Synthesis and biological activity of N-acyl O-indolylalkyl ethanolamines

Article abstract of DOI:10.1271/bbb.100804

The plant-growth regulators, indole-3-carboxylic acids, were introduced into N-acyl ethanolamines, and a series of N-acyl O-indolylalkyl ethanolamines were prepared. Their biological activities to regulate rape hypocotyl elongation, cucumber cotyledon expansion and common wheat coleoptile growth were tested. The results indicate that the title compounds inhibited rape hypocotyl elongation, especially the indole-3-propionic acid derivatives, whose bioactivity was better than that of indole-3-acetic acid.

Full text of DOI:10.1271/bbb.100804

Biosci. Biotechnol. Biochem., 75 (4), 768–770, 2011
Note
Synthesis and Biological Activity of N-Acyl O-Indolylalkyl Ethanolamines
y
2;
Shaoliang JIANG,1 Jianrong GAO,2 and Liang HAN
1College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310014, China
2State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Zhejiang University of Technology,
Hangzhou 310014, China
Received November 12, 2010; Accepted January 3, 2011; Online Publication, April 22, 2011
[doi:10.1271/bbb.100804]
The plant-growth regulators, indole-3-carboxylic
acids, were introduced into N-acyl ethanolamines, and
a series of N-acyl O-indolylalkyl ethanolamines were
prepared. Their biological activities to regulate rape
hypocotyl elongation, cucumber cotyledon expansion
and common wheat coleoptile growth were tested. The
results indicate that the title compounds inhibited rape
hypocotyl elongation, especially the indole-3-propionic
acid derivatives, whose bioactivity was better than that
of indole-3-acetic acid.
solution of chloroform and acetone instead of the 95%
ethanol used in Ref. 13. NAEs were then acylated by
indole-3-carboxylic acids at room temperature in the
presence of DCC and DMAP. After the usual workup,
the title compounds were obtained as yellow solids after
purification by column chromatography. The structures
of these compounds were confirmed by elemental
1
analyses and H-NMR.
The bioactivities of these new compounds were tested
for regulating rape hypocotyl elongation, cucumber
cotyledon expansion and common wheat coleoptile
growth. The percentage increase or decrease in each of
these assays over control samples with no regulator is
listed in Table 1, together with the data for NAE18:0
and the conventional plant growth regulator, indole-3-
acetic acid, for comparison. All compounds except b
inhibited hypocotyl elongation in rape; stronger inhib-
ition was observed for all the indole-3-propionic acid
derivatives when compared with that of the indole-3-
acetic acid derivatives, and compounds e-h with differ-
ent chain lengths even had better growth inhibiting
activity than indole-3-acetic acid. For examples, com-
pound f inhibited the hypocotyl elongation of rape
by 38.57%, while the respective inhibiting percentage
by compound b and indole-3-acetic acid were only
ꢀ12:04% and 25.68%. The fatty chain length seemed
to have an intricate effect on the bioactivity. Compound
h had comparable bioactivity to e in inhibiting the
hypocotyl elongation of rape, although there is a
difference of six methylenes in their fatty chain
structure. Unfortunately, none of the title compounds
were effective in stimulating the cotyledon expansion of
cucumber or inhibiting the coleoptile growth of common
wheat.
Key words: indole carboxylic acid; N-acylethanolamine;
N-acyl O-indolylalkyl ethanolamine; syn-
thesis; plant growth bioactivity
N-Acylethanolamines (NAEs) and N-acylphosphati-
dylethanolamines (NAPEs) are naturally occurring
amphiphilic molecules present in biological mem-
branes.1) Their content increases dramatically when the
parent organisms are subjected to such conditions of
stress as injury in animals, and dehydration in plant
seeds.2,3) A phospholipase D-type enzyme has cleaved
NAPE in vivo to generate NAE which plays a lipid
mediator role in plants and is implicated as a transducer
in plant defense signaling, and at an elevated level
interfered with normal seedling root development.4–9)
Chapman et al. have shown that the treatment and
storage of cut flowers, Christmas trees, fruits, and other
severed plant parts with NAEs could preserve the
appearance, freshness, fragrance and/or aesthetic qual-
ities of the botanical products, this further confirming
the recognition of their important role in plants.10)
Although these cited reports prompt great interest,
NAEs have low solubility in water and most common
organic solvents which has discouraged their further
study and application. We found in our previous work
that NAE derivatives displayed improved bioactivity
and solubility.11,12) In particular, the compounds synthe-
sized by acylating NAEs with aryloxyacetic acids
showed better activity than 2,4-dichlorophenyloxyacetic
acid (a traditional plant-growth regulator) in stimulating
hypocotyl elongation of rape. Encouraged by these
results, we introduced indole-3-carboxylic acids with
auxin bioactivity into NAEs and prepared a series of
N-acyl O-indolylalkyl ethanolamines (Scheme 1).
Experimental
The starting materials were all commercial chemicals and were used
without further purification. The following instruments were used for
collecting data: mp, Taike X-4 melting point apparatus; IR spectra,
Nicolet 6700 Fourier transform infrared spectrometer; 1H-NMR
spectra, Bruker AVANCE III 500 MHz spectrometer in CDCl3 at
500 MHz with ꢀ in ppm; elemental analyses, Yanaco MT-3CHN
CORDER. The reaction progress was followed with TLC plates run in
a PE-EtOAc solvent system. Spots were visualized by I2 vapor after
exposure to UV light (254 nm).
General method for preparing the title compounds. A mixture of
NAE (1 mmol), DCC (1.13 mmol) and DMAP (0.1 mmol) in CHCl3
(10 mL) was stirred at room temperature and then a solution of indolyl
carboxylic acid (1.13 mmol) in acetone (6 mL) was added drop by
drop. NAE was gradually dissolved during this addition, and the
NAEs were prepared in a 60–90% yield by refluxing
1 mol of fatty acid with 1.5 mol of ethanolamine for 6 h.
The product was purified by recrystallization from a
y
To whom correspondence should be addressed. Fax: +86-571-88320544; E-mail: hanliang814@163.com

Study of N-Acyl O-Indolylalkyl Ethanolamines
769
(s, 2H, indole-CH2CO), 4.15 (t, J ¼ 5:08 Hz, 2H, OCH2CH2NH), 5.44
(bs, 1H, CH2NH), 7.13–7.16 (m, 2H, ArH), 7.21 (t, J ¼ 7:20 Hz, 1H,
ArH), 7.30 (d, J ¼ 8:14 Hz, 1H, ArH), 7.63 (d, J ¼ 7:29 Hz, 1H, ArH),
8.49 (s, 1H, indole-NH). Anal. Calcd. for C30H48N2O3: C, 74.34; H,
9.98; N, 5.78. Found: C, 74.45; H, 9.78; N, 6.03.
CH3(CH2)nCONHCH2CH2OH
CH3(CH2)nCOOH
NH2CH2CH2OH
+
(CH2)mCOOH
DCC/DMAP
CH3(CH2)nCONHCH2CH2OH
+
N
H
N-Lauroyl O-indolylpropyl ethanolamine (e). Yield, 51.7%; mp,
93–95 ꢁC; IR ꢁmax (KBr pellet) cmꢀ1: 3394 (ꢁ N–H of indole ring),
3305 (ꢁ N–H of CONH), 2917 (ꢁas CH2), 2848 (ꢁs CH2), 1730
(ꢁ O=CO), 1636 (ꢁ O=CNH), 1535 (ꢁ aryl ring skeleton), 1455
(ꢀ CH2), 740 (ꢀ CH of benzene ring); NMR ꢀH (CDCl3): 0.88
(t, J ¼ 6:82 Hz, 3H, CH3), 1.25 (bs, 16H, CH2), 1.52 (t, J ¼ 7:27 Hz,
2H, COCH2CH2), 1.97 (t, J ¼ 7:45 Hz, 2H, COCH2), 2.76 (t, J ¼
7:35 Hz, 2H, indole-CH2CH2CO), 3.12 (t, J ¼ 7:30 Hz, 2H, indole-
CH2CH2CO), 3.35 (q, J ¼ 5:48 Hz, 2H, CH2CH2NH), 4.11 (t, J ¼
5:12 Hz, 2H, CH2CH2NH), 5.37 (bs, 1H, CH2NH), 7.00 (s, 1H, ArH),
7.13 (t, J ¼ 7:89 Hz, 1H, ArH), 7.19 (t, J ¼ 8:04 Hz, 1H, ArH), 7.36
(d, J ¼ 8:16 Hz, 1H, ArH), 7.60 (d, J ¼ 7:86 Hz, 1H, ArH), 8.25
(s, 1H, indole-NH); Anal. Calcd. for C25H38N2O3: C, 72.43; H, 9.24;
N, 6.76. Found: C, 72.74; H, 9.52; N, 6.83.
O
a.n=10,m=1
b.n=12,m=1
c.n=14,m=1
d.n=16,m=1
e.n=10,m=2
f.n=12,m=2
g.n=14,m=2
h.n=16,m=2
C
OCH2CH2NHCO(CH2)nCH3
(CH2)m
N
H
Scheme 1.
Table 1. Plant Growth Regulating Bioactivity in Vitro
Increased bioactivity (%, 10 mg/L)
Coleoptile
growth
Hypocotyl
elongation
(inhibition
of rape)
Cotyledon
expansion
Compound
(inhibition
of common
wheat)
N-Myristoyl O-indolylpropyl ethanolamine (f). Yield, 80.9%; mp,
102–104 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:81 Hz, 3H, CH3), 1.25
(bs, 20H, CH2), 1.52 (t, J ¼ 7:40 Hz, 2H, COCH2CH2), 1.97 (t, J ¼
7:44 Hz, 2H, COCH2), 2.75 (t, J ¼ 7:38 Hz, 2H, indole-CH2CH2CO),
3.12 (t, J ¼ 7:41 Hz, 2H, indole-CH2CH2CO), 3.37 (q, J ¼ 5:52 Hz,
2H, CH2CH2NH), 4.12 (t, J ¼ 5:13 Hz, 2H, CH2CH2NH), 5.33
(bs, 1H, CH2NH), 7.02 (s, 1H, ArH), 7.13 (t, J ¼ 8:01 Hz, 1H,
ArH), 7.20 (t, J ¼ 8:03 Hz, 1H, ArH), 7.37 (d, J ¼ 8:02 Hz, 1H, ArH),
7.62 (d, J ¼ 7:88 Hz, 1H, ArH), 8.13 (s, 1H, indole-NH). Anal. Calcd.
for C27H42N2O3: C, 73.26; H, 9.56; N, 6.33. Found: C, 72.98; H, 9.77;
N, 5.95.
(stimulation
of cucumber)
a
15.39
ꢀ12.04
13.98
13.40
32.32
38.57
30.42
26.37
25.68
ꢀ1.52
ꢀ6.57
ꢀ7.58
ꢀ9.85
ꢀ12.88
8.33
9.01
5.86
5.86
7.21
9.01
7.66
9.91
7.66
5.86
b
c
d
e
f
g
ꢀ4.55
12.12
8.33
h
Indole-3-acetic acid
N-Palmitoyl O-indolylpropyl ethanolamine (g). Yield, 57.3%; mp,
108–109 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:76 Hz, 3H, CH3), 1.25
(bs, 24H, CH2), 1.52 (t, J ¼ 7:28 Hz, 2H, COCH2CH2), 1.97 (t, J ¼
7:47 Hz, 2H, COCH2), 2.76 (t, J ¼ 7:36 Hz, 2H, indole-CH2CH2CO),
3.12 (t, J ¼ 7:34 Hz, 2H, indole-CH2CH2CO), 3.36 (q, J ¼ 5:51 Hz,
2H, CH2CH2NH), 4.12 (t, J ¼ 5:12 Hz, 2H, CH2CH2NH), 5.34 (bs,
1H, CH2NH), 7.02 (s, 1H, ArH), 7.13 (t, J ¼ 7:38 Hz, 1H, ArH), 7.20
(t, J ¼ 7:89 Hz, 1H, ArH), 7.36 (d, J ¼ 8:06 Hz, 1H, ArH), 7.60
(d, J ¼ 7:87 Hz, 1H, ArH), 8.17 (s, 1H, indole-NH). Anal. Calcd. for
solution first turned clear and then a white precipitate was formed.
After stirring for 12 h, the precipitate was filtered, and the solution was
washed with saturated NaHCO3 and water, and then dried with
MgSO4. The solvent was removed, and column chromatography of the
residue with PE/EtOAc (4:1, v/v) gave a yellow solid as the product.
N-Lauroyl O-indolylethyl ethanolamine (a). Yield, 69.5%; mp,
90–91 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:85 Hz, 3H, CH3), 1.25 (bs,
16H, CH2), 1.45 (t, J ¼ 7:11 Hz, 2H, COCH2CH2), 1.86 (t, J ¼
7:47 Hz, 2H, COCH2), 3.43 (q, J ¼ 5:56 Hz, 2H, NHCH2CH2O), 3.79
(s, 2H, indole-CH2CO), 4.15 (t, J ¼ 5:08 Hz, 2H, OCH2CH2NH), 5.45
(bs, 1H, CH2NH), 7.13–7.16 (m, 2H, ArH), 7.21 (t, J ¼ 7:10 Hz, 1H,
ArH), 7.37 (d, J ¼ 8:08 Hz, 1H, ArH), 7.62 (d, J ¼ 7:86 Hz, 1H, ArH),
8.51 (s, 1H, indole-NH). Anal. Calcd. for C24H36N2O3: C, 71.96; H,
9.06; N, 6.99. Found: C, 72.23; H, 8.79; N, 6.80.
C
29H46N2O3: C, 74.00; H, 9.85; N, 5.95. Found: C, 73.87; H, 9.47;
N, 6.03.
N-Stearoyl O-indolylpropyl ethanolamine (h). Yield, 52.5%; mp,
109–110 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:72 Hz, 3H, CH3), 1.25
(bs, 28H, CH2), 1.52 (t, J ¼ 7:32 Hz, 2H, COCH2CH2), 1.97 (t, J ¼
7:45 Hz, 2H, COCH2), 2.76 (t, J ¼ 7:37 Hz, 2H, indole-CH2CH2CO),
3.12 (t, J ¼ 7:38 Hz, 2H, indole-CH2CH2CO), 3.36 (q, J ¼ 5:49 Hz,
2H, CH2CH2NH), 4.12 (t, J ¼ 5:12 Hz, 2H, CH2CH2NH), 5.33 (bs,
1H, CH2NH), 7.02 (s, 1H, ArH), 7.13 (t, J ¼ 7:74 Hz, 1H, ArH), 7.20
(t, J ¼ 7:18 Hz, 1H, ArH), 7.37 (d, J ¼ 8:02 Hz, 1H, ArH), 7.62
(d, J ¼ 7:87 Hz, 1H, ArH), 8.13 (s, 1H, indole-NH). Anal. Calcd. for
C31H50N2O3: C, 74.65; H, 10.10; N, 5.62. Found: C, 74.26; H, 9.84;
N, 5.83.
N-Myristoyl O-indolylethyl ethanolamine (b). Yield, 64.6%; mp
97–99 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:81 Hz, 3H, CH3), 1.26
(bs, 20H, CH2), 1.45 (t, J ¼ 7:12 Hz, 2H, COCH2CH2), 1.86 (t, J ¼
7:44 Hz, 2H, COCH2), 3.43 (q, J ¼ 5:58 Hz, 2H, NHCH2CH2O), 3.79
(s, 2H, indole-CH2CO), 4.15 (t, J ¼ 5:07 Hz, 2H, OCH2CH2NH), 5.44
(bs, 1H, CH2NH), 7.13–7.16 (m, 2H, ArH), 7.21 (t, J ¼ 7:02 Hz, 1H,
ArH), 7.37 (d, J ¼ 8:15 Hz, 1H, ArH), 7.64 (d, J ¼ 7:92 Hz, 1H, ArH),
8.49 (s, 1H, indole-NH). Anal. Calcd. for C26H40N2O3: C, 72.86; H,
9.41; N, 6.54. Found: C, 72.52; H, 9.04; N, 6.33.
Hypocotyl elongation inhibition of rape. Each of the tested
compounds was dissolved in DMF to give a 10-mg/L solution and
then dropped evenly on to a 6-cm-diameter filter paper in a culture
dish. Twenty seeds were added and cultured at 28 ꢁC in an RTOP-
310D artificial climate box. The length of the hypocotyls was measured
after 5 d and compared with those treated with distilled water to
evaluate the activity. Two replicates were included in the evaluation.
Cotyledon expansion stimulation of cucumber. After soaking, the
seeds were germinated in covered enamelware containing 0.7% agar
and cultured for 3 d in dark at 26 ꢁC. Cotyledons of similar size were
chosen for testing. Each tested compound was dissolved in DMF to
give a 10-mg/L solution and then dropped evenly on to a 6-cm-
diameter filter paper in a culture dish. Ten pieces of cotyledon were
added and cultured at 28 ꢁC in the RTOP-310D artificial climate box.
The total weight of the cotyledons was measured after 3 d and
compared with that of the samples treated only with distilled water to
evaluate the activity. Two replicates were included in the evaluation.
Coleoptile growth inhibition of common wheat. The seeds after
soaking were germinated in covered enamelware containing 0.7% agar
and cultured for 3 d in the dark at 25 ꢁC. After the seedlings had grown
to 2.5–3.0 cm tall, the first 3 mm of each coleoptile top was rejected.
N-Palmitoyl O-indolylethyl ethanolamine (c). Yield, 65.7%; mp,
102–103 ꢁC; IR ꢁmax (KBr pellet) cmꢀ1: 3353 (ꢁ N–H of indole ring),
3308 (ꢁ N–H of CONH), 2915 (ꢁas CH2), 2847 (ꢁs CH2), 1737
(ꢁ O=CO), 1625 (ꢁ O=CNH), 1546 (ꢁ aryl ring skeleton), 1466
(ꢀ CH2), 736 (ꢀ CH of benzene ring); NMR ꢀH (CDCl3): 0.88
(t, J ¼ 6:80 Hz, 3H, CH3), 1.26 (bs, 24H, CH2), 1.45 (t, J ¼ 7:09 Hz,
2H, COCH2CH2), 1.86 (t, J ¼ 7:46 Hz, 2H, COCH2), 3.43 (q, J ¼
5:55 Hz, 2H, NHCH2CH2O), 3.80 (s, 2H, Indole-CH2CO), 4.16
(t, J ¼ 5:11, 2H, OCH2CH2NH), 5.40 (bs, 1H, CH2NH), 7.14–7.17
(m, 2H, ArH), 7.21 (t, J ¼ 8:17 Hz, 1H, ArH), 7.38 (d, J ¼ 8:17 Hz,
1H, ArH), 7.63 (d, J ¼ 7:31 Hz, 1H, ArH), 8.37 (s, 1H, indole-NH).
Anal. Calcd. for C28H44N2O3: C, 73.64; H, 9.71; N, 6.13. Found:
C, 73.86; H, 9.84; N, 6.32.
N-Stearoyl O-indolylethyl ethanolamine (d). Yield, 71.6%; mp,
106–107 ꢁC; NMR ꢀH (CDCl3): 0.88 (t, J ¼ 6:83 Hz, 3H, CH3), 1.26
(bs, 28H, CH2), 1.45 (t, J ¼ 7:11 Hz, 2H, COCH2CH2), 1.86 (t, J ¼
7:45 Hz, 2H, COCH2), 3.35 (q, J ¼ 5:50 Hz, 2H, NHCH2CH2O), 3.79

770
S. JIANG et al.
The coleoptile (5 mm) was truncated and dunked in distilled water for
2–3 h to remove the endogenous hormones, before being chopped into
10 segments. A 2-mL sample of each test solution (10 mg/L in DMF)
was put into a 10-mL tube, and ten coleoptile segments were then
added. Each tube was plugged and cultured for 20 h at 25 ꢁC in dark on
a rotating bed. The length of a coleoptile segment was measured and
compared with that not treated with a test compound to evaluate the
activity. Two replicates were included in the evaluation.
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This study was supported by Natural Science Foun-
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