Structural and spectroscopic studies of new o-, m- and p-nitrobenzyl esters of lasalocid acid

Article abstract of DOI:10.1016/j.molstruc.2007.07.020

New o-, m- and p-nitrobenzyl esters of lasalocid (o-ELAS, m-ELAS and p-ELAS) have been synthesised and studied by X-ray, ¹H, ¹³C NMR, FT-IR, UV-Vis, fluorescence as well as PM5 semiempirical methods. The crystal structure of o-ELAS i

Full text of DOI:10.1016/j.molstruc.2007.07.020

Available online at www.sciencedirect.com
Journal of Molecular Structure 877 (2008) 105–114
www.elsevier.com/locate/molstruc
Structural and spectroscopic studies of new
o-, m- and p-nitrobenzyl esters of lasalocid acid
a
a
a
a
´
Adam Huczynski , Tomasz Pospieszny , Rafał Wawrzyn , Małgorzata Ratajczak-Sitarz ,
a
a,
b
Andrzej Katrusiak , Bogumil Brzezinski *, Franz Bartl
a
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Institute of Medical Physics and Biophysics, Charite´ – Universita¨tsmedizin Berlin Campus Charite´ Mitte, Ziegelstr. 5/9, 10117 Berlin, Germany
b
Received 29 June 2007; accepted 16 July 2007
Available online 21 July 2007
Abstract
New o-, m- and p-nitrobenzyl esters of lasalocid (o-ELAS, m-ELAS and p-ELAS) have been synthesised and studied by X-ray, 1H, 13
C
NMR, FT-IR, UV–Vis, fluorescence as well as PM5 semiempirical methods. The crystal structure of o-ELAS is stabilized by three intra-
molecular hydrogen bonds in which the ketone is not engaged. The FT-IR spectra of o-ELAS, m-ELAS and p-ELAS in the chloroform
and acetonitrile solutions indicate that in these solvents other structures are realized in which the ketone group is hydrogen bonded. In
the solution the hydrogen bonds in which the carbonyl ester groups are involved becomes slightly weaker and partially dissociated. The
dissociation of these hydrogen bonds increases with increasing solvent polarity. The structures of the o-, m- and p-nitrobenzyl esters of
lasalocid acid are discussed in detail.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Lasalocid; Nitrobenzyl esters; FT-IR; 1H NMR; 13C NMR; COSY
1. Introduction
alkyl chains the oxygen atoms become more active in the
complexation process of the monovalent cations.
Lasalocid acid is very important ionophore antibiotic
because it is capable of transporting monovalent and biva-
lent metal cations across natural and artificial lipid mem-
branes [1–11]. In the cell membrane, lasalocid exchanges
metal ions against protons, leading to changes in the pH
values and to an increase in the osmotic pressure inside
the cell, which finally leads to the cell death. The effective-
ness of this process strongly depends on the structure of the
lasalocid metal cation complexes. This ionophore antibi-
otic is a good anticoccidial agent for cattle, sheep and
chicken [12–17].
Presently we report the syntheses of new types of the
o-, m- and p-nitrobenzyl lasalocid esters (o-ELAS,
m-ELAS, p-ELAS). The structures of these esters in the
chloroform and acetonitrile solutions as well as in the solid
1
state were studied using the H and 13C NMR, FT-IR,
UV–Vis and fluorescence, PM5 and X-ray methods.
2. Experimental
2.1. Preparation of o-, m- and p-nitrobenzyl
lasalocid esters
Up to now some esters of lasalocid, in particular those
including polyoxaalkyl chains, were synthesised and their
structure was studied using various methods [18–23]. It
was demonstrated that with increasing length of the oxa-
Lasalocid sodium salt was dissolved in dichlorometh-
ane and stirred vigorously with a layer of aqueous sul-
phuric acid (pH 1.5). The organic layer containing
lasalocid (LAS) was washed with distilled water, and
dichloromethane was evaporated under reduced pressure
to dryness.
*
Corresponding author. Tel.: +48 618291330.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.07.020

106
A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
A mixture of the corresponding o-(m- or p-)nitrobenzyl
Table 2. The crystallographic-information-file (CIF) has
been deposited with the Cambridge Crystallographic
Database Centre as a Supplementary Publication No.
CCDC 651061 (Table 3).
chloride (300 mg, 1.69 mmol), LAS (500 mg, 0.85 mmol)
and 1,8-diazabicyclo[5.4.0]undec-7-en (DBU) (130 mg,
0.85 mmol) and 40 ml toluene was heated at 90 ꢁC for
5 h. After cooling, the precipitate DBU–hydrochloride
(DBUÆHCl) was filtered and washed with hexane. The
filtrate was evaporated under reduced pressure and the
residue purified by chromatography on silica gel (Fluka
type 60) to give: o-ELAS (347 mg, 57% yield, m.p.
85 ꢁC), m-ELAS (292 mg, 47% yield), p-ELAS (460 mg,
75% yield), respectively.
2.3. NMR measurements
The NMR spectra were recorded in CDCl3 and CD3CN
using a Varian Gemini 300 MHz spectrometer. All spectra
were locked to deuterium resonance of CDCl3 and
1
CD3CN. The error in ppm values was 0.01. All H NMR
Elementary analysis: Calculated: C 67.84%; H 8.19%; N
1.93%. Found o-ELAS: C 67.88%, H 8.22%; N 1.97%,
m-ELAS: C 67.89%, H 8.24%; N 1.95%, p-ELAS: C
67.83%, H 8.18%; N 1.92%.
measurements were carried out at the operating frequency
300.075 MHz; flip angle, pw = 45ꢁ; spectral width,
sw = 4500 Hz; acquisition time, at = 2.0 s; relaxation
delay, d1=1.0 s; T = 293.0 K and TMS as the internal
standard. No window function or zero filling was used.
Digital resolution = was 0.2 Hz/point. 13C NMR spectra
were recorded at the operating frequency 75.454 MHz;
pw = 60ꢁ; sw = 19,000 Hz; at = 1.8 s; d1=1.0 s; T =
293.0 K and TMS as the internal standard.
2.2. X-ray measurements
The crystals selected for the single-crystal X-ray diffrac-
tion measurement had the form of colourless parallelepi-
peds with well-developed faces. They were stable in
normal conditions and the X-ray diffraction measurements
were carried out on a Kuma KM-4 CCD diffractometer at
room temperature. The structure was solved by direct
methods [24] and refined by full-matrix least squares [25].
The positions of all the H-atoms were determined on the
basis of the molecular geometry (C–H 0.98–0.93, O–H
1
The H and 13C NMR signals were assigned indepen-
dently for each species using one or two-dimensional
(COSY, HETCOR, HMBC, NOESY) spectra.
2.4. FT-IR measurements
˚
The FT-IR spectra of o-ELAS, m-ELAS and p-ELAS
were recorded in the mid infrared region in acetonitrile
solutions and potassium bromide tablet using a Bruker
IFS 113v spectrometer. A cell with Si windows and
wedge-shaped layers was used to avoid interferences (mean
layer thickness 170 lm). The spectra were taken with an
IFS 113v FT-IR spectrophotometer (Bruker, Karlsruhe)
0.82 A) and their Uiso’s were related to the thermal vibra-
tions of their carriers. The absolute conformation of
o-ELAS in the crystal was consistent with the chemical
information. Selected details about the crystal structure,
experiment and structure solution and refinement are given
in Table 1, the fractional atomic coordinates are listed in
equipped with a DTGS detector; resolution 2 cmꢀ1
,
Table 1
NSS = 125. The Happ-Genzel apodization function was
used.
Crystal data and structure refinement (o-ELAS)
Empirical formula
Wavelength
C41H59NO10
˚
0.71073 A
Crystal system, space group
Orthorhombic, P212121
2.5. UV–Vis and fluorescence measurements
Unit cell dimensions
˚
a (A)
9.2440(7)
15.9407(12)
27.6036(17)
4067.6(5)
The absorption spectra of o-, m- and p-nitrobenzyl esters
of lasalocid acid were recorded in 1 cm cells on a spectro-
photometer Jasco V-550 (JASCO, Tokyo, Japan). The
solutions of o-, m- and p-nitrobenzyl esters of lasalocid acid
(1 · 10ꢀ5 mol dmꢀ3) in spectral-grade CH3CN were used in
the UV–Vis spectrometry experiments. The intensity of
fluorescence emitted was measured for o-, m- and p-nitrob-
enzyl esters at the angle 90ꢁ relative to the incident excita-
tion light. During the absorption and fluorescence
measurements the samples were kept at room temperature.
The samples were excited at 260 nm. The fluorescence
quantum yields o-, m- and p-nitrobenzyl esters of lasalocid
acid were estimated from the equation:
˚
b (A)
˚
c (A)
3
˚
Volume (A )
Z
4
Calculated density
Absorption coefficient
F(000)
Crystal size
h Range for data collection
Limiting indices
Reflections collected/unique
Completeness to h = 29.33
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2r(I)]
R indices (all data)
Largest diff. peak and hole
1.185 g cmꢀ3
0.084 mmꢀ1
1568
0.45 · 0.40 · 0.30 mm
2.55–29.33ꢁ
ꢀ7 6 h 6 12, ꢀ21 6 k 6 21, ꢀ37 6 l637
31,368/10,285; Rint = 0.0449
94.7%
Full-matrix least-squares on F2
10,285/0/469
0.988
R1 = 0.0506, wR2 = 0.0782
R1 = 0.1371, wR2 = 0.0962
0.224 and ꢀ0.205 e A
ꢀ
ꢁ
2
AR F S nS
US ¼ UR ꢁ
ꢁ
ꢀ3
˚
F R
AS
nR

A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
107
Table 2
Atomic coordinates (·104) and equivalent isotropic displacement param-
eters (A · 10 ), (U(eq) is defined as one-third of the trace of the
orthogonalized Uij tensor)
Table 3
˚
Bond lengths (A) and angles (ꢁ) (o-ELAS)
2
3
˚
O(1)–C(1)
O(1)–C(35)
O(2)–C(1)
1.318(3)
1.449(3)
1.205(3)
1.353(3)
1.449(2)
1.209(3)
1.432(3)
1.465(3)
1.443(2)
1.444(3)
1.442(2)
1.226(3)
1.226(3)
1.473(3)
1.488(3)
1.408(3)
1.429(3)
1.401(3)
1.351(3)
1.516(4)
1.395(3)
1.383(3)
1.513(3)
1.544(3)
1.530(3)
1.525(3)
1.533(3)
1.526(3)
1.529(3)
1.540(3)
1.532(3)
1.525(3)
1.558(3)
1.534(3)
1.531(4)
1.535(4)
1.530(3)
1.527(4)
1.542(3)
1.507(3)
1.522(3)
1.529(3)
1.525(3)
1.526(3)
1.541(3)
1.528(3)
1.514(3)
1.534(4)
1.508(3)
1.389(3)
1.398(3)
1.379(4)
1.373(4)
1.367(4)
1.386(4)
119.75(19)
110.86(17)
115.12(16)
124.3(3)
117.6(3)
118.0(3)
120.8(2)
124.4(2)
114.8(2)
(continued on next page)
x
y
z
U(eq)
O(3)–C(3)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
748(2)
5590(1)
6657(1)
7642(1)
5702(1)
5350(1)
5715(1)
6976(1)
6154(1)
3830(2)
4758(2)
4171(2)
6261(2)
6471(2)
7173(2)
7430(2)
6987(2)
6279(2)
5992(2)
5232(2)
5488(1)
4760(1)
5092(1)
4438(1)
4835(2)
4554(2)
4913(2)
5054(2)
5742(2)
6258(2)
6458(2)
5719(2)
6012(2)
6606(2)
7312(2)
7986(2)
6917(2)
7521(2)
7036(2)
7743(2)
4254(2)
4770(2)
4324(2)
3715(2)
4239(2)
8188(2)
5332(2)
4391(2)
3842(2)
2984(2)
2645(2)
3155(3)
4019(2)
6835(1)
6397(1)
6005(1)
8535(1)
9327(1)
9538(1)
8971(1)
8038(1)
8011(1)
7532(1)
7615(1)
6569(1)
6505(1)
6213(1)
6121(1)
6327(1)
6609(1)
6704(1)
7028(1)
7562(1)
7922(1)
8437(1)
8840(1)
9318(1)
9785(1)
9771(1)
10,259(1)
10,126(1)
9727(1)
9316(1)
9055(1)
8643(1)
8297(1)
8585(1)
8781(1)
7907(1)
7535(1)
9918(1)
10,107(1)
10,471(1)
10,229(1)
10,236(1)
8743(1)
7859(1)
5802(1)
6929(1)
6870(1)
7210(1)
7190(1)
6797(2)
6440(1)
6480(1)
60(1)
85(1)
74(1)
46(1)
57(1)
50(1)
45(1)
54(1)
105(1)
78(1)
63(1)
46(1)
37(1)
48(1)
54(1)
60(1)
51(1)
38(1)
41(1)
42(1)
37(1)
37(1)
37(1)
39(1)
44(1)
46(1)
60(1)
64(1)
50(1)
44(1)
52(1)
54(1)
41(1)
47(1)
72(1)
55(1)
75(1)
63(1)
101(1)
95(1)
61(1)
96(1)
54(1)
52(1)
93(1)
54(1)
45(1)
49(1)
70(1)
86(1)
81(1)
65(1)
O(4)–C(11)
O(5)–C(13)
O(6)–C(15)
O(6)–C(18)
O(7)–C(19)
O(7)–C(23)
O(8)–C(22)
O(9)–N(1)
O(10)–N(1)
N(1)–C(37)
C(1)–C(2)
C(2)–C(3)
C(2)–C(7)
C(3)–C(4)
C(4)–C(5)
C(4)–C(34)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(10)–C(33)
C(11)–C(12)
C(12)–C(13)
C(12)–C(32)
C(13)–C(14)
C(14)–C(30)
C(14)–C(15)
C(15)–C(16)
C(16)–C(29)
C(16)–C(17)
C(17)–C(18)
C(18)–C(27)
C(18)–C(19)
C(19)–C(20)
C(20)–C(21)
C(21)–C(22)
C(22)–C(25)
C(22)–C(23)
C(23)–C(24)
C(25)–C(26)
C(27)–C(28)
C(30)–C(31)
C(35)–C(36)
C(36)–C(37)
C(36)–C(41)
C(37)–C(38)
C(38)–C(39)
C(39)–C(40)
C(40)–C(41)
C(1)-O(1)–C(35)
C(15)-O(6)–C(18)
C(19)-O(7)–C(23)
O(10)–N(1)–O(9)
O(10)–N(1)–C(37)
O(9)–N(1)–C(37)
O(2)–C(1)-O(1)
O(2)–C(1)–C(2)
O(1)–C(1)–C(2)
1481(2)
ꢀ320(2)
ꢀ830(2)
ꢀ3404(2)
ꢀ150(2)
1317(2)
1802(2)
3564(3)
4504(2)
3684(3)
497(3)
ꢀ1060(2)
ꢀ1371(3)
ꢀ2794(3)
ꢀ3879(3)
ꢀ3609(3)
ꢀ2225(3)
ꢀ2090(2)
ꢀ1861(2)
ꢀ1779(2)
ꢀ1955(2)
ꢀ1963(2)
ꢀ2444(2)
ꢀ1693(2)
ꢀ125(3)
633(3)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
1725(3)
998(3)
2075(2)
2731(3)
3699(3)
2910(2)
2200(3)
3242(3)
3946(3)
3303(3)
222(3)
1158(3)
1294(3)
ꢀ2601(3)
ꢀ4072(3)
ꢀ3029(3)
ꢀ398(2)
ꢀ3064(3)
2224(2)
2245(2)
2820(3)
2635(3)
1938(4)
1409(3)
1528(3)
where UR is the quantum yield of the standard, A is the
absorbance at the wavelength of the excitation, F is the
integrated intensity of the emission spectra, n is the refrac-
tive index of solution, the index (S) means sample and (R )
means reference. The standard fluorophore for the quan-
tum yield measurements was Quinine sulfate in
0.2 mol dmꢀ3 H2SO4 (UR = 0.51) [26].

108
A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
Table 3 (continued)
Table 3 (continued)
C(3)–C(2)–C(7)
C(3)–C(2)–C(1)
C(7)–C(2)–C(1)
O(3)–C(3)–C(4)
119.3(2)
116.4(2)
124.2(2)
115.8(2)
C(36)–C(37)–N(1)
C(39)–C(38)–C(37)
C(40)–C(39)–C(38)
C(39)–C(40)–C(41)
C(40)–C(41)–C(36)
119.7(2)
118.7(3)
120.1(3)
120.5(3)
121.3(3)
O(3)–C(3)–C(2)
122.4(2)
C(4)–C(3)–C(2)
121.8(2)
C(5)–C(4)–C(3)
118.0(2)
C(5)–C(4)–C(34)
C(3)–C(4)–C(34)
C(4)–C(5)–C(6)
122.6(3)
119.5(3)
121.6(3)
122.5(2)
R
C(7)–C(6)–C(5)
31
15
O(2)
O(1)
C(6)–C(7)–C(2)
C(6)–C(7)–C(8)
C(2)–C(7)–C(8)
C(7)–C(8)–C(9)
116.6(2)
116.9(2)
126.4(2)
1
32
12
O
O
33
30
29
16
8
2
HO
3
7
13
11
14
10
111.39(18)
115.15(19)
109.59(18)
112.47(18)
112.27(19)
109.33(17)
108.99(18)
116.33(18)
110.38(19)
112.81(18)
105.91(18)
120.9(2)
120.9(2)
118.3(2)
111.20(19)
116.7(2)
107.05(17)
105.7(2)
108.90(19)
117.16(19)
113.3(2)
115.1(2)
101.25(19)
105.5(2)
105.23(19)
104.9(2)
113.2(2)
109.14(19)
112.9(2)
110.9(2)
O(3)
17
9
28
21
C(10)–C(9)–C(8)
C(11)–C(10)–C(9)
C(11)–C(10)–C(33)
C(9)–C(10)–C(33)
O(4)–C(11)–C(10)
O(4)–C(11)–C(12)
C(10)–C(11)–C(12)
C(11)–C(12)–C(13)
C(11)–C(12)–C(32)
C(13)–C(12)–C(32)
O(5)–C(13)–C(12)
O(5)–C(13)–C(14)
C(12)–C(13)–C(14)
C(30)–C(14)–C(13)
C(30)–C(14)–C(15)
C(13)–C(14)–C(15)
O(6)–C(15)–C(16)
O(6)–C(15)–C(14)
C(16)–C(15)–C(14)
C(29)–C(16)–C(15)
C(29)–C(16)–C(17)
C(15)–C(16)–C(17)
C(18)–C(17)–C(16)
O(6)–C(18)–C(27)
O(6)–C(18)–C(17)
C(27)–C(18)–C(17)
O(6)–C(18)–C(19)
C(27)–C(18)–C(19)
C(17)–C(18)–C(19)
O(7)–C(19)–C(20)
O(7)–C(19)–C(18)
C(20)–C(19)–C(18)
C(19)–C(20)–C(21)
C(20)–C(21)–C(22)
O(8)–C(22)–C(25)
O(8)–C(22)–C(23)
C(25)–C(22)–C(23)
O(8)–C(22)–C(21)
C(25)–C(22)–C(21)
C(23)–C(22)–C(21)
O(7)–C(23)–C(22)
O(7)–C(23)–C(24)
C(22)–C(23)–C(24)
C(22)–C(25)–C(26)
C(28)–C(27)–C(18)
C(14)–C(30)–C(31)
O(1)–C(35)–C(36)
C(37)–C(36)–C(41)
C(37)–C(36)–C(35)
C(41)–C(36)–C(35)
C(38)–C(37)–C(36)
C(38)–C(37)–N(1)
H33C4
O(6)
OH
O
O
6
4
18
19
27
20
O(5)
O(4)
5
O(7)
O
23
26
25
22
24
OH
O(8)
35
35
35
R =
CH2
36
37
CH2
36
CH2
36
NO2
41
40
37
38
41
40
41
40
37
38
38
39
NO2
39
39
NO2
o-ELAS
p-ELAS
m-ELAS
Scheme 1. The structures and atom numbering of o-ELAS, m-ELAS and
p-ELAS.
Table 4
The parameters (length and angle) of intramolecular hydrogen bonds of o-
ELAS, m-ELAS and p-ELAS determined from X-ray studies and
calculated by PM5 semiempirical method
109.08(19)
106.87(18)
116.7(2)
Compound
Used
Atoms engaged in
method hydrogen bonds
Length Angle
˚
(A)
(ꢁ)
o-ELAS(type A-crystal) X-ray
O(3)ꢀHÆÆÆO(2)
O(4)ꢀHÆÆÆO(8)
O(8)ꢀHÆÆÆO(4)
O(3)ꢀHÆÆÆO(2)
O(4)ꢀHÆÆÆO(8)
O(8)ꢀHÆÆÆO(4)
O(3)ꢀHÆÆÆO(2)
O(4)ꢀHÆÆÆO(5)
O(8)ꢀHÆÆÆO(4)
O(3)ꢀHÆÆÆO(2)
O(4)ꢀHÆÆÆO(5)
O(8)ꢀHÆÆÆO(4)
2.531(2) 147.54
2.884(2) 147.51
2.884(2) 166.42
110.8(2)
112.07(19)
104.94(19)
108.79(18)
113.5(2)
109.77(19)
109.99(19)
109.7(2)
110.67(19)
110.8(2)
115.3(2)
115.8(2)
117.1(2)
113.1(2)
106.0(2)
115.7(3)
124.0(2)
119.9(3)
123.5(3)
o-ELAS(type A)
o-ELAS(type B)
m-ELAS(type B)
p-ELAS(type B)
PM5
PM5
PM5
PM5
2.63
2.89
2.89
143.2
141.7
162.2
2.61
2.81
2.87
142.5
131.2
121.1
2.63
2.81
2.81
143.0
130.3
126.7
O(3)ꢀHÆÆÆO(2)
O(4)ꢀHÆÆÆO(5)
O(8)ꢀHÆÆÆO(4)
2.62
2.84
2.84
142.8
131.0
132.3
(type A) – Structure of o-ELAS in which the C13@O group is not engaged
in hydrogen bond; (type B) – structure of o-ELAS, m-ELAS and p-ELAS
in which the C13@O group is engaged in hydrogen bond.
116.8(3)

A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
109
2.6. Semiempirical calculations
PM5 semiempirical calculations were performed using
the WinMopac 2003 program. In all cases full geometry
optimisation of o-ELAS, m-ELAS and p-ELAS was carried
out without any symmetry constraints [27–30].
2.7. Elemental analysis
The elemental analysis of o-ELAS, m-ELAS and
p-ELAS were carried out on Vario ELIII (Elementar,
Germany).
2.8. Melting point
Melting point (uncorrected) was determined on a Bo¨e-
tius microscope hot stage.
3. Results and discussion
The structures and the numbering of the atoms of
o-ELAS, m-ELAS and p-ELAS are shown in Scheme 1.
3.1. X-ray analysis
o-ELAS crystallizes as a non-solvate from the acetoni-
trile solution. The molecular dimensions (Table 2) fully
confirm the chemical formula of the substance. Two
intramolecular hydrogen bonds are characteristic of all
the ELAS structures. The O(3)–H(3)ÆÆÆO(2) is very short
(Table 4) most likely due to the overcrowding effect of
the two adjacent substituents. On the other hand, the
nitro group could rotate to release the strain. The
other hydrogen bonds, between the hydroxyl groups
O(4)H and O(8)H are considerably longer and have a
character of a ‘‘tandem’’ in which the O(8)HÆÆÆO(4) angle
is much greater There are no intermolecular hydrogen
bonds in this molecular crystal (Fig. 3). It is thus plausi-
ble that the molecular conformation is primarily due to
the intramolecular interactions, which has been con-
firmed by the semiempirical calculations for the isolated
molecule.
3.2. NMR measurements
1
The H and 13C NMR data of o-ELAS, m-ELAS and
p-ELAS are collected in Tables 5 and 6, respectively. The
differences D (ppm) between the respective chemical shifts
observed in the spectra of the esters in acetonitrile and
chloroform are collected in Table 7.
Fig. 1. (a) A perspective view of o-ELAS in the crystal structure. Hydrogen
bonds have been indicated by dashed lines; (b) The structures of o-ELAS
without the engagement of the C@O carbonyl group in hydrogen bond (type
A), calculated by semiempirical PM5 method (WinMopac 2003).
1
The assignments of the H NMR and 13C NMR sig-
nals in the spectra o-, m- and p-nitrobenzyl lasalocid
esters were deduced on the basis of signal multiplications
and by the concerted application of the two dimensional
1H and 13C long-range Heteronuclear Multiple Bond Cor-
relation (HMBC) spectra. The analysis of the corrections
observed indicates that the C(1) and C(3) carbon atoms
are localized at 172.00 ppm and 160.65 ppm, respectively
indicating that the esters exist in the solutions as the enol
forms.

110
A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
Table 5
1H NMR and 13C NMR chemical shifts (ppm) of o-ELAS, m-ELAS and
p-ELAS in CD3CN
No. of o-ELAS
m-ELAS
p-ELAS
atom
1H NMR
13C
1H NMR
13C
1H NMR
13C
NMR
NMR
NMR
1
2
3
4
5
6
7
8
–
–
–
–
171.79
112.36
160.55
124.57
135.89
122.60
144.21
34.78
37.19
34.51
74.27
48.56
214.26
55.25
85.05
35.84
39.39
86.78
72.01
21.39
30.07
70.71
78.03
14.67
31.18
6.77
–
–
–
–
172.00
112.37
160.63
124.53
135.91
122.57
144.19
34.61
37.19
34.76
74.07
48.52
214.18
55.19
85.05
35.79
39.36
86.80
71.98
21.35
30.17
70.69
78.03
14.67
31.17
6.77
–
–
–
–
172.00
112.28
160.65
124.44
135.88
122.56
143.61
34.76
37.15
34.66
73.94
48.41
213.96
55.06
85.10
35.67
39.25
86.88
71.92
21.28
30.13
70.63
78.07
14.67
31.24
6.76
7.24
6.74
–
2.90
1.41, 1.58
1.30
3.86
2.95
–
2.71
3.88
2.15
1.52, 1.83
–
3.44
1.50, 1.70
1.49
–
3.62
1.13
1.22, 1.52
0.80
1.24
0.78
0.99
1.34, 1.80
0.78
0.75
0.83
2.15
5.75
–
7.22
6.72
–
2.90
1.40, 1.59
1.31
3.86
2.95
–
2.71
3.90
1.63
1.51, 1.85
–
3.43
1.51, 1.71
1.50
–
3.61
1.12
1.20, 1.53
0.83
1.25
0.80
0.98
1.36, 1.80
0.79
0.74
0.81
2.14
5.57
–
7.22
6.72
–
2.89
1.40, 1.60
1.30
3.86
2.94
–
2.72
3.88
2.14
1.50, 1.84
–
3.43
1.51, 1.70
1.47
–
3.62
1.13
1.20, 1.51
0.80
1.23
0.77
0.99
1.35, 1.81
0.78
0.76
0.81
2.17
5.57
–
7.69 (d)
8.26 (d)
–
8.26 (d)
7.69 (d)
11.00
3.27
4.01
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Fig. 2. The structures of o-ELAS with the engagement of the C@O
carbonyl group in hydrogen bond (type B) calculated by the semiempirical
PM5 method (WinMopac 2003).
31.64
8.87
31.64
8.90
31.63
8.92
15.87
17.58
12.74
14.05
12.41
15.70
64.84
131.64
148.91
125.78
130.42
131.44
134.82
–
15.88
17.54
12.75
13.95
12.49
15.69
66.39
138.39
124.08
149.02
124.26
130.76
135.19
–
15.87
17.41
12.53
13.91
12.74
15.60
66.90
148.87
130.24
124.51
144.23
124.51
130.24
–
–
8.34 (s)
–
8.12 (d)
7.57 (t)
7.63 (t)
7.74 (d)
7.86 (d)
7.63 (t)
8.20 (d)
11.00
3.26
3.91
O(3)H 10.88
O(4)H
O(8)H
Fig. 3. Arrangement of complex o-ELAS in the crystal lattice, projected
along the [100] crystal direction.
3.24
3.89
–
–
–
–
–
–
In the 1H NMR spectra of o-ELAS, m-ELAS and
p-ELAS in CD3CN and CDCl3 solutions, the signals of pro-
tons of three OH groups are separated. The most shifted
signal is found in both solvents at about 11 ppm, which is
assigned to the proton of the O(3)H group at the benzene
ring. This proton is involved in the intramolecular hydrogen
bond with the oxygen atom of the ester group. The signals
of two other protons of the O(4)H and O(8)H groups are
found in the range of 4.01–3.24 ppm indicating that these
protons are involved in the weak hydrogen bonds.
8.6–6.6 ppm (Fig. 4). The proton signals of the salicylic ring
of the esters are independent of the ester type and arise as
two doublets at about 7.24–7.18 and 6.74–6.68 ppm,
assigned to the C(5)H and C(6)H protons, respectively.
The proton signals of the nitrobenzyl ring arise at various
fields and are strongly dependent on the substitution part
of the nitro groups due to their anisotropic effect. The chem-
ical shits of these protons are shown in Tables 5 and 6 as well
in Fig. 4.
In the 1H NMR spectrum of o-ELAS, m-ELAS and
p-ELAS in both solutions, the signals of the o-, m- or
p-nitrobenzene ring protons are found in the range of
The nitro group in benzyl ring determines also the sig-
nals of the protons of the methylene benzyl group. In the
1H NMR spectrum of o-ELAS the protons of CH2 group

A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
111
Table 6
Table 7
1H NMR and 13C NMR chemical shifts (ppm) o-ELAS, m-ELAS and p-
The differences D (ppm) between the respective chemical shifts
ELAS in CDCl3
No. of atom
o-ELAS
D1H
m-ELAS
D1H*
p-ELAS
D1H#
No. of o-ELAS
m-ELAS
p-ELAS
D13
C
D13C*
D13C#
atom
1H NMR
13C
NMR
1H NMR
13C
NMR
1H NMR
13C
NMR
1
2
–
–
0.41
1.66
ꢀ0.41
0.33
0.46
0.83
0.70
0.41
0.76
0.50
2.80
ꢀ0.54
ꢀ0.46
0.58
0.04
0.82
0.25
0.88
ꢀ1.80
0.45
0.71
0.26
1.45
0.62
1.12
0.36
1.04
0.42
0.01
ꢀ0.46
0.63
0.64
ꢀ0.29
ꢀ0.21
1.13
0.10
1.24
0.64
1.34
1.63
0.85
–
–
–
0.43
1.67
ꢀ0.30
0.30
0.49
0.75
0.78
0.02
0.79
0.71
2.88
ꢀ0.42
0.19
0.69
0.13
0.95
0.49
0.55
ꢀ1.48
0.60
0.70
0.07
1.46
0.59
1.03
0.38
0.93
0.33
0.04
ꢀ0.08
0.32
0.58
ꢀ0.20
ꢀ0.10
0.61
0.86
0.43
0.76
0.86
0.94
ꢀ2.34
–
–
–
0.59
1.62
ꢀ0.14
1.17
0.54
0.81
0.27
0.10
0.66
0.54
2.66
ꢀ0.46
0.18
0.53
0.09
0.79
0.29
0.63
ꢀ1.31
0.40
0.52
0.19
1.50
0.46
0.89
0.23
0.82
0.29
0.00
ꢀ0.24
0.02
0.37
ꢀ0.10
ꢀ0.34
1.12
1.14
1.02
0.33
1.69
0.33
1.02
–
1
2
3
4
5
6
7
8
–
–
–
–
7.19
6.70
–
2.95
1.56, 1.71
1.46
3.44
2.92
–
2.77
3.83
2.21
1.52, 1.86
–
3.89
1.49, 1.69
1.40
–
3.76
1.17
1.59
0.86
1.27
0.82
1.02
1.41, 1.90
0.81
0.85
0.81
2.21
5.84
–
–
8.15 (d)
7.51 (t)
7.64 (t)
7.68 (d)
171.38
110.70
160.96
124.24
135.43
121.77
143.51
34.37
36.43
34.01
71.47
49.10
214.72
54.67
85.01
35.02
39.14
85.90
73.81
20.94
29.36
70.45
76.58
14.05
30.06
6.41
–
–
–
–
171.57
110.70
160.93
124.23
135.42
121.82
143.41
34.59
36.40
34.05
71.19
48.94
213.99
54.50
84.92
34.84
38.87
86.25
73.46
20.75
29.47
70.62
76.57
14.08
30.14
6.39
–
–
–
–
171.41
110.66
160.79
123.34
135.34
121.75
143.34
34.66
36.49
34.12
71.28
48.87
213.78
54.53
85.01
34.88
38.96
86.25
73.23
20.88
29.61
70.44
76.57
14.21
30.35
6.53
3
4
5
6
7
8
9
–
–
–
–
–
–
0.05
0.04
–
0.04
0.04
–
0.05
–
ꢀ0.16
0.41
0.05
–
ꢀ0.02
0.04
ꢀ0.57
–
0.04
0.04
–
–
–
ꢀ0.17
0.42
ꢀ0.04
–
ꢀ0.01
0.00
ꢀ0.07
–
7.18
6.68
–
2.85
1.57, 1.84
1.47
3.45
2.90
–
2.73
3.86
2.20
1.52, 1.86
–
3.83
1.49, 1.69
1.42
–
3.77
1.17
1.51
0.90
1.30
0.82
1.20
1.44, 1.91
0.83
0.85
0.87
2.17
5.60
–
7.18
6.68
–
2.78, 3.05
1.49, 1.82
1.47
3.44
2.98
–
2.73
3.88
2.21
1.51, 1.86
–
3.97
1.54, 1.76
1.41
–
3.94
1.39
1.60
0.89
1.29
0.79
1.21
1.34, 1.84
0.82
0.84
0.82
2.21
5.51
–
7.66 (d)
8.23 (d)
–
8.23 (d)
7.66 (d)
11.26
3.40
3.76
ꢀ0.05
–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
O(3)H
O(4)H
O(8)H
ꢀ0.16
0.42
0.03
–
ꢀ0.06
0.05
ꢀ0.06
–
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
–
–
–
ꢀ0.45
ꢀ0.40
ꢀ0.54
–
–
–
0.09
–
ꢀ0.14
ꢀ0.04
–
ꢀ0.06
ꢀ0.03
ꢀ0.04
ꢀ0.03
–
ꢀ0.03
ꢀ0.10
0.02
ꢀ0.06
ꢀ0.09
–
0.08
–
ꢀ0.16
ꢀ0.05
–
ꢀ0.07
ꢀ0.05
ꢀ0.02
ꢀ0.22
–
ꢀ0.04
ꢀ0.11
ꢀ0.06
ꢀ0.03
ꢀ0.03
–
0.06
–
ꢀ0.32
ꢀ0.26
–
ꢀ0.09
ꢀ0.06
ꢀ0.02
ꢀ0.22
–
ꢀ0.04
ꢀ0.08
ꢀ0.01
ꢀ0.04
0.06
–
0.03
0.03
–
0.03
0.03
ꢀ0.26
ꢀ0.13
0.25
30.60
8.45
30.71
8.57
30.81
8.63
15.86
18.04
12.11
13.41
12.70
15.91
63.71
131.54
147.67
125.14
129.08
129.81
133.97
–
15.84
17.62
12.43
13.37
12.69
15.79
65.78
137.53
123.65
148.26
123.40
129.82
137.53
–
15.87
17.65
12.51
13.54
12.84
15.94
65.78
147.73
129.22
124.18
142.54
124.18
129.22
–
–
–
–
ꢀ0.03
0.06
ꢀ0.01
0.06
ꢀ0.32
ꢀ0.16
0.18
8.34 (s)
–
0.01
0.03
–
7.85 (d)
7.60 (t)
8.20 (d)
11.27
3.41
3.77
ꢀ0.27
ꢀ0.15
0.14
–
–
–
–
–
–
O(3)H 11.20
O(4)H
O(8)H
3.40
3.71
–
–
–
–
–
–
D1H = d(o-ELAS in CD3CN) ꢀ d(o-ELAS in CDCl3); D13C = d(o-ELAS
in CD3CN) ꢀ d(o-ELAS in CDCl3).
D1H* = d(m-ELAS in CD3CN) ꢀ d(m-ELAS in CDCl3); D13C* =
d(m-ELAS in CD3CN) ꢀ d(m-ELAS in CDCl3).
D1H# = d(p-ELAS in CD3CN) ꢀ d(p-ELAS in CDCl3); D13C#
d(p-ELAS in CD3CN) ꢀ d(p-ELAS in CDCl3).
=
are found as a singlet at 5.84 ppm and 5.75 ppm in CD3CN
and CDCl3, respectively. The signals of these protons in the
spectra of m-ELAS and p-ELAS are found at 5.60–
5.51 ppm as a doublet of doublets due to the spin–spin
geminal coupling (Fig. 4). The appearance of such cou-
plings indicates the location of both protons in different
fields and formation of a typical AB spin–spin coupling
structure.
are assigned to the carbons of the ester group and the car-
bon of the salicylic O(3)H group indicating direct associa-
tion of the chemical shift changes with the coupling of the n
and p electrons within the pseudo-aromatic [31] hydrogen
bonded ring of o-ELAS, m-ELAS and p-ELAS esters. This
interpretation is further confirmed by the FT-IR spectra of
o-(m- and p-) nitrobenzyl esters of lasalocid acid discussed
below.
The visible differences in chemical shifts of the signals in
the 13C NMR spectra of esters in chloroform and in aceto-
nitrile solutions appear for C(1), C(2), C(3). These signals

112
A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
Fig. 4. 1H NMR in the region of the phenyl ring CH proton signals of o-ELAS, m-ELAS and p-ELAS.
3.3. FT-IR measurements
strates that in the solutions the ketone C(13)@O group
becomes hydrogen-bonded, whereas the intramolecular
hydrogen bond in which the ester C(1)@O group is
involved becomes slightly weaker. Besides these two intense
bands, a low intense one in acetonitrile solution and only a
shoulder in chloroform solution are observed at about
1732 cmꢀ1 indicating that also the strongest intramolecular
C(1)@OÆÆÆH(3)O hydrogen bond in the pseudo-aromatic
ring becomes partially broken. It is understandable that
this broken effect increases with increasing polarity of the
solvent, i.e. it is more pronounced in acetonitrile than in
chloroform.
Spectral features very similar to those above described
for the o-ELAS ester appear also in the respective spectra
of m-ELAS and p-ELAS. This indicates that the position
of the nitro group in benzyl ester has almost no influence
on the structure of the esters in the solutions.
In Fig. 5 the spectra of o-ELAS in acetonitrile, chloro-
form and in KBr pallet are shown. The most characteristic
in the FT-IR spectrum of water free o-ELAS in the KBr
pallet, are the bands at 3440 cmꢀ1, 3424 cmꢀ1 and
3028 cmꢀ1 assigned to the m(OH) vibrations of the
O(4)H, O(8)H and O(3)H groups, respectively, as well as
the band of the m(C@O) vibrations at 1717 cmꢀ1 and
1653 cmꢀ1 assigned to the ketone C(13)@O group and to
the C(1)@O group of the ester group in solid state. Such
assignments are in agreement with the NMR data as well
as with the spectra of salicylic acid esters [32–34].
The spectra of o-ELAS in chloroform and acetonitrile
are comparable, except for same details especially in the
ranges shown in Fig. 5b and c. In the spectrum in chloro-
form solution a broad band with a maximum about
3453 cmꢀ1 and a new weak one at about 3580 cmꢀ1 are
observed. The latter band indicates that at least one of
the hydrogen bonded OH groups becomes free. In acetoni-
trile this free OH group is further hydrogen bonded to the
solvent, which is manifested as a shoulder in the region
3600–3500 cmꢀ1. In both solvents the positions of the
bands assigned to the stretching vibrations of the ketone
C(13)@O and ester C(1)@O groups are also comparable.
They are however different in comparison with the respec-
tive ones in the solid state, in which the band of the ketone
C(13)@O group is shifted towards smaller (1712 cmꢀ1) and
the band of the ester C(1)@O group towards higher
(1659 cmꢀ1) wavenumbers. This spectral feature demon-
3.4. UV–Vis and fluorescence studies
The absorption and emission spectral data of o-ELAS,
m-ELAS and p-ELAS are collected in Table 8 and the
respective spectra are shown in Fig. 6.
Mitra and Narurkar [35] have previously reported that
the relative fluorescence quantum yield (U) and the wave-
length of the fluorescence maximum (kmax) of lasalocid
depend on the solvent character. They demonstrated that
a decrease in the hydrogen-bonding ability of the solvent
causes an increase in U and a red shift of the kmax. It has
been also reported that lasalocid has relatively high U in

A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
113
a
100
50
0
3028
4000
3500
3000
2500
2000
1500
1000
500
b
c
100
50
0
3453
3580
Fig. 6. Absorption (left) and emission corrected spectra (right) of:
o-ELAS (—), m-ELAS (---) and p-ELAS (ÆÆÆ).
3440
3500
3424
3400
3700
3600
3300
3200
acid moiety of the lasalocid molecule is an active contribu-
tor to the emission spectra obtained in this study because
the positions of the fluorescence maximum in the emission
spectra of o-ELAS, m-ELAS and p-ELAS do not depend
on the location of the nitro substituents in the nitrobenzyl
ester (Fig. 6, Table 8). The fluorescence quantum yields
determined for o-ELAS, m-ELAS and p-ELAS are very
low, although for m-ELAS the quantum yield is definitely
higher (Table 8).
100
50
0
1659
1732
1712
1700
1717
1653
1750
1650
Wavenumber [cm-1]
1600
1550
3.5. PM5 calculations
Fig. 5. FT-IR spectra of o-ELAS: (—) in KBr pallet, (ÆÆÆ) in chloroform
solutions and (---) in acetonitrile solutions: (a) 4000–400 cmꢀ1; (b) 3700–
On the basis of the spectroscopic as well as X-ray
results, the structure of o-ELAS was calculated by the
PM5 semiempirical method and it is compared in Fig. 1
with the crystal structure. The hydrogen bond parameters
of o-ELAS as well as m-ELAS and p-ELAS are collected
in Table 4 together with the respective X-ray data. Based
on the spectroscopic observations the respective structures
of o-ELAS, m-ELAS and p-ELAS, in which the C(13)@O
is involved in the formation of intramolecular hydrogen
bond (B type structures).
The calculated hydrogen bond parameters are compara-
ble with those determined by the X-ray method, although
these two methods describe two different states, i.e. the
gas and the solid. Thus, the PM5 semiempirical method
is a reliable method of visualization of the structures also
in the solid state. This result is in a very good agreement
with other findings as well as with our previous calculations
[30,37,38].
The structures of o-ELAS, m-ELAS and p-ELAS of B
type are very similar and therefore, only the structure of
o-ELAS is shown in Fig. 2. The structure is stabilized by
the formation of three intramolecular hydrogen bonds
that cause the existence of two parts of the ester molecule.
One part including the salicylic group is stabilized by the
one O(3)ÆÆÆO(2) intramolecular hydrogen bond and the rest
of the molecule is stabilized by two O(8)–HÆÆÆO(4) and
3200 cmꢀ1; (c) 1750–1550 cmꢀ1
.
Table 8
UV–Vis and fluorescence spectral characteristics of o-ELAS, m-ELAS and
p-ELAS
Compound
UV–Vis
Fluorescence
kexc (nm)
260
kmax (nm)
Loge
kem (nm)
U
o-ELAS
216.0
252.0
317.0
4.36
4.12
3.71
359
414
1.3 · 10ꢀ5
m-ELAS
p-ELAS
212.5
252.5
317.0
4.35
4.03
3.56
260
260
359
412
1.8 · 10ꢀ5
1.2 · 10ꢀ5
214.5
257.5
321.5
4.38
4.17
3.71
359
414
kmax – Maximum of the absorption band, e – decadic molar extinction
coefficient (dmꢀ3 molꢀ1 cmꢀ1), kexc – excitation wavelength, kem – maxi-
mum of the fluorescence band, U – quantum yield of fluorescence relative
to Quinine sulphate in 0.1 N H2SO4 [26].
acetonitrile solutions and that this solvent is suitable for
fluorescence measurements. The hydroxyl and carboxyl
groups in salicylic compounds have been shown to make
a fluorophore emitting at 420 nm [36]. Thus, the salicylic

114
A. Huczyn´ski et al. / Journal of Molecular Structure 877 (2008) 105–114
[17] H. Tsukube, Cation-Binding by Macrocycles, Marcel-Dekker, New
York, 1990.
[18] R. Pankiewicz, G. Schroeder, B. Brzezinski, F. Bartl, J. Mol. Struct.
699 (2004) 53.
[19] R. Pankiewicz, G. Schroeder, B. Brzezinski, F. Bartl, J. Mol. Struct.
749 (2005) 128.
O(4)–HÆÆÆO(5) intramolecular hydrogen bonds. In all struc-
tures the hydrogen bond parameters (Table 4) are compa-
rable indicating that they are independent of the
nitrobenzyl substituent in the lasalocid ester.
[20] R. Pankiewicz, G. Schroeder, B. Brzezinski, J. Mol. Struct. 733 (2005)
217.
Acknowledgements
[21] R. Pankiewicz, G. Schroeder, B. Brzezinski, J. Mol. Struct. 829 (2007)
120.
[22] R. Pankiewicz, A. Pawłowska, G. Schroeder, P. Przybylski, B.
Brzezinski, F. Bartl, J. Mol. Struct. 694 (2004) 55.
[23] R. Pankiewicz, G. Schroeder, B. Brzezinski, J. Mol. Struct. 733 (2005)
155.
´
Adam Huczynski wishes to thank the Foundation for
Polish Science for fellowship. The authors thank the Polish
Ministry of Science and Higher Education for financial
support under Grant No. R 0501601.
[24] G. Sheldrick, SHELXS-97 Program for Crystal Structure Solution,
University of Goettingen, 1997.
References
[25] G. Sheldrick, SHELXL-97 Program for Crystal Structure Refine-
ment, University of Goettingen, 1997.
[1] J.W. Westley, J. Antibiot. 29 (1974) 584.
[26] S.R. Meech, D. Phillips, J. Photochem. 23 (1983) 193.
[27] J.J.P. Stewart, Method J. Comp. Chem. 10 (1989) 209.
[28] J.J.P. Stewart, J. Comp. Chem. 12 (1991) 320.
[29] CAChe 5.04 UserGuide, Fujitsu 2003.
[2] S. Lindenbaum, L. Sternson, S. Rippel, J. Chem. Soc. Chem.
Commun. (1977) 268.
[3] M. Schadt, G. Haeusler, J. Memb. Biol. 18 (1974) 277.
[4] J. Bolte, C. Demuynck, G. Jeminet, J. Juilard, C. Tissier, Can. J.
Chem. 60 (1982) 9821.
´
[30] P. Przybylski, A. Huczynski, B. Brzezinski, J. Mol. Struct. 826 (2007)
156.
[5] L. Blau, R.B. Stern, R. Bittman, Biochim. Biophys. Acta778(1984)219.
[6] Y.N. Antonenko, L.S. Yaguzhinski, FEBS Lett. 163 (1983) 42.
[7] J.G.D. Phillies, H.E. Stanley, J. Am. Chem. Soc. 98 (1976) 3892.
[8] D.J. Patel, C. Shen, Proc. Natl. Acad. Sci. USA 73 (1976) 4277.
[9] C.C. Chiang, I.C. Paul, Science 196 (1977) 1441.
[10] E.C. Bissell, I.C. Paul, J. Chem. Soc. Chem. Commun. (1972) 967.
[11] J. Berger, A.I. Rachlin, W.E. Scott, L.H. Sternbach, M.W. Goldberg,
J. Am. Chem. Soc. 73 (1951) 5295.
[12] V.C. Langston, F. Galey, R. Lovell, W.B. Buck, Vet. Med. 80 (1985)
75–84.
[13] Y. Miyazaki, M. Shibuya, M. Sugasawa, O. Kawaguchi, C. Hirose, J.
Nagatsu, S. Esumi, J. Antibiot. 27 (1974) 814.
[31] L. Sobczyk, S.J. Grabowski, T.M. Krygowski, Chem. Rev. 105 (2005)
3513.
[32] M.J.M. Takacˇ, D.V. Topic, Acta Pharm. 54 (2004) 177.
´
´ _
[33] G. Schroeder, B. Gierczyk, B. Brzezinski, B. Rozalski, F. Bartl, G.
´
Kundel, J. Sosnicki, E. Grech, J. Mol. Struct. 516 (2000) 91.
[34] SDBSWeb : http://www.aist.go.jp/RIODB/SDBS/ (National Insti-
tute of Advanced Industrial Science and Technology, date of
access).
[35] A.K. Mitra, M.M. Narurkar, J. Org. Chem. 49 (1984) 1293.
[36] A.H. Caswell, B.C. Pressman, Biochem. Biophys. Res. Commun. 49
(1972) 282.
´
[37] A. Huczynski, M. Ratajczak-Sitarz, A. Katrusiak, B. Brzezinski, J.
[14] B.C. Granzim, G.McL. Dryden, Anim. Feed Sci. Technol. 120 (2005)
116.
Mol. Struct. 832 (2007) 84.
´
[38] A. Huczynski, M. Ratajczak-Sitarz, A. Katrusiak, B. Brzezinski, J.
[15] V. Rada, M. Marounek, Ann. Zeotech. 45 (1996) 283.
[16] B. Kohler, H. Karch, H. Schmidt, Microbiology 146 (2000) 1085.
Mol. Struct. 871 (2007) 92–97.