2-Arylalkyl-substituted anthracenones as inhibitors of 12-lipoxygenase enzymes. 2. Structure-activity relationships of the linker chain

Article abstract of DOI:10.1016/S0223-5234(01)01291-0

A series of 2-arylalkyl-substituted anthracenones were tested as inhibitors of three types of 12-lipoxygenase isoforms in epidermal homogenate of mice, bovine platelets and porcine leukocytes. Their inhibitory activities were compared with those to inhibit the 5-lipoxygenase enzyme in bovine leukocytes. The compounds were synthesised by Marschalk, Wittig or Horner-Emmons reaction at the anthracenedione stage and then reduced to the anthracenones. Structure-activity relationship for the chain linking the anthracenone nucleus and the phenyl ring terminus was investigated. The 2-phenylethyl analogues were among the most potent inhibitors, and 3,4-dimethoxy-substituted 10f was identified as a selective inhibitor of the 12-LO enzymes over 5-LO. Selectivity for 12-LO isoforms was observed with an increase in the overall lipophilicity of the inhibitors. However, none of the linker chains of the 2-substituted anthracenones provided inhibitors that were able to discriminate between the 12-LO isoforms.

Full text of DOI:10.1016/S0223-5234(01)01291-0

Eur. J. Med. Chem. 37 (2002) 83–89
Short communication
2-Arylalkyl-substituted anthracenones as inhibitors of
12-lipoxygenase enzymes. 2. Structure–activity relationships of the
linker chain
Klaus Mu¨ller a,*, Reinhold Altmann b, Helge Prinz a
a Westfa¨lische Wilhelms-Uni6ersita¨t Mu¨nster, Institut fu¨r Pharmazeutische und Medizinische Chemie, Hittorfstraße 58-62, D-48149 Mu¨nster,
Germany
b Klinik und Poliklinik fu¨r Innere Medizin I, Uni6ersita¨t Regensburg, D-93042 Regensburg, Germany
Received 20 July 2001; received in revised form 5 November 2001; accepted 5 November 2001
Abstract
A series of 2-arylalkyl-substituted anthracenones were tested as inhibitors of three types of 12-lipoxygenase isoforms in
epidermal homogenate of mice, bovine platelets and porcine leukocytes. Their inhibitory activities were compared with those to
inhibit the 5-lipoxygenase enzyme in bovine leukocytes. The compounds were synthesised by Marschalk, Wittig or Horner–Em-
mons reaction at the anthracenedione stage and then reduced to the anthracenones. Structure–activity relationship for the chain
linking the anthracenone nucleus and the phenyl ring terminus was investigated. The 2-phenylethyl analogues were among the
most potent inhibitors, and 3,4-dimethoxy-substituted 10f was identified as a selective inhibitor of the 12-LO enzymes over 5-LO.
Selectivity for 12-LO isoforms was observed with an increase in the overall lipophilicity of the inhibitors. However, none of the
linker chains of the 2-substituted anthracenones provided inhibitors that were able to discriminate between the 12-LO isoforms.
´
© 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: anthracenone; 12(S)-HETE; lipophilicity; 5-lipoxygenase; 12-lipoxygenase
pressed in hematopoietic cell types, as well as in epider-
mal cells [2].
1. Introduction
The 5-LO pathway has been the major focus of study
due to the pronounced pro-inflammatory role of
leukotrienes and the approval of 5-LO inhibitors for
the clinical treatment of asthma [3]. Although less well
characterized, the 12-LO pathway may also play an
important role in the progression of human diseases
such as cancer [4] and psoriasis [5].
Three isoforms of 12-LO have been characterized.
They are platelet-type (p12-LO), leukocyte-type (l12-
LO) and the epidermal-type (e12-LO) 12-lipoxyenase
[2,6,7]. The 12(S)-HETE enantiomer can arise from
these isoforms [8–11]. In the mouse and in human skin
also, a cDNA was shown to encode a 12(R)-lipoxyge-
nase [12,13].
12-Hydroxyeicosatetraenoic acid (12-HETE) is a hy-
droxylated lipid formed as a product of the 12-lipoxy-
genases, a class of dioxygenase enzymes containing a
non-heme iron [1]. Lipoxygenases (LO) catalyze the
stereospecific insertion of molecular oxygen into arachi-
donic acid, and the products formed are optically active
(S)- or (R)-enantiomers of hydroperoxy fatty acids,
which are further metabolized to hydroxy derivatives as
end products [1]. According to their positional specific-
ity with respect to arachidonic acid, mammalian LO are
categorized into different groups predominantly ex-
Abbre6iations: 12(S)-HETE, 12(S)-hydroxyeicosatetraenoic acid;
LO, lipoxygenase; SAR, structure–activity relationships.
* Correspondence and reprints.
Even though many inhibitors of LO are known, very
few with selectivity against 12-LO have been published
E-mail address: kmuller@uni-muenster.de (K. Mu¨ller).
´
0223-5234/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0223-5234(01)01291-0

84
K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
2. Chemistry
The 2-phenylethyl analogues were prepared by one of
the three synthetic routes shown in Fig. 2. In the first
approach, Marschalk reaction [19] of 1-hydroxy-8-
methoxy-9,10-anthracenedione (3) [20] with 4-
chlorophenylacetaldehyde provided anthracenedione
4b. In the second approach, the bromide 5 [21] was
converted into the phosphonium bromide (6) with
triphenylphosphine in n-butyl acetate, in analogy to a
literature method [22]. In a Wittig-type reaction, the
yield of 6, which was formed in the presence of sodium
hydride, reacted with appropriate benzaldehydes to
yield the olefins 7c and 7f–7h. In the third approach,
olefins 7d and 7e were obtained from the Horner–Em-
mons reaction [23] of carbaldehyde 8 [24] and diethyl
benzylphosphonates in the presence of sodium tert-bu-
toxide. Olefins 7c–7h were catalytically hydrogenated
to provide the 2-phenylethyl-substituted anthracene-
diones 9c, 9d, 9f–9i, in the course of which 3,4-bis-ben-
zyloxy analogue 7e was hydrogenolytically cleaved to
the catechol analogue 9i. Subsequent reduction of the
anthracenediones to the desired anthracenones 10b–10d
and 10f–10i with SnCl2–HCl proceeded with concomi-
tant ether cleavage of the methoxy groups at position 1
and 8 of the anthracenedione nucleus. This was selec-
tive for those compounds having an additional methoxy
group in the terminal phenyl ring of the 2-substituent
Fig. 1. Structures of anthralin (1) and a 2-phenylmethyl-substituted
analogue (2).
[14]. A selective inhibitor of 12(S)-HETE biosynthesis
would greatly aid in the evaluation of the role of this
12-LO metabolite in human disease. Such an agent
might provide a new therapeutic approach to diseases
such as psoriasis and cancer. During the course of our
search for antipsoriatic agents, we have established
10-substituted derivatives of anthralin (1, Fig. 1) as
inhibitors of 5-lipoxygenase [15–17]. Furthermore, a
series of derivatives with lipophilic side chains at the
2-position was synthesized and found to selectively
inhibit the 12-LO isoforms as opposed to 5-LO. Struc-
ture–activity relationships (SAR) were studied for these
compounds to determine which structural elements
were required for activity and to improve their selecti-
vities. Our recent paper discussed SAR for modifica-
tions of the terminal aryl ring of 2-phenylmethyl-substi-
tuted anthracenone 2 [18]. This paper will discuss SAR
involving structural modifications of the chain linking
the anthracenone nucleus and the phenyl ring terminus.
Fig. 2. Reagents: (a) Na2S2O4, NaOH, 4-chlorophenlylacetaldehyde, N2, 90 °C; (b) PPh3, n-BuOAc, 100 °C; (c) NaH, DMSO, R-PhCHO, N2,
60 °C; (d) R-BnPO(OEt)2, DMF, Me3COK, N2, 0 °C; (e) H2, Pd–C, EtOH, RT, (f) SnCl2, HCl, glacial HOAc, 118 °C.

K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
85
those reported in other studies [29,30], although the
values are not strictly comparable because of diffe-
rences in the assay conditions. In particular, IC50 va-
lues for LO inhibition are dependent on cell density
[31] and may thus vary with the assay performed.
The parent anthracenone anthralin (1) was only a
moderate inhibitor of 5-LO in bovine leukocytes and
an equal potent inhibitor of the 12-LO isoforms,
whereas the phenylmethyl analogue 2 was a selective
inhibitor of p12-LO. In the following, SAR of com-
pounds with connecting chains other than methyl were
explored. The higher homologue of 2, phenylethyl
analogue 10a, was a somewhat more potent inhibitor,
but exhibited activity against all 12-LO isoforms. Ex-
panding the phenylethyl to a phenylpropyl chain (12a)
(10f, 10g). Anthracenone 10e was directly obtained
from anthracenedione 7e under identical conditions.
Unfortunately, reduction of anthracenediones hav-
ing olefin linker chains (7c–7e) to the corresponding
anthracenones under the conditions described failed.
Also, other methods such as metal hydride reagents,
Clemmensen (zinc amalgam in HCl) or Wolff–Kish-
ner (hydrazine and KOH) reduction were not success-
ful. In no case could the desired structures with the
stilbene skeleton be isolated, but large amounts of 1,
derived by cleavage of the 2-phenylethenyl chain, to-
gether with the 2-phenylethyl-substituted anthra-
cenones were observed. The exception was 2-
phenylethenyl analogue 11d with a 4-methyl group.
1
The H-NMR of this compound showed the charac-
provided
a
non-selective LO inhibitor, whereas
teristic coupling pattern of an ethenyl spacer, and cou-
pling constants of the olefinic protons (J=16.5 Hz)
indicated compound 11d was in the E-configuration.
Other 2-phenylalkyl (10a, 12a–12e, 13) analogues
and the 2-benzoyl (14a–14d) analogues were available
from previous work [25,26].
phenylbutyl analogue 13 was a moderate inhibitor
with selectivity for the 12-LO enzymes.
Introduction of a phenolic group (10g, 10h, 12d)
resulted in activity against 5-LO and therefore pro-
duced non-selective inhibitors. The 5-LO inhibitory
potency was greatly enhanced by the addition of fur-
ther hydroxyl groups (10i, 12e). Although catechol
analogue 10i and pyrogallol analogue 12e were also
among the most potent inhibitors of the 12-LO en-
zymes, these agents would be poor choices as poten-
tially selective inhibitors.
Exchanging the methyl linker of 2 with a carbonyl
linker, as in 14a, was detrimental for selectivity. This
was due to a strong decrease in lipophilicity. Even
though the benzonitrile 14b and the benzoic acid 14c
were devoid of phenolic groups in the terminal phenyl
ring, they also inhibited the 5-LO enzyme, as these
analogues exhibited the lowest log P values of the
compounds assayed in this study. In general, selecti-
vity for 12-LO inhibition was largely dependent on the
overall lipophilicity of the compounds, as already ob-
served with arylmethyl analogues [18]. Except for the
phenylpropyl analogues, inhibitors having a log P
value of higher than 5 were not active against 5-LO.
Among the phenylethyl analogues (10a–10i) with a
3. Lipoxygenase inhibition
Although the products of 5-LO have attracted much
attention and the development of 5-LO inhibitors has
been extensively described [3,27], not many inhibitors
of 12-LO are available. However, specific inhibitors of
12-LO would be useful tools for characterising the
different physiological roles of the two enzymes. Par-
ticularly, their metabolites have been suspected to play
an important role in the pathogenesis of psoriasis,
because a number of phenomena observed in this skin
disease can be explained, at least in part, by the ac-
tion of leukotrienes and 12-HETE [5]. Therefore, we
have evaluated the effects of the 2-substituted anthra-
cenones on 12-LO activity in epidermal homogenate
of mice [28]. Further, we also evaluated their in-
hibitory action against 12-LO isoenzymes in bovine
platelets and porcine leukocytes as well as their ability
to inhibit 5-LO in bovine leukocytes, in order to in-
vestigate a SAR and to explore their selectivity.
substituted phenyl ring, 10f, which has
a 3,4-
dimethoxy substitution pattern, was the most selective
inhibitor of the 12-LO enzymes as opposed to 5-LO.
Unfortunately, 10f did not exhibit specificity for a
single 12-LO isoform. Exchanging merely one of the
methoxy groups of 10f with a hydroxyl group (10g)
destroyed selectivity.
The phenylethyl analogues are flexible structures,
which can interact with all 12-LO isoforms. However,
specific 12-LO inhibitors would be useful tools for
differentiating the physiological roles of the 12-LO
isoenzymes in disease states such as psoriasis and can-
cer. To develop an isoform-selective inhibitor of the
anthracenone class, the conformational mobility of
4. Results and discussion
The IC50 values for the inhibitory actions of the
novel anthracenones against LO enzymes, together
with their structures, are listed in Table 1. The general
LO inhibitor nordihydroguaiaretic acid (NDGA) was
used as a positive control and this compound ap-
peared to be a more selective inhibitor of 5-LO. How-
ever, it should be noted that the IC50 values against
the 12-LO enzymes reported here are not as low as

86
K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
Table 1
Inhibition of mouse epidermal 12-LO, bovine platelet 12-LO, porcine leukocyte 12-LO, and bovine leukocyte 5-LO by 1,8-dihydroxy-2-phenyl-
alkyl-9(10H)-anthracenones.
a
cpd
X
R
log P
e12-LO b IC50
(mM)
p12-LO c IC50
(mM)
l12-LO d IC50
(mM)
5-LO e IC50
(mM)
2
CH2
H
H
4-Cl
4-CN
5.62
6.23
6.35
5.20
6.52
7.78
5.36
4.86
4.81
4.46
8.16
6.44
6.46
5.64
5.27
3.96
6.81
4.47
3.32
2.92
4.20
4.23
\30
7
13
7
14
7
12
\30
6
6
8
4
\30
10
4
9
8
5
7
6
4
\30
9
\30
\30
\30
\30
\30
\30
\30
6
10a
10b
10c
10d
10e
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
E-CHꢀCH
(CH2)3
(CH2)3
(CH2)3
(CH2)3
(CH2)3
(CH2)4
CO
23
18
16
30
6
6
12
5
\30
12
14
\30
11
7
19
16
8
11
24
21
\30
5
4
16
5
\30
13
14
7
6
4
16
18
11
14
\30
9
4-Me
3,4-(OBn)2
3,4-(OMe)2
3-OH-4-OMe
4-OH
3,4-(OH)2
4-Me
10f
10g
10h
10i
11d
12a
12b
12c
12d
12e
13
14a
14b
14c
14d
Anthralin
NDGA f
2
0.7
\30
11
\30
6
H
4-OMe
3,4,5-(OMe)3
4-OH
3,4,5-(OH)3
H
H
4-CN
4-CO2H
4-CO2Me
2
0.6
\30
18
CO
CO
CO
2
2
7
30
9
11
27
9
\30
37
21
12
24
0.5
a Experimentally determined partition coefficient.
b Inhibition of 12(S)-HETE biosynthesis in mouse epidermal homogenates.
c Inhibition of 12(S)-HETE biosynthesis in bovine platelets.
d Inhibition of 12(S)-HETE biosynthesis in porcine leukocytes.
e Inhibition of LTB4 biosynthesis in bovine leukocytes. For each value of the LO assays, inhibition was significantly different with respect to
that of the control (n=3 or more, S.D.510%, PB0.01).
f Nordihydroguaiaretic acid (NDGA) was used as the standard inhibitor.
analogues such as 10d was restricted by introduction of
a trans double bond. Thus, stilbene derivative 11d
maintained the electronic character of 10d, but intro-
duced additional structural rigidity and steric barriers,
interactions potentially either beneficial or detrimental
to the inhibition of the 12-LO isoenzymes. None of the
LO, including 5-LO, were inhibited by 11d, which
seemed to indicate that introduction of this structural
modification was unfavourable, however. It is not clear
at the moment if this is simply related to the stilbene
structure of 11d or if the high overall lipophilicity of
this compound prevents activity. In support of this,
with a log P value of 8.16 the lipophilicity of 11d is
comparable to that of the inactive 10e (log P=7.78).
Further work directed toward successful synthesis of
less lipophilic compounds will be required to elucidate
the nature of the interactions of stilbenes with the
12-LO isoenzymes.
5. Conclusions
Among the 2-phenylethyl analogues, 10f was iden-
tified as a selective inhibitor of the 12-LO enzymes as
compared with 5-LO. In general, selectivity for 12-LO
isoforms was observed for the more lipophilic in-
hibitors. However, none of the linker chains of the
2-substituted anthracenones provided inhibitors that
were able to discriminate between the 12-LO isoforms.
6. Experimental protocols
6.1. Chemistry
6.1.1. General
For analytical instruments and methods, see refe-
rence [15].

K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
87
6.1.2. General procedure for the preparation of 2-
substituted anthracenediones by Marschalk alkylation
was obtained from 6 and 3,4-dimethoxybenzaldehyde as
described for 7c and chromatographed (CH2Cl2–Et2O,
90/10) to provide orange–yellow crystals; 42% yield;
1
6.1.2.1. 2-[2-(4-Chlorophenyl)ethyl]-1-hydroxy-8-me-
thoxy-9,10-anthracenedione (4b). To a solution of 1.5%
NaOH in water (300 mL) was added 3 [20] (5.08 g, 20.0
mmol) and a solution of Na2S2O4 (6.0 g, 34.5 mmol) in
water (25 mL) at 40 °C under N2. The solution was
heated to 50 °C for 15 min. 4-Chlorophenylacetaldehyde
[32] (15.5 g, 100 mmol) was added, dropwise over 30 min
at 70 °C, and the reaction mixture was stirred for 2 h.
It was stirred for an additional 12 h at 90 °C, then cooled
to room temperature (r.t.), aerated for 30 min, and
acidified with 6 N HCl. The orange suspension thus
obtained was extracted with CH2Cl2 (3×200 mL), the
organic phase was washed with water and dried over
Na2SO4. The solvent was evaporated, and the residue was
purified by column chromatography (SiO2–CH2Cl2) to
provide yellow crystals; 21% yield; melting point (m.p.)
m.p. 181–182 °C; H-NMR (CDCl3) l 7.95–6.80 (m,
10H), 4.00 (s, 6H), 3.92 (s, 3H), 3.88 (s, 3H); FTIR 1680
(CO) cm−1. Anal. C26H22O6 (C, H).
6.1.3.4. 2-(E)-[2-(3-Hydroxy-4-methoxyphenyl)ethenyl]-
1,8-dimethoxy-9,10-anthracenedione (7g). The title com-
pound was obtained from
6
and 3-hydroxy-4-
methoxybenzaldehyde as described for 7c and chro-
matographed (CH2Cl2–Et2O, 90/10) to provide orange
crystals; 40% yield; m.p. 201–202 °C; 1H-NMR (CDCl3)
l 8.05–6.90 (m, 10H), 5.81 (s, 1H), 4.10 (s, 6H), 4.00 (s,
3H); FTIR 1667 (CO) cm−1. Anal. C25H20O6 (C, H).
6.1.3.5. 2-(E)-[2-(4-Hydroxyphenyl)ethenyl]-1,8-dime-
thoxy-9,10-anthracenedione (7h). The title compound
was obtained from 6 and 4-hydroxybenzaldehyde as
described for 7c and chromatographed (CH2Cl2) to
1
135–136 °C; H-NMR (CDCl3) l 13.42 (s, 1H), 7.92–
1
provide red crystals; 35% yield; m.p. 247–248 °C; H-
7.24 (m, 9H), 3.99 (s, 3H), 2.95 (m, 4H); FTIR 3450
(OH), 1669 (CO), 1632 cm−1 (CO···OH). Anal.
C23H17ClO4 (C, H).
NMR (CDCl3) l 9.42 (s, 1H), 8.00–6.80 (m, 11H), 4.05
(s, 3H), 4.00 (s, 3H); FTIR 3384 (OH), 1663 (CO) cm−1
Anal. C24H18O5 (C, H).
.
6.1.3. General procedure for the preparation of
2-substituted anthracenediones by Wittig reaction
6.1.4. diEthyl 4-methylbenzylphosphonate
Freshly distilled triethyl phosphite (19.9 g, 120 mmol)
was added to 4-methylbenzylbromide (13.0 g, 70 mmol),
and the mixture was heated at 200 °C for 1 h. Excess
triethyl phosphite was removed at 60 °C in vacuo to yield
6.1.3.1. 2-(1,8-Dimethoxy-9,10-dioxo-2-anthracenyl)-
methyl)triphenylphosphonium bromide (6). To a solution
of 2-bromomethyl-1,8-dimethoxy-9,10-anthracenedione
[21] (5, 1.0 g, 2.76 mmol) in n-butylacetate (10 mL) at
100 °C was slowly added triphenylphosphine (1.25 g,
4.76 mmol). After 5 min, the reaction was cooled to r.t.
and the precipitate filtered by suction. The crude product
was dried and used in the subsequent Wittig reaction.
1
a colourless oil; 82% yield; m.p. 247–248 °C; H-NMR
(CDCl3) l 7.27–7.09 (m, 4H), 4.01 (quint, J=7 Hz, 4H),
3.11 (d, JCHP=21 Hz, 2H), 2.32 (s, 3H), 1.25 (m, J=7
Hz, 6H).
The crude product was used in the subsequent
Horner–Emmons reaction.
6.1.3.2. 4-[2-(9,10-diHydro-1,8-dimethoxy-9,10-dioxo-
2-anthracenyl)-(E)-ethenyl]benzonitrile (7c). A suspen-
sion of NaH (0.1 g, 3.3 mmol) in DMSO (10 mL) was
heated to 70 °C for 30 min under N2 and then cooled.
A solution of the phosphonium salt 6 (1.0 g, 1.9 mmol)
in DMSO (10 mL) was added. After 10 min, a solution
of 4-cyanobenzaldehyde (0.25 g, 1.9 mmol) in DMSO (10
mL) was added and the reaction mixture heated at 60 °C
for 1 h. The cooled mixture was extracted with CH2Cl2
(3×100 mL), the organic phase was washed with a
saturated solution of NaCl, then with water, and dried
over Na2SO4. The solvent was evaporated, and the
residue was purified by column chromatography (SiO2;
CH2Cl2–EtOAc, 95/5) to provide orange crystals; 45%
yield; m.p. 255–256 °C; 1H-NMR (CDCl3) l 8.00–6.75
(m, 11H), 4.00 (s, 6H); FTIR 2220 (CN), 1676 (CO)
cm−1. Anal. C25H17NO4 (C, H, N).
6.1.5. General procedure for the preparation of
2-substituted anthracenediones by Horner–Emmons
reaction
6.1.5.1. 1,8 - diMethoxy - 2 - (E) - [2 - (4 - methylphenyl) -
ethenyl]-9,10-anthracenedione (7d). To a well-stirred so-
lution of diethyl 4-methylbenzylphosphonate (0.242 g,
1.0 mmol) in absol. DMF (20 mL) was added to sodium
tert-butoxide (0.11 g, 1.0 mmol) at 25 °C under N2. The
mixture was added dropwise to a solution of the car-
baldehyde 8 [24] (0.30 g, 1.0 mmol) in DMF (10 mL),
cooled to 0 °C. After 15 min, the product was precipi-
tated with water–methanol (2/1, 20 mL) and filtered by
suction. The residue was washed with water and dried.
Purification by chromatography (SiO2–CH2Cl2) pro-
vided yellow crystals; 34% yield; m.p. 181–183 °C;
1H-NMR (CDCl3) l 8.05–7.20 (m, 9H), 7.55 (d, J=16
Hz, 1H), 7.30 (d, J=16 Hz, 1H), 4.04 (s, 3H), 4.01 (s,
3H), 2.39 (s, 3H); FTIR 1667 (CO) cm−1; MS m/z=384
(100, [M]+). Anal. C25H20O4 (C, H).
6.1.3.3. 1,8-diMethoxy-2-(E)-[2-(3,4-dimethoxyphenyl)-
ethenyl]-9,10-anthracenedione (7f). The title compound

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K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
6.1.5.2.
2-(E)-[2-(3,4-diBenzyloxyphenyl)ethenyl]-1,8-
6.1.7.3. 1,8 - diHydroxy - 2 - [2 - (4 - methylphenyl)ethyl]-
9(10H)-anthracenone (10d). The title compound was
directly obtained from 7d as described for 10b to
provide yellow crystals; 52% yield; m.p. 126–128 °C;
1H-NMR (CDCl3) l 12.64 (s, 1H), 12.28 (s, 1H), 8.05–
7.20 (m, 9H), 4.32 (s, 2H), 2.93 (m, 4H), 2.37 (s, 3H);
FTIR 3436 (OH), 1619 cm−1 (CO···OH); MS m/z=
344 (19, [M]+), 239 (100). Anal. C23H20O3 (C, H).
dimethoxy-9,10-anthracenedione (7e). The title com-
pound was obtained from and diethyl 3,4-
8
dibenzyloxybenzylphosphonate [33] as described for 7d
to provide yellow crystals; 56% yield; m.p. 149–152 °C;
1H-NMR (CDCl3) l 8.02–6.93 (m, 20H), 5.24 (s, 2H),
5.21 (s, 2H), 4.03 (s, 3H), 3.97 (s, 3H); FTIR 1661 (CO)
cm−1; MS m/z=582 (0.34, [M]+), 91 (100). Anal.
C38H30O6 (C, H).
6.1.7.4. 2 - [2 - (3,4 - diBenzyloxyphenyl)ethyl] - 1,8 - dihy-
droxy-9(10H)-anthracenone (10e). The title compound
was directly obtained from 7e as described for 10b to
provide yellow crystals; 39% yield; m.p. 141–144 °C;
1H-NMR (CDCl3) l 12.64 (s, 1H), 12.35 (s, 1H), 8.02–
6.93 (m, 18H), 5.24 (s, 2H), 5.17 (s, 2H), 4.31 (s, 2H),
2.93 (m, 4H); FTIR 3440 (OH), 1618 cm−1 (CO···OH).
Anal. C36H30O5 (C, H).
6.1.6. General procedure for hydrogenation
6.1.6.1. 2 - [2 - (3,4 - Dihydroxyphenyl)ethyl] - 1,8 - dime -
thoxy-9,10-anthracenedione (9i). To a suspension of 5%
Pd–C (500 mg) in absol. EtOH (35 mL), saturated with
H2, was added 7e (1.17 g, 2.0 mmol). The mixture was
hydrogenated at r.t. and atmospheric pressure, until the
requisite amount of H2 was taken up (12 h, TLC
control). Then the catalyst was removed by filtration
and the solvent evaporated in vacuo. Purification by
chromatography (SiO2; CH2Cl2–MeOH, 50/50) pro-
vided red–brown crystals; 55% yield; m.p. 212–214 °C;
1H-NMR (CDCl3) l 7.86–6.62 (m, 8H), 5.49 (s, 1H),
5.30 (s, 1H), 4.03 (s, 3H), 3.97 (s, 3H), 2.90 (m, 4H);
FTIR 1655 (CO) cm−1. Anal. C24H20O6 (C, H).
Analogously, compounds 7c, 7d, 7f–h were hydro-
genated. The crude products were used in the subse-
quent reduction step.
6.1.7.5. 1,8 - diHydroxy - 2 - [2 - (3,4 - dimethoxyphenyl) -
ethyl]-9(10H)-anthracenone (10f). The title compound
was obtained from hydrogenation of 7f as described for
9i and subsequent reduction as described for 10b.
Purification by chromatography (CH2Cl2–Et2O, 90/10)
provided yellow crystals; 28% yield; m.p. 156–157 °C;
1H-NMR (CDCl3) l 12.39 (s, 1H), 12.09 (s, 1H), 7.55–
6.75 (m, 8H), 4.28 (s, 2H), 3.89 (s, 6H), 2.95 (m, 4H);
FTIR 1618 cm−1 (CO···OH); MS m/z=390 (35, [M]+),
151 (100). Anal. C24H22O5 (C, H).
6.1.7.6. 1,8-diHydroxy-2-[2-(3-hydroxy-4-methoxy-
phenyl)ethyl]-9(10H)-anthracenone (10g). The title com-
pound was obtained from hydrogenation of 7g as de-
scribed for 9i and subsequent reduction as described for
10b. Purification by chromatography (CH2Cl2–Et2O,
95/5) provided yellow crystals; 36% yield; m.p. 177–
6.1.7. General procedure for the reduction of
9,10-anthracenediones to 9(10H)-anthracenones [34]
6.1.7.1. 2 - [2 - (4 - Chlorophenyl)ethyl] - 1,8 - dihydroxy -
9(10H)-anthracenone (10b). To a solution of 4b (0.40 g,
1.0 mmol) in glacial HOAc (20 mL) heated to reflux
was added, dropwise over 3 h, a solution of 40% SnCl2
in 37% HCl (10 mL). The solution was then cooled, and
the resulting crystals were collected by filtration. Purifi-
cation by chromatography (SiO2–CH2Cl2) provided
1
178 °C; H-NMR (CDCl3) l 12.50 (s, 1H), 12.18 (s,
1H), 8.35 (s, 1H), 7.50–6.65 (m, 8H), 4.32 (s, 2H), 3.78
(s, 3H), 2.95 (m, 4H); FTIR 3382 (OH), 1611 cm−1
(CO···OH); MS m/z=376 (29, [M]+), 137 (100). Anal.
C23H20O5 (C, H).
1
yellow crystals; 44% yield; m.p. 156–158 °C; H-NMR
6.1.7.7. 1,8-diHydroxy-2-[2-(4-hydroxyphenyl)ethyl]-
9(10H)-anthracenone (10h). The title compound was
obtained from hydrogenation of 7h as described for 9i
and subsequent reduction as described for 10b. Purifica-
tion by chromatography (CH2Cl2–Et2O, 90/10) pro-
vided orange–yellow crystals; 31% yield; m.p.
(CDCl3) l 12.39 (s, 1H), 12.09 (s, 1H), 7.55–6.75 (m,
9H), 4.28 (s, 2H), 2.95 (m, 4H); FTIR 3442 (OH), 1618
cm−1 (CO···OH); MS m/z=364 (12, [M]+), 239 (100).
Anal. C22H17ClO3 (C, H).
1
6.1.7.2. 4-[2-(9,10-Dihydro-1,8-dihydroxy-9-oxo-2-an-
thracenyl)ethyl]benzonitrile (10c). The title compound
was obtained from hydrogenation of 7c as described for
9i and subsequent reduction as described for 10b to
provide yellow crystals; 41% yield; m.p. 221–222 °C;
1H-NMR (CDCl3) l 12.65 (s, 1H), 12.38 (s, 1H), 7.60–
6.80 (m, 9H), 4.30 (s, 2H), 3.00 (m, 4H); FTIR 2226
(CN), 1618 cm−1 (CO···OH); MS m/z=355 (21, [M]+),
239 (100). Anal. C23H17NO3 (C, H, N).
156–157 °C; H-NMR (CDCl3) l 12.49 (s, 1H), 12.16
(s, 1H), 8.85 (s, 1H), 7.48–6.58 (m, 9H), 4.25 (s, 2H),
2.95 (m, 4H); FTIR 3314 (OH), 1622 cm−1 (CO···OH);
MS m/z=346 (29, [M]+), 239 (100). Anal. C22H18O4
(C, H).
6.1.7.8. 1,8 - diHydroxy - 2 - [2 - (3,4 - dihydroxyphenyl) -
ethyl]-9(10H)-anthracenone (10i). The title compound
was obtained from 9i as described for 10b and

K. Mu¨ller et al. / European Journal of Medicinal Chemistry 37 (2002) 83–89
[3] R.N. Young, Eur. J. Med. Chem. 34 (1999) 671–685.
89
chromatographed (CH2Cl2–MeOH, 50/50) to provide
brown–yellow crystals; 62% yield; m.p. 183–185 °C;
1H-NMR (CDCl3) l 12.61 (s, 1H), 12.35 (s, 1H), 7.85–
6.60 (m, 8H), 5.06 (s, 1H), 4.95 (s, 1H), 4.31 (s, 2H),
2.99–2.80 (m, 4H); FTIR 3342 (OH), 1616 cm−1
(CO···OH); MS m/z=362 (24, [M]+), 123 (100). Anal.
C22H18O5 (C, H).
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6.1.7.9.
1,8-diHydroxy-2-(E)-[2-(4-methylphenyl)-
ethenyl]-9(10H)-anthracenone (11d). The title compound
was obtained from 7d, together with 10d, as described for
10b to provide brown–yellow crystals; 24% yield; m.p.
170–174 °C; 1H-NMR (CDCl3) l 12.91 (s, 1H), 12.29 (s,
1H), 7.83–6.90 (m, 9H), 7.49 (d, J=16.5 Hz, 1H), 7.17
(d, J=16.5 Hz, 1H), 4.37 (s, 2H), 2.32 (s, 3H); FTIR
3450 (OH), 1615 cm−1 (CO···OH); MS m/z=342 (23,
[M]+), 239 (100), 117 (1.35), 115 (6), 105 (43). Anal.
C23H18O3 (C, H).
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Anthracenones 2, 10a, 12a–e, 13, 14a [25] and 14b–d
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6.2. Biological assay methods
Epidermal homogenates from NMRI mice were pre-
pared as described [28], platelets were obtained from
sodium EDTA-anticoagulated bovine blood and were
suspended at a concentration of 4×107 cells per mL,
porcine leukocytes were prepared from porcine blood in
a similar fashion as described [35] and were suspended
at a concentration of 1×106 cells per mL. The 12-LO
[28] and the 5-LO [35] assays were performed essentially
as described previously in full detail. 12(S)-HETE was
analysed by chiral phase chromatography as described
[28]. Inhibition was calculated by the comparison of the
mean values of test compound (n=3) with control
(n=6–8) activity: (one-test compound/control)×100;
S.D.510%. Inhibition was statistically significant com-
pared with that of the control (Student’s t-test; PB0.01).
Each IC50 value was derived by interpolation of a log
inhibitor concentration versus response plot using four
or more concentrations of the compound, spanning the
50% inhibition point.
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6.3. Lipophilicity
Determination of log P values was performed by a
standard reversed-phase HPLC procedure as described
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