A novel palladium-catalyzed cyclization of indole phytoalexin brassinin and its 1-substituted derivatives

Article abstract of DOI:10.1039/c3ra46843g

A novel simple synthetic approach to spiroindoline phytoalexins and their derivatives has been developed. The spirocyclization of brassinin and its 1-substituted derivatives was achieved using palladium catalyst PdCl ₂(CH₃CN)₂ in DMSO at 80°C in the presence of water, methanol or aniline.

Full text of DOI:10.1039/c3ra46843g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
A novel palladium-catalyzed cyclization of indole
phytoalexin brassinin and its 1-substituted
derivatives†
Cite this: RSC Adv., 2014, 4, 5575
Mariana Budovska*
´
Received 19th November 2013
Accepted 13th December 2013
A novel simple synthetic approach to spiroindoline phytoalexins and their derivatives has been developed.
DOI: 10.1039/c3ra46843g
The spirocyclization of brassinin and its 1-substituted derivatives was achieved using palladium catalyst
ꢀ
www.rsc.org/advances
PdCl
2
(CH
3
CN)
2
in DMSO at 80 C in the presence of water, methanol or aniline.
2
002, spirocyclization methodology toward spiroindoline
Introduction
phytoalexins was developed. Reaction of 1-methoxybrassinin (2)
In response to pathogen invasion and other types of stress with dioxane dibromide (DDB) in dioxane in the presence of
physical, biological or chemical), plants produce de novo an water afforded a mixture of diastereoisomers of 1-methox-
(
1,2
arsenal of chemical defenses called phytoalexins. Indole yspirobrassinol (5) in 90% yield. The synthesis of a mixture of
phytoalexins are biosynthesized by economically important natural trans-[(ꢁ)-6a] and unnatural cis-[(ꢁ)-6b] diastereoisomer
plants of the family Cruciferae syn. Brassicaceae (e.g., cabbage, of 1-methoxyspirobrassinol methyl ether is based on a DDB-
turnip, Chinese cabbage, Japanese radish, wasabi, broccoli, mediated cyclization of 1-methoxybrassinin (2) in the presence
11
rapeseed and arabidopsis). More than 40 indole phytoalexins of methanol as a nucleophile. Syntheses of analogs of indole
have been isolated to date. Selected examples are shown in phytoalexin 1-methoxyspirobrassinol methyl ether with NR
Fig. 1. Characteristic structural feature of cruciferous phyto- group instead of SCH were accomplished by bromine-medi-
1 2
R
3
12
alexins is indole, 1-methoxyindole, oxindole or indoline moiety ated spirocyclization of 1-Boc-thioureas. Racemic 1-methox-
with a linear side chain, 2,3-fused or 3-spiro attached hetero- yspirobrassinin [(ꢁ)-4] was prepared by oxidation of (ꢁ)-5 using
2
,3
11
cycle. In addition to their antimicrobial (antifungal and CrO
3
(40%) or (ꢁ)-6 with pyridinium chlorochromate in 37%
3
13
antibacterial) activities, indole phytoalexins have been previ- yield. Racemic spirobrassinin [(ꢁ)-3] was obtained by thionyl
ously reported to exert cytotoxic effects against human leukemia chloride or methanesulfonyl chloride mediated cyclization of
and solid tumour cell lines in vitro and are also interesting dioxibrassinin.
4,5
14,15
The one-pot biomimetic syntheses of spiro-
lead compounds for anticancer drug development. The phyto- brassinin [(ꢁ)-3] and 1-methoxyspirobrassinin [(ꢁ)-4] were
alexins brassinin (1), spirobrassinin (3) and cyclobrassinin (9) achieved by oxidative cyclization of brassinin (1) and
exhibited cancer chemopreventive activity in models of 1-methoxybrassinin
mammary and skin carcinogenesis. Several indole phyto- chlorochromate.
alexins have been shown to be potentiate vincristine-induced
Catalytic cyclization approaches using palladium catalysts
(2)
with
CrO
or
pyridinium
3
6,7
16
growth inhibition of U-87 MG human glioblastoma-derived for formation C–S bond are extremely rare in the literature. Only
8
cells. Brassinin (1) is also moderately active competetive a few reports describe the generation of C–S bond in which Pd
1
7–20
inhibitor of indolamine 2,3-dioxygenase (IDO, EC 1.13.11.42), catalysts have been employed.
9
an enzyme that drives immune escape in cancer. Cruciferous
As a continuation of our work in the indole chemistry, our
present aim was to devise new route for the synthesis of spi-
10
phytoalexins demonstrated antitrypanosomal properties.
Stressed plants produced indole phytoalexins in small roindoline derivatives. We decided to study the palladium-
quantities and their isolation from plant tissues is unpractical. mediated intramolecular cyclization of brasssinin and its
Chemical synthesis is a valuable tool to obtaining reasonable derivatives. We investigated the scope and limitation of the
amounts of indole phytoalexins. A some methods to synthesis reaction by employing of brasssinin derivatives in the presence
of indole phytoalexins and their analogs have been reported. In of water, methanol and aniline.
Results and discussion
Department of Organic Chemistry, Institute of Chemical Sciences, Faculty of Science,
P. J. Sˇ af a´ rik University, Moyzesova 11, 040 01, Ko ˇs ice, Slovak Republic. E-mail:
The key intermediate of our new synthetic approach,
mariana.budovska@upjs.sk; Tel: +421 552341196
1
-methoxybrassinin (2) was obtained by reaction of amine 10,
†
Electronic supporting information (ESI) available: Copies of 1H and 13C NMR
21
spectra for all new compounds. See DOI: 10.1039/c3ra46843g
2 3
CS and CH I in methanol according to published procedures.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5575–5582 | 5575

View Article Online
RSC Advances
Paper
Fig. 1 Structures of selected indole phytoalexins.
of palladium was not optimized. For conversion was required
DMSO. The use of other solvents (CH Cl , CH CN, MeOH,
2 2 3
dioxane, DMF, toluene) resulted in no reaction. Only starting
compound was in the reaction mixture aer 24 hours.
ꢀ
Decreasing the reaction temperature to 50 C led to extension of
reaction time from 1 h to 6 h (Table 1, entry 5). At the room
temperature no reaction took place (Table 1, entry 4). From
subsequent examinations of various palladium sources,
Scheme 1 Synthesis of brassinin (1) and analogs 2, 14–17.
PdCl
1, 14), producing mixtures of diastereoisomers (ꢁ)-5a-(ꢁ)-5b,
ꢁ)-6a-(ꢁ)-6b, (ꢁ)-19a-(ꢁ)-19b and (ꢁ)-20a-(ꢁ)-20b in good
All the others key intermediates, brassinin (1), 1-Boc-brassinin yields (53%, 60%, 53% and 54%). The cyclization of 2 using
14) and 1-Me-brassinin (15), were prepared by the modied Pd(OAc) in the presence water or methanol afforded products 5
procedure used previously for 1-methoxybrassinin (2). The or 6 in low yields (Table 1, entry 2, 8). None of desired products
thiourea 16 was synthesized by reaction of amine 10 with phenyl 19 and 20 was obtained with palladium catalyst Pd(OAc) and
isothiocyanate in methanol in the presence of triethylamine. PdCl (Ph P) (Table 1, entry 12, 13, 16). No stereoselectivity was
2 3 2
(CH CN) proved to be the best catalyst (Table 1, entry 1, 6,
1
(
(
2
2
2
3
2
The thiourea 17 was obtained by the previously reported reac- observed in the reactions of substrates 2 and 14. The spirocyclic
tion of amine 11 with phenyl isothiocyanate in dioxane/chlo- products (ꢁ)-6a-(ꢁ)-6b, (ꢁ)-19a-(ꢁ)-19b and (ꢁ)-20a-(ꢁ)-20b
12
roform (Scheme 1).
were obtained as a mixture of trans and cis-diastereoisomers in
The initial palladium-catalyzed reactions were performed the ratio 1 : 1. Diastereoisomers of 1-methoxyspirobrassinol
using 2 and 14 as substrates (Scheme 2). Substrates 2 and 14 trans-(ꢁ)-5a and cis-(ꢁ)-5b were isolated as a mixture of dia-
were subjected to the conditions of the cyclization using stereoisomers in the ratio 1 : 4 that easily isomerize owing to
ꢀ
24
PdCl
water or methanol. Application of these conditions resulted in this palladium-catalyzed cyclization is efficient without reox-
2 3 2
(CH CN)
(10 mol%), DMSO at 80 C in the presence of their hemiaminal structure. Our experiments revealed that
the formation of a diastereomeric mixture of spiroindoline idant. Cyclization of 2 with 10 mol% of PdCl
2
(CH
3
CN)
2
and
ꢀ
products 5, 6, 19 and 20. As the proposed mechanism is based 33 mol% of CuCl in DMSO at 80 C resulted in the formation
in a palladacycle, studies show that high concentrations of mixture of (ꢁ)-6a-(ꢁ)-6b in 63% (Table 1, entry 7), while the
22
catalyst (palladacycle) are harmful to the reaction yield. In reaction with the sole Pd catalyst delivered mixture of (ꢁ)-6a-
another study of phytoalexin cyclization with Pd(OAc)
the Pd concentration was 6–10 mol%. Therefore, the amount 10 mol% of PdCl (CH CN) and 33 mol% of CuCl in DMSO at
2
/BINAP, (ꢁ)-6b in a 60% yield (Table 1, entry 6). Reaction of 14 with
23
2
3
2
Scheme 2 Cyclization reactions of 1-methoxybrassinin (2) and 1-Boc-brassinin (14) using palladium catalysts.
5576 | RSC Adv., 2014, 4, 5575–5582
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
a
Table 1 Reaction conditions, yields and ratios of trans- and cis-diastereoisomers produced via Scheme 2
ꢀ
Entry
Conditions
Temp. ( C)
R
1
R
2
Reaction time
Yield (%)
Ratio trans : cis
1
2
3
4
5
6
7
8
9
PdCl
Pd(OAc)
2
(CH
, H
(Ph P)
3
CN)
2
, H
2
O
80
80
80
rt
OCH
3
OH
OH
OH
1 h
5 h
3 h
24 h
6 h
1 h
1 h
4 h
1 h
53
12
43
22 : 78
20 : 80
25 : 75
—
55 : 45
55 : 45
56 : 44
50 : 50
52 : 48
49 : 51
57 : 43
—
—
54 : 46
—
—
54 : 46
2
2
O
PdCl
PdCl
PdCl
PdCl
PdCl
2
2
2
2
2
3
2
, H
2
O
(CH
(CH
(CH
(CH
3
3
3
3
CN)
CN)
CN)
CN)
2
2
2
2
, MeOH
, MeOH
, MeOH
OCH
OCH
OCH
OCH
OCH
OCH
NHPh
OH
OH
3
3
3
3
3
3
Starting compound
60
60
63
28
43
54
53
Trace
—
54
—
Trace
36
50
80
80
80
80
80
80
80
80
80
80
80
80
b
, CuCl , MeOH
Pd(OAc)
2
, MeOH
PdCl
PdCl
PdCl
2
2
2
(Ph P) , MeOH
3
2
c
2
10
11
12
13
14
15
16
17
(CH
(CH
3
CN)
CN)
2
, PhNH
, H
2 h
1.5 h
4 h
3
2
2
O
Boc
Pd(OAc)
2
, H
2
O
, H
PdCl
PdCl
PdCl
2
2
2
(Ph P)
3
2
2
O
OH
4 h
(CH
(CH
3
CN)
CN)
2
, MeOH
, CuCl , MeOH
OCH
OCH
OCH
OCH
3
3
3
3
3.5 h
0.5 h
3 h
b
3
2
Pd(OAc)
2
, MeOH
P) , MeOH
PdCl (Ph
2
3
2
3.5 h
a
b
c
Reaction conditions: 2 or 14 (0.15 mmol), Pd catalyst (10 mol%), DMSO (2.7 mL), H
2
O or MeOH (0.3 mL), 0.5–24 h. 33 mol% was used. 1.1 equiv.
was used. Yield of isolated product.
2 3 2
Scheme 3 Cyclization reactions of thioureas 16 and 17 catalyzed by PdCl (CH CN) .
ꢀ
8
0 C led to the formation of unidentied product. Performing
In order to check the efficiency and limitation of this new
the cyclization reaction of 1-methoxybrassinin (2) in the pres- method, we explored PdCl (CH CN) -catalyzed cyclization of
2
3
2
ence of aniline led to the formation of a mixture of diastereo- thioureas 16 and 17. The reaction conditions [PdCl (CH CN) –
2
3
2
ꢀ
isomers
of
the
2-aminoderivate
of
phytoalexins 10 mol%, DMSO, 80 C] developed above were also successfully
1
-methoxyspirobrassinol methyl ether (ꢁ)-18a-(ꢁ)-18b in a good applied to the cyclization of thioureas 16 and 17 (Scheme 3). As
0
a results, were obtained 2 -aminoanalogs of indole phytoalexins
yield (Table 1, entry 10).
1
-methoxyspirobrassinol (ꢁ)-21 and (ꢁ)-23 and 1-methoxyspir-
obrassinol methyl ether (ꢁ)-22 and (ꢁ)-24. Yields and ratios of
prepared diastereoisomers are reported in the Table 2. trans and
cis-Diastereoisomers (ꢁ)-21a-(ꢁ)-21b, (ꢁ)-22a-(ꢁ)-22b and
(ꢁ)-24a-(ꢁ)-24b arised in the ratio 1 : 1. Diastereoisomers
Table 2 Yields and ratios of trans- and cis-diastereoisomers (ꢁ)-21a-
a
(ꢁ)-24b produced via Scheme 3
Reaction
time
Ratio
Yield (%) trans : cis
Entry Conditions
R
1
R
2
1
2
3
4
PdCl
H O
2
2
(CH
3
3
3
3
CN)
CN)
CN)
CN)
2
,
2
,
2
,
2
,
OCH
3
OH
4 h
47
59
52
56
44 : 56
54 : 46
68 : 32
53 : 47
PdCl
2
(CH
OCH
3
3
2 h
MeOH
PdCl
2
(CH
Boc
OH
4 h
2
H O
PdCl
2
(CH
OCH
1.5 h
MeOH
a
Reaction conditions: 16 or 17 (0.15 mmol), PdCl
2
(CH
3
CN)
2
(10 mol%),
ꢀ
DMSO (2.7 mL), H
isolated product.
2
O or MeOH (0.3 mL), 80 C, 1.5–4 h. Yield of Scheme 4 Cyclization reactions of brassinin (1) and 1-methyl-bras-
sinin (15) using palladium catalysts.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5575–5582 | 5577

View Article Online
RSC Advances
Paper
Table 3 Reaction conditions and yields of spirobrassinin (3) and 1-Me- inuenced and the enantiomers of spirobrassinin [(+)-3], [(ꢂ)-3]
a
spirobrasinin (25) produced via Scheme 4
were obtained in a ratio 50 : 50.
We suppose that this palladium-catalyzed cyclization of
brassinin (1) and its derivatives proceeds via intermediates 26
Reaction
time
Entry
Conditions
R
Yield (%)
or 27. Subsequent formation of six-member palladacycle
22,25,26
1
2
3
4
5
6
7
8
9
PdCl
PdCl
PdCl
2
2
2
(CH
3
CN)
P)
CN) , MeOH
2
2
, H
2
O
H
1 h
2 h
1 h
4 h
1 h
1 h
2 h
1 h
3 h
1 h
13
—
34
8
18
17
—
40
8
28,
followed by reductive elimination provides products
(Ph
3
2
, H O
2
(ꢁ)-5, (ꢁ)-6 or (ꢁ)-3 (Scheme 5).
(CH
3
Pd(OAc)
2
, MeOH
(Ph P) , MeOH
(CH CN) , H
, H
PdCl
PdCl
PdCl
PdCl
2
2
2
2
3
2
3
2
2
O
CH
3
Conclusion
(Ph
(CH
3
P)
2
2
O
3
2
CN) , MeOH
In summary, we have developed a novel synthetic method of
spiroindoline derivatives through the unusual palladium-cata-
lyzed cyclization of brassinin and its derivatives. The spirocyc-
lization of brassinin and its derivatives proceeds using
Pd(OAc)
2
, MeOH
P) , MeOH
1
0
PdCl (Ph
2
3
2
18
a
Reaction conditions: 1 or 15 (0.15 mmol), Pd catalyst (10 mol%), DMSO
ꢀ
(2.7 mL), H
2
O or MeOH (0.3 mL), 80 C, 1–4 h. Yield of isolated product.
PdCl
2
(CH
3
CN)
2
as catalyst, DMSO as a solvent and temperature
ꢀ
80 C in the presence of water, methanol or aniline. The reac-
(
ꢁ)-23a and (ꢁ)-23b were isolated as a mixture of diastereoiso- tions were performed using 10 mol% of PdCl
2 3 2
(CH CN) and the
mers in the ratio 68 : 32 owing to its unstable hemiaminal amount of Pd catalyst was not optimized.
structure analogues to 1-methoxyspirobrassinol (5).
To test the cyclization process under palladium catalysis,
brassinin (1) and 1-methylbrassinin (15) were also used
Experimental
(
Scheme 4). In the cases of substrates 1 and 15, oxindoles (ꢁ)-3
and (ꢁ)-25 were obtained in low to moderate yields. The rs Melting points were determined on a Koffler micro melting
attempt to cyclize brassinin (1) and 1-methylbrassinin (15) point apparatus and are uncorrect. IR spectra were recorded on
1
13
under conditions PdCl
2
(CH
3
CN)
2
(10 mol%), water, DMSO at 80 an IR-75 spectrometer (Zess Jena). H NMR (400 MHz) and
C
ꢀ
C afforded spirobrassinin [(ꢁ)-3] and 1-methylspirobrassinin NMR (100 MHz) spectra were measured on a Varian Mercury
[
(ꢁ)-25] in a low isolated yields (13%, 17%, Table 3, entry 1 or 6). Plus spectrometer. Chemical shis (d) are reported in ppm
When MeOH was used instead of water, 34% or 40% conversion downeld from TMS as internal standard and coupling
was observed aer one hour (Table 3, entry 3 and 8). Adducts constants (J) are given in hertz. Microanalyses were performed
(
ꢁ)-3 and (ꢁ)-25 were not observed using of a palladium catalyst with a Perkin-Elmer, Model 2400 analyzer. HRMS were recorded
PdCl (Ph P) in the presence of water (Table 3, entry 2 and 7). on a JEOL JMS-FAB spectrometer at ionization energy of 70 eV.
Cyclization of 1 and 15 using PdCl (Ph P) as a catalyst in the The EI mass spectra were recorded on a GS-MS Trio 1000 (Fisons
presence of methanol afforded products (ꢁ)-3 and (ꢁ)-25 in an Instruments) spectrometer at ionization energy of 70 eV,
8% yield (Table 3, entry 5 and 10). Reactions of 1 and 15 with whereas MALDI-TOF mass spectra were measured on a MALDI
catalyst Pd(OAc) in the presence of methanol resulted in the IV (Kratos Analytical). The samples were ionized with a N -laser
2
3
2
2
3
2
1
2
2
formation products (ꢁ)-3 and (ꢁ)-25 in only an 8% yields (Table (l ¼ 337 nm). The progress of chemical reactions was moni-
, entry 4 and 9).
tored by thin layer chromatography, using Macherey-Nagel
We have also studied the effect of the ligand (R)-BINAP on plates Alugram® Sil G/UV254. Preparative column chromatog-
the stereoselectivity of PdCl (CH CN) -mediated cyclization of raphy was performed on Kieselgel 60 Merck Type 9385
brassinin (1). The enantioselectivity of the reaction was not (0.040-0.063).
3
2
3
2
Scheme 5 A plausible reaction mechanism.
5578 | RSC Adv., 2014, 4, 5575–5582
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
29
1.1 Synthesis of starting brassinins 1, 14, 15 and thiourea 16
presence of TiCl
3
(5.5 mL, 16 mmol) was dissolved in methanol
(10 mL). Triethylamine (1.39 mL, 1.01 g, 10 mmol) and phenyl
1.1.1 1-(tert-butoxycarbonyl)brassinin (14). Crude product
isothiocyanate (0.24 mL, 0.27 g, 2 mmol) were added and mixture
was stirred for 25 min at room temperature. The residue
obtained aer evaporation of the solvent was dissolved in
dichloromethane, small amount of silica gel was added,
dichloromethane evaporated and product preabsorbed on silica
gel was chromatographed on silica gel (15 g, n-hexane/ethyl
acetate 3 : 1). The obtained compound was further crystallized
from dichloromethane/n-hexane to afford pure product 16.
of 1-[(tert-butoxycarbonyl)indol-3-yl]methylamine (11) freshly
prepared by the reduction of 1-(tert-butoxycarbonyl)indole-3-
carboxaldehyde oxime (0.780 g, 3 mmol) with NaBH
0 mmol) in the presence NiCl $6H O (0.710 g, 3 mmol) was
dissolved in methanol (24 mL). Triethylamine (1.25 mL, 0.91 g,
mmol) and carbon disulde (0.54 mL, 0.69 g, 9 mmol) were
4
(1.11 g,
3
2
7
2
2
9
added and mixture was stirred for 5 min at room temperature.
Then iodomethane (0.56 mL, 1.28 g, 9 mmol) was added and the
stirring was continued for 15 min. The residue obtained aer
evaporation of the solvent was dissolved in dichloromethane,
small amount of silica gel was added, dichloromethane evapo-
rated and product preabsorbed on silica gel was chromato-
graphed on silica gel (30 g, n-hexane/acetone 5 : 1). The
obtained compound was further crystallized from dichloro-
methane/n-hexane to afford pure product 14. Yield: 0.69 g, 68%.
Spectral data of the obtained 1-(tert-butoxycarbonyl)brassinin
ꢀ
Yield: 0.49 g, 79%, white crystals; mp 103–104 C (dichloro-
methane/n-hexane); R ¼ 0.26 (n-hexane/ethyl acetate 3 : 1). n
f
max
ꢂ1
(CHCl
3
)/cm : 3387, 2973, 1487, 1440, 1287, 1213, 1187, 1100,
0
1
020, 953. d
H
(400 MHz, CDCl
3
): 8.07 (bs, 1H, NH ), 7.62 (ddd, J
¼
0.8 Hz, 0.9 Hz, 8.0 Hz, 1H, H-4), 7.41 (ddd, J ¼ 0.8 Hz, 0.8 Hz,
0
0
8
.2 Hz, 1H, H-7), 7.32 (dd, J ¼ 7.8 Hz, 7.8 Hz, 2H, H-3 , H-5 ), 7.26
(
(
s, 1H, H-2), 7.26 (ddd, J ¼ 0.9 Hz, 7.2 Hz, 8.0 Hz, 1H, H-6), 7.20
0
0
dd, J ¼ 7.7 Hz, 7.7 Hz, 1H, H-4 ), 7.14 (d, J ¼ 7.7 Hz, 2H, H-2 , H-
0
2
7
6 ), 7.13 (ddd, J ¼ 1.0 Hz, 7.1 Hz, 8.0 Hz, 1H, H-5), 6.18 (bs, 1H,
NH), 4.98 (d, J ¼ 4.9 Hz, 2H, CH ), 4.05 (s, 3H, OCH ). d
(
14) were identical with those described previously.
.1.2 Brassinin (1). Crude product of indol-3-yl-methyl-
amine (12) freshly prepared by the reduction of indole-3-car-
boxaldehyde oxime (1.0 g, 6.24 mmol) with NaBH (2.36 g,
2,4 mmol) in the presence NiCl $6H O (1.48 g, 6.24 mmol) was
dissolved in methanol (55 mL). Triethylamine (0.87 mL, 0.63 g,
.24 mmol) and carbon disulde (2.63 mL, 3.32 g, 43,7 mmol)
2
3
C
1
0
(
100 MHz, CDCl ): 180.3 ((C]S)), 136.3 (C-1 ), 132.6 (C-7a),
3
0
0
0
0
0
1
1
30.4 (C-3 , C-5 ), 127.4 (C-4 ), 125.2 (C-2 , C-6 ), 123.1 (C-2),
22.5 (C-6), 120.5 (C-5), 119.3 (C-4), 108.7 (C-7), 107.4 (C-3a),
4
6
2
7
2
2
3 2
66.2 (OCH ), 41.5 (CH ). MALDI-TOF MS, m/z (% relative int.):
+
+
3
1
5
34.7 [M + Na] (29), 312.7 [M + H] (14), 305.0 (16), 280.9 (21),
6
61.6 (100). Anal. Calc. for C H N OS requires: C, 65.57; H,
.50; N, 13.49. Found: C, 65.79; H, 5.40; N, 13.71.
1
7
17 3
were added and mixture was stirred for 5 min at room
temperature. Then iodomethane (1.95 mL, 4.41 g, 31.2 mmol)
was added and the stirring was continued for 15 min. The
residue obtained aer evaporation of the solvent was dissolved
in dichloromethane, small amount of silica gel was added,
dichloromethane evaporated and product preabsorbed on silica
gel was chromatographed on silica gel (25 g, n-hexane/
dichloromethane 2 : 5). The obtained compound was further
crystallized from dichloromethane/n-hexane to afford pure
product 1. Yield: 1.19 g, 81%. Spectral data of the obtained
1.2 Typical procedure for Pd-catalyzed cyclization of
brassinin and 1-substituted derivatives
brassinin derivatives 1, 2, 14–17 (0.15 mmol) and
PdCl (CH CN) (0.0045 g, 0.015 mmol) in DMSO (2.7 mL) and
A
2
3
2
methanol, water (0.3 mL) or aniline (0.015 mL, 0.015 g,
ꢀ
0
.165 mmol) were heated at 80 C for 1.5–4 h. The reaction
28
mixture was cooled to room temperature and brine (10 mL) was
brassinin (1) were identical with those described previously.
.1.3 1-Methylbrassinin (15). Crude product of (1-methyl-
added. The aqueous phase was extracted with ethyl acetate (2 ꢃ
1
5
mL) and the combined organic layer was dried over Na SO .
2 4
indol-3-yl)methylamine (13) freshly prepared by the reduction
of 1-methylindole-3-carboxaldehyde oxime (0.87 g, 5 mmol)
with NaBH4 (1.82 g, 50 mmol) in the presence NiCl $6H O
The solvent was evaporated and the residue was puried by
silica gel column chromatography. The glassware was washed
with aqua regia (to remove residual Pd). Each reaction was
performed 3 times.
2
2
27
(
1.30 g, 5.5 mmol) was dissolved in methanol (50 mL). Tri-
ethylamine (0.70 mL, 0.50 g, 5 mmol) and carbon disulde
0.60 mL, 0.76 g, 10 mmol) were added and mixture was stirred
for 5 min at room temperature. Then iodomethane (0.37 mL,
1
.2.1 trans and cis-(ꢁ)-1-methoxyspirobrassinol [(ꢁ)-5a
(
and (ꢁ)-5b]. Following the general procedure, products (ꢁ)-5a
and (ꢁ)-5b were obtained using 0.040 g (0.15 mmol) of
0
1
.85 g, 6 mmol) was added and the stirring was continued for
5 min. The residue obtained aer evaporation of the solvent
1
-methoxybrassinin (2) and water (0.3 mL). Reaction mixture was
stirred for 1 h. The residue obtained aer evaporation of the
solvent was subjected to ash chromatography on 5 g silica gel
was dissolved in dichloromethane, small amount of silica gel
was added, dichloromethane evaporated and product pre-
absorbed on silica gel was chromatographed on silica gel (40 g,
n-hexane/ethyl acetate 2 : 1). Yield: 0.91 g, 73%. Spectral data of
the obtained 1-methylbrassinin (15) were identical with those
(
n-hexane/ethyl acetate 2 : 1), affording (ꢁ)-5a and (ꢁ)-5b
(0.022 g, 53%) as a semi-solid colourless material with all spec-
24
tral data fully identical with the described natural product.
27
1.2.2 trans and cis-(ꢁ)-1-methoxyspirobrassinol methyl
ether [(ꢁ)-6a and (ꢁ)-6b]. Following the general procedure,
products (ꢁ)-6a and (ꢁ)-6b were obtained using 0.040 g
described previously.
.1.4 N-(1-methoxyindol-3-yl)methyl-N -phenylthiourea (16).
0
1
Crude product of (1-methoxyindol-3-yl)methylamine (10) freshly
prepared by the reduction of 1-methoxyindole-3-carboxaldehyde
(0.15 mmol) of 1-methoxybrassinin (2) and methanol (0.3 mL).
Reaction mixture was stirred for 1 h. The residue obtained aer
evaporation of the solvent was subjected to ash
oxime (0.380 g, 2 mmol) with NaBH CN (1.26 g, 20 mmol) in the
3
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5575–5582 | 5579

View Article Online
RSC Advances
Paper
chromatography on 5 g silica gel (n-hexane/diethyl ether 3 : 2), 3.46 (s, 3H, OCH
affording mixture of diastereoisomers (ꢁ)-6a and (ꢁ)-6b (100 MHz, DMSO, 60 C): 164.2 (C]N), 151.5 (C]O), 139.4 (q),
3
), 2.57 (s, 3H, SCH
3
), 1.55 (s, 9H, [C(CH
3
)
3
]). d
C
ꢀ
(
0.026 g, 60%) as a colourless oil with all spectral data fully 132.6 (q), 129.3, 123.4, 123.3 and 114.8 (C-arom), 95.6 (C-2), 81.8
24
13
identical with the described natural and unnatural product.
[C(CH ) )], 74.7 (CH ), 73.3 (C-3), 57.9 (OCH ), 27.9 [C(CH ) )],
3 3 2 3 3 3
0
1
.2.3 trans and cis-(ꢁ)-1-methoxy-2-phenylamino-2 (methyl- 14.6 (SCH
3
). NOESY correlations (400 MHz, DMSO): H
b
/H-2, H-
0
0
0
sulfanyl)spiro{indoline-3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-18a and 2/OCH
3
, H
a
/H , [C(CH ]/OCH , [C(CH ]/SCH . EIMS m/z (%
b
3
)
3
3
3
)
3
3
+
(
ꢁ)-18b]. Following the general procedure, products (ꢁ)-18a and relative int.): 366 [M] (18), 310 (17), 265 (20), 234 (21) 192 (16),
(
ꢁ)-18b were obtained using 0.040 g (0.15 mmol) of 1-methoxy- 161 (30), 57 (100). HRMS m/z Calc. for C17
brassinin (2) and aniline (0.015 mL, 0.015 g, 0.0165 mmol). found: 366.1087.
Reaction mixture was stirred for 2 h. The residue obtained aer
H
22
N
2
O
3
S
2
: 366.1072,
0
1.2.6 trans and cis-(ꢁ)-1-methoxy-2-hydroxy-2 -(phenyl-
0
0
0
evaporation of the solvent was subjected to ash chromatography amino)spiro{indoline-3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-21a and
on 5 g silica gel (n-hexane/ethyl acetate 2 : 1), affording mixture of (ꢁ)-21b]. Following the general procedure, products (ꢁ)-21a
diastereoisomers (ꢁ)-18a and (ꢁ)-18b (0.029 g, 54%) as a yellow and (ꢁ)-21b were obtained using 0.047 g (0.15 mmol) of thio-
oil with all spectral data fully identical with the described urea 16 and water (0.3 mL). Reaction mixture was stirred for 4 h.
products.
.2.4 trans
21
The residue obtained aer evaporation of the solvent was sub-
1
and
cis-(ꢁ)-1-(tert-butoxycarbonyl)spiro- jected to ash chromatography on 5 g silica gel (n-hexane/ethyl
brassinol [(ꢁ)-19a and (ꢁ)-19b]. Following the general proce- acetate 2 : 1), affording mixture of diastereoisomers (ꢁ)-21a and
dure, products (ꢁ)-19a and (ꢁ)-19b were obtained using 0.050 g (ꢁ)-21b (0.023 g, 47%) as a yellow oil.
(0.15 mmol) of 1-Boc-brassinin (14) and water (0.3 mL). Reac-
Yield: 0.023 g, 47%, yellow oil; R ¼ 0.14 (n-hexane/ethyl acetate
f
tion mixture was stirred for 1.5 h. The residue obtained aer 2 : 1). d (400 MHz, CDCl ): 7.33 (d, J ¼ 7.4 Hz, 1H, H-4), 7.29–7.13
H
3
0
0
0
0
evaporation of the solvent was subjected to ash chromatog- (m, 5H, H-3 , H-5 , H-2 , H-6 , H-6), 7.02 (dd, J ¼ 7.4 Hz, 7.5 Hz, 2H,
0
raphy on 5 g silica gel (n-hexane/ethyl acetate 4 : 1), affording H-5, H-4 ), 6.93 (d, J ¼ 7.8 Hz, 1H, H-7), 5.48 (bs, 1H, OH), 5.27 (s,
mixture of diastereoisomers (ꢁ)-19a and (ꢁ)-19b (0.028 g, 53%) 1H, H-2 trans), 4.88 (s, 1H, H-2 cis), 4.47 (d, J ¼ 12.0 Hz, 1H, H
b
as a white solid with all spectral data fully identical with the trans), 4.26 (d, J ¼ 12.6 Hz, 1H, H
a
cis), 4.01 (d, J ¼ 12.6 Hz, 1H, H
b
11
described products.
.2.5 trans and
cis), 3.93 (s, 3H, OCH
3
cis), 3.88 (s, 3H, OCH
3
trans), 3.73 (d, J ¼
1
cis-(ꢁ)-1-(tert-butoxycarbonyl)spiro- 12.0 Hz, 1H, H trans). d (100 MHz, CDCl ): 160.8 (C]N trans),
a
C
3
0
brassinol methyl ether [(ꢁ)-20a and (ꢁ)-20b]. Following the 158.5 (C]N cis), 148.5 (C-7a trans), 147.8 (C-7a cis), 145.8 (C-1 cis),
0
0
general procedure, products (ꢁ)-20a and (ꢁ)-20b were obtained 144.5 (C-1 trans), 130.0 (C-6 cis), 129.8 (C-6 trans), 129.0 (C-3 , C-
0
using 0.050 g (0.15 mmol) of 1-Boc-brassinin (14) and methanol 5 ), 127.1 (C-3a cis), 126.5 (C-3a trans), 124.0, 123.8, 123.8, 123.7,
0 0
(
0.3 mL). Reaction mixture was stirred for 3.5 h. The residue 123.5, 123.4 (C-4 cis, C-4 trans, C-5 cis, C-5 trans, C-4 cis, C-4
0
0
0
0
obtained aer evaporation of the solvent was subjected to trans), 121.4 (C-2 , C-6 trans), 120.9 (C-2 , C-6 cis), 112.9 (C-7 cis),
chromatography on 5 g silica gel (dichloromethane), affording 112.8 (C-7 trans), 99.3 (C-2 trans), 98.0 (C-2 cis), 66.9 (C-3 cis), 64.4
(
2
ꢁ)-20a (0.016 g, 29%) as a colourless solid and (ꢁ)-20b (0.014 g, (N–OCH
5%) as a colourless oil. 55.7 (CH trans). NOESY correlations (400 MHz, CDCl ): H trans/
trans-(ꢁ)-1-(tert-butoxycarbonyl)spirobrassinol methyl ether H trans, H trans/H-4, H cis/H cis, H-2 cis/H cis. Anal. Calc. for
3 3 2
cis), 64.0 (C-3 trans), 63.8 (OCH trans), 61.8 (CH cis),
2
3
a
b
a
a
b
b
ꢀ
[
(
(ꢁ)-20a]. Yield: 0.016 g, 29%, colourless solid; mp 68–70 C C H N O S requires: C, 62.36; H, 5.23; N, 12.83. Found: C,
1
7 17 3 2
dichloromethane); R
f
¼ 0.12 (dichloromethane). nmax (CHCl
3
)/ 62.11; H, 5.32; N, 12.71.
ꢂ1
ꢀ
0
cm : 1713 (C]O), 1573 (C]N). d
7
H
(400 MHz, DMSO, 60 C):
1.2.7 trans and cis-(ꢁ)-1-methoxy-2-methoxy-2 -(phenyl-
0
0
0
.57 (d, J ¼ 7.3 Hz, 1H, H-7), 7.44 (d, J ¼ 7.5 Hz, 1H, H-4), 7.30 amino)spiro{indoline-3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-22a and
(
dd, J ¼ 7.8 Hz, J ¼ 7.6 Hz, 1H, H-6), 7.07 (dd, J ¼ 7.5 Hz, (ꢁ)-22b]. Following the general procedure, products (ꢁ)-22a
J ¼ 7.5 Hz, 1H, H-5), 5.42 (s, 1H, H-2), 4.69 (d, J ¼ 15.7 Hz, 1H, and (ꢁ)-22b were obtained using 0.047 g (0.15 mmol) of thio-
H ), 4.40 (d, J ¼ 15.7 Hz, 1H, H ), 3.43 (s, 3H, OCH ), 2.56 (s, 3H, urea 16 and methanol (0.3 mL). Reaction mixture was stirred for
b
a
3
ꢀ
SCH ), 1.54 (s, 9H, [C(CH ) ]). d (100 MHz, DMSO, 60 C): 162.3 2 h. The residue obtained aer evaporation of the solvent was
3
3 3
C
(
C]N), 151.4 (C]O), 140.8 (q), 130.3 (q), 129.7, 123.7, 123.6 subjected to ash chromatography on 5 g silica gel (cyclo-
and 115.2 (C-arom), 98.6 (C-2), 82.0 [C(CH
CH ), 57.4 (OCH ), 27.9 [C(CH ], 14.7 (SCH
lations (400 MHz, DMSO): H /H-4, H-2/OCH , H
OCH , [C(CH ]/SCH
3
)
3
], 70.6 (C-3), 65.8 hexane/acetone 8 : 1), affording (ꢁ)-22a (0.016 g, 32%) as a
(
2
3
3
)
3
3
). NOESY corre- white crystals and (ꢁ)-22b (0.014 g, 27%) as a white crystals.
0
a
3
/H
a b
, [C(CH
3
)
3
]/
trans-(ꢁ)-1-methoxy-2-methoxy-2 -(phenylamino)spiro{indoline-
+
0
0
0
3
3
)
3
3
. EIMS m/z (% relative int.): 366 [M] (19), 3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-22a]. Yield: 0.016 g, 32%, white
ꢀ
3
10 (17), 265 (17), 234 (20) 192 (14), 161 (23), 57 (100). HRMS m/z crystals; mp ¼ 149–151 C (dichloromethane/n-hexane); R
f
¼
ꢂ1
Calc. for C H N O S : 366.1072, found: 366.1083.
0,11 (cyclohexane/acetone 8 : 1). n
(CHCl )/cm 3413, 2990,
1
7
22
2
3
2
max 3
cis-(ꢁ)-1-(tert-butoxycarbonyl)spirobrassinol
methyl
ether 2935, 1630, 1585, 1490, 1305, 1185, 1140, 1080, 1040, 690. dH
[
(
(
7
1
2
(ꢁ)-20b]. Yield: 0.014 g, 25%, colourless oil; R ¼ 0.19 (400 MHz, CDCl ): 7.35 (dd, J ¼ 0.5 Hz, 7.6 Hz, 1H, H-4), 7.29
f
3
ꢂ1
0
0
dichloromethane). nmax (CHCl
3
ꢀ
)/cm : 1727 (C]O), 1570 (dd, J ¼ 7.4 Hz, 8.2 Hz, 2H, H-3 , H-5 ), 7.26 (ddd, J ¼ 1.1 Hz,
0
0
C]N). d
H
(400 MHz, DMSO, 60 C): 7.60 (d, J ¼ 7.5 Hz, 1H, H- 7.5 Hz, 7.7 Hz, 1H, H-6), 7.18 (d, J ¼ 8.2 Hz, 2H, H-2 , H-6 ), 7.04
0
), 7.28 (dd, J ¼ 7.7 Hz, J ¼ 7.8 Hz, 1H, H-6), 7.25 (d, J ¼ 7.5 Hz, (dd, J ¼ 7.4 Hz, 7.4 Hz, 1H, H-4 ), 7.02 (dd, J ¼ 7.7 Hz, 7.7 Hz, 1H,
H, H-4), 7.05 (dd, J ¼ 7.4 Hz, J ¼ 7.4 Hz, 1H, H-5), 5.31 (s, 1H, H- H-5), 6.95 (d, J ¼ 7.8 Hz, 1H, H-7), 4.95 (s, 1H, H-2), 4.47 (d, J ¼
), 4.45 (d, J ¼ 15.2 Hz, 1H, H ), 3.85 (d, J ¼ 15.2 Hz, 1H, H ), 11.8 Hz, 1H, H ), 3.94 (s, 3H, N–OCH ), 3.75 (s, 3H, 2-OCH ),
b
a
b
3
3
5580 | RSC Adv., 2014, 4, 5575–5582
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
3
1
.64 (d, J ¼ 11.8 Hz, 1H, H
a
). d
C
(100 MHz, CDCl
3
): 158.7 (C]N), 5 g silica gel (n-hexane/ethyl acetate 2 : 1), affording (ꢁ)-3
0
0
0
48.1 (C-7a), 146.2 (C-1 ), 129.8 (C-6), 129.0 (C-3 , C-5 ), 127.7 (0.013 g, 34%) as a colourless crystals with all spectral data fully
0 0 0
30
(C-3a), 123.9 (C-4), 123.8 (C-5), 123.5 (C-4 ), 121.0 (C-2 , C-6 ), identical with the described natural product.
1
12.9 (C-7), 108.6 (C-2), 63.8 (N–OCH ), 63.5 (C-3), 59.9 (2-
1.2.11 (ꢁ)-1-Methylspirobrassinin [(ꢁ)-25]. Following the
general procedure, product (ꢁ)-25 were obtained using 0.038 g
3
OCH
H
3
), 57.1 (CH
2
). NOESY correlations (400 MHz, CDCl
3
): H
a
/
b
; 2-OCH
3
3
/H-2. Difference NOE spectra (CDCl ): irr. at d 4.47 (0.15 mmol) of brassinin (15) and methanol (0.3 mL). Reaction
(H
b
a
) enhanced signal d 3.64 (H , 24.1%), irr. at d 4.95 (H-2) mixture was stirred for 1 h. The residue obtained aer evapo-
enhanced signal d 3.75 (2-OCH , 7.5%). MALDI-TOF MS, m/z (% ration of the solvent was subjected to ash chromatography on
3
+
relative int.): 342.0 [M + H] (100), 312.2 (17), 200.1 (8). Anal. 5 g silica gel (n-hexane/ethyl acetate 2 : 1), affording (ꢁ)-25
Calc. for C H N O S requires: C, 63.32; H, 5.61; N, 12.31. (0.016 g, 40%)as a white solid with all spectral data fully iden-
1
8
19 3 2
3
1
Found: C, 63.01; H, 5.72; N, 12.13.
tical with the described product.
0
cis-(ꢁ)-1-methoxy-2-methoxy-2 -(phenylamino)spiro{indoline-
0
0
0
3
,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-22b]. Yield: 0.014 g, 27%, white
ꢀ
Acknowledgements
crystals; mp
¼
166–168
C
(dichloromethane/n-hexane);
ꢂ1
R
3
f
¼ 0,06 (cyclohexane/acetone 8 : 1). nmax (CHCl
3
)/cm 3410,
We would like to thank the Slovak Grant Agency for Science
Grant no. 1/0954/12) for nancial support of this work.
000, 2940, 1627, 1590, 1433, 1307, 1200, 1140, 1090. d
H
(
(
400 MHz, CDCl
3
): 7.37 (dd, J ¼ 0.5 Hz, 7.6 Hz, 1H, H-4), 7.26–
0
0
0
0
7
8
6
1
.29 (m, 5H, H-2 , H-3 , H-5 , H-6 , H-6), 7.04 (dd, J ¼ 8.5 Hz,
0
.5 Hz, 1H, H-4 ), 7.03 (ddd, J ¼ 1.0 Hz, 7.5 Hz, 7.6, 1H, H-5),
References
.98 (d, J ¼ 7.8 Hz, 1H, H-7), 4.66 (s, 1H, H-2), 4.26 (d, J ¼
2.6 Hz, 1H, H
a
), 4.12 (d, J ¼ 12.6 Hz, 1H, H
b
), 3.95 (s, 3H, N–
): 159.3 (C]N),
1 R. P. Purkayastha, in Handbook of Phytoalexin Metabolism
and Action, ed. M. Daniel and R. P. Purkayastha, Progress
in phytoalexin research during the past 50 years, Marcel
Dekker, New York, 1995, pp. 1–39.
2 M. S. C. Pedras, E. E. Yaya and E. Glawischnig, Nat. Prod.
Rep., 2011, 28, 1381.
OCH
1
3
), 3.74 (s, 3H, 2-OCH
3
). d
C
(100 MHz, CDCl
3
0
0
0
47.6 (C-7a), 143.3 (C-1 ), 129.9 (C-6), 129.1 (C-3 , C-5 ), 128.8 (C-
0
0
0
3
a), 124.0 (C-5), 123.6 (C-4 ), 123.1 (C-4), 120.4 (C-2 , C-6 ), 112.8
), 63.8 (N–OCH ), 59.7 (2-
OCH ). NOESY correlations (400 MHz, CDCl ): H /H ; 2-OCH /
(C-7), 105.0 (C-2), 66.5 (C-3), 64.2 (CH
2
3
3
3
a
b
3
H-2; H /H-2. Difference NOE spectra (CDCl ): irr. at d 4.66 (H-2)
3 M. S. C. Pedras, Q. Zheng and V. K. Sarma-Mamillapale, Nat.
Prod. Commun., 2007, 2, 319.
b
3
enhanced signal d 4.12 (H , 3.2%) and 3.74 (2-OCH , 7.0%), irr.
b
3
at d 4.12 (H
4.7%). MALDI-TOF MS, m/z (% relative int.): 342.0 [M + H]
100), 312 (14), 200.1 (5). Anal. Calc. for C18 S requires:
C, 63.32; H, 5.61; N, 12.31. Found: C, 63.59; H, 5.32; N, 12.08.
b
) enhanced signal d 4.66 (H-2, 8.9%) and 4.26 (H
a
,
4 R. Mezencev, J. Moj ˇz i ˇs , M. Pil ´a tov ´a and P. Kutschy,
Neoplasma, 2003, 50, 239.
+
1
(
H
19
N
3
O
2
5 P. Kutschy and R. Mezencev, Indole Phytoalexins from
Brassicaceae: Synthesis and Anticancer Activity, in Targets
in Heterocyclic Systems – Chemistry and Properties, ed. O. A.
Attanasi and D. Spinelli; Italian Society of Chemistry,
Urbino, Italy, 2009, vol. 12, pp. 120–148, ISBN: 978-88-
86208-56-7, ISSN 1724-9449.
6 R. G. Mehta, J. Liu, A. Constantinou, M. Hawthorne,
J. M. Pezzuto, R. C. Moon and R. M. Moriarty, Anticancer
Res., 1994, 14, 1209.
0
1
.2.8 trans and cis-(ꢁ)-1-(tert-butoxycarbonyl)-2-hydroxy-2 -
0
0
0
(
phenylamino)spiro{indoline-3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-23a
and (ꢁ)-23b]. Following the general procedure, products (ꢁ)-23a
and (ꢁ)-23b were obtained using 0.058 g (0.15 mmol) of thiourea
1
7 and water (0.3 mL). Reaction mixture was stirred for 4 h. The
residue obtained aer evaporation of the solvent was subjected
to ash chromatography on 5 g silica gel (n-hexane/ethyl acetate
2
: 1), affording mixture of diastereoisomers (ꢁ)-23a and (ꢁ)-23b
7 R. G. Mehta, J. Liu, A. Constantinou, C. F. Thomas,
M. Hawthorne, M. You, C. Gerh ¨a user, J. M. Pezzuto,
R. C. Moon and R. M. Moriarty, Carconogenesis, 1995, 16, 399.
8 R. Mezencev, J. Moj ˇz i ˇs , M. Pil ´a tov ´a , P. Kutschy and
Z. Curillov ´a , in Effects of phytoalexins on the growth of
cancer cells, ed. F. Columbus, Trends in cancer prevention
Research, Nova Science Publishers, New York, 2007,
pp. 81–91.
(0.031 g, 52%) as a white solid with all spectral data fully iden-
12
tical with the described products.
.2.9 trans and cis-(ꢁ)-1-(tert-butoxycarbonyl)-2-methoxy-2 -
0
1
0
0
0
ˇ
(
phenylamino)spiro{indoline-3,5 -[4 ,5 ]-dihydrothiazol} [(ꢁ)-24a
and (ꢁ)-24b]. Following the general procedure, products (ꢁ)-24a
and (ꢁ)-24b were obtained using 0.058 g (0.15 mmol) of thiourea
1
7 and methanol (0.3 mL). Reaction mixture was stirred for 1.5 h.
The residue obtained aer evaporation of the solvent was sub-
jected to ash chromatography on 5 g silica gel (n-hexane/ethyl
acetate 2 : 1), affording mixture of diastereoisomers (ꢁ)-24a and
9 P. Gaspari, T. Banerjee, W. P. Malachowski, A. J. Muller,
J. D. Prendergast, J. DuHadaway, S. Bennett and
A. M. Donovan, J. Med. Chem., 2006, 49, 684.
(
ꢁ)-24b (0.035 g, 56%) as a white solid with all spectral data fully 10 R. Mezencev, M. Galizzi, P. Kutschy and R. Docampo, Exp.
12
identical with the described products.
Parasitol., 2009, 122, 66.
1
.2.10 (ꢁ)-Spirobrassinin [(ꢁ)-3]. Following the general 11 P. Kutschy, M. Such ´y , K. Monde, N. Harada, R. Maru ˇs kov ´a ,
ˇ
´
ˇ ´
procedure, product (ꢁ)-3 were obtained using 0.035
g
Z. Curillova, M. Dzurilla, M. Miklosova, R. Mezencev and
(
0.15 mmol) of brassinin (1) and methanol (0.3 mL). Reaction
J. Moj ˇz i ˇs , Tetrahedron Lett., 2002, 43, 9489.
mixture was stirred for 1 h. The residue obtained aer evapo- 12 M. Budovsk ´a , M. Pil ´a tov ´a , L. Varinsk ´a , J. Moj ˇz i ˇs and
ration of the solvent was subjected to ash chromatography on
R. Mezencev, Bioorg. Med. Chem., 2013, 21, 6623.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5575–5582 | 5581

View Article Online
RSC Advances
Paper
ˇ
´
1
3 K. Monde, T. Taniguchi, N. Miura, P. Kutschy, Z. Curillova, 22 G. R. Rosa and D. S. Rosa, RSC Adv., 2012, 2, 5080.
M. Pil ´a tov ´a and J. Moj ˇz i ˇs , Bioorg. Med. Chem., 2005, 13, 5206. 23 M. Schmidt and H.-J. Kn ¨o lker, Synlett, 2009, 15,
4 M. Such ´y , P. Kutschy, K. Monde, H. Goto, N. Harada,
2421.
M. Takasugi, M. Dzurilla and E. Balentov ´a , J. Org. Chem., 24 K. Monde, M. Takasugi and A. Shirata, Phytochemistry, 1995,
001, 66, 3940. 39, 581.
5 K. Monde, S. Osawa, N. Harada, M. Takasugi, M. Such ´y , 25 G. R. Rosa, G. Ebeling, J. Dupont and A. L. Monteiro,
1
2
1
P. Kutschy, M. Dzurilla and E. Balentov ´a , Chem. Lett., 2000,
86.
6 M. S. C. Pedras, M. Such ´y and P. W. K. Ahiahonu, Org.
Synthesis, 2003, 2894.
8
26 J. Dupont and M. Pfeffer, Palladacycles-Synthesis,
Characterization and Applications, Wiley-VCH Verlag GmbH
& Co., Weinheim, Germany, 1st edn, 2008.
1
1
1
1
2
2
Biomol. Chem., 2006, 4, 691.
7 K. Inamoto, Y. Arai, K. Hiroya and T. Doi, Chem. Commun., 27 P. Kutschy, M. Dzurilla, M. Takasugi, M. T ¨o r ¨o k,
2008, 5529.
I. Achbergerov ´a , R. Homzov ´a and M. R ´a cov ´a , Tetrahedron,
8 D. Orain, A.-C. Blumstein, E. Tasdelen and S. Haessig,
Synlett, 2008, 16, 2433.
1998, 54, 3549.
28 M. Takasugi, K. Monde, N. Katsui and A. Shirata, Bull. Chem.
9 C. Benedi, F. Bravo, P. Uriz, E. Fernand ´e z, C. Claver and
S. Castill ´o n, Tetrahedron Lett., 2003, 44, 6073.
Soc. Jpn., 1988, 61, 285.
29 M. S. C. Pedras and I. L. Zaharia, Phytochemistry, 2000, 55,
0 M. C. Willis, D. Taylor and A. T. Gillmore, Tetrahedron, 2006,
213.
6
2, 11513.
30 M. Takasugi, K. Monde, N. Katsui and A. Shirata, Chem. Lett.,
1 P. Kutschy, A. Salayov ´a , Z. Curillova, T. Ko ˇz ar, R. Mezencev,
ˇ
´
´
1987, 1631.
J. Moj ˇz i ˇs , M. Pil ´a tov ´a , E. Balentov ´a , P. Pazdera, M. Sabol and 31 M. S. C. Pedras, M. Hossain, M. G. Sarwar and S. Montaut,
M. Zburov ´a , Bioorg. Med. Chem., 2009, 17, 3698.
Bioorg. Med. Chem. Lett., 2004, 14, 5469.
5582 | RSC Adv., 2014, 4, 5575–5582
This journal is © The Royal Society of Chemistry 2014