The synthesis of novel oxime ethers and their effects on the senescence of cut carnation flowers

Article abstract of DOI:10.1007/s11164-011-0363-2

The high levels of ethylene in plants are involved in a range of harmful effects, such as the senescence of plants and the rotting of fruits. A series of novel oxime ethers were synthesized to counteract the ethylene effects. Their structures were characterized by IR, MS, and ¹H NMR, and their effects on the senescence of cut carnation flowers were investigated. The results show that all of the target compounds extended the vase life of cut carnation, especially for compound 3i, which prolonged the vase life of cut carnation flowers to about 11 days, nearly 75% longer vase life compared to the control groups. Most of them were more effective than AgNO₃ and aminooxyacetic acid. Springer Science+Business Media B.V. 2011.

Full text of DOI:10.1007/s11164-011-0363-2

Res Chem Intermed (2012) 38:463–470
DOI 10.1007/s11164-011-0363-2
The synthesis of novel oxime ethers and their effects
on the senescence of cut carnation flowers
•
•
•
Zhen Zeng Hong Jiang Haoyong Zhang
Zhenhua Jiang
Received: 3 July 2011 / Accepted: 9 August 2011 / Published online: 24 August 2011
Ó Springer Science+Business Media B.V. 2011
Abstract The high levels of ethylene in plants are involved in a range of harmful
effects, such as the senescence of plants and the rotting of fruits. A series of novel
oxime ethers were synthesized to counteract the ethylene effects. Their structures
were characterized by IR, MS, and 1H NMR, and their effects on the senescence of
cut carnation flowers were investigated. The results show that all of the target
compounds extended the vase life of cut carnation, especially for compound 3i,
which prolonged the vase life of cut carnation flowers to about 11 days, nearly 75%
longer vase life compared to the control groups. Most of them were more effective
than AgNO3 and aminooxyacetic acid.
Keywords Ethylene inhibitor Á Oxime Á Cut carnation Á Senescence
Introduction
Ethylene plays an important role in a wide range of aspects of plant growth and
development, such as promoting the germination of seeds, the differentiation of
tissues, the expansion of stems and the growth of roots, the formation of
adventitious roots, and the ripening of fruits [1–3]. Certain periods of plant growth,
for example, seeds germination, fruits after-ripening, leaves falling, and flowers
senescence, will induce ethylene formation, which, in turn, the accumulation of
ethylene will further stimulate the production of ethylene.
Electronic supplementary material The online version of this article (doi:
10.1007/s11164-011-0363-2) contains supplementary material, which is available to authorized users.
Z. Zeng Á H. Jiang (&) Á H. Zhang Á Z. Jiang
Department of Chemistry, Huazhong Agricultural University, Wuhan 430070, China
e-mail: jianghong0066@126.com
123

464
Z. Zeng et al.
High levels of ethylene in plants can result in many deleterious effects, especially
for the acceleration of the senescence of plants and the rotting of fruits, so ethylene
inhibitors are strongly needed in order to preserve agricultural products [4, 5].
Inhibitors of ethylene action and inhibitors of ethylene biosynthesis are two kinds of
typical ethylene inhibitors [6]. Common inhibitors of ethylene action include silver
ions (e.g., silver thiosulfate, STS), 2,5-norbornadiene (NBD), diazocyclopentadiene
(DACP), and cyclopropene derivatives. Ethylene action inhibitors compete with
ethylene for the binding receptor to counteract ethylene effects [7–10]. The practical
use of STS is limited because it is environmentally critical [11, 12]. NBD, DACP,
and cyclopropene derivatives are gas per se; the inconvenience and the hidden
safety dangers for operation makes their practical uses limited [13].
Familiar ethylene biosynthesis inhibitors include aminooxyacetic acid (AOA),
aminoethoxyvinylglycine (AVG), and methoxyvinylglycine (MVG). These inhib-
itors are able to block the pathway of ethylene biosynthesis, leading to a low
ethylene level in plants [14, 15]. AVG and MVG are difficult to be prepared, and,
thus, too expensive for practical use; additionally, their phytotoxicity is also a
problem [16, 17].
The intensive pungent smell of AOA makes it unacceptable for practical use [18,
19]. Therefore, people managed to synthesize some oxime ether derivatives of AOA
(see Scheme 1). Inspired by this, a series of novel oxime ether derivatives of AOA
were designed and synthesized (see Fig. 1), and their effects on the senescence of
cut carnation flowers were investigated in this article.
H
Cl
CO2H
C
OH
R1
R1
R3
NH2OH HCl
Na2CO3
N
O
R2
R2
1
O
C
O
O
R4
R4
R1
Br
NEt3
O
CO2H
R1
N
N
R3
R3
R2
R2
3a-3k
2
Scheme 1 The synthesis route. 3a R1 = CH3, R2 = CH3, R3 = H, R4 = CH(CH3)CO2Et; 3b R1 = CH3,
R2 = CH3, R3 = H, R4 = CH2CO2Et; 3c R1 = CH3, R2 = CH3, R3 = H, R4 = (CH2)3CO2Et; 3d
R1 = CH3, R2 = CH3, R3 = CH3, R4 = CH2CO2Et; 3e R1 = CH3, R2 = CH3, R3 = CH3,
R4 = CH(CH3)CO2Et; 3f R1 = CH3, R2 = CH3, R3 = CH3, R4 = (CH2)3CO2Et; 3g R1 = Ph, R2 = H,
R3 = H, R4 = CH2CO2Et; 3h R1 = Ph, R2 = H, R3 = H, R4 = CH(CH3)CO2Et; 3i R1 = Ph, R2 = H,
R3 = H, R4 = (CH2)3CO2Et; 3j R1 = Ph, R2 = H, R3 = CH3, R4 = CH2CO2Et; 3k R1 = Ph, R2 = H,
R3 = CH3, R4 = CH(CH3)CO2Et
123

The synthesis of novel oxime ethers and their effects
465
O
O
O
O
O
Et
O
Et
O
O
O
N
O
O
N
O
O
N
O
O
Et
3c
3b
3a
O
O
O
O
O
Et
O
Et
O
O
O
N
O
O
N
O
O
N
O
O
Et
3e
3d
3f
O
O
O
O
O
Et
O
Et
O
N
O
N
O
O
O
O
O
N
O
O
Ph
Ph
Et
3g
3h
3i
Ph
O
O
O
O
Et
O
Et
O
O
N
O
N
O
O
O
HO
H N
O
2
Ph
Ph
3j
AOA
3k
Fig. 1 The structure of the synthesized compounds
Results and discussion
Synthesis
For the synthesis of compound 2, which was prepared by the reaction of the
corresponding oxime 1 and halocarboxylic acid, chlorocarboxylic acid gave a
poorer yield, while bromocarboxylic acid behaved much better, so bromocarboxylic
acid is recommended to be used in the preparation of compound 2. The temperature
should be controlled at around 0 °C. When the temperature was higher, the side
reaction between halocarboxylic acids themselves would take place, that is, the
acyloxy anion group of one molecule could attack the halo-bearing carbon of
another halocarboxylic acid molecule.
123

466
Z. Zeng et al.
For the preparation of 3a–3k by the reaction of carboxymethoxime 2 with
halocarboxylic acid ester, triethylamine was used as the acid binding agent. The
hydroxyl group of metal base would attack the halo atom of the halocarboxylic acid
ester and replace the halo atom, so it is unadvisable to use metal base in this step.
Effect of oxime ethers on the preservation of cut carnation flowers
In preliminary experiments, the concentration (100 mg/L) of 3a that sufficed to
extend flower vase life was selected. According to the literature, 0.2 mM STS
concentration was recommended to extend vase life [20]. It was also reported that
the application of 1.0 mM AOA caused chemical injury to the cut flowers, but
0.1 mM AOA did not [21]. Accordingly, the concentration of AgNO3 and AOA
applied in this work were 50 and 70 mg/L, respectively. Table 1 describes their
influence on the senescence of cut carnation flowers. Compared to the control group,
the vase life of cut carnation flowers treated with 3a–3k was significantly prolonged.
Especially for compounds 3b, 3c, 3e, 3f, 3h, and 3i, all of them prolonged the vase
life by more than 50%. 50 mg/L silver ion treatment extended the vase life of cut
carnation by about 30.8%, and AOA extended the vase life by nearly 40% longer
than the control. So, compounds 3b, 3c, 3e, 3f, 3h, and 3i were more effective than
70 mg/L AOA and 50 mg/L AgNO3. The common structural feature of 3b, 3c, and
3i was that R4 is a straight line when R3 was H. Especially for 3i and 3c, which were
the best in each subset, they shared the same substructure of R4 (i.e., ethyl
butanoate). For 3e and 3f, which also demonstrated high activities, R4 was a
carboxylic acid with more than two carbons when R3 was CH3. However, it is only a
preliminary conclusion. This suggests that the structure of R3 and R4 likely plays an
important role in the mechanism of their action.
Table 1 Influence of
compounds on the vase life
of cut carnation flowers
Compound
Concentration
(mg/L)
Vase life
(days)
Prolongation
rate (%)
CK (DBS)
0.1%
70
14.3 0.8f
20.0 0.5d
18.7 0.8de
20.0 0.7d
23.0 0.9bc
23.0 1.0bc
17.5 1.1e
23.5 0.6b
22.0 1.0c
18.0 0.7e
22.0 0.8c
25.0 0.5a
15.5 1.2f
18.0 0.9e
–
AOA
AgNO3
3a
39.9
30.8
39.9
60.8
60.8
22.4
64.3
53.8
25.9
53.8
74.8
8.4
50
100
100
100
100
100
100
100
100
100
100
100
3b
3c
3d
3e
The values in one column with
different letters are significantly
different (p \ 0.05, Duncan’s
multiple range test). Senescence:
the petals have lost turgidity and
the flowers are partially closed,
advanced inrolling symptoms
and browning. The control was
0.1% DBS solution
3f
3g
3h
3i
3j
3k
25.9
123

The synthesis of novel oxime ethers and their effects
467
Conclusion
The title oxime ether derivatives can prolong the vase life of cut carnation flowers
and deserve further research as cut flowers preservatives.
Experimental section
The structures were confirmed by an AVATAR 330 Infrared Spectrometer (KBr), a
Saturn 2200 Mass Spectrograph, and a Bruker AV400 400-MHz H Nuclear
Magnetic Resonance Spectrometer (d, CDCl3).
Typical procedure for the synthesis of oxime ether derivatives
The synthesis method was exemplified by the preparation of compound 3a.
Acetoxime 1 was prepared by the direct addition between acetone and hydroxyl-
amine. Acetone carboxymethoxime 2 was prepared by the reaction of acetoxime 1 and
chloroacetic acid or bromoacetic acid, according to the literature [22].
3a was prepared by the reaction of acetone carboxymethoxime 2 with ethyl
2-bromopropanoate. Briefly, 1.97 g (0.015 mol) compound acetone carbo-
xymethoxime 2, 2.1 mL (0.015 mol) triethylamine, and 7.5 mL N,N-dimethylform-
amide (DMF) was placed into a two-necked flask. After the mixture was stirred for
about 30 min at 20 °C, a solution of 2.72 g (0.015 mol) ethyl 2-bromopropanoate in
10 mL DMF was added dropwise within 1 h. Then, the mixture was reacted at
20 °C for 4 h and at 80 °C for 8 h with stirring. After cooling, the triethylamine
hydrobromide was filtered, and then the DMF solvent was removed under reduced
pressure; 30 mL chloroform and 15 mL water was added to the residue. The
chloroform layer was collected and washed with 10 mL 1 mol/L HCl, 10 mL 5%
aqueous NaHCO3, and 10 mL water subsequently. Then, it was dried with
anhydrous sodium sulfate. After the removal of chloroform by distillation, the target
product was produced as a yellow liquid.
Ethyl 2-[[2-[[(1-methylethylidene)amino]oxy]acetyl]oxy] propionate (3a)
A light yellow liquid, yield 66.4%. IR (KBr, cm-1), 2,920–2,965 (CH3), 2,885–
1
2,915 (CH2), 1,764 (C=O), 1,635 (C=N), 1,120 (C–O–C), H NMR (400 MHz,
CDCl3, d ppm), d 1.24–1.29 (3H, t, J = 9.6 Hz), 1.48–1.50 (3H, d, J = 9.2 Hz),
1.86 (3H, s), 1.92 (3H, s), 4.15–4.22 (2H, q, J = 9.6 Hz), 4.63 (2H, s), 5.11–5.18
(1H, q, J = 9.2 Hz), MS (m/z, %): 232 (M?, 35%), 56 (100%).
Ethyl 2-[[2-[[(1-methylethylidene)amino]oxy]acetyl]oxy] acetate (3b)
A light yellow liquid, yield 54.1%. IR (KBr, cm-1), 2,955–2,987 (CH3), 2,875–
1
2,926 (CH2), 1,759 (C=O), 1,644 (C=N), 1,178 (C–O–C), H NMR (400 MHz,
CDCl3, d ppm), d 1.23–1.28 (3H, t, J = 9.6 Hz, C–CH3), 1.84 (3H, s, N=C–CH3),
1.90 (3H, s, N=C–CH3), 4.15–4.22 (2H, q, J = 9.6 Hz, O=C–O–CH2), 4.63 (2H, s,
123

468
Z. Zeng et al.
O–CH2–C=O), 4.64 (2H, s, O–CH2–C=O), MS (m/z, %): 218 ((M?1)?, 57%), 56
(100%).
Ethyl 4-[[2-[[(1-methylethylidene)amino]oxy]acetyl]oxy] butanoate (3c)
A light yellow liquid, yield 60.2%. IR (KBr, cm-1), 2,961–2,983 (CH3), 2,907–
1
2,927 (CH2), 1,733 (C=O), 1,644 (C=N), 1,258 (C–O–C), H NMR (400 MHz,
CDCl3, d ppm), d 1.24–1.28 (3H, t, J = 7.2 Hz, C–CH3), 1.88 (3H, s, N=C–CH3),
1.93 (3H, s, N=C–CH3), 1.97–2.00 (2H, t, J = 7.0 Hz O–C–CH2), 2.37–2.41 (2H, t,
J = 7.2 Hz, O=C–CH2), 4.13–4.22 (4H, m), 4.56 (2H, s, O–CH2–C=O), MS (m/z,
%): 246 ((M?1)?, 13%), 115 (40%), 56 (100%).
Ethyl 2-[[2-[[(1-methylethylidene)amino]oxy]propionyl]oxy] acetate (3d)
A light yellow liquid, yield 35.2%. IR (KBr, cm-1), 2,964–2,988 (CH3), 2,879–
1
2,941 (CH2), 1,757 (C=O), 1,654 (C=N), 1,273 (C–O–C), H NMR (400 MHz,
CDCl3, d ppm), d 1.26–1.31 (3H, m, C–CH3), 1.52–1.54 (3H, d, J = 7.2 Hz,
O–C–CH3), 1.86 (3H, s, N=C–CH3), 1.93 (3H, s, N=C–CH3), 4.19–4.25 (2H, m,
O=C–O–CH2), 4.55–4.59 (1H, q, J = 5.2 Hz, O–CH–C=O), 4.74–4.79 (2H, m,
O–CH2–C=O), MS (m/z, %): 232 ((M?1)?, 55%), 56 (100%).
Ethyl 2-[[2-[[(1-methylethylidene)amino]oxy]propionyl]oxy] propionate (3e)
A light yellow liquid, yield 61.2%. IR (KBr, cm-1), 2,958–2,989 (CH3),
2,831–2,941 (CH2), 1,751 (C=O), 1,645 (C=N), 1,272 (C–O–C), 1H NMR
(400 MHz, CDCl3, d ppm), d 1.25–1.30 (3H, m, C–CH3), 1.43–1.54 (6H, m,
O–C–CH3), 1.86 (3H, s, N=C–CH3),1.92 (3H, s, N=C–CH3), 4.15–4.22 (2H, m,
O=C–O–CH2), 4.71–4.74 (1H, q, J = 4.0 Hz O–CH–C=O), 5.13–5.15 (1H, q,
J = 2.1 Hz, O=C–O–CH–C=O), MS (m/z, %): 246 ((M?1)?, 58%), 56 (100%).
Ethyl 4-[[2-[[(1-methylethylidene)amino]oxy]propionyl]oxy] butanoate (3f)
A light yellow liquid, yield 41.6%. IR (KBr, cm-1), 2,961–2,986 (CH3), 2,872–
1
2,920 (CH2), 1,745 (C=O), 1,656 (C=N), 1,181 (C–O–C), H NMR (400 MHz,
CDCl3, d ppm), d 1.24–1.28 (3H, m, C–CH3), 1.40–1.46 (3H, m, O–C–CH3), 1.86
(3H, s, N=C–CH3), 1.92 (3H, s, N=C–CH3), 1.95–2.41 (4H, m, O–C–CH2–C–O,
O=C–CH2), 4.11–4.23 (4H, m, O=C–O–CH2, O=C–O–CH2), 4.63–4.64 (1H, d,
J = 7.2 Hz, O–CH–C=O), MS (m/z, %): 260 ((M?1)?, 23%), 115 (70%), 56
(100%).
Ethyl 2-[[2-[[(1-phenylmethylidene)amino]oxy]acetyl]oxy] acetate (3g)
The reaction solvent was chloroform. A light yellow liquid, yield 40.3%. IR (KBr,
cm-1), 3,059 (Ar–H), 1,759 (C=O), 1,611 (C=N), 1,571, 1,491, 1,474 (phenyl),
1
1,230 (C–O–C), H NMR (400 MHz, CDCl3, d ppm), d 1.26–1.29 (3H, q, J =
2.8 Hz, C–CH3), 4.22–4.23 (2H, q, J = 2.8 Hz, O=C–O–CH2), 4.71 (2H, s,
123

The synthesis of novel oxime ethers and their effects
469
O–CH2–C=O), 4.84 (2H, s, O=C–O–CH–C=O), 7.36–7.59 (5H, m, ArH), 8.21 (1H,
s, Ar–CH=N), MS (m/z, %): 266 ((M?1)?, 100%), 104 (50%), 77 (5%).
Ethyl 2-[[2-[[(1-phenylmethylidene)amino]oxy]acetyl]oxy] propionate (3h)
The reaction solvent was chloroform. A light yellow liquid, yield 45.3%. IR (KBr,
cm-1), 3,059 (Ar–H), 1,751 (C=O), 1,603 (C=N), 1,584, 1,489, 1,448 (phenyl),
1,272 (C–O–C), 1H NMR (400 MHz, CDCl3, d ppm), d 1.25–1.28 (3H, m, C–CH3),
1.52–1.53 (3H, d, J = 4.0 Hz, O–C–CH3), 4.18–4.23 (2H, q, J = 6.8 Hz, O=C–O–
CH2), 4.81 (2H, s, O–CH2–C=O), 5.19–5.21 (1H, q, J = 2.4 Hz, O=C–O–CH–
C=O), 7.36–7.59 (5H, m, ArH), 8.21 (1H, s, Ar–CH=N), MS (m/z, %): 280
((M?1)?, 100%), 104 (75%), 77(27%).
Ethyl 4-[[2-[[(1-phenylmethylidene)amino]oxy]acetyl]oxy] butanoate (3i)
The reaction solvent was chloroform. A light yellow liquid, yield 42.7%. IR (KBr,
cm-1), 3,059 (Ar–H), 1,732 (C=O), 1,613 (C=N), 1,571, 1,491, 1,447 (phenyl),
1,185 (C–O–C), 1H NMR (400 MHz, CDCl3, d ppm), d 1.22–1.25 (3H, t,
J = 6.0 Hz, C–CH3), 1.98–2.02 (2H, m, C–CH2–C), 2.38–2.40 (2H, t, J = 5.6 Hz,
O=C–CH2), 4.10–4.15 (4H, m, CH2–O–C=O), 4.71 (2H, s, O=C–O–CH2–C=O),
7.36–7.37 (5H, m, ArH), 8.20 (1H, s, Ar–CH=N), MS (m/z, %): 294 ((M?1)?, 5%),
115 (20%), 104 (100%), 77 (13%).
Ethyl 2-[[2-[[(1-phenylmethylidene)amino]oxy] propionyl]oxy] acetate (3j)
The reaction solvent was chloroform. A light yellow liquid, yield 47.1%. IR (KBr,
cm-1), 3,062 (Ar–H),1,754 (C=O), 1,616 (C=N), 1,600, 1,492, 1,448 (phenyl),
1,212 (C–O–C), 1H NMR (400 MHz, CDCl3, d ppm), d 1.25–1.28 (3H, t,
J = 5.2 Hz, C–CH3), 1.60–1.62 (3H, d, J = 8.0 Hz, O–C–CH3), 4.19–4.23 (2H, q,
J = 5.2 Hz, O–CH2), 4.71–4.77 (1H, q, J = 8.0 Hz, O–CH–C=O), 4.95 (2H, s, O–
CH2–C=O), 7.26–7.57 (5H, m, ArH), 8.18 (1H, s, Ar–CH=N), MS (m/z, %): 280
((M?1)?, 25%), 104 (100%), 77 (18%).
Ethyl 4-[[2-[[(1-phenylmethylidene)amino]oxy] propionyl]oxy] butanoate (3k)
The reaction solvent was chloroform. A light yellow liquid, yield 39.1%. IR (KBr,
cm-1), 3,062 (Ar–H), 1,744 (C=O), 1,609 (C=N), 1,596, 1,495, 1,449 (phenyl), 1,272
1
(C–O–C), H NMR (400 MHz, CDCl3, d ppm), d 1.26–1.30 (3H, t, J = 8.0 Hz,
C–CH3), 1.60–1.61 (3H, d, J = 4.0 Hz, O–C–CH3), 1.82–1.83 (3H, d, J = 4.0 Hz,
O–C–CH3), 4.19–4.24 (2H, q, J = 6.6 Hz, O–CH2), 4.89–4.92 (1H, q, J = 4.0 Hz,
O–CH–C=O), 5.17–5.20 (1H, q, J = 4.0 Hz, O–CH–C=O), 7.26–7.58 (5H, m, ArH),
8.18 (1H, s, Ar–CH=N), MS (m/z, %): 294 ((M?1)?, 40%), 104 (100%), 77 (19%).
123

470
Z. Zeng et al.
Cut carnation flowers preservation test
Fresh, uniform carnation flowers (Dianthus caryophyllus L.) were harvested from
plants grown under greenhouse conditions. The cut flowers were placed with their
cut ends in test solutions. The concentrations of tested compounds were 100 mg/L.
The depth of the test solution was 6 cm. The cut carnation flowers were kept in a
growth chamber at 25 °C in diffuse light. Each treatment had three cut carnation
flowers, every treatment was duplicated five times, and the test solutions were
replaced every other day. In the whole test process, the senescence condition of cut
carnation flowers was observed and recorded. Full senescence: petals have lost
turgidity and the flowers are partially closed, advanced inrolling symptoms and
browning.
The data were analyzed by SAS 8.1.
Acknowledgments This study was supported by the University-Industry-Science Partnership sponsored
by Gongdong province government, and the Chinese Education Ministry (no. 2009B090300358).
References
1. J.Y. Qin, Plant and Plant Physiology (Chemical Industry Press, Beijing, 2006), pp. 219–220
2. A.B. Bleecker, H. Kende, Annu. Rev. Cell Dev. Biol. 16, 1 (2000)
3. H. Tan, X.H. Liu, N. Ma, J.Q. Xue, W.J. Lu, J.H. Bai, J.P. Gao, Postharvest Biol. Technol. 40, 97
(2006)
4. S.L. Saleema, P.G. Varvara, E.C. Sisler, B.R. Glick, J. Plant Growth Regul. 23, 307 (2005)
5. E. Lomaniec, Z. Aharon, N. Aharoni, L. Amnon, Postharvest Biol. Technol. 30, 67 (2003)
6. M. Callan, U.S. Patent 5834403, 11 October 1998
7. E.C. Sisler, A. Thair, R. Goren, M. Serek, A. Apelbaum, Plant Growth Regul. 40, 223 (2003)
8. S.M. Blankenship, J.M. Dole, Postharvest Biol. Technol. 28, 1 (2003)
9. C.H. Zhang, J.Y. Wu, Cells Enzyme Microb. Technol. 32, 71 (2003)
10. A. Apelbaum, E.C. Sisler, X. Feng, R. Goren, Plant Growth Regul. 55, 101 (2008)
11. E.C. Sisler, M. Serek, Physiol. Plant. 100, 577 (1997)
12. J.Y. Song, S.S. Ma, J.S. Zhang, Z.T. Chang, Plant Physiol. Commun. 40, 699 (2004)
13. M. Serek, E.C. Sisler, M.S. Reid, Acta. Hort. 394, 337 (1995)
14. P.K. Mohapatra, P.K. Naik, R. Patel, Aust. J. Plant Physiol. 27, 311 (2000)
15. M.S. Reid, M.J. Wu, Plant Growth Regul. 11, 37 (1992)
16. K. Grossmann, E. Sauerbrey, H. Fritsch, O. Schmidt, W. Rademacher, G. Schulz, H. Sauter, J. Jung,
J. Plant Growth Regul. 10, 163 (1991)
17. J.S. Zhai, W.M. Guo, K. Zhou, Q. Zheng, Acta Hort. Sin. 32, 165 (2005)
18. P.Y. Jia, C.J. Li, L. Dong, Chin. Agri. Sci. Bull. 22, 246 (2006)
19. W. Rademacher, H. Walter, E.P. Schott, D.R. Carlson, U.S. Patent 6369003, 9 April 2002
20. A. Uda, M. Yamanaka, A. Yoshino, K. Kawae, S. Tada, J. Japan. Soc. Hort. Sci. 69, 492 (2000)
21. O.-O. Naomi, M. Nakayama, K. Ichimura, J. Japan. Soc. Hort. Sci. 80, 190 (2011)
22. H.S. Anker, H.T. Clarke, Org. Synth. Coll. Vol. 3, 172 (1955)
123