Synthesis of chiral cyclic β-amino ketones by Ru-catalyzed asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetlet.2013.10.093

Synthesis of chiral cyclic β-amino ketones has been first reported via Ru-catalyzed asymmetric hydrogenation. High enantioselectivities were achieved by using (S)-C₃-TunePhos chiral ligand (up to 94% ee).

Full text of DOI:10.1016/j.tetlet.2013.10.093

Accepted Manuscript
Synthesis of chiral cyclic β-Amino ketones by Ru-catalyzed asymmetric hy-
drogenation
Kexuan Huang, Zheng-Hui Guan, Xumu Zhang
PII:
S0040-4039(13)01841-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.10.093
TETL 43731
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
21 August 2013
17 October 2013
20 October 2013
Please cite this article as: Huang, K., Guan, Z-H., Zhang, X., Synthesis of chiral cyclic β-Amino ketones by Ru-
catalyzed asymmetric hydrogenation, Tetrahedron Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.
2013.10.093
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Synthesis of chiral cyclic ȕ-Amino ketones by
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Kexuan Huang, Zheng-Hui Guan and Xumu Zhangꢀ

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Synthesis of chiral cyclic ȕ-Amino ketones by Ru-catalyzed asymmetric
hydrogenation
Kexuan Huang, Zheng-Hui Guan and Xumu Zhangꢀ
Department of Chemistry and Chemical Biology & Department of Pharmaceutical Chemistry, Rutgers, The State University of New Jersey, Piscataway, NJ
08854, USA.
ARTICLE INFO
ABSTRACT
Article history:
Received
Synthesis of chiral cyclic ȕ-Amino ketones has been first reported via Ru-catalyzed asymmetric
hydrogenation. High enantioselectivities were achieved by using (S)-C3-TunePhos chiral ligand
(up to 94% ee).
Received in revised form
Accepted
2009 Elsevier Ltd. All rights reserved.
Available online
Keywords:
Asymmetric hydrogenation
Ruthenium
Chiral phosphine ligands
Amino ketones
Chiral amines and their derivatives are important synthetic
targets and powerful pharmacophores for defining new
pharmaceutical drugs.1 Over the past few decades,
enantioselective hydrogenation has proven to be an efficient
method for chiral amine synthesis.2 Our group has recently
developed a Rh-catalyzed enantioselective hydrogenation of ȕ-
keto enamides as an efficient way to prepare optically pure ȕ-
amino ketones and their derivatives (Scheme 1).3 We later
envisioned that chiral cyclic ȕ-Amino ketones are also interesting
structural motifs. For example, these amino ketones can serve as
key synthetic precursors for some antitumor agents (Scheme 2).4,5
To the best of our knowledge, there is no report on synthesis of
optically pure cyclic ȕ-amino ketones through catalytic
asymmetric hydrogenation.
Herein, we present a Ru-catalyzed highly enantioselective
hydrogenation of cyclic ȕ-keto enamides to afford chiral cyclic ȕ
-amino ketones.
Scheme 2. Examples of commercial available antitumor agents.
Preparation of cyclic ȕ-keto enamide substrates were tried though
the direct condensation of commercial available cyclic 1,3-
diketones with acetamide.6 However, all attempts afforded low
yields (< 30%). Thus, a two-step procedure was applied. Cyclic
1,3 -diketones were first converted to the corresponding cyclic ȕ-
enaminones,7 followed by acylation with acyl chloride to give the
enamide substrates in moderate to good yields (up to 87%,
scheme 3). We have to mention that aromatic cyclic 1,3-
diketones such as 1,3-indanediones didn¶t give any desired
products following this procedure, which dramatically narrowed
the substrate scope.
Scheme 1.
²²²
ꢀ Corresponding author. Tel.: +1-732-445-1489; Fax: +1-732-445-6312; e-mail: xumu@rci.rutgers.edu

2
Tetrahedron
6
C3-TunePhos- Ru(OAc)2
C3-TunePhos- Ru(OAc)2
53
86
94
94
7d
a Unless otherwise mentioned, reaction conditions: Catalyst/substrate =1:100,
at room temperature, under 1 atm of hydrogen for 24 h.
b Conversions were determined by 1H NMR of the crude product.
c
Determined by GC on a chiral phase.
Under 5 atm of hydrogen.
d
8
Thus, different Ru precursors were systematically investigated.
As showed in Table 2, Ru(OAc)2/C3-TunePhos complex still
gave the highest enantioselectivities (Table 2, entries 1-4).
Further solvent screening indicated that MeOH served as the best
solvent (Table 2, entries 5-11). Increasing the hydrogen pressure
or catalyst loading would cause more formation of the
corresponding amino-alcohol 3a as side product.
Scheme 3. Preparation of cyclic ȕ-keto enamide substrates.
We began our study by investigating the asymmetric
hydrogenation of 1a as the model substrate. Rh/TangPhos and
Rh/DuanPhos catalysts were initially tested since they have been
previously proved efficient for enantioselective hydrogenation of
acyclic ȕ-ketoenamides.3 However, neither of them gave
satisfactory enantioselectivities under various reaction conditions
(Table 1, entries 1-2). Other commercial available Rh complexes
such as Rh/DuPhos and Rh/BINAPINE were also tested to give
lower than 60% ee¶s (Table 1, entries 3-4). After catalyst
screening, to our surprise, we found that commercial available
Ru(OAc)2/Binap catalyst gave the highest 92% ee. Later on, our
results showed that Ru(OAc)2/C3-Tunephos give better
enantioselectivities as well as good conversions (94% ee, Table 1,
entries 6-7).
Table 2. Selected results from initial screening of Ru-
catalysts for hydrogenation of 1aa
Entry {Ru}
Solvent
MeOH
Yield of
2a (%)b
22
ee of
2a (%)c
42
1
[NH2Me2][{RuCl(L)}2
(µ-Cl)3]
2
3
4
5
6
7
8
9
10
[RuCl(p-pymene)L]Cl
[RuCl(benzene)L]Cl
RuCl2L (DMF)n
Ru(OAc)2L
Ru(OAc)2L
Ru(OAc)2L
Ru(OAc)2L
Ru(OAc)2L
Ru(OAc)2L
Ru(OAc)2L
MeOH
MeOH
MeOH
36
31
<5
31
34
29
47
69
63
73
51
55
n.d.
82
83
42
75
91
85
94
THF
1,4-dioxane
toluene
ethyl acetate
EtOH
iPrOH
11
MeOH
a Unless otherwise mentioned, reaction conditions: Catalyst/substrate =1:100,
at room temperature, under 5 atm of hydrogen for 24 h. L= (S)-C3-TunePhos.
Ru complexes were prepared according to reported procedure. 8
b Conversions were determined by 1H NMR of the crude product.
c Determined by GC on a chiral phase.
Table 3. Substrate scope and limitationsa
Entry
1
Substrate
Product
Yieldb
73
eec
94
Picture 1. Selected structure of screened phosphine ligands.
Table 1. Selected results from initial screening of catalysts for
hydrogenation of 1aa
2
3
4
68
36
45
88
67
61
Entry
Catalyst
Convb
(%)
90
eec
(%)
61
44
35
52
92
1
2
3
4
5
TangPhos-Rh(cod)BF4
DuanPhos-Rh(cod)BF4
BINAPINE- Rh(cod)BF4
Me-BPE-Rh(cod)BF4
BINAP-Ru(OAc)2
86
68
76
70

3
a Unless otherwise mentioned, reaction conditions: Ru(OAc)2/C3-TunePhos as
catalyst, Catalyst/substrate =1:100, Methanol as solvent, at room temperature,
under 5 atm of hydrogen for 24 h.
b Conversions were determined by 1H NMR of the crude product.
c Determined by GC on a chiral phase.
Uricchio, V.; Colabufo, N. A.; Niso, M.; Perrone, R. Journal of
Medicinal Chemistry 2009, 52, 7817-7828; (c) Chu, W.; Xu, J.;
Zhou, D.; Zhang, F.; Jones, L. A.; Wheeler, K. T.; Mach, R. H.
Bioorganic & Medicinal Chemistry 2009, 17, 1222-1231.
5. (a) Dallemagne, P.; Khanh, L. P.; Alsaidi, A.; Renault, O.; Varlet,
I.; Collot, V.; Bureau, R.; Rault, S. Bioorganic & Medicinal
Chemistry 2002, 10, 2185-2191; (b) Khanh, L. P.; Dallemagne, P.;
Landelle, H.; Rault, S. From Journal of Enzyme Inhibition and
Medicinal Chemistry 2002, 17, 439-442; (c) Omran, Z.; Cailly, T.;
Lescot, E.; Sopkova-de Oliveira, S. J.; Agondanou, J.-H.;
Lisowski, V.; Fabis, F.; Godard, A.-M.; Stiebing, S.; Le Flem, G.;
Michel, B; Francois, D; Patrick, D; Sylvain, R. European Journal
of Medicinal Chemistry 2005, 40, 1222-1245; (d) Omran, Z.;
Dallemagne, P.; Rault, S. Journal of Enzyme Inhibition and
Medicinal Chemistry 2007, 22, 632-637; (e) Omran, Z.; Stiebing,
S.; Godard, A.-M.; Sopkova-de Oliveira, S., J.; Dallemagne, P.
Journal of Enzyme Inhibition and Medicinal Chemistry 2008, 23,
696-703.
With the optimized reaction conditions, 5,5-dimethyl substituted
substrate 1b was tested to give moderate hydrogenation results
(Table 3, entry 2). However, hydrogenation of tetra-substituted
olefin substrates 1c showed dramatic loss of reactivities and
enantioselectivities (Table 3, entry 3). Low reactivity and
enantioselectivity were also observed when cyclopentyl substrate
1d was tested (Table 3, entry 4).
In conclusion, we reported
a Ru-catalyzed asymmetric
hydrogenation of cyclic ȕ-keto enamides to afford chiral cyclic ȕ-
amino ketones, which afforded a new approach for the synthesis
of optically pure cyclic ȕ-amino ketones. Further studies focusing
on expanding the substrate scope and improving the reactivities
and enantioselectivities are ongoing.
6. Geng, H.; Zhang, W.; Chen, J.; Hou, G.; Zhou, L.; Zou, Y.; Wu,
W.; Zhang, X. Angew. Chem., Int. Ed. 2009, 48, 6052-6054.
7. Putkonen, T.; Tolvanen, A.; Jokela, R.; Salvatore Caccamesec, S.;
Experimental section
Parrinelloc, N. Tetrahedron 2003, 59 8589±8595.
8. For preparation of Ru/C3-Tunephos complexes, see: (a) Wu, S.;
Wang, W.; Tang, W.; Lin, M.; Zhang, X. Org. Lett. 2002, 4, 4495-
4497; (b) Zhang, Z.; Qian, H.; Longmire, J.; Zhang, X. J. Org.
Chem. 2000, 65, 6223-6226.
General Procedure for Asymmetric Hydrogenation
In a glovebox filled with nitrogen, Ru catalyst (0.02 mmol) was
dissolved in MeOH (5 mL). 0.5 mL of this solution (0.002 mmol)
was added into a solution of 0.2 mmmol substrate in 3 mL of
degassed MeOH. The resulting solution was then transferred into
an autoclave and charged with 5 atm of hydrogen. The
hydrogenation was performed at room temperature for 24 h.
After carefully releasing the hydrogen, the reaction mixture was
passed through a short silica gel column to remove the catalyst.
The ee values of all compounds were determined by GC on a
chiral stationary phase.
Acknowledgments
We thank the National Institutes of Health (GM58832) for
financial support.
Supplementary data
Supplementary data associated with this article can be found,
in the online version
References and notes
1. Chiral Amine Synthesis. Methods, Developments and
Applications; Nugent, T. C.; Wiley-VCH, 2010.
2. (a) Handbook of Homogeneous Hydrogenation; de Vries, J. G.;
Elsevier, C. J.; WILEY-VCH, 2006; (b) Knowles, W. S.
Asymmetric Hydrogenations (Nobel Lecture), Angew. Chem., Int.
Ed. 2002; (c) Xie, J.-H.; Zhu, S.-F.; Zhou, Q.-L. Chem. Rev. 2011,
111, 1713-1760.
3. (a) Huang, K.; Zhang, X,; Geng, H.; Li, S.-K.; Zhang, X. ACS
Catal. 2012, 2, 1343±1345; (b) Geng, H.; Huang, K.; Sun, T.; Li,
W.; Zhang, X.; Zhou, L.; Wu, W.; Zhang, X. J. Org. Chem. 2011,
76, 332-334.
4. (a) Abate, C.; Perrone, R.; Berardi, F. Current Pharmaceutical
Design 2012, 18, 938-949; (b) Berardi, F.; Abate, C.; Ferorelli, S.;

Support information
Synthesis of chiral cyclic β-amino ketones by Ru-catalyzed asymmetric hydrogenation
Kexuan Huang, Zheng-Hui Guan and Xumu Zhang∗
Department of Chemistry and Chemical Biology & Department of Pharmaceutical
Chemistry, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA,
E-mail: xumu@rci.rutgers.edu
1. General Information--------------------------------------------------------------------------------
---S2
2. Synthesis of substrate ------------------------------------------------------------------------------
---S2
3. NMR spectra-----------------------------------------------------------------------------------------
---S4
4. General procedure for asymmetric hydrogenation and GC spectra--------------------------
--S19
General Methods. Starting materials, reagents and solvents were purchased from
commercial sources and were used as received. All reactions and manipulations that were
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sensitive to moisture or air were performed in a nitrogen-filled glovebox or using
standard Schlenk techniques, unless otherwise noted. Solvents were dried with standard
procedures and degassed with N2. Column chromatography was performed using 200-
400 mesh silica gel supplied by Natland International Corp. Thin-layer chromatography
1
(TLC) was performed on EM reagents 0.25 mm silica 60-F plates. H and 13C NMR
spectra were recorded on Bruker Avance 400 MHz spectrometers and a Varian VNMRS-
500 MHz instrument. GC analysis was carried out on Hewlett-Packard 7890 gas
chromatography using chiral capillary columns.
General Procedure for substrate synthesis
10 mmol cyclic 1,3-diketone was added to a mixture of 10 mmol ammonium acetate in
dry toluene (20 mL). The mixture was heated for 3 h under reflux using a Dean–Stark
water separator. The resulting oily product was separated and recrystallized with ethyl
acetate to give the corresponding enaminone as crystals. The enaminone product was
dissolved in 50ml THF and 2 equiv. of pyridine were added. To the mixed solution, acetyl
chloride (2 equiv.) in 5ml THF was added dropwise at 0 °C. The reaction mixture was
warmed up to ambient temperature and stirred additional 5 h at 60oC. The solvent was
removed under vacuum and the crude product purified by flash chromatography.
1
N-(3-oxocyclohex-1-en-1-yl)acetamide (1a) H NMR (400 MHz, CDCl3) δ 7.61 (1H,
br), 6.49 (1H, s), 2.51 (2H, t, J = 6.0), 2.30 (2H, t, J = 6.3), 2.07 (3H, s), 1.96 (2H, q, J =
6.4); 13C NMR (100 MHz, CDCl3) δ 21.4, 24.7, 28.2, 36.6, 111.2, 158.9, 170.1, 201.1
ꢈꢁ
ꢁ

1
N-(5,5-dimethyl-3-oxocyclohex-1-en-1-yl)acetamide (1b) H NMR (400 MHz, CDCl3)
δ 8.67 (1H, br), 6.74 (1H, s), 2.51 (2H, t, J = 6.0), 2.37 (2H, s), 2.19 (2H, s), 2.11 (3H, s),
13
1.05 (6H, s); C NMR (100 MHz, CDCl3) δ 24.7, 28.1, 32.7, 42.1, 50.5, 110.1, 154.7,
170.1, 201.0
N-(2-methyl-3-oxocyclohex-1-en-1-yl)acetamide (1c) 1H NMR (400 MHz, d6-DMSO) δ
9.24 (1H, br), 2.77 (2H, t, J = 6.0), 2.33 (2H, t, J = 6.2), 2.10 (3H, s), 1.88 (2H, q, J =
6.4), 1.67 (3H, s); 13C NMR (100 MHz, CDCl3) δ 7.95, 23.72, 23.75, 26.9, 36.04, 117.1,
152.0, 167.9, 197.8
O
NHAc
1
N-(2-methyl-3-oxocyclopent-1-en-1-yl)acetamide (1d) H NMR (400 MHz, CDCl3) δ
13
8.41 (1H, br), 3.13 (2H, t, J = 2.4), 2.34 (2H, t, J = 2.5), 2.16 (3H, s), 1.59 (3H, s); C
NMR (100 MHz, CDCl3) δ 6.69, 24.5, 27.7, 33.6, 118.3, 165.1, 168.9, 206.7
1
H NMR (400 MHz, CDCl3)
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NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Nov26-2009-kh
1
1
20091126
16.36
spect
5 mm PABBO BB-
zg30
65536
CDCl3
128
SOLVENT
NS
DS
0
8223.685 Hz
SWH
FIDRES
AQ
RG
0.125483 Hz
3.9846387 sec
406
DW
DE
TE
D1
60.800 usec
6.50 usec
299.1 K
2.00000000 sec
1
TD0
======== CHANNEL f1 ========
NUC1
P1
1H
8.76 usec
-2.00 dB
PL1
PL1W
SFO1
SI
31.17179108 W
400.1324710 MHz
32768
400.1300351 MHz
EM
SF
WDW
SSB
LB
GB
PC
0
0.30 Hz
0
1.00
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
ppm
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NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Feb17-2009-kh
1
1
20090217
12.55
spect
5 mm PABBO BB-
zg30
65536
DMSO
16
SOLVENT
NS
DS
2
8223.685 Hz
SWH
FIDRES
AQ
RG
0.125483 Hz
3.9846387 sec
161
DW
DE
TE
D1
60.800 usec
6.50 usec
297.3 K
1.00000000 sec
1
TD0
======== CHANNEL f1 ========
1H
NUC1
P1
PL1
PL1W
SFO1
SI
8.76 usec
-2.00 dB
31.17179108 W
400.1324710 MHz
32768
400.1299794 MHz
EM
SF
WDW
SSB
LB
GB
PC
0
0.30 Hz
0
1.00
10
9
8
7
6
5
4
3
2
1
ppm
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NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Feb19-2009-kh
1
1
20090220
1.37
spect
5 mm PABBO BB-
zgpg30
65536
SOLVENT
NS
DS
CDCl3
1024
4
24038.461 Hz
SWH
FIDRES
AQ
RG
0.366798 Hz
1.3631988 sec
2050
DW
DE
TE
D1
D11
TD0
20.800 usec
6.50 usec
300.2 K
2.00000000 sec
0.03000000 sec
1
======== CHANNEL f1 ========
NUC1
P1
PL1
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8.50 usec
1.00 dB
PL1W
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75.02186584 W
100.6228298 MHz
======== CHANNEL f2 ========
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PCPD2
PL2
PL12
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PL12W
PL13W
SFO2
SI
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90.00 usec
-2.00 dB
18.23 dB
19.00 dB
31.17179108 W
0.29563907 W
0.24760634 W
400.1316005 MHz
32768
SF
WDW
100.6128640 MHz
EM
SSB
LB
0
1.00 Hz
GB
PC
0
1.40
200
180
160
140
120
100
80
60
40
20
0
ppm
O
NHAc
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NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Feb26-2009-kh
2
1
20090226
12.56
spect
5 mm PABBO BB-
zg30
65536
CDCl3
16
SOLVENT
NS
DS
2
8223.685 Hz
SWH
FIDRES
AQ
RG
0.125483 Hz
3.9846387 sec
71.8
DW
DE
TE
D1
60.800 usec
6.50 usec
297.4 K
1.00000000 sec
1
TD0
======== CHANNEL f1 ========
1H
NUC1
P1
PL1
PL1W
SFO1
SI
8.76 usec
-2.00 dB
31.17179108 W
400.1324710 MHz
32768
400.1300235 MHz
EM
SF
WDW
SSB
LB
GB
PC
0
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0
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10
9
8
7
6
5
4
3
2
1
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O
NHAc
NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Feb26-2009-kh
3
1
20090226
23.20
spect
5 mm PABBO BB-
zgpg30
65536
SOLVENT
NS
DS
CDCl3
1024
4
SWH
24038.461 Hz
0.366798 Hz
1.3631988 sec
2050
FIDRES
AQ
RG
DW
DE
TE
D1
D11
TD0
20.800 usec
6.50 usec
300.3 K
2.00000000 sec
0.03000000 sec
1
======== CHANNEL f1 ========
NUC1
P1
PL1
13C
8.50 usec
1.00 dB
PL1W
SFO1
75.02186584 W
100.6228298 MHz
======== CHANNEL f2 ========
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90.00 usec
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18.23 dB
19.00 dB
31.17179108 W
0.29563907 W
0.24760634 W
400.1316005 MHz
32768
SF
WDW
100.6127690 MHz
EM
SSB
LB
0
1.00 Hz
GB
PC
0
1.40
200
180
160
140
120
100
80
60
40
20
0
ppm
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NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Nov28-2009-kh
4
1
20091128
18.02
spect
5 mm PABBO BB-
zg30
65536
SOLVENT
NS
DS
CDCl3
128
0
8223.685 Hz
SWH
FIDRES
AQ
RG
0.125483 Hz
3.9846387 sec
128
DW
DE
TE
D1
60.800 usec
6.50 usec
298.1 K
2.00000000 sec
1
TD0
======== CHANNEL f1 ========
NUC1
P1
1H
8.76 usec
-2.00 dB
PL1
PL1W
SFO1
SI
31.17179108 W
400.1324710 MHz
32768
400.1300261 MHz
EM
SF
WDW
SSB
LB
GB
PC
0
0.30 Hz
0
1.00
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
ppm
ꢀꢆꢁ
ꢁ

NAME
EXPNO
PROCNO
Date_
Time
INSTRUM
PROBHD
PULPROG
TD
Nov28-2009-kh
1
1
20091128
16.18
spect
5 mm PABBO BB-
zgpg30
65536
SOLVENT
NS
DS
CDCl3
1024
4
24038.461 Hz
SWH
FIDRES
AQ
RG
0.366798 Hz
1.3631988 sec
2050
DW
DE
TE
D1
D11
TD0
20.800 usec
6.50 usec
299.7 K
2.00000000 sec
0.03000000 sec
1
======== CHANNEL f1 ========
NUC1
P1
PL1
13C
8.50 usec
1.00 dB
PL1W
SFO1
75.02186584 W
100.6228298 MHz
======== CHANNEL f2 ========
CPDPRG2
NUC2
PCPD2
PL2
PL12
PL13
PL2W
PL12W
PL13W
SFO2
SI
waltz16
1H
90.00 usec
-2.00 dB
18.23 dB
19.00 dB
31.17179108 W
0.29563907 W
0.24760634 W
400.1316005 MHz
32768
SF
WDW
100.6128688 MHz
EM
SSB
LB
0
1.00 Hz
GB
PC
0
1.40
200
180
160
140
120
100
80
60
40
20
0
ppm
General Procedure for Asymmetric Hydrogenation
In a glovebox filled with nitrogen, Ru catalyst (0.02 mmol) was dissolved in MeOH (5
mL). 0.5 mL of this solution (0.002 mmol) was added into a solution of 0.2 mmmol
substrate in 3 mL of degassed MeOH. The resulting solution was then transferred into an
autoclave and charged with 5 atm of hydrogen. The hydrogenation was performed at
room temperature for 24 h. After carefully releasing the hydrogen, the reaction mixture
was passed through a short silica gel column to remove the catalyst. The ee values of all
compounds were determined by GC on Supelco beta DexTM 390 column.
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Supelco beta DexTM 390 column (30 m ×0.25 mm × 0.25 µm), He 1.0 mL/min, column
temperature: 180 oC; tR = 13.4 min (minor), tR = 13.7 min (major). (2a)
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