Solid-phase synthesis of diverse spiroisoxazolinodiketopiperazines

Article abstract of DOI:10.1021/co4000248

A convenient, efficient protocol to prepare diverse spiroisoxazolino- diketopiperazines via a parallel solid-supported synthesis was developed. The key steps are (1) a coupling reaction of an amino acid; (2) tosylation with concomitant β-elimination to form an α, β-unsaturated ester; (3) a 1,3-dipolar cycloaddition with an oxime to form isoxazoline rings; and (4) cyclic cleavage to release the product from the resin. All reaction steps and workup procedures were modified to allow the use of automated or semiautomated equipment. A 100-member demonstration library with two diversity sites was prepared in good purity and acceptable overall yields.

Full text of DOI:10.1021/co4000248

Research Article
pubs.acs.org/acscombsci
Solid-Phase Synthesis of Diverse Spiroisoxazolinodiketopiperazines
Yi-Wen Pan, Chih-Wei Guo, Huang-Yao Tu, Chih-Wei Tsai, and Wei-Chieh Cheng*
The Genomics Research Center, Academia Sinica, No. 128, Academia Road Sec. 2, Nankang District, Taipei, 11529, Taiwan
S
* Supporting Information
ABSTRACT: A convenient, efficient protocol to prepare
diverse spiroisoxazolino-diketopiperazines via a parallel solid-
supported synthesis was developed. The key steps are (1) a
coupling reaction of an amino acid; (2) tosylation with
concomitant β-elimination to form an α, β-unsaturated ester;
(3) a 1,3-dipolar cycloaddition with an oxime to form
isoxazoline rings; and (4) cyclic cleavage to release the product
from the resin. All reaction steps and workup procedures were
modified to allow the use of automated or semiautomated
equipment. A 100-member demonstration library with two
diversity sites was prepared in good purity and acceptable
overall yields.
KEYWORDS: solid-phase organic synthesis, spiroisoxazolino-diketopiperazine, 1,3-dipolar cycloaddition
INTRODUCTION
■
Small molecule combinatorial chemistry has dramatically
accelerated the development of biologically interesting
molecules in chemical biology and drug discovery.1 To allow
the efficient preparation of small molecule libraries, solid-phase
organic synthesis (SPOS)1 has been developed for use with
automated equipment, such as liquid handlers,2 and techni-
ques3 such as the fluorous-tag approach and solid-phase
extraction. These offer the opportunity for rapid synthesis of
libraries of heterocyclic compounds for pharmaceutical and
agrochemical discovery.4
Natural products and synthetic molecules that include a
spirocyclic skeleton in their structures show a wide range of
biological properties.5−9 For example, spiroisoxazoline natural
products exhibiting diverse antimicrobial, cytotoxic, and anti-
inflammatory activities have been identified as a new class of
novel alkaloids from marine sponges (Figure 1).7 Additionally,
spirodiketopiperazines have been reported with attractive
bioactivities (Figure 1).8 For example, aplaviroc is a potent
CCR-5 antagonist for the treatment for HIV infection.6,9
Because of their broad-spectrum biological activities, the
spirocyclic cores have been considered privileged scaffolds for
drug design. Not surprisingly, many spirodiketopiperazine or
spiroisoxazoline syntheses have been extensively studied.5−9
Our research interests include the design and synthesis of
small heterocyclic libraries via a solid- or solution-phase
combinatorial approach,2,10,11 and in previous papers, we
Figure 1. Examples of bioactive molecules containing spirooxazoline
or spirodiketopiperazine scaffolds.
reported the development of a novel solution-phase synthetic
route for the preparation of spiroisoxazolinohydantions and
spirooxazolinoisoxazolines, by the direct fusion of an isoxazo-
line ring with a hydantoin ring and a oxazoline ring, respectively
(Scheme 1).2,10 To the best of our knowledge, though synthetic
procedures for the simple spiro-diketopiperazines have been
reported,8,12,13 the direct combination of the diketopiperazine
Received: February 21, 2013
Revised: July 20, 2013
Published: July 26, 2013
© 2013 American Chemical Society
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Research Article
monium triphenyldifluorosilicate) was used instead of TBAF
(tetrabutylammonium fluoride) as a source of fluoride, a longer
reaction time (24 h) was required to completely convert to 6.
As shown in Scheme 3 and Table 1, a mixture of 7 and 8 (the
elimination product) was obtained (entry 1, Table 1) when
Scheme 1. General Synthetic Route for the Preparation of
Isoxazoline-based Spiromolecules
Scheme 3. Solution Model Studies of the Preparation of
Compound 1{1,7}
and isoxazoline moieties to efficiently afford a spirocyclic
skeleton on solid support has not been reported. In addition,
preparation of 2,5-diketopiperazine scaffolds via isocyanide-
based multicomponent reactions has also been extensively
studied13d,e but this approach may not be suitable to our
request because no isoxazoline building blocks are available and
further chemical transformations are needed to construct an
isoxazoline ring. Herein, we report an efficient, solid-phase
parallel synthetic method (steps i−iv) under mild reaction
conditions for combining these two interesting structural
features within a single framework to form spiroisoxazolino-
diketopiperazines 1{1−10,1−10} with two points of diversity
(R1 and R2 in 1, see Scheme 1).2,10
RESULTS AND DISCUSSION
■
Model Synthetic Studies in the Solution Phase.
Preliminary solution-phase experiments were undertaken to
explore the feasible reaction conditions and to establish the
required modifications for a practical SPOS. As shown in
Scheme 2, N-Boc-O-TBDPS-DL-serine 210,14 was prepared from
Table 1. Optimization of Conditions for the Preparation of
α,β-Unsaturated Ester 8
a
entry
conditions (base/solvent/time)
yield (%) of 8 (7)
1
2
3
TsCl, NEt3/THF/overnight
TsCl, imidazole/THF/overnight
TsCl, DBU/THF/2 h
66 (20)
0 (>92)
78 (0)
Scheme 2. Solution Model Studies for the Preparation of
Compound 6
a
Isolated yield by silica-gel column chromatography.
Et3N was used as the base for the tosylation of 6. Fortunately, 7
was obtained as the only product (>92%, entry 2, Table 1) by
using imidazole as the base. Interestingly, one-pot conditions
(entry 3, Table 1) to directly generate alkene 8 were found
using DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as the base
wherein 6 undergoes tosylation with concomitant with β-
elimination (78%).17 Treatment of alkene 8 with hydroximi-
noyl chloride 9{7}18 in the presence of Et3N gave isoxazoline
10 (96%) via 1,3-dipolar reaction.19 On the basis of preliminary
literature studies,2,10 we were not surprised to find that 8 → 10
proceeded with complete regioselectivity during 1,3-dipolar
cycloaddition (only one of the regioisomer could be detected).
After removal of the Boc group in 10 under acidic conditions,
followed by treatment with morpholine to undergo cycliza-
tion,20 the desired spiroisoxazolinodiketopiperazine 1{1,7} was
obtained in an overall 79% yield for two steps. As expected,
compound 1{1,7} contained two diastereoisomers with a ratio
of around 1: 1−1.4: 1 as determined by NMR analysis.21
Notably, this procedure also imitated the cyclization cleavage
conditions to release the desired product from the solid
support. Although these two isomers (A and B) were hard to
separate by silica-gel column chromatography, small amounts of
isomers A and B (see in Scheme 3) were fortunately obtained
DL-serine in an 84% yield. Subsequent esterification of the
protected serine 2 with benzyl alcohol under DIC-medicated
coupling conditions gave the benzyl ester 315 in good yield
(92%). Treatment of 3 with TFA to undergo N-Boc
deprotection, followed by coupling with N-Boc amino acid
4{1} gave 5 in an overall 83% yield for the two steps.10,16 After
silane (TBDPS) deprotection under fluoride-based conditions
for 2 h, alcohol 6 was smoothly obtained after purification by
column chromatography. Notably, when TBAT (tetrabutylam-
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1
after repeating the separation process several times. The H
NMR spectra of two isomers in 1{1,7} showed the methine
proton (Ha) of the piperazinedione ring at δ 4.3 and 4.0 ppm,
respectively, which indicated that the methine group in isomer
A is oriented toward the proximal oxygen atom of the
isoxazoline ring to result in the more downfield shift than
that of isomer B.
Model Studies in Solid-Phase synthesis. With the
reaction conditions and protocols developed in the above-
mentioned solution phase synthesis in hand, we started to
prepare the model product 1{1,7} on a solid support. As shown
in Scheme 4, the synthetic work began with step i, esterification
of a diagnostic Si−O bond absorption at ∼1111 cm−1). Resin
14{1} was treated with fresh hydroximinoyl chloride 9{7} to
give spiroisoxazoline resin 15{1,7} (step vi). The acid-mediated
deprotection of resin 15{1,7} (step vii), followed by intra-
molecular cyclization under basic conditions afforded the crude
spiroisoxazolinodiketopiperazine 1{1,7}.
Notably, when bases such as NH3 and NEt3 were used for
the cleavage-cyclization step, the overall yields were not
satisfactory (<15%) since their volatility and unpleasant odor
made the operation unfriendly when we used a solid-phase
synthesizer as our reactor. Next, morpholine was tested because
of its higher boiling point (129 °C). Unfortunately, attempts to
remove all the excess morpholine by the automated liquid−
liquid extraction2,23 module in acidic conditions were not
successful and the yield dropped due to the repeated extraction
process. Finally, we found an expedient way with assistance of
solid-phase extraction technique (SPE) to remove the excess
morpholine and impurities. Thus, the solid-phase synthetic
conditions for the model compound 1{1,7} were successfully
established.
Scheme 4. Solid-Phase Model Studies of the Preparation of
Spiroisoxazolino-diketopiperazine 1{1,7}
Library Synthesis. On the basis of our design, ten amino
acids 4{1−10} including eight L-amino acids 4{1} and 4{4−10}
(Figure 2) and ten hydroximinoyl chlorides 9{1−10} (Figure
Figure 2. Set of amino acids 4{1−10} for the library.
3), freshly prepared using a solution-phase synthesizer, were
utilized as the first and second diversity substituents,
respectively. Following the same protocol developed in the
model reaction (Scheme 4), one hundred desired molecules
containing diastereoisomers were generated without further
purification in an average yield of ∼65% and the average yield
was around 65%. This library was characterized by HPLC and
mass (ESI) analysis with the purity of the crude products
ranging from 70 to 99% (see in Table 2). The average purity
was 94%, and more than with 80% of compounds had a purity
of more than with 80%.
of the hydroxylmethyl resin 11 (hydroxylmethyl loading = 0.83
mmol/g)22 with protected serine 2. The reaction progress
could be monitored by FTIR spectra, which showed appearance
of the carboxylate absorption at ∼1720 and ∼1160 cm−1 and
Si−O bond absorption at ∼1111 cm−1. Notably, although the
reaction could be achieved at room temperature for 24 h, we
realized this crucial step could be efficiently performed by using
a microwave reactor to shorten the reaction time to 30 min.
The transformations including N-Boc deprotection (step ii)
and the conjugation with N-Boc amino acids 4{1} (step iii)
could be monitored by the Kaiser test and FTIR spectra. The
TBAF-mediated O-deprotection of 13{1} (step iv), followed by
tosylation and in situ elimination afforded resin 14{1} (step v).
Step iv was amenable to FTIR monitoring (e.g., disappearance
CONCLUSION
■
We have developed a practical and efficient, solid-phase parallel
synthetic route for spiroisoxazolinodiketopiperazines with two
diversity points. The key transformations in the synthesis were
the preparation of the α,β-unsaturated ester 8 via tosylation and
concomitant β-elimination, as well as the 1,3-dipolar cyclo-
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Solvent evaporation was performed on Thermo Scientific
Savant Explorer SpeedVac Concentrator Explorer 220. Mini-
Block (24 position reactor from Mettler Toledo) with C18
cartridges was applied for solid-phase extraction.
Synthesis of N-Boc-O-TBDPS-DL-serine 2.10,14 A sol-
ution of di-tert-butyl dicarbonate [(Boc)2O, 2.84 g, 13.0 mmol]
in 1,4-dioxane (11 mL) was added to the solution of DL-serine
(1.14 g, 10.8 mmol) in 1 N NaOH(aq) (22 mL, 21.9 mmol) at 0
°C. After The reaction was stirred at rt for 8 h and then
concentrated to remove 1,4-dioxane, acidified to pH 2−3, and
extracted with EtOAc (15 mL × 3). The combined extracts
were dried with MgSO4 and concentrated to give N-Boc-DL-
serine as a colorless oil. A mixture of N-Boc-DL-serine (1.79 g,
8.7 mmol) and imidazole (1.78 g, 26.1 mmol) was dissolved in
DMF (15 mL), and added with TBDPSCl (2.88 g, 10.5 mmol)
at 0 °C. The reaction was stirred at rt for 8 h and then poured
into a mixture of H2O (15 mL) and ether (30 mL). The
organic layer was separated and the aqueous layer was extracted
with ether. Combined organic layers were finally dried with
MgSO4, concentrated and recrystallized with hexanes/Et2O to
Figure 3. Set of hydroximinoyl chlorides 9{1−10} for the library.
1
give product 2 (4.06 g, 9.1 mmol, 84%) as a white solid. H
addition for isoxazoline formation and intramolecular diketo-
piperazine formation to release our desired molecules from the
resin. Equipment, such as a microwave reactor, solid- and
solution-phase synthesizer, multichannel liquid handler, and
vacuum centrifuge allowed the efficient preparation of a 100-
membered demonstration library.
NMR (600 MHz, CDCl3): δ 1.01 (s, 9H), 1.45 (s, 9H), 3.89
(dd, 1H, J = 10.1, 2.7 Hz), 4.10 (dd, 1H, J = 9.9, 2.0 Hz), 4.41−
4.43 (br, 1H), 5.37 (d, 1H, J = 8.3 Hz), 7.34−7.43 (m, 6H),
7.59−7.61 (m, 4H); 13C NMR (150 MHz, CDCl3): δ 175.1,
155.5, 135.5 (×2), 132.8, 132.5, 129.9 (×2), 127.8 (×6), 80.2,
64.2, 55.2, 28.3 (×3), 26.7 (×3), 19.3; MS calcd for
[C24H33NO5Si + H]+ 444.2, found 444.1.
EXPERIMENTAL PROCEDURES
■
Solution Phase Model Synthesis Studies. Synthesis of
Benzyl Ester of N-Boc-O-TBDPS-DL-serine: Benzyl 2-(tert-
butoxycarbonylamino)-3-(tert-butyldiphenylsilyloxy)-
propanoate 3.15 To a solution of benzyl alcohol (0.94 g, 8.7
mmol) in CH2Cl2/DMF 9:1 (10 mL), was added DMAP
(0.21g, 1.7 mmol), and N-Boc-O-TBDPS-DL-serine 2 (3.86 g,
8.7 mmol), followed by DIC (2.21 g, 17.5 mmol) at rt. The
mixture was subsequently irradiated in the microwaves cavity at
100 W with magnetic stirring (T = 44 °C) for 30 min. The
reaction was cooled down and filtered. The clear liquid was
concentrated under vacuum and purified by CC (EtOAc/
hexanes = 1/4) to afford the desired ester 3 (4.16 g, 7.79 mmol,
General Information. The hydroxymethyl resin (1% DVB,
100−200 mesh, loading = 0.83 mmol/g determined by analysis
of the Fmoc loading on resins)22 was purchased from
ADVANCED CHEMTECH. Analytical HPLC spectra were
recorded at 220 nm on a HITACHI L-2455 equipped with
photodiode array detector, and a Zorbax column (XDB-C18,
GP 50 × 2.1 mm, 3.5 μm) isocratic flow with 50% MeOH/50%
H2O over 10 min, flow rate = 0.2 mL/min. High resolution
mass spectra were obtained by Bruker Daltonics BioTOF III.
Microwave irradiation was carried by CEM focused microwave
synthesis system. Solid-phase organic synthesis was carried out
using FlexChem Blocks (96 well reactor with volume of 1.7 mL
per well, which composed of polytetrafluoroethylene),
FlexChem Rotating Oven (model 404) for stirring and heating,
Vacuum manifold with collection tray for washing resin or
collecting samples, and Hydra 96 Microdispenser for solvent or
reagent dispensed. Multiple-functional liquid handler (Freedom
EVO, TECAN) was utilized for extraction and separation.
1
89%). H NMR (600 MHz, CDCl3): δ 1.00 (s, 9H), 1.44 (s,
9H), 3.87 (dd, 1H, J = 10.2, 2.8 Hz), 4.10 (dd, 1H, J = 10.2, 2.7
Hz), 4.42 (m, 1H), 5.17 (s, 2H), 5.43 (d, 1H, J = 8.8 Hz),
7.29−7.42 (m, 11H), 7.54−7.59 (m, 4H). 13C NMR (150
MHz, CDCl3): δ 170.7, 155.4, 135.3 (×4), 135.2, 132.8, 132.7,
129.8 (×2), 128.6 (×3), 128.3 (×3), 127.7 (×3), 79.9, 67.2,
a,b,c
Table 2. Yields and Purities of the Spiroisoxazolinodiketopiperazine Library
R1 =
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
42 (90)
77 (89)
84 (99)
91 (98)
93 (99)
42 (99)
40 (99)
50 (96)
62 (95)
61 (99)
36 (99)
32 (99)
50 (81)
41 (89)
81 (99)
32 (99)
55 (99)
52 (90)
35 (97)
46 (99)
37 (99)
43 (99)
37 (89)
59 (99)
45 (99)
34 (99)
49 (80)
49 (81)
46 (99)
46 (70)
76 (99)
43 (91)
67 (92)
18 (99)
86 (99)
66 (92)
66 (99)
86 (99)
74 (98)
65 (99)
37 (92)
32 (79)
55 (94)
36 (84)
48 (99)
31 (78)
53 (99)
55 (88)
53 (83)
64 (99)
68 (99)
47 (96)
69 (96)
66 (85)
67 (96)
40 (75)
77 (99)
54 (82)
50 (83)
41 (99)
65 (91)
39 (95)
70 (91)
43 (81)
74 (93)
37 (83)
49 (99)
57 (99)
70 (83)
72 (98)
77 (99)
77 (99)
66 (99)
61 (99)
70 (90)
60 (94)
88 (88)
81 (77)
93 (91)
96 (90)
58 (91)
47 (88)
54 (99)
46 (98)
55 (99)
56 (93)
43 (99)
58 (97)
71 (99)
59 (99)
63 (99)
44 (99)
57 (99)
60 (99)
50 (99)
56 (99)
37 (99)
53 (99)
45 (99)
46 (99)
a
b
c
Crude yields after overall synthesis. Average purity determined by HPLC and mass (ESI) analysis of the material at 220 nm. Purities shown in
parentheses.
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64.6, 55.6, 28.3 (×3), 26.7 (×3), 19.2. MS calcd for
[C31H39NO5Si + H]+ 534.2, found 534.1.
of diastereomers of substituted isoxazoline ester 10 as colorless
oil (0.68 g, 1.4 mmol, 96%, a 7:3 (trans/cis) ratio based on
NMR analysis). 1H NMR (600 MHz, CDCl3, mixture of
diastereomers): δ 1.24 (d, 3H, J = 7.1 Hz), 1.37 (s, 9H), 2.33
(s, 3H), 3.75 and 3.79 (d, 0.3H and 0.7H, J = 17.4 Hz), 4.03
and 4.05 (d, 0.7H and 0.3H, J = 17.2 Hz), 4.22 (br, 0.7H), 5.13
(br, 0.3H), 5.23 (s, 2H), 7.14 (m, 2H), 7.29 (m, 5H), 7.50 (m,
2H), 7.80 (br, 1H), 7.94 (br, 1H). 13C NMR (150 MHz,
CDCl3, mixture of diastereomers): δ 172.8, 166.8, 156.8, 155.4,
140.8, 134.5, 129.3 (×2), 128.4 (×2), 128.1 (×3), 126.9 (×2),
125.2 and 128.4, 91.9, 80.1 and 68.4, 68.4 and 49.7, 44.0, 36.5
and 23.3, 28.2 (×3), 21.3, 17.6. HRMS calcd for [C26H31N3O6
+ H]+ 482.2286, found 482.2271.
Model Study for the Synthesis of Spiroisoxazolinodiketo-
piperazine 1{1,7}.21 A solution of TFA/1,2-dichloroethane (1/
1, 2 mL) was added to the solution of 10 (0.32 g, 0.67 mmol)
in 1,2-dichloroethane (2 mL) at 0 °C and then the reaction was
stirred at rt for 2 h. After removal of TFA, a solution of
morpholine/1,2-dichloroethane (1/1, 0.12 mL) was added to
the reaction mixture in 1,2-dichloroethane (5 mL) at rt. After 8
h, additional 1,2-dichloroethane (10 mL) was added to the
reaction solution. The mixture was extracted by H2O (10 mL ×
3), dried (MgSO4), and concentrated. The crude sample was
purified by CC (EtOAc/hexanes = 4/1) to yield 1{1,7}18 (0.09
g, 0.33 mmol, 79%, a 2:1 trans/cis ratio based on NMR analysis.
Small amounts of isomer A (trans form) and B (cis form) forms
were purified by repeating column chromatography.
Synthesis of Benzyl Ester of Boc-Ala-DL-serine: (S)-Benzyl 2-
(2-(tert-butoxycarbonylamino)propanamido)-3-(tert-
butyldiphenylsilyloxy)propanoate 5.10,16 A solution of TFA/
CH2Cl2 (1/1, 17 mL) was added to the solution of N-Boc-O-
TBDPS-DL-serine benzoic ester 3 (3.13 g, 5.8 mmol) in 1,2-
dichloroethane (6 mL) at 0 °C. The solution was stirred for 10
min and then warmed up to rt. After 2 h, the reaction was
concentrated to give the amine intermediate as colorless oil
without further purification. A mixture of the amine
intermediate (2.92 g, 5.3 mmol), Boc-Ala-OH 4{1} (3.02 g,
15.9 mmol), and HBTU (6.06 g, 15.9 mmol) was dissolved in
DMF (40 mL) in the presence of DIPEA (3.5 mL, 21.1 mmol)
and the reaction was stirred for overnight. The reaction was
extracted by Et2O (20 mL × 3) and water. The combined
organic layer was dried (MgSO4), concentrated, and purify by
CC (EtOAc/hexanes = 1/4) to give Boc-Ala-DL-serine benzoic
ester 5 (2.93 g, 4.8 mmol, 83% over two steps). 1H NMR (600
MHz, CDCl3): δ 1.02 (s, 9H), 1.34 (d, 3H, J = 8.9 Hz), 1.44 (s,
9H), 3.88 (dd, 1H, J = 10.3, 2.9 Hz), 4.16 (br, 1H), 4.71 (br,
1H), 5.17 (s, 2H), 7.29−7.42 (m, 11H), 7.54−7.59 (m, 4H).
13C NMR (150 MHz, CDCl3): δ 172.3, 169.9, 155.2, 135.4
(×4), 135.0, 132.5, 132.4, 129.8 (×2), 128.5 (×3), 128.3 (×3),
127.7 (×3), 79.8, 67.3, 64.0, 54.1, 49.9, 28.2 (×3), 26.6 (×3),
19.1, 18.5. MS calcd for [C34H44N2O6Si + H]+ 605.3, found
605.3.
trans-8-Methyl-3-(4-methylphenyl)-1-oxa-2,6,9-triaza-
Synthesis of Benzyl Ester of Boc-Ala-DL-serin-2-ene: (S)-
Benzyl 2-[2-(tert-Butoxycarbonylamino)propanamido]-
acrylate 8.17 The solution of Boc-Ala-DL-serine benzoic ester
5 (1.41 g, 2.3 mmol) in THF (10 mL) was stirred with TBAF
(1 M solution in THF, 3.5 mL) at ambient temperature for 4 h.
The mixture was concentrated and purify by CC (EtOAc/
spiro[4.5]dec-2-ene-7,10-dione: Isomer A (trans Form) of
1
1{1,7}. H NMR (600 MHz, CDCl3): δ 1.45 (d, 3H, J = 7.0
Hz), 2.39 (s, 3H), 3.43 (d, 1H, J = 17.6 Hz), 4.27 (d, 1H, J =
17.6 Hz), 4.32 (q, 1H, J = 7.0 Hz), 4.59 (br, NH), 7.27 (d, 2H,
J = 8.0 Hz), 7.60 (d, 2H, J = 8.0 Hz). 13C NMR (150 MHz,
CDCl3): δ 173.2, 165.9, 158.2, 142.5, 130.7 (×2), 128.1 (×2),
127.3, 93.5, 51.8, 43.3, 21.6, 17.4. HRMS calcd for
[C14H15N3O3 + H]+ 274.1186, found 274.1133.
cis-8-Methyl-3-(4-methylphenyl)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione: Isomer B (cis Form) of 1{1,7}.21 1H
NMR (600 MHz, CDCl3): δ 1.61 (d, 3H, J = 7.0 Hz), 2.39 (s,
3H), 3.42 (d, 1H, J = 17.7 Hz), 4.06 (q, 1H, J = 7.1 Hz), 4.27
(d, 1H, J = 17.7 Hz), 4.59 (br, NH), 7.27 (d, 2H J = 8.1 Hz),
7.60 (d, 2H J = 8.0 Hz). 13C NMR (150 MHz, CDCl3): δ
173.3, 165.1, 158.1, 142.5, 130.7 ( × 2), 128.1 ( × 2), 127.3,
92.9, 53.7, 43.8, 22.6, 21.6; HRMS calcd for [C14H15N3O3 +
H]+ 274.1186, found 274.1157.
Synthesis of the Spiroisoxazolinodiketopiperazine
Library. General Procedure for Step i. Resin 11 (1% DVB,
loading = 0.83 mmol/g, 5.0 g), preswollen in CH2Cl2/DMF
(9/1, 5 mL) for 10 min, was reacted with a mixture of N-Boc-
O-TBDPS-DL-serine 1 (13.6 g, 30.7 mmol), DIC (3.2 mL, 20.4
mmol), and a catalytic amount of DMAP (0.25 g, 2.0 mmol) in
CH2Cl2/DMF (9/1, 10 mL) at rt. The reaction mixture was
subsequently irradiated in the microwaves cavity at 100 W with
magnetic stirring (T = 44 °C) for 30 min. The resin was
collected, washed with MeOH (10 mL), DCM (10 mL), DMF
(10 mL), THF/H2O (10 mL), THF (10 mL), DCM (10 mL),
MeOH (10 mL), and Et2O (10 mL) and then dried by vacuum
oven (40 °C) overnight to give resin 12 as yellow beads: IR
(single bead reflectance) 1716, 1492, 1160, 1112, 822 cm−1.
General Procedures for Steps ii and iii. Resin 12 (50 mg per
well) was loaded to the reaction block by a trap-door loader
first and then the resin, preswollen by 1,2-dichloroethane (500
μL/well) for 10 min, was reacted with a solution of TFA/1,2-
1
hexanes =1/1) to give alcohol 6 (0.82 g, 2.2 mmol, 98%). H
NMR (600 MHz, CDCl3): δ 1.33 (d, 3H, J = 7.1 Hz), 1.40 (s,
9H), 3.95 (br, 2H), 4.15 (br, 1H), 4.71 (q, 1H, J = 3.7 Hz),
5.18 (s, 2H), 7.15 (m, 1H), 7.29−7.35 (m, 4H). 13C NMR (150
MHz, CDCl3): δ 172.9, 170.2, 155.8, 135.1, 128.6 (×2), 128.5,
128.1 (×2), 80.6, 67.46, 62.6, 54.9, 50.5, 28.2 (×3), 18.0.
HRMS calcd for [C18H26N2O6 + H]+ 367.1864, found
367.1860. A mixture of alcohol 6 (0.82 g, 2.2 mmol), TsCl
(0.65 g, 3.4 mmol) and DBU (1 mL, 7.2 mmol) was dissolved
in THF (8 mL) at 0 °C and then the reaction was stirred at rt
for 2 h. The solution was washed by H2O (10 mL × 3), dried
(MgSO4), concentrated, and purified by CC (EtOAc/hexanes =
1/4) to afford the desired α,β-unsaturated benzoic ester 8 (0.63
1
g, 1.8 mmol, 78%). H NMR (600 MHz, CDCl3): δ 1.36 (d,
3H, J = 7.1 Hz), 1.41 (s, 9H), 5.15 (br, 1H), 5.23 (s, 2H), 5.92
(s, 1H), 6.58 (s, 1H), 7.30−7.34 (m, 4H). 13C NMR (150
MHz, CDCl3): δ 171.6, 163.6, 155.4, 135.0, 130.8, 128.6 (×2),
128.4, 128.1 (×2), 109.4, 80.3, 67.6, 50.9, 28.2 (×3), 17.8.
HRMS calcd for [C18H24N2O5 + Na]+ 371.1577, found
371.1576.
Synthesis of Substituted Isoxazoline Esters: Benzyl 5-[(S)-
2-(tert-Butoxycarbonylamino)propanamido]-3-p-tolyl-4,5-
dihydroisoxazole-5-carboxylate 10.2,10,19 Triethyl amine (0.2
mL, 1.4 mmol) was slowly added to the mixture of α,β-
unsaturated benzoic ester 8 (0.51 g, 1.4 mmol) and
hydroximinoyl chloride 9{7} (0.74 g, 4.3 mmol) in 1,2-
dichloroethane (10 mL) at 0 °C. The reaction was stirred at rt
for overnight and then the solution was extracted by H2O (10
mL × 3), dried (MgSO4), and concetrated. The crude product
was purified by CC (EtOAc/hexanes =1/4) to yield the mixture
429
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ACS Combinatorial Science
Research Article
dichloroethane =1/1 (300 μL/well). The reactor was rotated at
rt for 2 h and the resin was washed with MeOH (10 mL),
DCM (10 mL), DMF (10 mL), THF/H2O (10 mL), THF (10
mL), DCM (10 mL), MeOH (10 mL), and Et2O (10 mL) to
give N-Boc-deprotected serine resin. The resin, preswollen by
DMF (500 μL/well) for 10 min, was reacted with a solution of
Boc-amino acid 4{1−10} (0.13 g/well, 0.42−0.74 mmol/well),
HBTU (0.12 g/well, 0.31 mmol/well) and DIPEA (0.07 mL/
well, 0.41 mmol/well) in DMF (300 μL/well) at rt for 2 h. The
resin was collected by filtration, washed with MeOH (5 mL),
DCM (5 mL), DMF (5 mL), THF/H2O (5 mL), DCM (5
mL), MeOH (5 mL), and Et2O (5 mL). The resin was dried in
vacuum oven (40 °C) overnight to give Boc-amino serine resin
13{1−10} as yellow beads: IR (single bead reflectance) 1685,
1492, 1165, 1112, 823 cm−1.
General Procedures for Steps iv and v. Resin 13{1−10},
preswollen by THF (500 μL/well) for 10 min, was reacted with
TBAF (1 M solution in THF, 150 μL/well) at rt for 2 h. The
resin was collected by filtration, washed by MeOH (5 mL),
DCM (5 mL), DMF (5 mL), THF/H2O (5 mL), THF (5 mL),
DCM (5 mL), MeOH (5 mL), and Et2O (5 mL). A mixture of
this intermediate resin and TsCl (0.03 g/well, 0.15 mmol/well)
in THF (200 μL/well) in the presence of DBU (40 μL/well)
was rotated at rt for 2 h. The resin was collected, washed with
MeOH (5 mL), DCM (5 mL), DMF (5 mL), THF/H2O (5
mL), DCM (5 mL), MeOH (5 mL), and Et2O (5 mL) and
dried in vacuum oven (40 °C) overnight to afford resin 14{1−
10} as yellow beads: IR (single bead reflectance) 1690, 1492,
1452, 1164 cm−1.
d4, mixture of isomers) δ 1.46 and 1.63 (d, 1.1H and 1.9H, J =
7.0 Hz), 3.22 and 3.35 (br, 0.4H and 0.6H), 4.07 and 4.36 (q,
0.6H and 0.4H, J = 7.0 Hz), 4.34 (br, 1H), 7.46 (m, 1H), 7.52
(m, 2H); 13C NMR (150 MHz, methanol-d4, mixture of
diastereomers) δ 184.1 and 179.8, 173.6 and 164.9, 155.1,
136.5, 133.3, 129.7 (×3), 128.8, 94.2 and 93.6, 53.8 and 51.7,
45.2 and 44.6, 22.5 and 17.0; HRMS m/z calcd for
[C13H11Cl2N3O3 + Na]+ 350.0170, found 350.0182; crude
purity =99%; tR = 1.65 min.
8-Methyl-3-(4-methylphenyl)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione 1{1,7}: crude yield =40%; diaster-
eomeric ratio (dr value) = 9/5; 1H NMR (600 MHz, methanol-
d4, mixture of isomers) δ 1.45 and 1.61 (d, 1.9H and 1.1H, J =
7.1 Hz), 2.39 (s, 3H), 3.42 and 3.43 (d, 0.4H and 0.6H J = 17.7
Hz), 4.06 (q, 0.4H, J = 7.1 Hz), 4.34 (br, 1H), 4.36 (q, 0.6H, J
= 7.1 Hz), 4.59 (br, NH), 7.46 (m, 1H), 7.52 (m, 2H); 13C
NMR (150 MHz, methanol-d4, mixture of diastereomers) δ
173.3 and 173.1, 165.9 and 165.1, 158.2 and 158.1, 142.5, 130.7
(×2), 128.1 (×2), 127.3, 93.5 and 92.9, 53.7 and 51.8, 43.8 and
43.3, 22.5 and 21.6, 21.6 and 17.4; HRMS m/z calcd for
[C14H15N3O3 + H]+ 274.1186, found 274.1133; crude purity =
99%; tR = 1.66 min.
8,8′-Dimethyl-3-(2-chlorophenyl)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione 1{2,3}: crude yield =50%; 1H NMR
(600 MHz, acetone-d6,) δ 1.51 (s, 3H), 1.63 (s, 3H), 3.54 (d,
1H, J = 17.8 Hz), 4.55 (d, 1H, J = 17.8 Hz), 7.43−7.56 (m,
3H), 7.71−7.73 (m, 1H), 7.88 (br s, 1H), 8.66 (br s, 1H); 13C
NMR (150 MHz, acetone-d6) δ 173.7, 163.4, 156.4, 133.3,
132.3, 132.0, 131.6, 129.3, 128.2, 93.7, 57.9, 45.5, 26.9; HRMS
m/z calcd for [C14H14ClN3O3 + Na]+ 330.0616, found
330.0661; crude purity =81%; tR = 2.67 min.
General Procedure for Step vi. A mixture of resin 14{1−
10}, preswollen by 1,2-dichloroethane (500 μL/well) for 10
min, and hydroximinoyl chloride 9{1−10} (0.08 g/well, 0.40−
0.59 mmol/well) in 1,2-dichloroethane (500 μL/well) in the
presence of Et3N (15 μL/well, 0.10 mmol/well) was rotated at
rt for overnight. The resin was collected, washed with MeOH
(5 mL), DCM (5 mL), DMF (5 mL), THF/H2O (5 mL), THF
(5 mL), DCM (5 mL), MeOH (5 mL), and Et2O (5 mL), and
then dried in vacuum oven (40 °C) overnight to give resin
15{1−10,1−10} as yellow beads: IR (single bead reflectance of
the representative 15{1,7}) 1748, 1681, 1492, 1452, 1162 cm−1.
General Procedures for Steps vii and viii. A mixture of resin
15{1−10,1−10}, preswollen by 1,2-dichloroethane (500 μL/
well) for 10 min, and a solution of TFA/1,2-dichloroethane =
1/1 (300 μL/well) was rotated at rt. After 2 h, the resin was
collected and washed with MeOH (5 mL), DCM (5 mL),
DMF (5 mL), THF/H2O (5 mL), THF (5 mL), DCM (5 mL),
MeOH (5 mL), and Et2O (5 mL). A mixture of this
intermediate resin and a solution of morpholine/1,2-dichloro-
ethane = 1/1 (60 μL/well) was rotated at rt for overnight. The
reaction mixture was filtered and washed with DMF (200 μL/
well ×3), MeOH (200 μL/well ×2). The filtrate was
concentrated and the pH value of the mixture was adjusted
to ∼6 with 0.3 mL 1 N HCl(aq). The residue, dissolved in
MeOH/H2O (1:4, 0.3 mL), was loaded onto the top of a solid-
phase exchange cartridge (2 g, C18 cartridge; 1.4 × 2.3 cm),
and eluted with MeOH/H2O (1:4, 10 mL; first fraction) to
remove morpholine salt and impurities, followed by eluting
with MeOH/H2O (4:1, 10 mL; second fraction) to directly
collect into a sample vial and dried by SpeedVac to give desired
compound 1{1−10,1−10} without further purification.
8,8′-Dimethyl-3-(2,6-dichlorophenyl)-1-oxa-2,6,9-triaza-
1
spiro[4.5]dec-2-ene-7,10-dione 1{2,5}: crude yield = 81%; H
NMR (600 MHz, acetone-d6) δ 1.51 (s, 3H), 1.64 (s, 3H), 3.44
(d, 1H, J = 18.0 Hz), 4.41 (d, 1H, J = 18.0 Hz), 7.56 (m, 3H),
7.85 (br s, 1H), 8.50 (br, 1H); 13C NMR (150 MHz, acetone-
d6) δ 173.8, 163.4, 156.4, 135.9, 133.0, 129.4 (×3), 128.8 and
127.1, 93.9, 57.9, 45.1, 26.9; HRMS m/z calcd for
[C14H13Cl2N3O3 + H]+ 342.0407, found 342.0403; crude
purity = 99%; tR = 1.81 min.
8,8′-Dimethyl-3-(4-methylphenyl)-1-oxa-2,6,9-triaza-
1
spiro[4.5]dec-2-ene-7,10-dione 1{2,7}: crude yield =55%; H
NMR (600 MHz, acetone-d6) δ 1.50 (s, 3H), 1.62 (s, 3H), 2.37
(s, 3H), 3.48 (d, 1H, J = 17.5 Hz), 4.29 (d, 1H, J = 17.5 Hz),
7.28 (d, 2H, J = 6.2 Hz), 7.61 (d, 2H, J = 6.2 Hz), 7.84 (br s,
1H), 8.54 (br s, 1H); 13C NMR (150 MHz, acetone-d6) δ
173.7, 163.7, 156.9, 141.5, 130.3 (×2), 127.7 (×2), 127.4, 93.3,
57.9, 43.4, 21.5; HRMS m/z calcd for [C15H17N3O3 + H]+
288.1343, found 288.1355; crude purity =99%; tR = 1.83 min.
8,8′-Dimethyl-3-(1-naphthalene)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione 1{2,8}: crude yield = 52%; 1H NMR
(600 MHz, methanol-d4) δ 1.46 (s, 3H), 1.62 (s, 3H), 3.56 (d,
1H, J = 17.5 Hz), 4.46 (d, 1H, J = 17.5 Hz), 7.50−8.00 (m,
6H), 8.84−8.85 (m, 1H); 13C NMR (150 MHz, methanol-d4) δ
175.6, 165.4, 158.5, 135.7, 132.4, 132.0, 129.9, 129.7, 128.6,
127.9, 127.6, 126.9, 126.2, 92.4, 58.3, 46.7, 30.4, 26.9; HRMS
m/z calcd for [C18H17N3O3 + H]+ 324.1343, found 324.1367;
crude purity =90%; tR = 1.53 min.
8-(1-Methylpropyl)-3-(4-chlorophenyl)-1-oxa-2,6,9-triaza-
spiro[4.5]dec-2-ene-7,10-dione 1{4,1}: crude yield =76%;
1
8-Methyl-3-(2,6-dichlorophenyl)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione 1{1,5}: crude yield = 93%; diaster-
eomeric ratio (dr value) = 3/5; 1H NMR (600 MHz, methanol-
diastereomeric ratio (dr value) = 1/3; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 0.95 and 0.99 (t, 0.8H and
2.2H J = 7.5 Hz), 1.08 (d, 3H, J = 7.0 Hz), 1.33 and 1.71 (dq,
430
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ACS Combinatorial Science
Research Article
1.5H and 0.5H J = 1.7, 7.5 Hz), 2.05 and 2.14 (dqt, 0.75H and
0.25H, J = 5.4, 7.0, 1.7 Hz), 3.47 (d, 1H, J = 18.0 Hz), 3.88 and
4.19 (d, 0.75H and 0.25H, J = 5.4 Hz), 4.44 and 4.47 (d, 0.25H
and 0.75H, J = 18.0 Hz), 7.40−7.71 (m, 4H); 13C NMR (150
MHz, methanol-d4, mixture of isomers) δ 171.0, 165.6, 157.3,
134.1, 132.8, 132.2, 129.3, 128.5, 93.4 and 93.1, 62.4 and 60.9,
47.1 and 46.1, 41.5 and 39.3, 26.0 and 25.6, 15.9 and 15.4, 12.6
and 12.0; HRMS m/z calcd for [C16H18ClN3O3 + H]+
336.1109, found 336.1105; crude purity =99%; tR = 2.39 min.
8-(1-Methylpropyl)-3-(2,6-dichlorophenyl)-1-oxa-2,6,9-tri-
aza-spiro[4.5]dec-2-ene-7,10-dione 1{4,5}: crude yield = 86%;
132.0, 129.3, 128.5, 93.7 and 93.3, 56.3 and 54.6, 47.0, 46.0,
25.4, 23.7, 22.0; HRMS m/z calcd for [C16H18ClN3O3 + H]+
336.1109, found 336.1102; crude purity = 94%; tR = 2.09 min.
8-(2-Methylpropyl)-3-(4-methoxyphenyl)-1-oxa-2,6,9-tria-
za-spiro[4.5]dec-2-ene-7,10-dione 1{5,10}: crude yield = 64%;
1
diastereomeric ratio (dr value) = 1/2; H NMR (600 MHz,
Methanol−d4, mixture of isomers) δ 0.95 and 0.99 (d, 1H and
2H, J = 6.4 Hz), 0.98 and 1.02 (d, 1H and 2H, J = 6.4 Hz), 1.77
(m, 1H), 1.91 (m, 2H), 3.41 (d, 1H, J = 17.7 Hz), 4.00 (dd,
1H, J = 9.3, 4.9 Hz), 4.27 (d, 1H, J = 17.7 Hz), 7.00 (d, 2H, J =
8.8 Hz), 7.66 (d, 2H, J = 8.8 Hz); 13C NMR (150 MHz,
Methanol−d4, mixture of isomers) δ 173.2, 165.4, 163.3, 157.8,
129.8 ( × 2), 122.4, 115.5 ( × 2), 92.7, 56.3 and 56.0, 54.6, 47.0
and 43.8, 44.0 and 41.5, 25.6 and 25.4, 23.7 and 23.4, 22.6 and
22.0; HRMS m/z calcd for [C17H21N3O4 + H]+ 332.1605,
found 332.1612; crude purity =99%; tR = 1.95 min.
8-(Benzyl)-3-(4-methylphenyl)-1-oxa-2,6,9-triaza-spiro-
[4.5]dec-2-ene-7,10-dione 1{6,7}: crude yield = 77%; 1H NMR
(600 MHz, methanol-d4, mixture of isomers) δ 2.39 (s, 3H),
3.23 (m, 2H), 3.43 (d, 1H, J = 17.0 Hz), 4.17 (m, 1H), 4.27 (d,
1H, J = 17.0 Hz), 7.28−7.61 (m, 9H); 13C NMR (150 MHz,
methanol-d4, mixture of isomers) δ 172.0, 165.4, 158.1, 142.5,
137.6, 130.9 (×2), 130.7 (×2), 129.9 (×2), 128.4, 128.1 (×2),
127.3, 92.6, 59.5, 44.1, 43.4, 21.6; HRMS m/z calcd for
[C20H19N3O3 + H]+ 350.1499, found 350.1516; crude purity =
98.9%; tR = 2.53 min.
1
diastereomeric ratio (dr value) = 1/2; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 0.97 and 1.00 (t, 1H and
2H J = 7.5 Hz), 1.08 and 1.09 (d, 1H and 2H, J = 6.9 Hz), 1.31
and 1.73 (dq, 1.3H and 0.7H, J = 1.7, 6.9 Hz), 2.07 and 2.15
(dqt, 0.7H and 0.3H, J = 6.2, 6.9, 1.7 Hz), 3.31 (d, 1H, J = 18.1
Hz), 3.83 (d, 1H, J = 6.2 Hz), 4.24 and 4.31 (d, 0.3H and 0.7H,
J = 18.1 Hz), 7.45−7.51 (m, 3H); 13C NMR (150 MHz,
methanol-d4, mixture of isomers) δ 171.4, 165.5, 155.1, 136.5,
133.3, 129.7 (×3), 128.8, 93.4, 62.5 and 60.9, 46.3 and 45.4,
41.6 and 39.0, 26.2 and 25.7, 15.9 and 15.4, 12.6 and 11.9;
HRMS m/z calcd for [C16H17Cl2N3O3 + H]+ 370.0720, found
370.0724; crude purity = 99%; tR = 2.18 min.
8-(1-Methylpropyl)-3-(4-bromophenyl)-1-oxa-2,6,9-triaza-
spiro[4.5]dec-2-ene-7,10-dione 1{4,6}: crude yield =66%;
1
diastereomeric ratio (dr value) = 2/3; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 0.95 and 0.98 (t, 1.2H and
1.8H, J = 7.4 Hz), 1.08 (d, 3H, J = 6.8 Hz), 1.31 and 1.70 (dq,
1.2H and 0.8H, J = 1.7, 7.4 Hz), 2.04 and 2.13 (dqt, 0.6H and
0.4H, J = 5.1, 6.8, 1.7 Hz), 3.42 (d, 1H J = 17.7 Hz), 3.89 and
4.22 (d, 0.6H and 0.4H, J = 5.1 Hz), 4.19 and 4.24 (d, 0.4H and
0.6H, J = 17.7 Hz), 7.63 (s, 4H); 13C NMR (150 MHz,
methanol-d4, mixture of isomers) δ 170.9, 165.6, 157.1, 133.3 (
× 2), 130.3 and 129.6, 129.8 ( × 2), 129.4 and 125.9, 93.0, 62.3
and 61.0, 44.7 and 43.7, 41.5 and 39.4, 26.0 and 25.6, 15.9 and
15.4, 12.6 and 12.0; HRMS m/z calcd for [C16H18BrN3O3 +
H]+ 380.0604, found 380.0615; crude purity = 92%; tR = 2.51
min.
8-(O-Benzylmethoxyl)-3-(3-chlorophenyl)-1-oxa-2,6,9-tria-
za-spiro[4.5]dec-2-ene-7,10-dione 1{7,2}: crude yield = 39%;
1
diastereomeric ratio (dr value) = 1/1; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 3.18 and 3.44 (d, 0.5H and
0.5H, J = 17.8 Hz), 3.77−3.81 (m, 1H), 3.85 and 4.25 (d, 0.5H
and 0.5H, J = 17.8 Hz), 3.88−3.99 (m, 1H), 4.23−4.30 (m,
1H), 7.35−7.45 (m, 9H); 13C NMR (150 MHz, methanol-d4,
mixture of isomers) δ 169.6 and 169, 166.9 and 165.4, 156.9
and 156.7, 139.33 and 139.23, 136.1 and 136.0, 132.2 and
132.1, 131.7, 129.7, 129.6, 129.3, 129.0, 128.9, 127.8, 126.5,
93.3 and 93.2, 75.0 and 74.5, 73.2 and 71.6, 58.5 and 57.5, 45.3
and 44.4; HRMS m/z calcd for [C20H18ClN3O4 + H]+
400.1059, found 400.1080; crude purity =95%; tR = 2.69 min.
8-(O-Benzylmethoxyl)-3-(4-ethoxyphenyl)-1-oxa-2,6,9-tri-
aza-spiro[4.5]dec-2-ene-7,10-dione 1{7,9}: crude yield = 70%;
8-(1-Methylpropyl)-3-(4-ethoxyphenyl)-1-oxa-2,6,9-triaza-
spiro[4.5]dec-2-ene-7,10-dione 1{4,9}: crude yield = 74%;
1
diastereomeric ratio (dr value) = 2/5; H NMR (600 MHz,
1
methanol-d4, mixture of isomers) δ 0.95 and 0.98 (t, 0.9H and
2.1H, J = 6.0 Hz), 1.08 (d, 3H, J = 7.0 Hz), 1.31 and 1.70 (dq,
1.4H and 0.6H, J = 1.7, 6.0 Hz), 1.41 and 1.46 (t, 2.1H and
0.9H, J = 7.0 Hz), 2.03 and 2.05 (dqt, 0.7H and 0.3H, J = 5.3,
7.0, 1.7 Hz), 3.41 (d, 1H, J = 17.7 Hz), 3.87 (d, 0.7H, J = 5.3
Hz), 4.09 (q, 2H, J = 7.0 Hz), 4.17−4.24 (m, 1.3H), 6.97 (d,
2H, J = 8.7 Hz), 7.63 (d, 2H, J = 8.7 Hz); 13C NMR (150 MHz,
methanol-d4, mixture of isomers) δ 171.1, 165.9, 162.2, 157.6,
129.8 (×2), 122.2, 116.0 (×2), 92.8 and 92.4, 66.1 and 64.9,
62.3 and 60.9, 45.2 and 44.2, 41.5 and 39.3, 26.0 and 25.6, 15.9
and 15.2, 12.6 and 12.0; HRMS m/z calcd for [C18H23N3O4 +
H]+ 346.1761, found 346.1748; crude purity = 98%; tR = 2.13
min.
diastereomeric ratio (dr value) = 1/2; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 1.41 and 1.46 (t, 1H and
2H, J = 6.9 Hz), 3.16 and 3.41 (d, 0.7H and 0.3H, J = 17.8 Hz),
3.76−3.81 (m, 1H), 3.83 and 4.21 (d, 0.7H and 0.3H, J = 17.8
Hz), 3.76−3.81 (m, 1H), 4.09 and 4.17 (dq, 0.7H and 1.3H J =
2.3, 6.9 Hz), 4.18−3.30 (m, 2H), 7.09−7.75 (m, 9H); 13C
NMR (150 MHz, methanol-d4, mixture of isomers) δ 157.8 and
156.8, 139.3, 134.4 and 133.6, 129.7 (×2), 129.6 (×2), 129.5
(×2), 129.0, 12.9, 128.3, 128.2, 115.9, 114.5, 93.0, 75.0 and
74.5, 73.2 and 71.5, 66.1 and 64.9, 58.5 and 57.5, 45.5 and 44.7;
HRMS m/z calcd for [C22H23N3O5 + H]+ 410.1710, found
410.1731; crude purity = 83%; tR = 2.34 min.
8-(O-Benzylmethoxyl)-3-(4-mthoxyphenyl)-1-oxa-2,6,9-tri-
8-(2-Methylpropyl)-3-(2-chlorophenyl)-1-oxa-2,6,9-triaza-
aza-spiro[4.5]dec-2-ene-7,10-dione 1{7,10}: crude yield
=72%; diastereomeric ratio (dr value) = 1/1; H NMR (600
1
spiro[4.5]dec-2-ene-7,10-dione 1{5,3}: crude yield =55%;
1
diastereomeric ratio (dr value) = 1/2; H NMR (600 MHz,
MHz, Methanol−d4, mixture of isomers) δ 3.24 and 3.43 (d,
0.5H and 0.5H, J = 17.7 Hz), 3.77−3.82 (m, 1H), 3.84 (s, 3H),
3.91 and 4.26 (d, 0.5H and 0.5H, J = 17.7 Hz), 3.89−3.98 (m,
1H), 4.23−4.30 (m, 1H), 4.56−4.64 (m, 2H), 6.95−7.67 (m,
9H); 13C NMR (150 MHz, Methanol−d4, mixture of isomers)
δ 169.7 and 169.2, 167.1 and 165.7, 163.3, 157.7 and 157.4,
139.3, 129.7 ( × 2), 129.5 ( × 2), 129.2 and 128.9, 129.0 ( ×
methanol-d4, mixture of isomers) δ 0.96 and 1.00 (d, 1H and
2H, J = 6.0 Hz), 0.99 and 1.03 (d, 1H and 2H, J = 6.0 Hz), 1.78
(m, 1H), 1.91 (m, 2H), 3.45 (d, 1H, J = 17.9 Hz), 4.00 (dd,
1H, J = 8.7, 4.5 Hz), 4.52 (d, 1H, J = 17.9 Hz), 7.39−7.71 (m,
4H); 13C NMR (150 MHz, methanol-d4, mixture of isomers) δ
173.2 and 172.6, 165.8 and 165.1, 157.5, 134.1, 132.8, 132.2,
431
dx.doi.org/10.1021/co4000248 | ACS Comb. Sci. 2013, 15, 425−434

ACS Combinatorial Science
Research Article
2), 122.4 and 122.3, 115.4 ( × 2), 92.7 and 92.6, 74.9 and 74.5,
73.3 and 71.4, 58.5 and 57.4, 56.0, 45.8 and 44.9; HRMS m/z
calcd for [C21H21N3O5 + H]+ 396.1554, found 396.1580; crude
purity =98%; tR = 1.70 min.
[C19H19N3O3 + H]+ 338.1499, found 338.1525; crude purity
=99%; tR = 2.27 min.
ASSOCIATED CONTENT
■
8-(1-Methyl-O-benzylmethoxyl)-3-(2,6-dichlorophenyl)-1-
S
* Supporting Information
1
Copies of H and 13C NMR spectra for representative library
oxa-2,6,9-triaza-spiro[4.5]dec-2-ene-7,10-dione 1{8,5}. crude
1
yield = 70%; diastereomeric ratio (dr value) = 1/1; H NMR
members and characterization for this library. This information
is available free of charge via the Internet at http://pubs.acs.org.
(600 MHz, acetone-d6, mixture of isomers) δ 1.33 and 1.34 (d,
1.5H and 1.5H, J = 6.8 Hz), 3.44 and 3.46 (d, 0.5H and 0.5H, J
= 18.1 Hz), 3.93−4.16 (m, 1.5H), 4.36 and 4.54 (d, 0.5H and
0.5H, J = 18.1 Hz), 4.51−4.52 (m, 0.5H), 4.62−4.72 (m, 2H),
7.23−7.57 (m, 8H), 7.74 and 8.62 (br s, 0.5H and 0.5H), 8.01
and 8.68 (br s, 0.5H and 0.5H); 13C NMR (150 MHz, acetone-
d6, mixture of isomers) δ 168.5 and 167.3, 163.8, 154.0, 139.8
and 139.6, 135.9, 133.0, 129.4 (×3), 129.1 and 129.0 (×1.5 and
×1.5), 128.6 (×2), 128.3 and 128.2, 93.4 and 93.1, 78.2 and
77.1, 72.4 and 71.4, 63.0 and 60.0, 46.5 and 45.8, 17.4 and 15.5;
HRMS m/z calcd for [C21H19Cl2N3O4 + H]+ 448.0825, found
448.0844; crude purity = 90%; tR = 2.31 min.
AUTHOR INFORMATION
Corresponding Author
*E-mail: wcheng@gate.sinica.edu.tw. Fax: (+886)2-2789-8771.
■
Funding
This work was supported by National Science Council and
Academic Sinica.
Notes
The authors declare no competing financial interest.
8-(Indole-3-methyl)-3-(2,4-dichlorophenyl)-1-oxa-2,6,9-tri-
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diastereomeric ratio (dr value) = 2/3; H NMR (600 MHz,
acetone-d6, mixture of isomers) δ 2.81 and 3.58 (d, 0.4H and
0.6H, J = 17.9 Hz), 3.79 and 4.57 (d, 0.4H and 0.6H, J = 17.9
Hz), 3.41 and 4.56 (m, 0.6H and 0.4H), 3.39 and 3.49 (m, 0.4H
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8-(Isopropyl)-3-(2,4-dichlorophenyl)-1-oxa-2,6,9-triaza-
spiro[4.5]dec-2-ene-7,10-dione 1{10,4}: crude yield = 60%;
1
diastereomeric ratio (dr value) = 1/2; H NMR (600 MHz,
methanol-d4, mixture of isomers) δ 0.96 and 1.07 (d, 1H and
2H, J = 7.1 Hz), 1.096 and 1.10 (d, 2H and 1H, J = 7.1 Hz),
2.31 and 2.45 (m, 0.7H and 0.3H), 3.46 and 3.47 (d, 0.7H and
0.3H), 3.81 and 4.14 (d, 0.7H and 0.3H), 4.40 and 4.45 (d,
0.3H and 0.7H), 7.44 (d, 1H J = 8.4 Hz), 7.61 (s, 1H), 7.71 (d,
1H J = 8.4 Hz); 13C NMR (150 MHz, methanol-d4, mixture of
isomers) δ 171.1, 156.4, 138.0, 134.9, 133.2, 131.7, 128.9 (×2),
128.2, 93.2, 63.2 and 61.4, 46.8 and 46.0, 34.8 and 32.3, 19.7
and 18.6, 18.3 and 16.7; HRMS m/z calcd for [C15H15Cl2N3O3
+ H]+ 356.0563, found 356.0609; crude purity = 99%; tR = 2.58
min.
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