Synthesis and structural characterization of two nostoclide analogues

Article abstract of DOI:10.1016/j.molstruc.2006.10.014

The vinylogous aldol reaction between appropriate aldehydes and furan-based silyloxy diene synthon generated from 3-benzyl-5H-furan-2-one (3) afforded two truncated lactone analogues [compounds (4) and (5)] of nostoclides (2). The compounds were fully cha

Full text of DOI:10.1016/j.molstruc.2006.10.014

Journal of Molecular Structure 837 (2007) 197–205
www.elsevier.com/locate/molstruc
Synthesis and structural characterization of two nostoclide analogues
a,b
a,
a
b
c
*
R.R. Teixeira , L.C.A. Barbosa , J.O. Santana , D.P. Veloso , J. Ellena ,
d
e
f
A.C. Doriguetto , M.G.B. Drew , F.M.D. Ismail
a
Departamento de Qu ı´ mica, Universidade Federal de Vi c¸ osa, Avenida P.H. Rolfs, CEP 36570-000, Vi c¸ osa, MG, Brazil
Departamento de Qu ı´ mica, Universidade Federal de Minas Gerais, Avenida Ant oˆ nio Carlos, 6627, CEP 31270-901, Belo Horizonte, MG, Brazil
b
c
Instituto de F ı´ sica de S a˜ o Carlos – USP, Cx. postal 369, CEP 13560-970, S a˜ o Carlos, SP, Brazil
Laborat o´ rio de Cristalografia, Departamento de Ci eˆ ncias Exatas, Universidade Federal de Alfenas, Rua Gabriel Monteiro da Silva, 714, CEP 37130-000,
Alfenas, MG, Brazil
d
e
School of Chemistry, University of Reading, Reading RG6 6AD, United Kingdom
The Medicinal Chemistry Research Group, The School of Pharmacy and Chemistry, Liverpool John Moores University, Byrom Street,
Liverpool L3 3AF, United Kingdom
f
Received 6 September 2006; received in revised form 20 October 2006; accepted 21 October 2006
Available online 14 December 2006
Abstract
The vinylogous aldol reaction between appropriate aldehydes and furan-based silyloxy diene synthon generated from 3-benzyl-
H-furan-2-one (3) afforded two truncated lactone analogues [compounds (4) and (5)] of nostoclides (2). The compounds were fully
5
1
13
characterized by IR, NMR ( H and C), 2D NMR spectroscopy experiments (HMBC, HSQC and NOESY), MS spectrometry and
X-ray crystallography. Compounds (4) and (5) crystallized in the space group P2 and P2 /c, respectively. Although expected
2
1 1
2
1
1
correlations between hydrogen atoms in spatial close proximity were not observed for compound (5) using NMR, the stereochemistry
of the exocyclic double bond of both (4) and (5) was unambiguously determined to be Z and E, respectively, using X-ray crystallography.
The packing of both compounds within the crystal are stabilized by non-classical inter-molecular hydrogen bonds. DFT calculations
(
B3LYP/6-31+G level) confirmed that the crystal structures possessed the lowest energies in the gas phase when compared to their
*
geometric isomers.
ꢀ
2006 Elsevier B.V. All rights reserved.
Keywords: Lactones; Nostoclides; NMR analysis; X-ray; DFT
1
. Introduction
2,4-dichlorophenoxyacetic acid (2,4-D) in 1946 by a British
research team at the Rothamsted Experimental Station,
agrochemical companies have developed and brought a
plethora of herbicides to the market [2]. Although impor-
tant advances have been achieved in the chemical control
of weeds to maximize crop production, identification and
development of novel herbicides are highly desirable to
fight evolution of resistance in weeds [3]. In this context,
natural products may provide an economic source of new
herbicides or novel lead compounds that may be optimized
using known strategies [4,5].
A major challenge currently facing the developed world
is the necessity to increase food production for supporting
the current world population. To overcome this problem, it
is necessary to maximize the world’s agricultural efficiency,
which in turns requires the control of a variety of diseases
and pests among them weeds [1].
Consequently, the employment of herbicides has
become the most reliable and least expensive tool for weed
control throughout the world. Since the introduction of the
Cyanobacterin (1, Fig. 1) is a phytotoxic compound iso-
lated from the blue-green alga Scytonema hofmanni [6]. It is
toxic to most cyanobacteria at a concentration of 5 lM and
also inhibits the growth of most eukaryotic algae and
*
Corresponding author. Tel.: +55 31 3899 3068; fax: +55 31 3899 3065.
E-mail address: lcab@ufv.br (L.C.A. Barbosa).
0
022-2860/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.10.014

198
R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
Cl
O
diisopropylethylamine (DIPEA) were dried prior to use;
dichloromethane was distilled over calcium hydride; diiso-
propylethylamine was distilled over potassium hydroxide.
Commercially tert-butyldimethylsilyl trifluoromethanesulf-
onate (TBDMSOTf), piperonal, 2,4,6-trimethoxy benzal-
dehyde and 8-diazabyciclo[5.4.0]undec-7-ene (DBU) were
OH
O
O
O
O
O
R
1
13
utilized without further purification. The H and
NMR spectra were recorded on Brucker AVANCE DRX
00 spectrometer at 400 and 100 MHz, respectively, using
C
Cl
OMe
OH
(2a) R=Cl Nostoclide I
2b) R=H Nostoclide II
4
1
CDCl as solvent and TMS as internal standard. Mass
3
(
spectra were obtained on SHIMADZU GCMS-QP5050A
instrument by direct injection (DI temperature program:
Fig. 1. Structures of cyanobacterin and nostoclides.
4
0 ꢁC/min until temperature reaches 60 ꢁC; then 80 ꢁC/
several monocotyledonous and dicotyledonous angio-
sperms [7,8]. Cyanobacterin acts by inhibiting photosyn-
thetic electron transport in isolated chloroplasts in a
similar way to the herbicide 3-(3,4-diclorophenyl)-1,1-dim-
ethylurea [9], leading to a cascade of events which result in
the disruption of the thylakoid membrane [10].
Although several studies have been carried out on the
mode of action of cyanobacterin, the biological activity of
the structurally similar natural lactones, know as nostoclides
I and II (Fig. 1: 2a and 2b), produced by a cyanobacterium
min until temperature reaches 300 ꢁC; detector temp:
2
1
80 ꢁC). IR spectra were taken from Perkin-Elmer Paragon
000 FTIR spectrophotometer. Melting points are uncor-
rected and were obtained from MQAPF-301 melting point
apparatus (Microquimica, Brazil). Analytical thin-layer
chromatography was conducted on SILICYCLE alumi-
num backed TLC. Column chromatography was per-
formed over ULTRACHEM silica gel (200–400 mesh).
2.2. Synthesis of 5(Z)-3-benzyl-5-(1,3-
dioxalanebenzilidene)-5H-furan-2-one (4)
(
or blue-green alga; Nostoc sp.) symbiont partner within
Peltigera canina, has not yet been fully investigated. Nostoc-
lides I and II have been shown to possess moderate cytotox-
icity against the mouse neuroblastoma cell lines Neuro-2a
CCL and KB CCL 17 [11]. Owing to the structural similarity
of nostoclides and cyanobacterin (both compounds have in
common the presence of a 3-benzyl-5-benzylidene-4-isopro-
pyl-dihydro-furan-2-one ring system) and the fact that
P. canina cultures are usually not contaminated with micro-
organisms, it has been suggested that these chlorinated
compounds may be alleopathic agents.
The presence of chlorine, which is relatively rare com-
pared to bromine but more abundant than fluorine within
natural products, a property exploited in many herbicides,
probably improves uptake of this compound into target
organisms [12].
To a two neck round-bottomed flask, under nitrogen
atmosphere, were added 3-benzyl-5H-furan-2-one (3)
(
106 mg; 0.61 mmol), 3 mL of anhydrous dichloromethane,
tert-butyldimethylsilyl trifluoromethanesulfonate (170 lL;
.74 mmol), diisopropylethylamine (310 lL; 1.2 mmol)
0
and piperonal (180 mg; 1.2 mmol). The resulting mixture
was stirred at room temperature for 1 h. After adding
DBU (120 lL; 1.22 mmol), the reaction mixture was
refluxed for an additional 3 h and 70 mL of dichlorometh-
ane was added. The resulting organic layer was washed
with 3 mol/L HCl aqueous solution (2· 25 mL) and brine
(25 mL). After separation, the organic layer was dried over
MgSO , filtered, and concentrated under reduced pressure.
4
The resulting material was purified by column chromatog-
raphy on silica gel eluted with hexane–diethyl ether (6:1).
Since, some fractions revealed the presence of impurities,
after they were combined and evaporated, the resulting sol-
id was recrystallized from a mixture of hexane–dichloro-
methane. Compound (4) was obtained as pale yellow
crystals in 83% yield (155 mg, 0.51 mmol).
As part of a continuous effort to develop new herbicides
in our laboratory [13], we decided to investigate the poten-
tial phytotoxicity of nostoclide analogues. Herein, we
report the preparation of two lactones analogues to nostoc-
lides. The lactones were fully characterized by spectral and
spectrometric analyses as well as single crystal X-ray dif-
fraction techniques. It was important to establish the
molecular geometry since it is required for constructing
structure–activity relationships and, indirectly, spatial
requirements of the receptors at which these compounds
act.
Mp = 181.1–181.8 ꢁC; R = 0.28 (hexano–dichlorometh-
f
ꢀ
1
ane, 1:1); IR (KBr, mmax=cm ): 3108, 3055, 3025, 2892,
1
9
2
6
736, 1654, 1600, 1489, 1446, 1379, 1341, 1262, 1036,
1
35; RMN de H (400 MHz, CDCl ) d (J/Hz): 3.71 (s,
3
H; H-6), 5.78 (s, 1H; H-5), 5.98 (s, 2H; -O–CH –O-),
2
00
.79 (d, 1H, J300 00 ¼ 8:2; H-3 ), 6.91 (s, 1H; H-3), 7.10
;2
00
2
. Experimental
(dd, J200 00 ¼ 8:2, J 00 00 ¼ 1:3; 1H, H-2 ), 7.25–7.36 (m,
;3
2 ;6
0
0
00
5
H; H-2 a H-6 ), 7.42 (d, 1H, J 00 00 ¼ 1:3; H-6 ). RMN
6
;2
1
3
2
.1. Material and methods
de C (100 MHz, CDCl ) d: 31.68 (C-6), 101.47 (-O–
3
00
00
CH –O-), 108.56 (C-3 ), 109.94 (C-6 ), 112.66 (C-5),
125.74 (C-2 ), 126.92 (C-4 ), 127.51 (C-1 ), 128.84 (C-3 /
0 0 0 0
C-5 ), 128.93 (C-2 /C-6 ), 131.56 (C-2), 137.36 (C-1 ),
2
00 0 00 0
All reactions were carried out under a protective
atmosphere of dry nitrogen. Dichloromethane and

R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
199
0
0
*
00
*
1
1
2
(
(
39.60 (C-3), 146.24 (C-4), 148.42 (C-4 ) , 148.26 (C-5 ) ,
gram [14]; integration and scaling of the reflections were
performed with the HKL Denzo-Scalepack system of
programs [15]. The structure was solved by direct meth-
ods with SHELXS-97 [16]. The model was refined by
+
70.42 (C-1); EM, m/z (%): 306, C H O , [M ], (100);
61 (4.2); 231 (7.7), 203 (7.5), 162 (32.0), 153 (7.0), 134
33.7), 115 (22.3), 104 (16.7), 101 (18.3), 91 (12.6), 77
8.9), 76 (41.2), 65 (7.7), 51 (11.1). The assignments could
1
9
14
4
*
2
full-matrix least-squares on F with SHELXL-97 [17].
be reversed.
All hydrogen atoms were stereochemically positioned
and refined with the SHELXL-97 riding model.
Hydrogen atoms were refined with C–H distances of
2.3. Synthesis of 5(E)-3-benzyl-5-(2,4,6-
trimetoxibenzilidene)-5H-furan-2-one (5)
˚
0.93–0.97 A and were set isotropic with a thermal
parameter 20% greater than the equivalent isotropic
displacement parameter of the atom to which they were
bonded. This percentage was set to 50% for the
To a two neck round-bottom flask, under nitrogen
atmosphere, were added 3-benzyl-5H-furan-2-one (3)
(
106 mg; 0.61 mmol), 3 mL of anhydrous dichloromethane,
tert-butyldimethylsilyl trifluoromethanesulfonate (170 lL;
.74 mmol), diisopropylethylamine (310 lL; 1.2 mmol)
hydrogen atoms of the CH groups.
3
In spite of compound (4) crystallizing in a non-centro-
symmetric space group, the Flack parameter was not
refined during X-ray crystallographic analysis. Given that
in this case the most electron-rich atom is oxygen, which
does not have an anomalous scattering large enough (using
0
and 2,4,6-trimethoxy benzaldehyde (146 mg; 0.74 mmol).
The resulting mixture was stirred at room temperature
for 1 h. After DBU (120 lL; 1.22 mmol) was added, the
reaction mixture was refluxed for additional 3 h and
MoK radiation) to permit determination of the absolute
a
7
0 mL of dichloromethane was added. The resulting organ-
ic layer was washed with 3 mol/L HCl aqueous solution (2·
5 mL) and brine (25 mL). Subsequently, the organic
structure using X-ray diffraction, Friedel pairs were aver-
aged before refinement.
2
Data collections and experimental details for (4) and
(5) are summarized in Table 1. The programs WinGX
[18] and enCIFer [19] were used to prepare materials
for publication. The programs MERCURY [20] and
ORTEP-3 [21] were used to generate the molecular
graphics.
layer was separated, dried over MgSO , filtered, and
4
concentrated under reduced pressure. The resulting
material was purified by column chromatography on silica
gel eluted with hexane–ethyl acetate (4:1). The procedure
described afforded compound (5) (184 mg, 0.52 mmol,
8
6% yield) as a yellow solid. Yellow crystals suitable for
X-ray analysis were obtained from a mixture of hexane–
dichloromethane.
Table 1
Mp = 107.9–109.0 ꢁC; R = 0.29 (hexano–EtOAc, 4:1);
Crystal data and structure refinement for compounds (4) and (5)
f
ꢀ
1
IV (KBr, mmax=cm ): 3001, 2938, 2840, 1747, 1602, 1583,
(4)
(5)
1
1
(
2
495, 1469, 1455, 1229, 1119, 953, 814, 701; RMN de H
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
C
19
H
14
O
4
21 20 5
C H O
400 MHz, CDCl ) d (J/Hz): 3.68 (s, H-6; 2 H); 3,72 (s,
3
306.30
Orthorhombic
P2 2 2
a = 6.7188(4) A
b = 12.6624(5) A
352.37
Monoclinic
P2 /c
0
0
00 00 00
/6 -OCH ; 6H); 3.82 (s, 4 -OCH ; 3H); 6.10 (s, H-3 /
3 3
0
0
H-5 ; 2H); 6.54 (s, H-5; 1H); 7.05 (s, H-3; 1H); 7.22–7.33
1
1
1
1
˚
˚
0
0
13
a = 6.861(5) A
b = 13.758(5) A
(
3
(
1
1
6
m, H-2 a H-6 , 5H); RMN de C (100 MHz, CDCl ) d:
3
˚
˚
00 00 00
1.82 (C-6); 55.42 (4 -OCH ); 55.57 (2 /6 -OCH ); 90.74
3 3
˚
˚
c = 17.3713(12) A
a = b = c = 90ꢁ
c = 19.351(5) A
0
0
00
00
0
C-3 /C-5 ); 103.82 (C-1 ); 105.65 (C-5); 126.72 (C-4 );
28.67 (C-3 /C-5 ); 128.96 (C-2 /C-6 ); 132.92 (C-2);
37.77 (C-1 ); 137.85 (C-3); 148.70 (C-4); 158.71 (C-2 /C-
); 161.89 (C-4 ); 170.25 (C-1); EM, m/z (%): 352,
a = c = 90ꢁ;
b = 106.03(2)ꢁ
1755.6(15)
0
0
0
0
Volume ( A˚ 3)
Z
0
00
1477.88(15)
4
0
0
00
4
3
Density – calculated
1.377 mg/m
1.333
0.095
+
C H O [M ], (100); 281 (7.4); 208 (7.8); 193 (11.4); 181
ꢀ1
2
1
20
5
Absorption coefficient 0.097 mm
(
(
15.0); 166 (26.5); 138 (23.3); 115 (16.3); 91 (19.1); 77
9.8); 76 (5.0); 69 (11.8); 65 (8.5); 51 (6.1) Da.
F(000)
Crystal size
h-Maximum
Reflections collected
Independent
640
744
3
3
0.08 · 0.10 · 0.30 mm
27.87ꢁ
3493
0.12 · 0.15 · 0.22 mm
25.00ꢁ
3056
2
.4. Single crystal X-ray diffraction studies
2009 [R(int) = 0.0248] 3056 [R(int) = 0.0534]
reflections
Suitably sized crystals of both (4) and (5) were select-
Completeness (%)
Data/restraints/
parameters
98.6
2009/0/209
98.8
3056/0/236
ed for single crystal X-ray diffraction experiments. Low
temperature (150 K) X-ray diffraction data collections
were performed on an Enraf–Nonius Kappa-CCD dif-
fractometer using graphite–monochromated MoKa radi-
2
Goodness-of-fit on F
Final R indices
1.068
1.124
R
1
= 0.0399,
wR = 0.1027
= 0.0479,
wR = 0.1081
Largest diff. peak and 0.148 and ꢀ0.176
R
1
= 0.1131,
wR = 0.3214
= 0.1535,
wR = 0.3456
[
I > 2r(I)]
2
2
˚
ation (0.71073 A). Data were collected up to 50ꢁ in 2h,
R indices (all data)
R
1
R
1
with a redundancy of 4 for both compounds. The final
unit cell parameters were based on all reflections. Data
collections were performed using the COLLECT pro-
2
2
0.599 and
ꢀ0.343 eÆA˚
˚
ꢀ3
eÆA
ꢀ3
hole

2
00
R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
13
1
2
.5. DFT calculations
group. The H and C NMR assignments for compounds
(
4) and (5) are summarized in Table 2.
1
Structures were built using the Cerius software package
The H NMR spectrum of (4) contained three signals at
00
[
22] and approximate structures were obtained using
d 6.79 (d, J = 8.2, 1H; H-3 ), d 7.10 (dd, J = 8.2 and 1.3,
H H
1H; H-2 ) and d 7.42 (d, J = 1.3, 1H; H-6 ) characteristics
00
00
molecular mechanics minimisation. The structures were
then geometry optimised at the B3LYP/6-31+G* level
using the GAUSSIAN03 program [23].
H
of 1,3,4-substituted aromatic rings. These signals were cor-
related with the corresponding carbons via HSQC experi-
ment. Thus, the signals at dC 108.56, 109.94 and 125.74
00
00
00
were assigned, respectively to C-3 , C-6 and C-2 . The sig-
nal observed at d 3.71 (s, 2H) was unequivocally attribut-
ed to the methylene hydrogens of the benzyl group while
the signal at d 31.68 could be assigned to the benzylic car-
bon. The olefinic hydrogens of (4) showed chemical shifts
at d 5.78 (s, 1H; H-5) and d 6.91 (s, 1H; H-3). The
3
. Results and discussion
H
Compounds (4) and (5) were constructed using the
C
vinologous aldol reaction with the silyloxy diene furan
synthon and the relevant aldehyde [24]. Thus, reaction of
lactone (3), prepared as shown in Fig. 2, with the corre-
sponding aldehydes in the presence of tert-butyldimethylsi-
lyl trifluoromethanesulfonate and diisopropylethylamine
followed by treatment of the silyl ether generated in situ
with DBU afforded the compounds (4) and (5) in good
yields.
H
H
assignments were possible based on the information pro-
vided by the HMBC experiment. In the contour plot it
was noticed long range correlations between H-3 and car-
bons C-1 and C-6. Correlations of this nature were also
00
00
observed between H-5 and carbons C-2 and C-6 .
Once the signals related to H-3 and H-5 were identified,
Compounds (4) and (5) were fully characterized based
on NMR, IR, MS and X-ray diffraction (XRD) analyses.
The mass spectrum of lactones (4) and (5) revealed mass
ions, respectively, at m/z 306 and 352 Da which correlated
with the respective molecular formulae C H O for com-
it was possible to assign the signals to carbons C-3 (d
139.60) and C-5 (d 112.66) through HSQC experiment.
The remaining assignments were possible based on the
information provided by HMBC and HSQC experiments.
For example, the long range correlations observed between
C
C
1
9
14
4
pound (4) and C H O for compound (5), respectively.
the signal at d
ed association to C-4. The signal at d
to C-2 based on the long range connectivity of this signal
C
146.24 and hydrogens H-3 and H-5 suggest-
131.56 was assigned
2
1
20
5
ꢀ
1
IR absorption bands at 1736 cm [compound (4)] and
732 [compound (5)], corresponding to the carbonyl
C
1
stretching of the unsaturated lactones, were observed.
The two bands at 1261 and 935 cm observed in the IR
spectrum of (4) are associated with the 1,3-dioxalane
with H-3 and H-6. The HMBC contour plot also revealed
ꢀ
1
00
a correlation between the signal at d
127.51 and H-2 , H-
C
00
00
00
6 and H-3 allowing assignment of this signal to C-1 . The
O
i
O P N(C H )
Table 2
2
5 2
O
O
1
13
O
3
H and C NMR data of compounds (4) and (5) using CDCl as solvent
and TMS as internal standard (d in ppm and coupling constants J in Hz)
N(C H )
2
5 2
where mult, multiplicity
ii
Position
4
5
d
C
d
H
(mult., J)
d
C
H
d (mult., J)
ArCHO
ii, iii
1
2
3
4
5
6
170.42
131.56
139.60
146.24
112.66
31.68
137.36
128.93
128.84
170.25
132.92
137.85 7.05 (s)
148.70
105.65 6.54 (s)
31.82 3.68 (s)
137.77
128.96 7.22–7.33 (m)
128.67 7.22–7.33 (m)
126.72 7.22–7.33 (m)
103.82
O
O
6.91 (s)
O
Ar
O
(3)
5.78 (s)
3.71 (s)
CH3
0
1
O
H
O
0
0
0
0
0
2
3
4
1
2
3
4
5
6
, 6
, 5
7.25–7.36 (m)
7.25–7.36 (m)
7.25–7.36 (m)
H C
3
O
126.92
127.51
125.74
O
O
(5)
O
0
00
0
00
0
00
0
O
(
4)
3
C
7,10 (dd, 8.2 and 1.3) 158.71
0
108.56
6.79 (d, 8.2)
90.74 6.10 (s)
161.89
90.74 6.10 (s)
158.71
O
a
148.42
O
0
a
148.26
8
3%
86%
109.94
7.42 (d, 1.3)
5.98 (s)
-
4
2
O–CH
2
–O- 101.47
Fig. 2. Reagents and conditions employed to prepare (4) and (5) where: (i)
POCl /i-Pr EtN; Me
NH (51%); (ii) n-BuLi, THF, ꢀ78 ꢁC (1 h);
PhCH
Br (ꢀ78 ꢁC fi rt); HCOOH (45 min) (67% overall yield); (iii)
TBDMSOTf, DIPEA, CH Cl , rt, 1 h; DBU, reflux, 3 h.
00
-OCH
/6 -OCH
3
55.42 3.82 (s)
55.57 3.72 (s)
3
2
2
00 00
3
2
a
The assignments could be reversed.
2
2

R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
201
signals at dC 137.61; 128.97; 128.84 and 126.92 were
assigned to the aromatic carbons of benzylic moiety and
specific attributions are shown in Table 2. The HSQC
experiment revealed correlations between these signals
and the multiplet at dH 7.25–7.36. Finally, the signals at
intra-molecular hydrogen bond involving C18–H18. . .O2
(see Table 4). As expected, the phenyl ring B is planar
˚
(Rms deviation of fitted atoms = 0.0033 A). The molecular
conformation of (4), analyzed using the MOGUL [25], a
knowledge base of molecular geometry derived from the
Cambridge Structural Database (CSD) [26] that provides
rapid access to information on the preferred values of bond
lengths, valence angles and acyclic torsion angles, indicated
that all bond lengths and bond angles are in agreement
with the expected values.
00
00
d 148.42/148.26 were related to carbons C-4 /C-5 . A cor-
C
relation between hydrogens H-3 and H-5, observed in
NOESY experiment, demonstrated that the exocyclic dou-
ble bond presented a Z configuration. Other correlations
observed in the NOESY contour plot are illustrated in
Fig. 3. The stereochemistry of the double bond of (4) was
unambiguously determined by X-ray crystallography
The lactone (4) exhibits five weak non-classical
inter-molecular hydrogen bonds (see Figs. 5 and 6 and
Table 4). Three inter-molecular hydrogen bonds involving
(
Fig. 4).
The lactone (4) is almost flat (with the least-square plane
i
i
i
C15—H15 ꢁ ꢁ ꢁ O4 , C5-H5. . .O1 and C3–H3ꢁ ꢁ ꢁO1 (sym-
metry code: (i) = x ꢀ 1, y, z) give rise to an infinite one-di-
mensional chain parallel to the [100] direction (Fig. 5). It is
important to emphasize that either the C5–H5 or C3–H3
groups act as an intermolecular H bond donor to the O1,
forming a bifurcated H bond. The chains form a planar
network, connected by two other weak inter-molecular
passing through rings A, C and D) with phenyl ring B
adopting an angle of 74.32(5)ꢁ (Fig. 4). The main geometric
parameters of (4) are given in Table 3. All atoms in the
rings A, C and D, including C5, C6, and O1, lie within
˚
ꢀ
0.187(2) A of the least-squares plane through the three-
˚
ring system (Rms deviation of fitted atoms = 0.0595 A).
The structural features responsible for maintaining
coplanarity is conjugation between the rings A and C
iv
iv
vi
hydrogen bonds: C19 –H19b ꢁ ꢁ ꢁO1 and C11–H11ꢁ ꢁ ꢁO2
(symmetry codes: (iv) = ꢀx + 1/2, ꢀy + 2, z + 1/2;
(vi) = ꢀx + 1, y ꢀ 1/2, ꢀz + 3/2). Therefore, the individual
chains are linked to one another, forming an infinite
two-dimensional network parallel to the (011) plane. Dou-
ble chains, stabilized by van der Waals (VDW) interac-
tions, are formed along [100] direction. The double
(
unsaturated C4–C5 bond) and the weak non-classical
H
H
6
'
5
'
H
H
chains are related by 2 screw axis symmetry along [100]
1
1
'
˚
H
and the distance between each individual chain is ꢂ3.3 A
H
6
4'
3
as shown in Fig. 6. Comparing Figs. 5 and 6 is that O1
atom reveal an interesting trifurcated H bonding motif:
2
1
3'
2
'
H
5
4
ii
ii
ii
ii
iv
iv
H
H
C5 –H5 ꢁ ꢁ ꢁO1, C3 –H3 ꢁ ꢁ ꢁO1, and C19 –H19b ꢁ ꢁ ꢁO1
O
1
''
O
(symmetry code: (ii) = x + 1, y, z; (iv) = ꢀx + 1/2,
ii iv ii iv
H
H
H
ii
ii
2
''
"
ꢀ
y + 2, z + 1/2). The angles between H5 ꢁ ꢁ ꢁO1ꢁ ꢁ ꢁH3 ,
6
''
H5 ꢁ ꢁ ꢁO1ꢁ ꢁ ꢁH19b , and H3 ꢁ ꢁ ꢁO1ꢁ ꢁ ꢁH19b are 62.03ꢁ,
5
''
3
8
0.45ꢁ, and 68.52ꢁ, respectively.
1
13
4
''
O
Information provided by H and C NMR analyses
along with the data furnished by HMBC and HSQC exper-
iments were also crucial to the characterization of lactone
(5). Specific assignments obtained for hydrogen and carbon
atoms are provided in Table 2. Inexplicably, the attempt to
determine the stereochemistry of the exocyclic double bond
based on NOESY experiment failed and anticipated
correlations between hydrogens in spatial close proximity
were not observed. Single crystal X-ray diffraction of (5),
in the solid state, revealed that it presents an E configura-
tion (Fig. 7). The ORTEP-3 view of the lactone (5) shows
that this compound is also almost flat excluding the phenyl
ring B, as observed for lactone (4). The main structural
features responsible for the coplanarity and the
conjugation between the rings A and C is the unsaturated
C4–C5 bond and two weak non-classical intra-molecular
hydrogen bonds involving, in this case, C3–H3. . .O3 and
C5–H5. . .O5 (see Table 6). The least-squares plane
through the planar phenyl ring B (Rms deviation of
O
Fig. 3. Correlations observed for compound (4) in the NOESY
experiment.
Fig. 4. ORTEP-3 view of the lactone (4) showing the ring and atom
labelling and 50% probability ellipsoids. H atoms are shown as spheres of
arbitrary radii.
˚
fitted atoms = 0.0056 A) forms an angle of 77.7(2)ꢁ
with the least-square plane (Rms deviation of fitted

202
R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
Table 3
Bond lengths (A) and angles (ꢁ) for lactone (4) determined by XRD (query value) and MOGUL (Mogul value) intra-molecular analysis
˚
Fragment
Query value
Mogul value
Fragment
Query value
Mogul value
C(1)–O(1)
C(1)–O(2)
C(1)–C(2)
C(2)–C(3)
C(2)–C(6)
C(3)–C(4)
C(4)–C(5)
C(4)–O(2)
C(5)–C(13)
C(6)–C(7)
C(13)–C(14)
C(13)–C(18)
C(14)–C(15)
C(15)–C(16)
C(16)–O(3)
C(16)–C(17)
C(17)–O(4)
C(17)–C(18)
a
1.213(3)
1.384(2)
1.462(3)
1.341(3)
1.503(3)
1.439(3)
1.345(3)
1.400(2)
1.455(3)
1.502(3)
1.401(3)
1.413(3)
1.395(3)
1.376(3)
1.371(2)
1.381(3)
1.370(2)
1.375(3)
1.21(2)
1.39(2)
1.47(3)
1.36(3)
1.51(3)
1.43(2)
1.3(1)
1.38(2)
1.47(2)
1.51(2)
1.39(2)
1.40(2)
1.38(2)
1.39(2)
1.38(2)
1.39(3)
1.38(2)
1.38(2)
C(19)–O(4)
C(19)–O(3)
C–Cring B
1.431(3)
1.434(3)
1.390(5)
1.43(2)
1.43(2)
1.38(3)
C–C–CRing B
120(1)
120(3)
120(2)
120(3)
C–C–CRing C
a
O(2)–C(1)–C(2)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
O(2)–C(4)–C(3)
C(4)–C(5)–C(13)
C(7)–C(6)–C(2)
O(3)–C(16)–C(17)
O(4)–C(17)–C(16)
O(4)–C(19)–O(3)
C(1)–O(2)–C(4)
C(16)–O(3)–C(19)
C(17)–O(4)–C(19)
108.6(2)
106.8(2)
109.5(2)
107.7(2)
131.1(2)
112.8(2)
110.2(2)
109.7(2)
107.9(2)
107.4(2)
105.7(2)
106.0(2)
108
No hits
No hits
108(1)
132(7)
113(2)
110(1)
110(1)
108(2)
107(1)
105(2)
105(2)
One hit appeared in the MOGUL intra-molecular analysis.
Table 4
Hydrogen bonding for lactone (4)
a
˚
Hꢁ ꢁ ꢁA ( A˚ )
Dꢁ ꢁ ꢁA ( A˚ )
D—Hꢁ ꢁ ꢁA
D–H (A)
D–Hꢁ ꢁ ꢁA (ꢁ)
C19–H18. . .O2
0.93
0.93
0.93
0.93
0.97
0.93
2.414
2.611
2.490
2.470
2.510
2.666
3.021(2)
3.333(2)
3.333(2)
3.332(2)
3.452(3)
3.370(3)
123
135
151
155
164
133
i
C3–H3ꢁ ꢁ ꢁO1
i
C5–H5ꢁ ꢁ ꢁO1
i
C15–H15ꢁ ꢁ ꢁO4
iv
iv
C19 –H19b ꢁ ꢁ ꢁO1
vi
C11–H11ꢁ ꢁ ꢁO2
a
Symmetry codes: i = x ꢀ 1, y, z; iv = ꢀx + 1/2, ꢀy + 2, z + 1/2; vi = ꢀx + 1, y ꢀ 1/2, ꢀz + 3/2.
Fig. 6. The crystal structure of (4) projected onto the bc plane (011).
Symmetry codes: iii = ꢀx + 1/2, ꢀy + 2, z ꢀ 1/2; iv = ꢀx + 1/2, ꢀy + 2,
z + 1/2; v = ꢀx + 1, y + 1/2, ꢀz + 3/2; vi = ꢀx + 1, y ꢀ 1/2, ꢀz + 3/2.
Fig. 5. View of the network of hydrogen bonds parallel to [001] which
stabilizes the packing of (4). Symmetry codes: i = x ꢀ 1, y, z; ii = x + 1, y, z.
˚
atoms = 0.0323A) passing through the remaining atoms.
The crystal packing of (5) is also stabilized by weak
non-classical hydrogen bonds (Fig. 8 and Table 6). A
dimeric chain is formed along [010] linked by bifurcated
Their main geometric experimental parameters and its
MOGUL analysis are given in Table 5.

R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
203
Fig. 7. ORTEP-3 view of the lactone (5), showing the ring and atom
labelling and 50% probability ellipsoids and H atoms are shown as spheres
of arbitrary radii.
Fig. 8. View of the network of hydrogen bonds parallel to [010] for
compound (5). Symmetry codes: i = x, y + 1, z; ii = ꢀx + 2, y + 1/2,
ꢀz + 3/2; iii = ꢀx + 2, y ꢀ 1/2, ꢀz + 3/2; iv = ꢀx + 1, y + 1/2, ꢀz + 1/2;
v = ꢀx + 1, y ꢀ 1/2, ꢀz + 1/2.
i
inter-molecular hydrogen bonds: C20–H20a . . .O1 and
ii
C21–H21a . . .O1 (symmetry code: i = x, y + 1, z;
ii = ꢀx + 2, y + 1/2, ꢀz + 3/2). As in (4) The dimeric
chains are associated with one another by van der Waals
and H. . .p-aryl interactions along [101], forming an infinite
two-dimensional network parallel to the (10-1) plane. The
planes are also linked to one another by four very weak
Table 6
Hydrogen bonding for lactone (5)
a
D–H (A) Hꢁ ꢁ ꢁA ( A˚ ) Dꢁ ꢁ ꢁA ( A˚ ) D–Hꢁ ꢁ ꢁA (ꢁ)
˚
D–Hꢁ ꢁ ꢁA
C3–H3. . .O3
C5–H5. . .O5
C19–H19c. . .O5
C19–H19b. . .O5
C20–H20a. . .O1
C20–H20b. . .O2
0.93
0.93
0.96
0.96
0.96
0.96
0.96
0.96
2.253
2.179
2.945
2.819
2.525
2.776
2.794
2.652
2.839
2.660
3.742
3.595
3.401
3.676
3.701
3.358
120
111
141
139
152
156
158
131
vi
non-classical hydrogen bonds (C20–H20b. . .O2 , C20–
vi
vii
vi
vii
H20c. . .O2 ,
where vi = ꢀx + 2, ꢀy, ꢀz + 1; vii = ꢀx + 1, ꢀy,
z + 1), as shown in Fig. 9. The resulting is an extended
C19–H19c. . .O2 ,
C19–H19b. . .O5
vii
viii
ꢀ
vi
vii
iii
three-dimensional supramolecular assembly mediated
mainly by C–H. . .O bonding.
C20–H20c. . .O2
C21–H21a. . .O1
a
In order to ascertain if the predicted stability of the var-
ious possible geometric isomers of (4) and (5), was kinetic
Symmetry codes: iii = ꢀx + 2, y ꢀ 1/2, ꢀz + 3/2; vi = ꢀx + 2, ꢀy,
ꢀz + 1; vii = ꢀx + 1, ꢀy, ꢀz + 1; viii = x, y ꢀ 1, z.
Table 5
˚
Bond lengths (A) and angles (ꢁ) for lactone (5) determined by XRD (Query value) and MOGUL (Mogul value) intra-molecular analysis
Fragment
Query value
Mogul Value
Fragment
Query value
Mogul value
C(1)–O(1)
C(1)–O(2)
C(1)–C(2)
C(2)–C(3)
C(2)–C(6)
C(3)–C(4)
C(4)–C(5)
C(4)–O(2)
C(5)–C(13)
C(6)–C(7)
C(13)–C(14)
C(13)–C(18)
C(14)–C(15)
C(15)–C(16)
C(16)–C(17)
C(17)–C(18)
C(14)–O(3)
C(16)–O(4)
C(21)–O(5)
C(18)–O(5)
a
1.213(7)
1.373(7)
1.433(9)
1.331(8)
1.505(9)
1.443(8)
1.344(8)
1.431(7)
1.449(7)
1.504(9)
1.406(7)
1.421(8)
1.394(8)
1.391(8)
1.376(8)
1.395(8)
1.351(6)
1.357(7)
1.422(7)
1.358(7)
1.21(2)
1.39(2)
1.47(3)
1.36(3)
1.51(3)
1.43(2)
1.3(1)
1.38(2)
1.47(2)
1.51(2)
1.41(2)
1.41(2)
1.38(2)
1.38(2)
1.38(2)
1.38(2)
1.37(2)
1.37(3)
1.42(4)
1.38(2)
C(19)–O(3)
C(20)–O(4)
C–Cring B
1.445(6)
1.428(7)
1.374(21)
1.42(4)
1.42(4)
1.38(3)
C–C–CRing B
C–C–CRing C
a
O(2)–C(1)–C(2)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
O(2)–C(4)–C(3)
C(4)–C(5)–C(13)
C(7)–C(6)–C(2)
C(14)–C(13)–C(5)
C(18)–C(13)–C(5)
C(1)–O(2)–C(4)
C(18)–O(5)–C(21)
C(14)–O(3)–C(19)
C(16)–O(4)–C(20)
C–C–CRing B(mean value)
C–C–CRing C(mean value)
108.3(5)
108.5(6)
109.7(6)
105.4(5)
136.4(5)
112.4(5)
127.2(5)
116.4(5)
108.1(4)
118.7(5)
119.4(4)
118.7(5)
120.0(4)
120(2)
108
No hits
No hits
107.8(5)
No hits
113(3)
121(3)
121(3)
107(1)
118(2)
118(2)
118(3)
120(2)
120(3)
One hit appeared in the MOGUL intra-molecular analysis.

204
R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
to these two structures being the lowest energy forms. The
transition states of the reactions involving formation of (4)
and (5) probably predispose formation of these geometric
isomers and the isomer selection forces appear to be ther-
modynamic rather than kinetic in origin. For instance,
the hydrogen bond seen in (5) is probably a result of a
destabilizing interaction (steric repulsion between O5 and
O2). Also, the hydrogen bonding motif detected between
O3 and H3 which may arise in the transition state in a
Michael type association preselects the geometry into the
observed form (Fig. 7). The structure of nostoclide I which
has the Z configuration has been determined by single crys-
tal X-ray diffraction [11]. In this case the presence of the
isopropyl group precludes adoption of the E form.
4. Conclusion
Fig. 9. View of the network of hydrogen bonds parallel to [10-1] for
In this study, we fully characterise two nostoclide ana-
compound (5). Symmetry codes: vi = ꢀx + 2, ꢀy, ꢀz + 1; vii = ꢀx + 1,
logues, and using a variety of structural and spectroscopic
methods, verify compound identity. In addition, the corre-
lation between spectral properties and the observed geom-
etries using X-ray diffraction will aid analysis of new
compounds and, importantly, aid future exploration of
structure activity relationships for ascertaining the nosto-
clide pharmacophore and the binding requirements of the
receptor.
ꢀy, ꢀz + 1.
or thermodynamic in origin, we performed density func-
tional theory calculations (B3LYP/6-31+G level)
Fig. 10) using the Gaussian03 program. After conver-
*
(
gence, the differences in energy between the two geometric
isomers (4Z & 4E) and (5Z & 5E) in the gas phase were
ꢀ
1
1
4.18 and 0.96 kJmol respectively, with the crystal struc-
tures 4Z and 5E having the lowest energies. Thus the fact
that isomers 4Z and 5E are found within the solid state
is not the result of crystal packing forces or intermolecular
bonding motifs depicted in Figs. 4 and 7, but rather is due
5. Supplementary material
Supplementary crystallographic data sets for (4) and (5)
are available through the Cambridge Structural Data Base,
Fig. 10. Energies in atomic units for conformers of 4Z: ꢀ1033.36053; 4E: ꢀ1033.35512; 5Z: ꢀ1188.39793; 5E: ꢀ1188.39829. Structure 4Z and 5E
correspond to conformations found within crystal structures. Large hashed circles, oxygen; medium circles, carbon, small circles, hydrogen.

R.R. Teixeira et al. / Journal of Molecular Structure 837 (2007) 197–205
205
deposition numbers CCDC 619585 and 619586, respective-
ly. Copies of this information may be obtained free of char-
ge from The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (Fax: +44 123 336 033; e-mail: deposit@
ccdc.cam.ac.uk or http:www.ccdc.ac.uk).
[13] (a) L.C.A. Barbosa, C.R.A. Maltha, A.J. Demuner, F.R. Gann, A.A.
Silva, Qu ´ı m. Nova 28 (2005) 444;
(
b) L.C.A. Barbosa, C.R.A. Maltha, A.J. Demuner, C. Filomeno,
A.A. Silva, Qu ´ı m. Nova 27 (2004) 241;
c) L.S. Lima, L.C.A. Barbosa, E.S. Alvarenga, A.J. Demuner, A.A.
Silva, Aust. J. Chem. 36 (2003) 625;
d) L.C.A. Barbosa, E.S. Alvarenga, A.J. Demuner, R. Figueiredo,
A.A. Silva, Pest. Manag. Sci. 59 (2003) 1043;
e) L.C.A. Barbosa, A.V. Costa, A.J. Demuner, A.A. Silva, J. Agric.
Food Chem. 47 (2000) 4807;
f) L.C.A. Barbosa, J. Braz. Chem. Soc. 8 (1997) 19.
(
(
Acknowledgements
(
We thank the Brazilian Research Council CNPq (Con-
selho Nacional de Desenvolvimento Cient ´ı fico e Tecnol o´ g-
ico) for research fellowships (LCAB, DPV, RRT), and
FAPEMIG (Funda c¸ a˜ o de Amparo a` Pesquisa do Estado
de Minas Gerais) for financial support. One of us,
A.C.D., thanks the Instituto Rocasolano-CSIC, Spain,
for the CSD licence.
(
[14] Enraf-Nonius COLLECT. Nonius BV, Delft, The Netherlands, 1997–
2000.
[
15] Z. Otwinowski, W. Minor, in: C.W. CarterJr., R.M. Sweet (Eds.),
Methods in Enzymology, vol. 276, Academic Press, New York, 1997,
p. 307.
[
16] G.M. Sheldrick, SHELXS-97. Program for Crystal Structure Reso-
lution, University of G o¨ ttingen, G o¨ ttingen, Germany, 1997.
17] G.M. Sheldrick, SHELXL-97. Program for Crystal Structures Anal-
ysis, University of G o¨ ttingen, G o¨ ttingen, Germany, 1997.
18] L.J. Farrugia, J. Appl. Cryst. 32 (1999) 837.
[
References
[
[
19] F.H. Allen, O. Johnson, G.P. Shields, B.R. Smith, M. Towler, J.
Appl. Cryst. 37 (2004) 335.
[
[
1] J. Stetter, F. Lieb, Angew. Chem. Int. Ed. 39 (2000) 1724.
2] C. Tomlin (Ed.), The Pesticide Manual, Royal Society of Chemistry,
Cambridge, 1994.
[
20] I.J. Bruno, J.C. Cole, P.R. Edgington, M.K. Kessler, C.F. Macrae, P.
McCabe, J. Pearson, R. Taylor, Acta Crystallogr. B58 (2002) 389.
21] L.J.J. Farrugia, Appl. Cryst. 30 (1997) 565.
[
[
3] M.D. Devine, A. Shukla, Crop Protection 19 (2000) 881–889.
4] (a) A.J. Demuner, L.C.A. Barbosa, T.A.M. Veiga, R.W. Barreto,
B.K. Diaz, B.L. Hennssen, Biochemical Systematics and Ecology 34
[
[
[
22] Cerius 2 software, Accelerys Inc., San Diego, CA, USA.
23] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery, R.E. Strat-
mann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N.
Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R.
Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski,
G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick,
A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V.
Ortiz, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,
C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W.
Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, M. Head-
Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN98 program, Gauss-
ian Inc., Pittsburgh, PA, 1998.
(
(
2006) 790–795;
b) L.C.A. Barbosa, A.V. Costa, D.P. Veloso, J.L.C. Lopes, M.G.
Hernandez-terrones, B.K. Diaz, B.L. Hennsen, Z. Naturforschung
9c (2004) 803;
c) L.C.A. Barbosa, M.L. Ferreira, A.J. Demuner, A.A. Silva, R.C.
Pereira, Qu ´ı m. Nova 24 (2001) 1;
d) L.C.A. Barbosa, E.S. Alvarenga, A.J. Demuner, L.S. Virtuoso,
5
(
(
A.A. Silva, Chem. Biodiversity 3 (2006) 553.
5] (a) J.R. Vyvyan, Tetrahedron 58 (2002) 1631;
[
(
b) S.O. Duke, F.E. Dayan, J.G. Romagni, A.M. Rimando, Weed
Res. 40 (2000) 49;
c) S.O. Duke, J.A. Romagni, F.E. Dayan, Crop Protection 19 (2000)
83;
d) S.O. Duke, F.E. Dayan, A.M. Rimando, K.K. Schrader, G.
Aliotta, A. Oliva, J.G. Romagni, Weed Sci. 50 (2002) 138;
e) S.O. Duke, in: J.M. Clark, H. Ohkawa (Eds.), New Discoveries in
(
5
(
[24] (a) G. Casiraghi, F. Zanardi, G. Appendino, G. Rassu, Chem. Rev.
1
00 (2000) 1929;
(
(
(
b) J. Boukouvalas, F. Maltais, N. Lachance, Tetrahedron Lett. 35
1994) 7897;
c) J. Boukouvalas, N. Lachance, M. Ouellete, M. Trudeau, Tetra-
(
Agrochemicals, ACS Symposium Series 892, 2005, Chap. 14, p. 151.
6] J.J. Pignatello, J. Porwooll, R.E. Carlson, A. Xavier, F.K. Gleason, J.
Org. Chem. 48 (1983) 4035.
[
hedron Lett. 39 (1998) 76665;
(
(
d) A. Kar, S. Gogoi, N.P. Argade, Tetrahedron 61 (2005) 5297;
e) F. Bellina, C. Anselmi, S. Viel, L. Mannina, R. Rossi, Tetrahedron
[
[
[
7] F.K. Gleason, C.A. Baxa, FEMS Microbiol. Lett. 33 (1986) 85.
8] F.K. Gleason, D.E. Case, Plant Physiol. 80 (1986) 834.
9] F.K. Gleason, J.L. Paulson, Arch. Microbiol. 138 (1984) 273.
5
7 (2001) 9997;
(
(
f) F. Bellina, C. Anselmi, R. Rossi, Tetrahedron Lett. 43 (2002) 2023;
g) L.C.A. Barbosa, A.J. Demuner, E.S. de Alvarenga, A. Oliveira,
[
[
10] F.K. Gleason, FEMS Microbiol. Lett. 68 (1990) 77.
11] X. Yang, Y. Shimizu, J.R. Steiner, J. Clardy, Tetrahedron Lett. 34
B.K. Diaz, B.L. Hennsen, Pest. Manag. Sci. 62 (2006) 214.
25] I.J. Bruno, J.C. Cole, M. Kessler, J. Luo, W.D.S. Motherwell, L.H.
Purkis, B.R. Smith, R. Taylor, R.I. Cooper, S.E. Harris, A.G. Orpen,
J. Chem. Inf. Comput. Sci. 44 (2004) 2133.
(1993) 761.
[
[
[
12] (a) G.W. Gribble, Pure Appl. Chem. 68 (1996) 1699;
(
(
b) G.W. Gribble, Chemosphere 52 (2003) 289;
c) F.M.D. Ismail, J. Fluorine Chem. 118 (2002) 27.
26] F.H. Allen, Acta Crystallogr. B58 (2002) 380.