Doohyun Lee1, Daehun Kim2, Seungyeon Lee3, Taegeum Kim4, Joobin Kim5, Sohee Kim6, Kwang-Hyeon Liu7, Sangkyu Lee3, Jong-Sup Bae8, Kyung-Sik Song9, Chang-Woo Cho10, Youn Kyung Son11, Dong Jae Baek12, Taeho Lee13. 1. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. newkiy@hanmail.net. 2. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. eogns1201@nate.com. 3. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. tmddusj@naver.com. 4. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. eksvnddlv321@naver.com. 5. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. joobin87@naver.com. 6. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. ksh71051@naver.com. 7. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. dstlkh@knu.ac.kr. 8. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. baejs@knu.ac.kr. 9. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. kssong@knu.ac.kr. 10. Department of Chemistry, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. cwcho@knu.ac.kr. 11. National Institute of Biological Resources, Hwangyeong-ro 42, Seo-gu, Incheon 404-708, Korea. sophy004@korea.kr. 12. College of Pharmacy, Natural Medicine Research Institute, Mokpo National University, 1666 Youngsan-ro, Muan-gun, Jeonnam 534-729, Korea. dbaek@mokpo.ac.kr. 13. College of Pharmacy, Research Institute of Pharmaceutical Sciences, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 702-701, Korea. tlee@knu.ac.kr.
Abstract
Efficient synthetic routes for the preparation of secondary and tertiary 1,2,3-triazoloamide derivatives were developed. A secondary α-1,2,3-triazoloamide library was constructed and expanded by a previously developed solid-phase synthetic route and a tertiary 1,2,3-triazoloamide library was constructed by a parallel solution-phase synthetic route. The synthetic routes rely on amide formation with secondary amines and chloro-acid chlorides; SN2 reaction with sodium azide; and the selective [3 + 2] Hüisgen cycloaddition with appropriate terminal alkynes. The target secondary and tertiary 1,2,3-triazoloamide derivatives were obtained with three-diversity points in excellent overall yields and purities using the reported solid- and solution-phase synthetic routes, respectively.
Efficient synthetic routes for the preparation of secondary and tertiary 1,2,3-triazoloamide derivatives were developed. A secondary α-1,2,3-triazoloamide library was constructed and expanded by a previously developed solid-phase synthetic route and a tertiary 1,2,3-triazoloamide library was constructed by a parallel solution-phase synthetic route. The synthetic routes rely on amide formation with secondary amines and chloro-acid chlorides; SN2 reaction with sodium azide; and the selective [3 + 2] Hüisgen cycloaddition with appropriate terminal alkynes. The target secondary and tertiary 1,2,3-triazoloamide derivatives were obtained with three-diversity points in excellent overall yields and purities using the reported solid- and solution-phase synthetic routes, respectively.
Combinatorial chemistry has emerged as a powerful technique for the synthesis of biologically active small molecules for the purpose of medicinal chemistry programs within the pharmaceutical industry [1,2,3,4,5]. Recently, the 1,2,3-triazole moiety, produced by Cu(I)-catalyzed [3 + 2] cycloaddition reactions, has been used as a scaffold for generating combinatorial libraries [6,7,8,9,10]. 1,2,3-Triazoles can mimic the topological and electronic features of an amide bond, and this be used as bioisosteres of the amide moiety. They are particularly stable to reduction, oxidation, and hydrolysis conditions.Various α-1,2,3-triazoloamide derivatives have been shown to exhibit a wide range of biological activities [11,12,13,14,15,16,17,18,19]. In recent examples, α-1,2,3-triazoloamide related compounds have been developed and studied as tropomysin receptor kinase A (TrkA) inhibitors [11], as inhibitors of Mycobacterium tuberculosis [12], as phosphodiesterase 4B (PDE4B) inhibitor for anticancer agents [13], as quorum sensing modulators [14], as β-haematin inhibitors for antimalarial agents [15], as γ-secretase modulators [16], as protein tyrosine phosphatase (PTPs) inhibitors [17], as lymphoid tyrosin phosphatase (Lyp, PTPN22) inhibitors [18], and as glucokinase (GK) acitvators [19].Previously, we have reported a solid-phase synthetic protocol for the preparation of secondary α-1,2,3-triazoloamides 1 (R2 = H, Figure 1) [20]. However, an expanded α-1,2,3-triazoloamide library was needed for our drug discovery project, which includes the secondary and tertiary 1,2,3-triazoloamides. Herein, we describe the construction of expanded libraries of secondary α-1,2,3-triazoloamides 1 on solid-phase and of tertiary 1,2,3-triazoloamides 2 in parallel solution-phase, which is applicable to high-throughput construction of drug-like compound libraries.
Figure 1
Structure and use of 1,2,3-triazoloamides 1 and 2.
Structure and use of 1,2,3-triazoloamides 1 and 2.
2. Results and Discussion
The synthetic sequence for secondary α-1,2,3-triazoloamides 1 (R2 = H) is shown in Scheme 1 [20]. According to the solid-phase synthetic approach with the polymer-bound amines 3, which were prepared by reductive amination reaction from Acid sensitive Methoxy Benzaldehyde (AMEBA) [20,21] resin 4 and primary amines 5 (the first diversity element R1; Figure 2), polymer-bound chloroamides 7 can be easily prepared by the reaction of amine resin 3 with chloro-acid chloride 6 (the second diversity element A; Figure 3) and triethylamine in CH2Cl2 at room temperature. Treatment of solid supported chloroamides 7 (R = Cl, A = CH2 or CHCH3) with sodium azide in DMF at room temperature, provides the α-azidoamide resin 8 (R = N3).
Scheme 1
Solid-phase synthesis of secondary α-1,2,3-triazoloamide derivatives 1.
Figure 2
Diversity reagents 5 for secondary α-1,2,3-triazoloamides 1.
Figure 3
Diversity reagents 6 for 1,2,3-triazoloamides 1 and 2.
Solid-phase synthesis of secondary α-1,2,3-triazoloamide derivatives 1.Diversity reagents 5 for secondary α-1,2,3-triazoloamides 1.Diversity reagents 6 for 1,2,3-triazoloamides 1 and 2.In the case of β-chloroamide 7ac, which was prepared by the reaction of amine resin 3a and 3-chloropropionyl chloride (6c), the SN2 reaction with sodium azide gave the undesired acrylamide 12 because of an elimination of β-chloroamide (Scheme 2). The reaction was confirmed by ATR-FTIR analysis of resin 11 and the cleavage of the resin 11 under 30% TFA in CH2Cl2 at room temperature provided an N-phenylacrylamide (12) [22,23] as a major product.
Scheme 2
Reaction of amine resin 3a and 3-chloropropionyl chloride (6c).
Reaction of amine resin 3a and 3-chloropropionyl chloride (6c).The selective [3 + 2] Hüisgen cycloaddition [24,25,26,27,28,29] was performed with α-azidoamide resin 8 and terminal acetylene 9 (the third diversity element R3; Figure 4) according to optimized reaction condition (3 equiv. CuI, 3 equiv. sodium ascorbate, DMF/piperidine (4:1), room temperature) [20]. The well-known methods for the synthesis of 1,2,3-triazoles (catalytic CuSO4/sodium ascorbate or CuI/diisopropylethylamine as reagents and H2O/t-BuOH, EtOH, or THF as solvent) were not very efficient. Under the general cleavage conditions of AMEBA resin (30% TFA, CH2Cl2, room temperature), the resulting polymer-bound product 10aaa gave the desired α-1,2,3-triazoloamide1aaa (44%) and by-product 13 (30%), while unreacted resin 10aaa remained as was confirmed by ATR-FTIR analysis (Scheme 3).
Figure 4
Diversity reagents 9 for 1,2,3-triazoloamides 1 and 2.
Scheme 3
Cleavage of α-1,2,3-triazoloamide resin 10aaa.
Diversity reagents 9 for 1,2,3-triazoloamides 1 and 2.Cleavage of α-1,2,3-triazoloamide resin 10aaa.Finally, the α-1,2,3-triazoloamide resin 10aaa was cleaved from the solid support under 30% TFA in CH2Cl2 at 45 °C to provide the desired α-1,2,3-triazoloamide1aaa [24,27,30] (93% over six steps, from Merrifield resin) without formation of by-product 13.The reaction progress on solid-phase was monitored by ATR-FTIR (Figure 5). The progress of reductive amination of AMEBA resin 4 and amine 5a (R1 = Ph) was checked by the appearance of the weak NH stretching band at 3424 cm−1 and the disappearance of the aldehyde stretching band at 1678 cm−1. The progression of amide formation for 7aa (R1 = Ph, A = CH2) was monitored by ATR-FTIR which displayed the disappearance of the characteristic NH band at 3424 cm−1 and appearance of the amide carbonyl stretching band at 1666 cm−1. The SN2 reaction of 7aa (R1 = Ph, A = CH2) with sodium azide was monitored by the appearance of the azide stretching band at 2101 cm−1. The completion of selective [3 + 2] Hüisgen cycloaddition of 7aa and 9a was confirmed by the disappearance of the azide stretching band.
Figure 5
ATR-FTIR spectra of resins 3, 4, 7, 8 and 10 (R1 = R2 = Ph, A = CH2).
ATR-FTIR spectra of resins 3, 4, 7, 8 and 10 (R1 = R2 = Ph, A = CH2).Prepared secondary α-1,2,3-triazoloamide derivatives 1
a.a All reactions were performed on 150–200 mg scale of resin 10 and the purities of compounds 1 were over 95% as judged from LC-MS traces (integration of diode array 200–400 nm traces); b Six-step overall yield from Merrifield resin (loading capacity = 0.94 mmol/g).Following the optimized solid-phase synthetic route, the secondary α-1,2,3-triazoloamide derivatives 1 were prepared starting from Merrifield resin and appropriate primary amines 5 (R1NH2; Figure 2), α-chloroacetyl chlorides 6a and 6b (Cl-A-COCl; Figure 3), and terminal acetylenes 9 (R3C≡CH; Figure 4) and the products displayed in Table 1. In most cases, secondary α-1,2,3-triazoloamide derivatives 1 (80 examples) were obtained with high yields (94%–75%) and high purities, >95% as judged from LC-MS traces (integration of 200–400 nm diode array traces).
Table 1
Prepared secondary α-1,2,3-triazoloamide derivatives 1
a.
Entry
Products
R1
A
R3
Yield (%) b
Entry
Products
R1
A
R3
Yield (%) b
1
1aaa
Ph
CH2
Ph
93
41
1dan
2-MeO-Ph
CH2
2,4-di-F-Ph
94
2
1aab
Ph
CH2
4-MeO-Ph
91
42
1dao
2-MeO-Ph
CH2
Bn
88
3
1aac
Ph
CH2
4-CN-Ph
83
43
1eaa
n-Bu
CH2
Ph
81
4
1aad
Ph
CH2
3-thiophenyl
82
44
1eab
n-Bu
CH2
4-MeO-Ph
88
5
1aae
Ph
CH2
2-pyridyl
85
45
1eac
n-Bu
CH2
4-CN-Ph
83
6
1aaf
Ph
CH2
n-Bu
92
46
1ead
n-Bu
CH2
3-thiophenyl
80
7
1baa
4-MeO-Ph
CH2
Ph
92
47
1eae
n-Bu
CH2
2-pyridyl
89
8
1bab
4-MeO-Ph
CH2
4-MeO-Ph
94
48
1eaf
n-Bu
CH2
n-Bu
89
9
1bac
4-MeO-Ph
CH2
4-CN-Ph
89
49
1faa
i-Pr
CH2
Ph
79
10
1bad
4-MeO-Ph
CH2
3-thiophenyl
85
50
1fab
i-Pr
CH2
4-MeO-Ph
87
11
1bag
4-MeO-Ph
CH2
3-MeO-Ph
87
51
1fac
i-Pr
CH2
4-CN-Ph
75
12
1baj
4-MeO-Ph
CH2
3-Me-Ph
89
52
1fad
i-Pr
CH2
3-thiophenyl
77
13
1bak
4-MeO-Ph
CH2
2-Me-Ph
84
53
1fae
i-Pr
CH2
2-pyridyl
84
14
1bal
4-MeO-Ph
CH2
4-NMe2-Ph
79
54
1faf
i-Pr
CH2
n-Bu
83
15
1bam
4-MeO-Ph
CH2
4-PhO-Ph
92
55
1dba
2-MeO-Ph
CHCH3
Ph
88
16
1ban
4-MeO-Ph
CH2
2,4-di-F-Ph
87
56
1dbb
2-MeO-Ph
CHCH3
4-MeO-Ph
91
17
1bao
4-MeO-Ph
CH2
Bn
85
57
1dbc
2-MeO-Ph
CHCH3
4-CN-Ph
87
18
1caa
3-MeO-Ph
CH2
Ph
91
58
1dbd
2-MeO-Ph
CHCH3
3-thiophenyl
80
19
1cab
3-MeO-Ph
CH2
4-MeO-Ph
90
59
1dbe
2-MeO-Ph
CHCH3
2-pyridyl
83
20
1cac
3-MeO-Ph
CH2
4-CN-Ph
87
60
1dbg
2-MeO-Ph
CHCH3
3-MeO-Ph
94
21
1cad
3-MeO-Ph
CH2
3-thiophenyl
76
61
1dbh
2-MeO-Ph
CHCH3
2-MeO-Ph
89
22
1cae
3-MeO-Ph
CH2
2-pyridyl
81
62
1dbi
2-MeO-Ph
CHCH3
4-Me-Ph
94
23
1cah
3-MeO-Ph
CH2
2-MeO-Ph
83
63
1dbj
2-MeO-Ph
CHCH3
3-Me-Ph
83
24
1caj
3-MeO-Ph
CH2
3-Me-Ph
93
64
1dbk
2-MeO-Ph
CHCH3
2-Me-Ph
74
25
1cak
3-MeO-Ph
CH2
2-Me-Ph
90
65
1dbl
2-MeO-Ph
CHCH3
4-NMe2-Ph
82
26
1cal
3-MeO-Ph
CH2
4-NMe2-Ph
91
66
1dbm
2-MeO-Ph
CHCH3
4-PhO-Ph
87
27
1cam
3-MeO-Ph
CH2
4-PhO-Ph
91
67
1dbn
2-MeO-Ph
CHCH3
2,4-di-F-Ph
92
28
1can
3-MeO-Ph
CH2
2,4-di-F-Ph
92
68
1dbo
2-MeO-Ph
CHCH3
Bn
86
29
1cao
3-MeO-Ph
CH2
Bn
88
69
1eba
n-Bu
CHCH3
Ph
83
30
1daa
2-MeO-Ph
CH2
Ph
94
70
1ebb
n-Bu
CHCH3
4-MeO-Ph
81
31
1dab
2-MeO-Ph
CH2
4-MeO-Ph
90
71
1ebc
n-Bu
CHCH3
4-CN-Ph
79
32
1dac
2-MeO-Ph
CH2
4-CN-Ph
86
72
1ebd
n-Bu
CHCH3
3-thiophenyl
78
33
1dad
2-MeO-Ph
CH2
3-thiophenyl
91
73
1ebe
n-Bu
CHCH3
2-pyridyl
84
34
1dae
2-MeO-Ph
CH2
2-pyridyl
84
74
1ebf
n-Bu
CHCH3
n-Bu
81
35
1dag
2-MeO-Ph
CH2
3-MeO-Ph
86
75
1fba
i-Pr
CHCH3
Ph
88
36
1dah
2-MeO-Ph
CH2
2-MeO-Ph
80
76
1fbb
i-Pr
CHCH3
4-MeO-Ph
83
37
1dai
2-MeO-Ph
CH2
4-Me-Ph
78
77
1fbc
i-Pr
CHCH3
4-CN-Ph
78
38
1daj
2-MeO-Ph
CH2
3-Me-Ph
85
78
1fbd
i-Pr
CHCH3
3-thiophenyl
75
39
1dal
2-MeO-Ph
CH2
4-NMe2-Ph
88
79
1fbe
i-Pr
CHCH3
2-pyridyl
81
40
1dam
2-MeO-Ph
CH2
4-PhO-Ph
92
80
1fbf
i-Pr
CHCH3
n-Bu
82
a All reactions were performed on 150–200 mg scale of resin 10 and the purities of compounds 1 were over 95% as judged from LC-MS traces (integration of diode array 200–400 nm traces); b Six-step overall yield from Merrifield resin (loading capacity = 0.94 mmol/g).
With a successful synthetic route for secondary α-1,2,3-triazoloamides 1, the stage progressed to the tertiary 1,2,3-triazoloamides 2 (R2 ≠ H) (Scheme 4). The chloroamides 15 [31,32,33,34,35,36,37] were prepared from the reaction of secondary amines 14 (the first diversity elements R1 and R2; Figure 6) and chloro-acid chlorides 6a and 6c (the second diversity element A; see Figure 3) with triethylamine in CH2Cl2 at room temperature (99%–92% yields). Followed by SN2 reaction of tertiary amides 15 with sodium azide to generated the corresponding azidoamides 16 [15,17,38,39,40,41] in high yields (99%–94% yields) (Figure 7). In contrast to the solid-phase synthesis of secondary 1,2,3-triazoloamides 1, treatment of tertiary β-chloroamide 15ac with sodium azide in DMF at room temperature, provided the corresponding β-azidoamide 16ac in high yield (94% yield) without formation of the undesired acrylamide. Under the general conditions [6,7,8,9,10,24,25,26,27,28] of the Cu-catalyzed 1,3-dipolar cycloaddition (catalytic CuSO4/sodium ascorbate) of azidoamide 16aa and terminal acetylene 9a in H2O/t-BuOH, the desired tertiary 1,2,3-triazoloamide 2aaa is generated in high yield (96%).
Scheme 4
Solution-phase synthesis of tertiary 1,2,3-triazoloamide derivatives 2.
Figure 6
Diversity reagents 14 for tertiary 1,2,3-triazoloamides 2.
Figure 7
Prepared tertiary amides 15 and sodium azidoamide 16.
Solution-phase synthesis of tertiary 1,2,3-triazoloamide derivatives 2.Diversity reagents 14 for tertiary 1,2,3-triazoloamides 2.Prepared tertiary amides 15 and sodium azidoamide 16.By using the parallel solution-phase synthetic route, we were able to prepare a number of tertiary 1,2,3-triazoloamide derivatives 2 displayed in Table 2 starting from appropriate secondary amines 14 (R1R2NH; Figure 6), chloro-acid chlorides 6a and 6c (Cl-A-COCl; Figure 3), and terminal acetylenes 9 (R3C≡CH; Figure 4). In most cases, tertiary 1,2,3-triazoloamide derivatives 1T (80 examples) were obtained with high yields (99%–84%) from azidoamide 16 and in high purities, >95% as judged from LC-MS traces (integration of 200–400 nm diode array traces).
Table 2
Prepared tertiary 1,2,3-triazoloamide derivatives 2. a
Entry
Products
NR1R2
A
R3
Yield (%) b
Entry
Products
NR1R2
A
R3
Yield (%) b
1
2aaa
morpholine
CH2
Ph
91
41
2can
pyrrolidine
CH2
2,4-di-F-Ph
86
2
2aab
morpholine
CH2
4-MeO-Ph
91
42
2cao
pyrrolidine
CH2
Bn
81
3
2aac
morpholine
CH2
4-CN-Ph
88
43
2daa
azepine
CH2
Ph
87
4
2aad
morpholine
CH2
3-thiophenyl
87
44
2dab
azepine
CH2
4-MeO-Ph
78
5
2aae
morpholine
CH2
2-pyridyl
80
45
2dac
azepine
CH2
4-CN-Ph
88
6
2aag
morpholine
CH2
3-MeO-Ph
89
46
2dad
azepine
CH2
3-thiophenyl
89
7
2aah
morpholine
CH2
2-MeO-Ph
88
47
2dae
azepine
CH2
2-pyridyl
78
8
2aai
morpholine
CH2
4-Me-Ph
86
48
2dag
azepine
CH2
3-MeO-Ph
84
9
2aaj
morpholine
CH2
3-Me-Ph
89
49
2dah
azepine
CH2
2-MeO-Ph
80
10
2aak
morpholine
CH2
2-Me-Ph
88
50
2dai
azepine
CH2
4-Me-Ph
88
11
2aal
morpholine
CH2
4-NMe2-Ph
81
51
2daj
azepine
CH2
3-Me-Ph
83
12
2aam
morpholine
CH2
4-PhO-Ph
94
52
2dak
azepine
CH2
2-Me-Ph
78
13
2aan
morpholine
CH2
2,4-di-F-Ph
87
53
2dal
azepine
CH2
4-NMe2-Ph
82
14
2aao
morpholine
CH2
Bn
89
54
2dam
azepine
CH2
4-PhO-Ph
90
15
2baa
piperidine
CH2
Ph
93
55
2dan
azepine
CH2
2,4-di-F-Ph
89
16
2bab
piperidine
CH2
4-MeO-Ph
80
56
2dao
azepine
CH2
Bn
86
17
2bac
piperidine
CH2
4-CN-Ph
92
57
2eaa
NPhMe
CH2
Ph
95
18
2bad
piperidine
CH2
3-thiophenyl
93
58
2eab
NPhMe
CH2
4-MeO-Ph
95
19
2bae
piperidine
CH2
2-pyridyl
95
59
2eac
NPhMe
CH2
4-CN-Ph
95
20
2bag
piperidine
CH2
3-MeO-Ph
97
60
2ead
NPhMe
CH2
3-thiophenyl
85
21
2bah
piperidine
CH2
2-MeO-Ph
88
61
2eae
NPhMe
CH2
2-pyridyl
95
22
2bai
piperidine
CH2
4-Me-Ph
97
62
2eag
NPhMe
CH2
3-MeO-Ph
89
23
2baj
piperidine
CH2
3-Me-Ph
93
63
2eah
NPhMe
CH2
2-MeO-Ph
90
24
2bak
piperidine
CH2
2-Me-Ph
86
64
2eai
NPhMe
CH2
4-Me-Ph
95
25
2bal
piperidine
CH2
4-NMe2-Ph
84
65
2eaj
NPhMe
CH2
3-Me-Ph
93
26
2bam
piperidine
CH2
4-PhO-Ph
93
66
2eak
NPhMe
CH2
2-Me-Ph
94
27
2ban
piperidine
CH2
2,4-di-F-Ph
93
67
2aca
morpholine
CH2CH2
Ph
84
28
2bao
piperidine
CH2
Bn
89
68
2acb
morpholine
CH2CH2
4-MeO-Ph
80
29
2caa
pyrrolidine
CH2
Ph
81
69
2acc
morpholine
CH2CH2
4-CN-Ph
80
30
2cab
pyrrolidine
CH2
4-MeO-Ph
77
70
2acd
morpholine
CH2CH2
3-thiophenyl
88
31
2cac
pyrrolidine
CH2
4-CN-Ph
81
71
2ace
morpholine
CH2CH2
2-pyridyl
79
32
2cad
pyrrolidine
CH2
3-thiophenyl
76
72
2acg
morpholine
CH2CH2
3-MeO-Ph
88
33
2cae
pyrrolidine
CH2
2-pyridyl
75
73
2ach
morpholine
CH2CH2
2-MeO-Ph
88
34
2cag
pyrrolidine
CH2
3-MeO-Ph
80
74
2aci
morpholine
CH2CH2
4-Me-Ph
83
35
2cah
pyrrolidine
CH2
2-MeO-Ph
77
75
2acj
morpholine
CH2CH2
3-Me-Ph
88
36
2cai
pyrrolidine
CH2
4-Me-Ph
83
76
2ack
morpholine
CH2CH2
2-Me-Ph
80
37
2caj
pyrrolidine
CH2
3-Me-Ph
83
77
2acl
morpholine
CH2CH2
4-NMe2-Ph
88
38
2cak
pyrrolidine
CH2
2-Me-Ph
79
78
2acm
morpholine
CH2CH2
4-PhO-Ph
88
39
2cal
pyrrolidine
CH2
4-NMe2-Ph
81
79
2acn
morpholine
CH2CH2
2,4-di-F-Ph
82
40
2cam
pyrrolidine
CH2
4-PhO-Ph
86
80
2aco
morpholine
CH2CH2
Bn
88
a All reactions were performed on 0.1 mmol scale of 16 and the purities of compounds 2 were over 95% as judged from LC-MS traces (integration of diode array 200–400 nm traces); b Three-step overall yield from secondary amine 14.
Prepared tertiary 1,2,3-triazoloamide derivatives 2. aa All reactions were performed on 0.1 mmol scale of 16 and the purities of compounds 2 were over 95% as judged from LC-MS traces (integration of diode array 200–400 nm traces); b Three-step overall yield from secondary amine 14.
3. Experimental Section
3.1. General
All chemicals were reagent grade and used as purchased. The Merrifield resin (loading capacity 1.29 mmol/g, 100–200 mesh) was purchased from BeadTech (Seoul, Korea). Reactions were monitored by TLC analysis using silica gel 60 F-254 thin layer plates (Merck, Darmstadt, Germany) or ATR-FRIR analysis using a Cary 630 instrument (Agilent Technologies, Santa Clara, CA, USA). Flash column chromatography was carried out on Merck silica gel 60 (230–400 mesh). The crude products were purified by parallel chromatography using CombiFlash (Isco, Lincoln, NE, USA). 1H-NMR (500 MHz) and 13C-NMR (125 MHz) spectra were recorded in δ units relative to deuterated solvent (CDCl3, DMSO-d6, etc.) as internal reference on a 500 MHz NMR instrument (Bruker, Billerca, MA, USA). LC-MS analysis was performed on ESI mass spectrometer with PDA detection. LC-MS area% purities of all products were determined by LC peak area analysis (XBD C18 column, 4.6 mm × 100 mm; PDA detector at 200–400 nm; isocratic, 5 mM ammonium formate/CH3CN (30:70)).
3.2. General Procedure for the Preparation of Secondary α-1,2,3-Triazoloamides on Solid-Phase
A typical procedure for the desired secondary α-1,2,3-triazoloamides 1, as exemplified for N-phenyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetamide (1aaa; R1 = R3 = Ph, A = CH2) follows.
3.2.1. Preparation of AMEBA Resin 4
Merrifield resin (53.2 g, 50.0 mmol, 0.94 mmol/g) was treated with 4-formyl-3-methoxyphenol (22.8 g, 150.0 mmol), potassium iodide (83.0 mg, 0.5 mmol), and potassium carbonate (20.7 g, 150.0 mmol) in DMF (300 mL). The mixture was shaken at room temperature for 10 h, and then filtered, washed several times with H2O, DMF, MeOH, and CH2Cl2, and dried in a vacuo to give AMEBA resin 4 (59.0 g): On-bead ATR-FTIR (neat) υmax 1678, 1598, 1259 (cm−1).
3.2.2. Preparation of Secondary Amine Resin 3
A mixture of AMEBA resin 4 (10 g, theoretically 8.5 mmol), aniline (5a; (2.3 mL, 25.5 mmol), sodium triacetoxyborohydride (5.4 g, 25.5 mmol), and acetic acid (0.49 mL, 8.5 mmol) in 1,2-dichloroethane was heated at 50 °C for 12 h. The reaction mixture was cooled to room temperature, and then filtered, washed several times with H2O, DMF, MeOH, and CH2Cl2, and dried in a vacuum oven to give secondary amine resin 3a (10.6 g): On-bead ATR-FTIR (neat) υmax 3424, 1597, 1489 (cm−1).
3.2.3. Preparation of α-Chloroamide Resin 7
The amine resin 3a (3.0 g, theoretically 2.4 mmol) was treated with 2-chloroacetyl chloride (6a; 0.57 mL, 7.2 mmol) and triethylamine (1.0 mL, 7.2 mmol) in CH2Cl2 at 0 °C. The reaction mixture was shaken at room temperature for 5 h, and then filtered, washed several times with H2O, DMF, MeOH, and CH2Cl2, and dried in a vacuum oven to give α-chloroamide resin 7aa (3.16 g): On-bead ATR-FTIR (neat) υmax 1666, 1593, 1489 (cm−1).
3.2.4. Preparation of α-Azidoamide Resin 8
The α-chloroamide resin 7aa (2.8 g, theoretically 2.1 mmol) was treated with sodium azide (0.47 g, 7.2 mmol) in DMF. The reaction mixture was shaken at room temperature for 12 h, and then filtered, washed several times with H2O, DMF, MeOH, and CH2Cl2, and dried in a vacuum oven to give α-azidoamide resin 8aa (2.8 g): On-bead ATR-FTIR (neat) υmax 2101, 1670, 1590, 1491 (cm−1).
3.2.5. Preparation of α-1,2,3-Triazoloamide Resin 10
To a mixture of α-azidoamide resin 8aa (570 mg, theoretically 0.42 mmol) and phenylacetylene (9a, 0.07 mL, 0.6 mmol) in DMF/piperidine (4:1) was added copper(I) iodide (229 mg, 1.27 mmol) and sodium ascorbate (57 mg, 1.27 mmol) at room temperature. The reaction mixture was shaken at room temperature for 12 h, and then filtered, washed several times with H2O, DMF, MeOH, and CH2Cl2, and dried in a vacuum oven to give α-1,2,3-triazoloamide resin 10aaa (606 mg): On-bead ATR-FTIR (neat) υmax 1669, 1590, 1489 (cm−1).
3.2.6. Preparation of α-1,2,3-Triazoloamide 1
The α-1,2,3-triazoloamide resin 10aaa (157 mg, theoretically 0.10 mmol) was added 30% TFA in CH2Cl2 (3 mL). The reaction mixture was stirred at 45 °C for 1day and the mixture was filtered and washed with CH2Cl2 and MeOH. The filtrate was evaporated in vacuo and the residue was dissolved in CH2Cl2 and extracted with saturated NaHCO3. The aqueous layer was extracted with CH2Cl2 twice and the combined organic extracts were washed with brine, dried over MgSO4, filtered and concentrated in vacuo to give the target N-phenyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetamide (1aaa) was obtained as a light yellow solid (23 mg, 93% from Merrifield resin). Mp 247–249 °C; 1H-NMR (DMSO-d6) δ 5.39 (s, 2H), 7.09 (m, 1H), 7.33–7.36 (m, 3H), 7.46 (m, 2H), 7.60 (m, 2H), 7.88 (m, 2H), 8.60 (s, 1H), 10.51 (s, 1H); 13C-NMR (DMSO-d6) δ 52.4, 119.3, 123.1, 123.8, 125.1, 127.9, 128.9, 130.7, 138.4, 146.2, 164.2; IR (ATR) υmax 3273, 3061, 1677, 1601, 1545, 1442, 1365, 1253, 1202, 1080, 753 (cm−1); LC-MS (ESI) m/z 279 ([M + 1]+); HRMS (FAB) calcd for C16H15N4O ([M + H]+) 279.1240, found 279.1239.
3.3. Characterization Data of Secondary α-1,2,3-Triazoloamides
3.4. General Procedure for the Preparation of Tertiary 1,2,3-Triazoloamides in Solution-Phase
A typical procedure for the desired tertiary 1,2,3-triazoloamide 2, as exemplified for 1-morpholino-2-(4-phenyl-1H-1,2,3-triazol-1-yl)ethanone (2aaa; R1R2N = morpholine, A = CH2, R3 = Ph).
3.4.1. Preparation of Chloro-Amide 15
To a solution of morpholine (14a; 4.50 mL, 51.45 mmol) and triethylamine (7.90 mL, 56.68 mmol) in CH2Cl2 (80 mL) was slowly added 2-chloroacetyl chloride (6a; 3.70 mL, 46.45 mmol) at 0 °C. The reaction mixture was stirred at room temperature for 6 h, and then diluted with CH2Cl2, washed with saturated NaHCO3 and brine, dried over MgSO4 and filtered. The residue was concentrated under reduced pressure to afford α-chloroamide 15aa (7.55 g, 99%) as a light yellow liquid: 1H-NMR (CDCl3) δ 3.54 (t, J = 4.5 Hz, 2H), 3.64 (t, J = 4.4 Hz, 2H), 3.70–3.74 (m, 4H), 4.07 (s, 2H); 13C-NMR (CDCl3) δ 40.7, 42.5, 46.8, 66.6, 66.7, 165.3; LC-MS (ESI) m/z 164 ([M + 1]+).
3.4.2. Preparation of Azidoamide 16
To a solution of α-chloroamide 15aa (1.41 g, 8.62 mmol) in acetonitrile (20 mL) and H2O (1 mL) was added sodium azide (700 mg, 10.77 mmol). The reaction mixture was stirred at room temperature for 1 day, and then diluted with EtOAc, washed with brine, dried over MgSO4 and filtered. The solvent was removed, and the residue was passed through a short plug of silica to give α-azidoamide 16aa (1.40 g, 99%) as a colorless oil: 1H-NMR (CDCl3) δ 3.38 (t, J = 4.8 Hz, 2H), 3.64 (t, J = 4.4 Hz, 2H), 3.67–3.71 (m, 4H), 3.92 (s, 2H); 13C-NMR (CDCl3) δ 42.3, 45.6, 50.6, 66.5, 66.8, 165.9; LC-MS (ESI) m/z 171 ([M + 1]+).
3.4.3. Preparation of Tertiary 1,2,3-Triazoloamide 2
To a mixture of α-azidoamide 16aa (34 mg, 0.20 mmol) and phenylacetylene (9a; 24 μL, 0.20 mmol) in t-BuOH/H2O (2 mL, 1:1) were added 0.5 M CuSO4 (0.020 mL, 0.010 mmol) and 1.0 M sodium ascorbate (0.020 mL, 0.020 mmol). The reaction mixture was stirred at room temperature for 1 day, and then the resulting reaction mixture was filtered. The separated solid was washed with H2O and hexanes, and triturated with hexane/EtOAc (10:1) to give the 1-morpholino-2-(4-phenyl-1H-1,2,3-triazol-1-yl)ethanone (2aaa; 52 mg, 96%) as a white solid: Mp 229–231 °C; 1H-NMR (CDCl3) δ 3.62 (t, J = 4.7 Hz, 2H), 3.66 (t, J = 4.6 Hz, 2H), 3.71 (m, 4H), 5.28 (s, 2H), 7.34 (m, 1H), 7.41–7.45 (m, 2H), 7.84–7.86 (m, 2H), 7.99 (s, 1H); 13C-NMR (CDCl3) δ 42.7, 46.0, 51.0, 66.5, 66.7, 121.3, 125.9, 128.4, 129.0, 130.5, 148.3, 163.7; IR (ATR) υmax 3134, 2984, 2858, 1661, 1643, 1471, 1426, 1236, 1112, 1036, 768 (cm−1); LC-MS (ESI) m/z 273 ([M + 1]+); HRMS (FAB) calcd for C14H17N4O2 ([M + H]+) 273.1346, found 273.1342.
3.5. Characterization Data of Tertiary 1,2,3-Triazoloamides
In summary, the yields for secondary α-1,2,3-triazoloamides (80 examples) produced by solid-phase synthetic route ranged from 75 to 94% for six linear steps starting with Merrifield resin (the average yield for each step was over 95%). The parallel solution-phase synthesis generated the target tertiary 1,2,3-triazoloamides (80 examples) with 97%–73% yields for three linear steps from the reaction of amines and chloro-acid chlorides. In addition, the target 1,2,3-triazoloamides were obtained in high purities (>95%) as judged from LC-MS and 1H-NMR analyses. This investigation, has led to the development of the solid- and solution-phase route for the synthesis of various 1,2,3-triazoloamides that contain three diversity sites that were introduced in reactions involving amines (R1 and R2), chloro-acid chlorides (A), and terminal acetylenes (R3). The strategy allows for a ready access to a large library and is potentially applicable to the preparation of other 1,2,3-triazole derivatives.