10-Phenylbutyryl-substituted anthracenones as inhibitors of keratinocyte growth and LTB4 biosynthesis

Article abstract of DOI:10.1016/S0223-5234(01)01212-0

A recent observation that phenylbutyryl anthracenone 2, an analogue of the antipsoriatic anthralin, is a potent inhibitor of leukotriene B₄ (LTB₄) biosynthesis has prompted a search of other anthracenones with improved antiproliferative activity. In that direction, a limited number of analogues related to 2 have been prepared and evaluated in the HaCaT keratinocytes proliferation and in the polymorphonuclear leukocyte LTB₄ assay. The 4-methoxy analogue 2a and the side chain methylated 2l retain the full inhibitory activity of 1 against LTB₄ biosynthesis while their antiproliferative activity is markedly enhanced and comparable to that of the antipsoriatic anthralin. In contrast to anthralin, cytotoxic effects against cell membranes are strongly reduced as documented by the LDH activity released from cytoplasm of keratinocytes.

Full text of DOI:10.1016/S0223-5234(01)01212-0

Eur. J. Med. Chem. 36 (2001) 179–184
´
© 2001 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved
PII: S0223-5234(01)01212-0/FLA
Original article
10-Phenylbutyryl-substituted anthracenones as inhibitors of keratinocyte growth
and LTB4 biosynthesis
Klaus Mu¨llera*, Klaus Breub, Hans Reindlb
aWestfa¨lische Wilhelms-Universita¨t Mu¨nster, Institut fu¨r Pharmazeutische Chemie, Hittorfstraße 58-62,
D-48149 Mu¨nster, Germany
bInstitut fu¨r Pharmazie, Pharmazeutische Chemie I, Universita¨t Regensburg, D-93040 Regensburg, Germany
Received 11 September 2000; accepted 19 December 2000
Abstract – A recent observation that phenylbutyryl anthracenone 2, an analogue of the antipsoriatic anthralin, is a potent inhibitor
of leukotriene B4 (LTB4) biosynthesis has prompted a search of other anthracenones with improved antiproliferative activity. In that
direction, a limited number of analogues related to 2 have been prepared and evaluated in the HaCaT keratinocytes proliferation
and in the polymorphonuclear leukocyte LTB4 assay. The 4-methoxy analogue 2a and the side chain methylated 2l retain the full
inhibitory activity of 1 against LTB4 biosynthesis while their antiproliferative activity is markedly enhanced and comparable to that
of the antipsoriatic anthralin. In contrast to anthralin, cytotoxic effects against cell membranes are strongly reduced as documented
´
by the LDH activity released from cytoplasm of keratinocytes. © 2001 Editions scientifiques et me´dicales Elsevier SAS
anthracenone / antiproliferative activity / HaCaT / hydroxyl radicals / lactate dehydrogenase release / LTB4 biosynthesis
1. Introduction
(LTB4) biosynthesis with diminished oxygen-radical-
producing intensity, and it was clearly demonstrated
Anthracenone derivatives such as anthralin (1,
that the terminal phenyl ring is required for high
figure 1) are important agents for the treatment of
potency [9].
psoriasis [1]. In contrast to novel agents such as
vitamin D and vitamin A derivatives, anthralin not
only reduces scales and thickness but is also able to
bleach out the erythema [2]. Since its therapeutic use
is accompanied by severe inflammation of the non-af-
fected skin, the development of a topically active
analogue which should obviate this drawback is
highly desirable [3]. As the mechanism of the
proinflammatory action of anthracenones is associ-
ated with the formation of oxygen radicals by these
agents [4], our strategy to overcome this problem was
to modulate the oxygen-radical-generating intensity
by modifying the critical 10-position of the pharma-
cophore [5–8]. The phenylbutyryl analogue 2 has
been shown to be a potent inhibitor of leukotriene B4
Figure 1. Reagents: (a) Method A, X=Cl: pyridine, toluene,
Abbreviations: LTB4, leukotriene B4; LDH, lactate dehydrogenase;
N2; Method B, X=OCO2Et: pyridine, acetone, N2; Method
C, X=OH: DCC, pyridine, THF, N2. A, B, C and R are
defined in table I.
MDA, malondialdehyde; PMNL, polymorphonuclear leukocytes.
* Correspondence and reprints.
E-mail address: kmuller@uni-muenster.de (K. Mu¨ller).

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K. Mu¨ller et al. / European Journal of Medicinal Chemistry 36 (2001) 179–184
This paper describes the continuation of our struc-
While antiproliferative action in cell cultures may
be critical in the management of the proliferative
nature of psoriasis, inhibition of the LTB4 biosynthe-
sis was evaluated as a measure of the potency to
resolve the inflammatory aspect of the disease. Al-
though still controversial [13], there is substantial
data that supports the involvement of leukotrienes in
the amplification of inflammatory reactions in psoria-
sis [14], and compounds that interfere with their
biosynthesis or antagonise their action are explored as
potential antipsoriatic agents [15, 16].
ture–activity relationship investigations into this new
series with particular emphasis on modifications to
the chain bearing the terminal phenyl ring. Antipsori-
atic anthracenones described to date are achiral and
we now wish to report the effect of chiral members of
this series on the biological activity.
2. Chemistry
Analogues 2a,b,f–h were prepared by reacting 1
with the appropriate acyl chlorides in the presence of
pyridine (figure 1, Method A). This method could not
be applied to obtain the 4-oxo-butyryl derivatives 2d,e
of this series since reaction of the 4-oxo-butyric acids
with thionyl chloride did not give the required acyl
chlorides, but rather cyclised to an unsaturated five-
ring lactone. Accordingly, acylation of 1 to give 2d,e
was performed via mixed anhydrides (Method B),
which were obtained from the corresponding acids
and ethyl chloroformate. As with the required pheny-
lacyl chlorides, which were prepared according to
standard literature methods, the crude products were
used in the subsequent acylation steps. In an alterna-
tive approach (Method C), analogues 2c,i,k,m were
obtained directly from the phenylalkylcarboxylic
acids and 1 by the use of the coupling agent dicyclo-
hexylcarbodiimide (DCC) [10]. Finally, the pure enan-
tiomers 2g and 2h were prepared from the optically
pure (R)- and (S)-3-phenylbutyric acids, respectively,
with an ee ]98% as documented by HPLC analysis
on a chiral support.
Further studies were performed on the redox be-
haviour of the new compounds using the deoxyribose
assay, which is a sensitive test for the production of
hydroxyl radicals [17]. The release of thiobarbituric
acid reactive material is expressed as malondialdehyde
(MDA). It is a measure for hydroxyl-radical genera-
tion and thus reflects prooxidant properties of the
anthracenones [9].
4. Results and discussion
The structures and biological activity of the novel
anthracenones 2a–m are listed in table I, together
with the straight chain phenylbutyryl analogue 2 and
parent anthralin 1 as reference compounds. From an
earlier investigation of the structure–activity relation-
ships of anthracenones for inhibition of 5-lipoxyge-
nase [9], the phenylbutyryl derivative 2 was two
orders of magnitudes more potent than the parent 1.
However, as can be seen from the results in table I,
this study shows that improvement of the LTB4 in-
hibitory action is accompanied by a twofold decrease
in antiproliferative activity. As a 4-methoxy sub-
stituent was beneficial for antiproliferative activity in
the phenylacetyl series, this feature was also added to
compound 2. The 4-methoxy analogue 2a demon-
strates that the potent antiproliferative activity of 1
could be regained without sacrificing potent LTB4
inhibitory properties of 2. Moreover, an extra
methoxy group as in 2b even has slightly improved
antiproliferative activity; however, the potency
against LTB4 biosynthesis was strongly reduced. In-
troduction of a further keto group into the side chain
linking the anthracenone nucleus and the terminal
phenyl ring (2d) resulted in decrease of both antipro-
liferative and LTB4 inhibitory activities. Although the
pertinent 4-methoxy analogue 2e retained the potency
against cell growth, inhibitory action against LTB4
biosynthesis was further decreased.
3. Pharmacology
The novel analogues were evaluated in vitro for
inhibition of the growth of HaCaT keratinocytes [11],
a model for highly proliferative epidermis of psoriasis.
Proliferation of the keratinocytes was determined di-
rectly by counting the dispersed cells under a phase-
contrast microscope after 48 h of treatment.
Furthermore, a major concern in the testing of
potential inhibitors of cell growth is to confirm that
the drug does not interfere with the functioning of cell
membrane by causing leakage of cytoplasm through
it. Accordingly, cytotoxicity against the cell cultures
by the potent cell-growth inhibitors was assessed by
the activity of lactate dehydrogenase (LDH) released
into the culture medium [12].

K. Mu¨ller et al. / European Journal of Medicinal Chemistry 36 (2001) 179–184
181
Table I. Antiproliferative activity and cytotoxicity against HaCaT cells, inhibition of LTB4 biosynthesis in bovine PMNL, and
deoxyribose degradation of 1,8-dihydroxy-10-phenylbutyryl-9(10H)-anthracenones and homologues.
’
a
c
Compound
A
B
C
R
AA IC50
LDH b (mU) LTB4 IC50
DD ( OH) d
(mM)
(mM)
1
Anthralin
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
0.7
1.5
0.9
0.5
1.0
1.6
0.9
0.8
0.8
0.4
1.7
1.3
0.8
0.8
294
167
188
183
174
172
130 f
146 f
ND
ND
196
149 f
171
253
37
0.3
0.3
15
1
8
20
1.5
2
1.5
0.8
2
0.3
2
2.8990.14 e
B0.3
2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CH2
CH2 CO
CH2 CO
H
4-OMe
3,4-(OMe)2
4-Me
H
4-OMe
H
H
2a
2b
2c
2d
2e
2f
2g
2h
2i
0.5690.11 e
0.5990.07 e
ND
B0.3
B0.3
CHCH3 (R,S)
CHCH3 (R)
CHCH3 (S)
CHCH3 (R,S) 4-OMe
CHCH3 (R,S) 4-Me
B0.3
B0.3
H
B0.3
ND
ND
2k
2l
2m
CH2 CHCH3 (R,S)
H
H
B0.3
ND
CHCH2CH3
(R,S)
a Antiproliferative activity against HaCaT cells. Inhibition of cell growth was significantly different with respect to that of the
control, N=3, PB0.01.
b Activity of LDH (mU) release in HaCaT cells after treatment with 2 mM test compound (N=3, SDB10%; controls 149913).
c Inhibition of LTB4 biosynthesis in bovine polymorphonuclear leukocytes. Inhibition was significantly different with respect to that
of the control; N=3 or more, PB0.01. Nordihydroguaiaretic acid (NDGA) was used as the standard inhibitor (IC50=0.4 mM).
d Deoxyribose degradation as a measure of hydroxyl-radical formation. Indicated values are mmol of malondialdehyde/mmol of
deoxyribose released by 75 mM test compound (controlB0.1).
e Values are significantly different with respect to vehicle control.
f Values are not significantly different with respect to vehicle control. ND=not determined.
ever, in the HaCaT proliferation assay, the (S)-enan-
tiomer was twofold more potent than the
(R)-enantiomer.
Compounds 2f–m illustrate the influence of
branched side chains. The racemic 2f, an isomer of 2,
exhibited potency against cell growth comparable
with 1, while inhibition of LTB4 biosynthesis was
somewhat weaker than that of 2. The higher homo-
logues 2l,m of 2f, which were also tested as racemic
mixtures, showed equally potent antiproliferative ac-
tivity, and in the case of 2l even the full inhibitory
action of 2 against LTB4 biosynthesis was retained.
The pure enantiomers 2g,h of the racemic 2f were
synthesised to explore the effect of chirality on the
biological activity of the anthracenone class of antip-
soriatic agents. With respect to LTB4 inhibition, no
appreciable difference in potency was observed as
compared with the racemic 2f. This is in contrast with
other chiral inhibitors of LTB4 biosynthesis for which
enantioselectivity has been reported [18, 19]. How-
As a final study, we examined the cytotoxic effects
of the novel anthracenones against the cell membrane.
Parent 1 has been reported to cause membrane dam-
age, but did not directly lead to substantial membrane
destruction [12]. In this assay, LDH release by 1 as a
measure of its potential to induce membrane damage
significantly exceeded that of the vehicle control,
whereas the activity of the novel compounds was due
to cytostatic rather than cytotoxic effects, as LDH
release was unchanged or only slightly enhanced as
compared to controls. Similar results were obtained in
the deoxyribose degradation assay, as a measure of
hydroxyl-radical generation. While 1 is a potent hy-
droxyl-radical generator, deoxyribose degradation by

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K. Mu¨ller et al. / European Journal of Medicinal Chemistry 36 (2001) 179–184
the novel analogues was either decreased to a mini-
mum or only slightly enhanced as compared to con-
trols, as observed for 2a,b.
orated. The residue was purified by column
chromatography.
Method B. The appropriate mixed anhydrides (5.50
mmol) in absolute acetone were used in place of the acyl
chlorides.
5. Conclusions
Method C. To a solution of 1 (1.00 g, 4.42 mmol), the
appropriate carboxylic acid (5.30 mmol), and dicyclo-
hexylcarbodiimide (1.10 g, 5.30 mmol) in absolute THF
(30 mL) was added dry pyridine (2.0 mL) under N2. The
reaction mixture was stirred at room temperature for 4
h, filtered, and the filtrate was evaporated. The residue
was purified by column chromatography.
In conclusion, 4-methoxy analogue 2a and the side
chain methylated 2l retain the full LTB4 inhibitory
activity of phenylbutyryl anthracenone 2, while their
antiproliferative activity is markedly enhanced and
comparable to that of the antipsoriatic anthralin. In
contrast to anthralin, cytotoxic effects against cell
membranes and hydroxyl-radical generation are re-
duced to a minimum.
6.1.4.1. 1,8-Dihydroxy-10-[4-(4-methoxyphenyl)-1-
oxobutyl]-9(10H)-anthracenone (2a).
The title compound was obtained from 1 and 4-(4-
methoxyphenyl)butyryl chloride [22] according to
Method A. Purification by column chromatography us-
ing CH2Cl2–hexane (19:1) gave a yellow powder; 24%
6. Experimental protocols
6.1. Chemistry
yield; m.p. 116–117°C; FTIR 1711, 1630 cm−1 1H-
;
NMR (CDCl3) l 12.20 (s, 2H), 7.57–6.72 (m, 10H), 5.14
(s, 1H), 3.73 (s, 3H), 2.30–1.90 (m, 4H), 1.70–1.40 (m,
2H); MS m/z=402 (2, M+), 226 (100). Anal. C25H22O5
(C, H).
6.1.1. General
For analytical instruments and methods see Ref. [7].
6.1.2. Preparation of acyl chlorides
Acyl chlorides were prepared from the corresponding
carboxylic acids according to the standard literature
procedures [20], and the crude products were used in the
subsequent acylation steps (Method A).
6.1.4.2. 1,8-Dihydroxy-10-[4-(3,4-dimethoxyphenyl)-1-
oxobutyl]-9(10H)-anthracenone (2b).
The title compound was obtained from 1 and 4-(3,4-
dimethoxyphenyl)butyryl chloride [22] according to
Method A. Purification by column chromatography us-
ing CH2Cl2–ether (49:1) gave a yellow powder; 30%
6.1.3. Preparation of mixed anhydrides
A solution of the appropriate carboxylic acid (10
mmol) and triethylamine (1.01 g, 10 mmol) in absolute
ether (25 mL) was cooled on an ice/NaCl bath to 0°C.
Ethyl chloroformate (1.09 g, 10 mmol) was added slowly
under stirring, and the temperature was kept at 0°C.
Then the mixture was warmed to room temperature
within 1 h and filtered. The filtrate was washed with a
solution of NaHCO3 (0°C) and then with water, dried
over MgSO4, and evaporated. The crude products were
used in the subsequent acylation steps (Method B).
yield; m.p. 117°C; FTIR 1713, 1628 cm−1 1H-NMR
;
(CDCl3) l 12.30 (s, 2H), 7.62–6.32 (m, 9H), 5.20 (s,
1H), 3.83 (s, 3H), 3.78 (s, 3H), 2.32–1.77 (m, 4H),
1.73–1.43 (m, 2H); MS m/z=432 (4, M+), 207 (100).
Anal. C26H24O5 (C, H).
6.1.4.3. 1,8-Dihydroxy-10-[4-(4-methylphenyl)-1-
oxobutyl]-9(10H)-anthracenone (2c).
The title compound was obtained from 1 and 4-tolyl-
butyric acid according to Method C. Purification by
column chromatography using CH2Cl2–petroleum ether
(8:2) and recrystallisation from benzene–petroleum
ether (1:1) gave yellow needles; 13% yield; m.p. 190°C
6.1.4. General procedure for the acylation of 1 to the
10-substituted 1,8-dihydroxy-9(10H)-anthracenones
Method A. To a solution of 1 [21] (1.00 g, 4.42 mmol)
in absolute toluene (75 mL) and dry pyridine (0.43 mL,
5.50 mmol) was added dropwise a solution of the appro-
priate acyl chloride (5.50 mmol) in absolute toluene (10
mL) under N2. The reaction mixture was stirred at room
temperature for 12 h, filtered, and the filtrate was evap-
1
(dec); FTIR 1711, 1632 cm−1; H-NMR (DMSO-d6) l
11.93 (s, 2H), 7.66–6.83 (m, 10H), 5.63 (s, 1H), 2.53 (t,
J=6.9 Hz, 2H), 2.29 (t, J=7.5 Hz, 2H), 2.23 (s, 3H),
1.55 (tt, J=7.5 Hz, J=6.9 Hz, 2H). Anal. C25H22O4 (C,
H).

K. Mu¨ller et al. / European Journal of Medicinal Chemistry 36 (2001) 179–184
183
6.1.4.4. 1,8-Dihydroxy-10-(1,4-dioxo-4-phenylbutyl)-
9(10H)-anthracenone (2d).
Purification by column chromatography using CH2Cl2–
hexane (7:3) gave a yellow powder; 29% yield; m.p.
121–122°C; FTIR 1713, 1630 cm−1; MS m/z=372 (10,
M+), 226 (100). Anal. C24H20O4 (C, H).
The title compound was obtained from 1 and ethyl
(4-oxo-4-phenyl)butyrylcarbonate (prepared from 3-ben-
zoylpropionic acid) according to Method B. Purification
by column chromatography using CH2Cl2–hexane (4:1)
gave a yellow powder; 10% yield; m.p. 162–164°C;
FTIR 1721, 1694, 1630 cm−1; 1H-NMR (CDCl3) l 12.27
(s, 2H), 7.90–6.91 (m, 11H), 5.28 (s, 1H), 3.02 (t, J=6
Hz, 2H), 2.39 (t, J=6 Hz, 2H); MS m/z=161 (100),
105 (31). Anal. C24H18O5 (C, H).
6.1.4.9. (R,S)-1,8-Dihydroxy-10-[3-(4-methoxy-
phenyl)-1-oxo-butyl)-9(10H)-anthracenone (2i).
The title compound was obtained from 1 and (R,S)-3-
(4-methoxyphenyl)butyric acid [26] according to Method
C. Purification by column chromatography using
CH2Cl2–petroleum ether (1:1) and recrystallisation from
benzene–petroleum ether (8:2) gave yellow crystals; 19%
yield; m.p. 125–127°C; FTIR 1705, 1628 cm−1 1H-
;
6.1.4.5. 1,8-Dihydroxy-10-[4-(4-methoxyphenyl)-1,4-
dioxobutyl]-9(10H)-anthracenone (2e).
NMR (DMSO-d6) l 11.93 (s, 1H), 11.92 (s, 1H), 7.61–
6.70 (m, 10H), 5.59 (s, 1H), 3.69 (s, 3H), 3.06–2.77 (m,
3H), 0.95 (d, J=6.7 Hz, 3H); MS m/z=402 (5.6, M+),
226 (78), 135 (100). Anal. C25H22O5 (C, H).
The title compound was obtained from 1 and ethyl
[4-(4-methoxyphenyl)-4-oxo]butyrylcarbonate (prepared
from 3-(4-methoxybenzoyl)propionic acid [23]) accord-
ing to Method B. Purification by column chromatogra-
phy using CH2Cl2–hexane (9:1) gave yellow crystals; 6%
6.1.4.10. (R,S)-1,8-Dihydroxy-10-[3-(4-methylphenyl)-
1-oxo-butyl)-9(10H)-anthracenone (2k).
yield; m.p. 183–185°C; FTIR 1717, 1676, 1628 cm−1
;
1H-NMR (CDCl3) l 12.30 (s, 2H), 7.90–6.84 (m, 10H),
5.32 (s, 1H), 3.85 (s, 3H), 3.00 (t, J=6 Hz, 2H), 2.40 (t,
J=6 Hz, 2H); MS m/z=191 (100), 135 (46). Anal.
C25H20O6 (C, H).
The title compound was obtained from 1 and (R,S)-3-
(4-methylphenyl)butyric acid [27] according to Method
C. Purification by column chromatography using
CH2Cl2–/petroleum ether (1:1) and recrystallisation
from benzene–petroleum ether (1:1) gave yellow crys-
tals; 6% yield; m.p. 135–137°C; FTIR 1719, 1630 cm−1
;
6.1.4.6. (R,S)-1,8-Dihydroxy-10-(1-oxo-3-phenylbutyl)-
9(10H)-anthracenone (2f).
1H-NMR (DMSO-d6) l 11.93 (s, 1H), 11.92 (s, 1H),
7.60–6.91 (m, 10H), 5.59 (s, 1H), 3.06–2.79 (m, 3H),
2.22 (s, 3H), 0.95 (d, J=6.7 Hz, 3H); MS m/z=386
(3.5, M+), 226 (83), 118 (100). Anal. C25H22O4 (C, H).
The title compound was obtained from 1 and (R,S)-3-
phenylbutyryl chloride [24] according to Method A.
Purification by column chromatography using CH2Cl2–
hexane (7:3) gave a yellow powder; 27% yield; m.p.
1
146–147°C; FTIR 1711, 1628 cm−1; H-NMR (CDCl3)
6.1.4.11. (R,S)-1,8-Dihydroxy-10-(1-oxo-4-
phenylpentyl)-9(10H)-anthracenone (2l).
l 12.31 (s, 1H), 12.25 (s, 1H), 7.58–6.48 (m, 11H), 5.10
(s, 1H), 3.08–2.98 (m, 1H), 2.28–2.15 (m, 2H), 0.93 (d,
J=7 Hz, 3H); MS m/z=372 (8, M+), 226 (100). Anal.
C24H20O4 (C, H).
The title compound was obtained from 1 and (R,S)-4-
phenylvaleryl chloride (prepared from 4-phenylvaleric
acid [28]) according to Method A. Purification by
column chromatography using CH2Cl2–hexane (3:2)
gave a yellow powder; 33% yield; m.p. 82°C; FTIR
6.1.4.7. (R)-1,8-Dihydroxy-10-(1-oxo-3-phenylbutyl)-
9(10H)-anthracenone (2g).
1711, 1628 cm−1 1H-NMR (CDCl3) l 12.19 (s, 2H),
;
7.57–6.76 (m, 11H), 5.12 (s, 1H), 2.55–2.17 (m, 1H),
1.97–1.42 (m, 4H), 1.02 (d, J=7 Hz, 3H); MS m/z=
386 (5, M+), 226 (100). Anal. C25H22O4 (C, H).
The title compound was obtained from 1 and (R)-3-
phenylbutyryl chloride [25] according to Method A.
Purification by column chromatography using CH2Cl2–
hexane (7:3) gave a yellow powder; 27% yield; m.p.
121–122°C; FTIR 1713, 1630 cm−1; MS m/z=372 (11,
M+), 226 (100). Anal. C24H20O4 (C, H).
6.1.4.12. (R,S)-1,8-Dihydroxy-10-(1-oxo-3-
phenylpentyl)-9(10H)-anthracenone (2m).
The title compound was obtained from 1 and (R,S)-3-
phenylvaleric acid [29] according to Method C. Purifica-
tion by column chromatography using CH2Cl2–
petroleum ether (1:1) and recrystallisation from ben-
zene–petroleum ether (7:3) gave yellow needles; 13%
6.1.4.8. (S)-1,8-Dihydroxy-10-(1-oxo-3-phenylbutyl)-
9(10H)-anthracenone (2h).
The title compound was obtained from 1 and (S)-3-
phenylbutyryl chloride [25] according to Method A.

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K. Mu¨ller et al. / European Journal of Medicinal Chemistry 36 (2001) 179–184
yield; m.p. 107–109°C; FTIR 1705, 1628 cm−1
;
1H-
[10] Mu¨ller K., Breu K., Arch. Pharm. Pharm. Med. Chem. 332
(1999) 31–35.
NMR (DMSO-d6) l 11.92 (s, 1H), 11.91 (s, 1H), 7.58–
6.92 (m, 10H), 5.59 (s, 1H), 2.97 (d, J=6.9 Hz, 2H),
2.78 (tt, J=6.9 Hz, J=6.8 Hz, 1H), 1.36 (dq, J=6.8
Hz, J=7.3 Hz, 2H), 0.56 (t, J=7.3 Hz, 3H); MS
m/z=386 (4.0, M+), 226 (100). Anal. C25H22O4 (C, H).
[11] Boukamp P., Petrussevska R.T., Breitkreutz D., Hornung J.,
Markham A., Fusenig N.E., J. Cell Biol. 106 (1988) 761–771.
[12] Bonnekoh B., Farkas B., Geisel J., Mahrle G., Arch. Dermatol.
Res. 282 (1990) 325–329.
[13] Brooks C.D.W., Summers J.B., J. Med. Chem. 39 (1996) 2629–
2654.
6.1.5. Analysis by chiral phase chromatography
[14] Ikai K., J. Dermatol. Sci. 21 (1999) 135–146.
Enantiomers 2g,h were analysed by chiral phase
HPLC on a Daicel Chiralpak AD 250×4.6 mm2 column
(Daicel, Tokyo, Japan). The isocratic elution conditions
were (+)-2-butanol–2-propanol–hexane (1.56:1.17:
92.27, v/v/v), flow rate 0.3 mL min−1 (Merck-Hitachi
L-6200 A), monitored at 220 nm with a Merck L 4000 A
UV detector. The retention times for 2g and 2h were
40.6 and 37.7 min, respectively.
[15] Kuehm-Caube`re C., Caube`re P., Jamart-Gre´goire B., Pfeiffer B.,
Guardiola-Lemaˆıtre B., Manechez D., Renard P., Eur. J. Med.
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