield). H NMR (500 MHz,
Chloroform-d) δ 8.06 (d, J = 7.4 Hz, 2H), 7.94 (s, 1H), 7.80 (d, J = 7.8 Hz, 1H), 7.74 (t, J = 7.5 Hz,
2H), 7.60 (t, J = 7.8 Hz, 2H), 7.53 (t, J = 8.0 Hz, 1H), 7.45 (t, J = 7.8 Hz, 2H), 7.33 (d, J = 8.3 Hz,
4H); 13C NMR (126 MHz, Chloroform-d) δ 166.45, 156.87, 138.13, 136.02, 131.40, 131.02, 130.29,
129.80, 129.59, 129.51, 128.88, 127.84, 127.27, 126.82, 124.82, 123.11, 120.93, 120.12; m.p. 245-
250 oC; LC-MS (ESI): m/z = 400.2 [M + H]+; HRMS (ESI) calcd for C22H17N5O3 [M + H]+ : 400.1404,
found : 400.1391.
Representative Procedure for the Preparation of resin 10{1,1}-Thiourea
A mixture of resin 10{1} (0.2 g, 0.21 mmol), and DMAP (14 mg, 0.12 mmol) in CHCl3 (2 mL) was
added phenyl isothiocyanate (143 mg, 1.06 mmol) and then the mixture was shaken at 60 oC for 12 h.
The resin was filtered and washed several times with DCM, MeOH, H2O, MeOH (×2), and DCM (×2),
and dried under high vacuum. Resin 10{1,1}-Thiourea was obtained as a brown solid.
Representative Procedure for the Preparation of 14{1,1}
A resin 10{1,1}-Thiourea (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:9,
v/v, 2 mL) and shaken for 6 h at room temperature. The resin was filtered and washed with DCM and
MeOH (×3), and organic filtrate was collected and evaporated. The crude mixture was purified by
trituration with diethyl ether and ethyl acetate (9:1, v/v) solvent mixture and dried under high vacuum.
1
The resulting product was beige color solid (17%, seven-step overall yield). H NMR (500 MHz,
DMSO-d6) δ 12.19 (s, 1H), 10.07 (d, J = 17.7 Hz, 1H), 8.20 (s, 1H), 8.05 (d, J = 6.8 Hz, 3H), 7.76 –
7.70 (m, 2H), 7.70 – 7.64 (m, 2H), 7.60 – 7.55 (m, 4H), 7.49 (d, J = 7.7 Hz, 2H), 7.36 (t, J = 7.8 Hz,
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2H), 7.16 (t, J = 7.4 Hz, 1H); 13C NMR (126 MHz, DMSO) δ 180.24, 170.80, 141.11, 140.84, 139.67,
133.41, 130.07, 129.26, 129.13, 129.03, 128.80, 127.06, 125.17, 124.25, 123.85, 122.18, 121.31,
118.87; m.p. 130-140 oC; LC-MS (ESI): m/z = 416.1 [M + H]+; HRMS (ESI) calcd for C22H17N5O2S
[M + H]+ : 416.1176, found : 416.1164.
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Representative Procedure for the Preparation of resin 10{1,1}-Reductive amination
To a suspension of resin 10{1} (0.2 g, 0.21 mmol) in 1,2-Dichloroethane (1.2 mL), Benzaldehyde
(112 mg, 1.06 mmol) was added successively. The mixture was shaken at room temperature for 3 h.
An acetic acid (38 mg, 0.64 mmol), MeOH (0.8 mL), NaBH3(CN) (67 mg, 1.06 mmol) was added,
and then the mixture was shaken at room temperature for 12 h. The resin was filtered and washed
several times with DCM, MeOH, H2O, MeOH (×2), and DCM (×2), and dried under high vacuum.
Resin 10{1,1}-Reductive amination was obtained as an orange solid.
Representative Procedure for the Preparation of 16{1,1}
A resin 10{1,1}-Reductive amination (200 mg, 0.21 mmol) was treated with a mixture of TFA and
DCM (1:9, v/v, 2 mL) and shaken for 6 h at room temperature. The resin was filtered and washed with
DCM and MeOH (×3), and organic filtrate was collected and evaporated. The crude mixture was
purified by trituration with diethyl ether and ethyl acetate (9:1, v/v) solvent mixture and dried under
1
high vacuum. The resulting product was beige color solid (57%, seven-step overall yield). H NMR
(500 MHz, DMSO-d6) δ 12.16 (s, 1H), 8.79 (s, 1H), 8.68 (d, J = 5.1 Hz, 1H), 8.22 (d, J = 8.0 Hz, 1H),
8.04 (d, J = 7.6 Hz, 2H), 7.78 – 7.74 (m, 1H), 7.68 (t, J = 7.4 Hz, 1H), 7.57 (t, J = 7.7 Hz, 3H), 7.30
(t, J = 7.9 Hz, 1H), 7.24 (s, 1H), 7.17 (d, J = 7.6 Hz, 1H), 6.83 (d, J = 8.1 Hz, 1H), 4.51 (s, 2H); 13C
NMR (126 MHz, Chloroform-d) δ 167.42, 159.56, 157.67, 149.89, 144.25, 143.30, 136.88, 133.11,
132.21, 130.30, 129.33, 129.28, 128.77, 128.67, 127.72, 123.38, 121.06, 52.61; m.p. 170-176 oC; LC-
MS (ESI): m/z = 371.2 [M + H]+; HRMS (ESI) calcd for C22H18N4O2 [M + H]+ : 371.1503, found :
371.1497.
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Representative Procedure for the Preparation of resin 10{1,1}-Acylation.
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A mixture of resin 10{1} (0.2 g, 0.21 mmol), and Pyridine (83 mg, 1.06 mmol) in THF (2 mL) was
added benzoyl chloride (149 mg, 1.06 mmol) and then the mixture was shaken at 60 oC for 12 h. The
resin was filtered and washed several times with THF, MeOH, H2O, MeOH (×2), and DCM (×2), and
dried under high vacuum. Single-bead ATR-FTIR: 2919, 1685(amide), 1680(amide), 1530, 1507, 1495,
1451, 1345, 1195, 1159, 1113, 818, 636 cm−1. Resin 10{1,1}-Acylation was obtained as a brown solid.
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Representative Procedure for the Preparation of 18{1,1}
A resin 10{1,1}-Acylation (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:9,
v/v, 2 mL) and shaken for 6 h at room temperature. The resin was filtered and washed with DCM and
MeOH (×3), and organic filtrate was collected and evaporated. The crude mixture was purified by
trituration with diethyl ether and ethyl acetate (9:1, v/v) solvent mixture and dried under high vacuum.
1
The resulting product was beige color solid (28%, seven-step overall yield). H NMR (500 MHz,
Chloroform-d) δ 8.71 (s, 1H), 8.33 (s, 1H), 8.08 (dd, J = 16.3, 7.8 Hz, 3H), 7.92 (d, J = 7.8 Hz, 1H),
7.88 (d, J = 7.6 Hz, 2H), 7.77 (t, J = 7.4 Hz, 1H), 7.64 (dq, J = 15.2, 7.4 Hz, 4H), 7.55 (t, J = 7.6 Hz,
2H); 13C NMR (126 MHz, Chloroform-d) δ 170.02, 166.38, 160.56, 157.05, 138.17, 135.90, 133.73,
132.49, 131.06, 129.79, 129.45, 128.93, 128.82, 127.46, 126.89, 124.40, 121.15, 120.16; m.p. 275-
280 oC; LC-MS (ESI): m/z = 385.1 [M + H]+; HRMS (ESI) calcd for C22H16N4O3 [M + H]+ : 385.1295,
found : 385.1285.
Representative Procedure for the Preparation of resin 10{1,1}-Amino acid
Resin 10{1} (0.2 g, 0.21 mmol) was swollen in DMF (2 mL) for 10 min. Amino acid (glycine) was
pre-activated for 2 min by HOBt (130 mg, 0.85 mmol) and DIC (107 mg, 0.85 mmol) treatment of
Fmoc-protected amino acids (4.0 eq.) in DMF. In each case, the mixture was added to the resin and
the syringe tumbled on a shaker for 2 h at room temperature and 160 rpm. The resin was washed with
DMF (5 × 1 min), DCM (5 × 1 min), and DMF (5 × 1 min). Removal of Fmoc groups was achieved
by treatment of the resin with 20 vol% piperidine in DMF (2 × 10 min). Washings between
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ACS Combinatorial Science
deprotection and coupling steps were performed with DMF (5 × 1 min), DCM (5 × 1 min), and DMF
(5 × 1 min). After Fmoc cleavage, free amine group was end-capped with acetic glycine. To achieve
this, the resin was swollen in DMF for 10 min. Acetic glycine (99 mg, 0.85 mmol) were pre-activated
for 2 min by HOBt (130 mg, 0.85 mmol) and DIC (107 mg, 0.85 mmol) treatment in DMF (2 mL).
The mixture was added to the resin and the syringe tumbled on a shaker for 2 h at room temperature
and 160 rpm. Following the final coupling, the resin was washed with DMF (5 × 1 min), DCM (5 × 1
min), and dried under high vacuum. Resin 10{1,1}-Amino acid was obtained as a brown solid.
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In case of methionine, to increase the yields, we used EDC.HCl instead of DIC. Resin 10{1} (0.2 g,
0.21 mmol) was swollen in DMF (2 mL) for 10 min. Amino acids were pre-activated for 2 min by
HOBt (97 mg, 0.64 mmol) and EDC∙HCl (121 mg, 0.64 mmol) treatment of Fmoc-protected
methionine (315 mg, 0.64 mmol) in DMF. The mixture was added to the resin and the syringe tumbled
on a shaker for 1 day at room temperature and 160 rpm. The resin was washed with DMF (5 × 1 min),
DCM (5 × 1 min), and DMF (5 × 1 min). Removal of Fmoc groups was achieved by treatment of the
resin with 20 vol% piperidine in DMF (2 × 10 min). After Fmoc cleavage, free amine group was end-
capped with acetic glycine. To achieve this, the resin was swollen in DMF (2 mL) for 10 min. Acetic
glycine (74 mg, 0.64 mmol) were pre-activated for 2 min by HOBt (97 mg, 0.64 mmol) and EDC∙HCl
(121 mg, 0.64 mmol) treatment in DMF. The mixture was added to the resin and the syringe tumbled
on a shaker for 1 day at room temperature and 160 rpm. Following the final coupling, the resin was
washed with DMF (5 × 1 min), DCM (5 × 1 min), and dried under high vacuum. Resin 10{1,4}-
Amino acid was obtained as a brown solid.
Representative Procedure for the Preparation of 20{1,1}
A resin 10{1,1}-Amino acid (200 mg, 0.21 mmol) was treated with a mixture of TFA and DCM (1:9,
v/v, 2 mL) and shaken for 6 h at room temperature. The resin was filtered and washed with DCM and
MeOH (×3), and organic filtrate was collected and evaporated. The crude mixture was purified by
trituration with diethyl ether and tetrahydrofuran (9:1, v/v) solvent mixture and dried under high
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