Synthesis, structural reassignment, and biological activity of type B MAO inhibitors based on the 5H-indeno[1,2-c]pyridazin-5-one core

Article abstract of DOI:10.1021/jm051091j

The synthesis and enzyme inhibitor properties of reversible type B monoamine oxidase inhibitors are described. These compounds belong to the 5H-indeno[1,2-c]pyridazine family and possess a hydrophobic benzyloxy or 4,4,4-trifluorobutoxy side chain which, i

Full text of DOI:10.1021/jm051091j

J. Med. Chem. 2006, 49, 3743-3747
3743
Brief Articles
Synthesis, Structural Reassignment, and Biological Activity of Type B MAO Inhibitors Based
on the 5H-Indeno[1,2-c]pyridazin-5-one Core
Raphae¨l Fre´de´rick,†,‡ Willy Dumont,§ Fre´de´ric Ooms,†,X Lindsey Aschenbach,| Cornelis J. Van der Schyf, Neal Castagnoli,|
Johan Wouters,† and Alain Krief*,§
Laboratoire de Chimie Biologique Structurale, Drug Design and DiscoVery Center, Faculte´s UniVersitaires N.D de la Paix, 61 rue de
Bruxelles, B-5000 Namur, Belgium, Department of Pharmacy, Drug Design and DiscoVery Center, Faculte´s UniVersitaires N.D de la Paix,
61 rue de Bruxelles, B-5000 Namur, Belgium, Laboratoire de Chimie Organique de Synthe`se (COS), Faculte´s UniVersitaires N.D de la Paix,
61 rue de Bruxelles, B-5000 Namur, Belgium, Department of Chemistry, Virginia Tech, Blacksburg, Virginia 02461-0212, and Department of
Pharmaceutical Sciences, Texas Tech UniVersity Health Sciences Center, School of Pharmacy, Amarillo, Texas 79106
ReceiVed October 27, 2005
The synthesis and enzyme inhibitor properties of reversible type B monoamine oxidase inhibitors are
described. These compounds belong to the 5H-indeno[1,2-c]pyridazine family and possess a hydrophobic
benzyloxy or 4,4,4-trifluorobutoxy side chain which, in contrast to a previous assignment, has been
unambiguously located at C(8) of the heterocyclic moiety. Investigation of the regioisomeric structures
establishes that substitution of the 5H-indeno[1,2-c]pyridazin-5-one core at C(7) vs C(8) dramatically
influences the MAO-inhibiting properties of these compounds.
Introduction
Numerous studies have established the potential utility of
reversible and selective monoamine oxidase B (MAO-B)
inhibitors, in particular in the treatment of neurodegenerative
disorders, including Parkinson’s disease (PD)1 and Alzheimer’s
disease (AD)2 as well as for tobacco detoxification.3 The 5H-
indeno[1,2-c]pyridazin-5-one-based structures 1a-d have been
reported by Kneubu¨hler et al.4,5 to be potent reversible and
selective MAO-B inhibitors (Figure 1).6
The most active compound 1a displayed an IC50 value for
Figure 1. 5H-Indeno[1,2-c]pyridazin-5-ones derivatives discussed in
this paper.
the inhibition of MAO-B of 90 nM whereas two related
compounds bearing an hydroxy (1c) (IC50 ) 5.10 µM) or a
methoxy (1d) (IC50 of 1.91 µM) group on the fused aromatic
ring showed considerably weaker MAO-B inhibitory properties
than the corresponding unsubstituted analogue 1b (IC50 ) 0.28
µM).5
We recently reported, on the basis of an MAO-B pharma-
cophoric model, that compounds 1e and 1f (Figure 1) bearing,
respectively, a benzyloxy and a 4,4,4-trifluorobutyloxy hydro-
phobic side chain in the 7-position of the 5H-indeno-[1,2-c]-
pyridazin-5-one system would possess improved activity com-
pared to 1a.7,8
bearing a methoxy group at C-7. We expected to be able to
prepare 1g regioselectively from the commercially available
methoxyninhydrin 3, by analogy to the method already used
by Kneubu¨hler et al.5 for related compounds 1c and 1d. This
strategy moreover offers an opportunity to access a large variety
of 7-alkoxy analogues (Scheme 1).
Scheme 1
Results and Discussion
We planned to synthesize 1e and 1f by a demethylation-
alkylation sequence starting from the common intermediate 1g
* To whom correspondence should be addressed. Phone: +32 (0)81 72
45 39. Fax: +32 (0)81 72 45 36. E-mail: alain.krief@fundp.ac.be.
† Laboratoire de Chimie Biologique Structurale, Faculte´s Universitaires
N.D de la Paix.
‡ Department of Pharmacy, Faculte´s Universitaires N.D de la Paix.
§ Laboratoire de Chimie Organique de Synthe`se (COS), Faculte´s Uni-
versitaires N.D de la Paix.
Compound 3 was subjected to an acid-catalyzed aldol reaction
(acetone in AcOH, 120 °C, 2 h), and the resulting adduct 4
was treated with an excess of hydrazine (aq hydrazine, AcOH,
20 °C, 3 h). Under these conditions,5 the expected product
| Virginia Tech.
Texas Tech University Health Sciences Center.
X Present address: Euroscreen S.A., 802 route de Lennik, 1070 Bruxelles,
Belgium.
10.1021/jm051091j CCC: $33.50 © 2006 American Chemical Society
Published on Web 05/17/2006

3744 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 12
Brief Articles
Figure 2. The molecular structure of compounds 2g. Displacement
ellipsoids are drawn at the 50% probability level.
Figure 3. The molecular structure of compound 2e. Displacement
ellipsoids are drawn at the 50% probability level.
Scheme 2
Scheme 3
intermediate 2h (Figure 1) that, in turn, was to be generated by
cleavage of the methyl ether present in 2g (Scheme 3). Reaction
of the latter with hydrobromic acid (aq HBr, AcOH, 120 °C,
24 h) produced 2h as an intractable mixture of compounds.
Alternative reagents such as thiolates12,13 or selenolates14,15 also
led to disappointing results apparently due to the intrinsic
instability of the resulting phenolate. Moreover, attempted
methylation of 2h in the crude reaction mixture with methyl
iodide in the presence of potassium carbonate neither produced
2g nor led to the recovery of 2h after workup.
Benzylation of 2h, present in the crude reaction mixture was,
however, successfully achieved upon reaction with benzyl
bromide in the presence of silver oxide and provided 2e in
modest yield (BnBr, Ag2O, DMF, 20 °C, 5 h, 40% yield,
Scheme 3).
should be 7-methoxy-3-methyl-5H-indeno[1,2-c]pyridazin-5-one
1g. Unexpectedly, the yellow solid that separated from the
reaction mixture proved to be 8-methoxy-3-methyl-5H-indeno-
[1,2-c]pyridazin-5-one (2g, 71% yield; Scheme 2: R ) Me),
an isomer of the expected compound, as confirmed from the
X-ray diffraction of a single crystal (obtained by slow evapora-
tion from a concentrated solution of acetonitrile).
An ORTEP view of the conformation of 2g is depicted in
Figure 2. The final atomic coordinates and equivalent isotropic
thermal parameters of the non-hydrogen atoms of 2g are given
as Supporting Information.
It has to be noted that control of the temperature is of prime
importance for the regioselective formation of 8-methoxy-3-
methyl-5H-indeno[1,2-c]pyridazin-5-one 2g. Indeed, when the
hydrazine hydrate is added to 4 at -10 °C, an intractable mixture
of both regioisomers 2g and 1g is formed (2g/1g: 70/30) as
The X-ray diffraction analysis of compound 2e confirmed
its structure. Crystals were obtained by slow evaporation of a
concentrated acetonitrile solution. The molecular structure of
2e, with its atomic numbering scheme, is depicted in Figure 3.
The final atomic coordinates and equivalent isotropic thermal
parameters of the non-hydrogen atoms of 2e are given as
Supporting Information.
Since the approach depicted in Scheme 3 suffered from a
poor yield in the final synthetic step and did not allow the
synthesis of 2f, we developed a slightly modified synthetic
strategy that allowed us to produce the latter compound
efficiently. This strategy is depicted in Scheme 4.
This novel approach uses commercially available and inex-
pensive 6-methoxy 6g1 or 7-methoxy-1-indanone 6g2 as starting
material. These indanones have been transformed to the desired
ninhydrins 3f that possess the required alkoxy group on the fused
aromatic ring and which, in turn, was regioselectively trans-
formed to 2f (Figure 1).
Demethylation of 6- or 7-methoxy-1-indanones (6g1 and 6g2)
was our first goal since the analogous transformation was the
weak step in our previous synthetic route (Scheme 3). As
anticipated from our previous results, acid treatment of 6-meth-
oxy-1-indanone 6g1 (aq HBr, 120 °C, 0.6 h, 16%; 1.5 h, 40%;
4 h, 19%, Scheme 3) led to 6-hydroxy-1-indanone 6h1 in a very
1
shown by analyses of the H NMR spectra.
These results led us to suspect that the original structural
assignment for 1d may have been incorrect.5 To assess this,
we repeated the reaction between 3 and methyl m-trifluoro-
methylphenyl ketone under the reported experimental conditions
(Scheme 2: R ) PhmCF3).5 A mixture of two compounds was
isolated and separated after repeated chromatographic purifica-
tions (SiO2, CH2Cl2). The major isomer (47% yield, yellow,
1
mp 214 °C) exhibits a H NMR spectrum identical to that
published5 but its structure, confirmed by X-ray crystallography,9
proved to be the C(8)-substituted compound 2d instead of 1d
as originally described. The minor isomer (3.5% yield, orange,
mp 204 °C), which has never been isolated previously, displays
a 1H NMR spectrum significantly different from that of 2d. The
structure of this product was confirmed by crystallography to
be the regioisomer 1d.9
The approach to our further studies required the synthesis of
2e and 2f instead of our original targets 1e and 1f. Our initial
synthetic approach to 2e and 2f proceeded via the phenolic

Brief Articles
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 12 3745
Table 1. MAO Inhibiting Properties for Compounds 1d, 2d, 2e, 2f, and 2g
i Standard errors less than 2%. ii Rat brain mitochondria. iii Taken from ref 8.
Scheme 4
the newly isolated and characterized compound 1d, and 2d
(Table 1). Intact mitochondria prepared from human placenta
and baboon liver served as sources for MAO-A and MAO-B,
respectively. Human placental mitochondria express MAO-A
almost exclusively10 while baboon liver mitochondria express
almost exclusively MAO-B.11 IC50 values for the inhibition of
MAO-B by 1d and 2d were estimated to be 38.0 nM and 0.1
nM, respectively. Moreover, neither compound inhibited MAO-A
at the maximum attained solubility (5 µM), confirming their
very good selectivity profile. The current data document
dramatic differences in MAO-B inhibitory potency of these
indeno[1,2-c]pyradzin-5-one regioisomers and provide a com-
pelling tool to refine the MAO-B pharmacophoric model
previously reported by us.8
The MAO inhibitory potencies of compounds 2e and 2g have
also been investigated (Table 1). Compound 2e, which possesses
a benzyloxy as side chain in the 8-position, exhibits a modest
MAO-B inhibitory potency (IC50 ) 170 nM). This compound
does not inhibit MAO-A. Compound 2g, which possesses a
methoxy group in the 8-position, is without MAO-A and
MAO-B inhibition properties. When compared with 2f (Table
1), these data show that the replacement of the 4,4,4-trifluo-
robutoxy side chain of 2f with a methoxy 2g or a benzyloxy 2e
strongly decreases the MAO-B inhibiting properties of the
compounds.
modest yield. Use of lithium chloride16 in DMF did not result
in any improvements (130 °C, 26 h, 46% yield). Sodium
ethylthiolate or sodium methylselenolate, which proved equally
efficient, however, led to 6h1 in good yield (DMF, 130 °C, 2 h,
70% yield, each). The same reaction carried out with the
isomeric 7-methoxy-1-indanone 6g2 proved to be much less
efficient.
The next steps proceeded without major problems. O-
alkylation of 6h1 with 1-tosyl-4,4,4-trifluoro-butane gave an 86%
yield of 4,4,4-trifluoromethylbutoxy-1-indanone 6f (K2CO3,
acetonitrile, 80 °C, 4 h, Scheme 4) which, in turn, underwent
smooth oxidation with selenium dioxide15,17 to afford 5-trifluo-
robutoxyninhydrin 3f in 74% yield (3 equiv, dioxane, reflux, 6
h). Finally, treatment of 3f sequentially with acetone and
hydrazine [(i) acetone, AcOH, 120 °C, 2 h; (ii) aq hydrazine,
AcOH, 20 °C, 24 h], as described above, gave 2f (mp 116 °C,
40% yield), the structure of which has been unambiguously
established by crystallography.9
Conclusion
In conclusion, in this paper we show that a procedure
described for the synthesis of 7-substituted 5H-indeno[1,2-c]-
pyridazin-5-ones 1d from methoxyninhydrin 3 affords, instead,
its 8-substituted regioisomer 2d. We have nevertheless isolated,
from the reaction mixture, small amounts of 7-methoxy-5H-
indeno[1,2-c]pyridazin-5-one 1d.
The MAO inhibitory potencies of these compounds proved
to be highly dependent on the position of the alkoxy-substituent.
The 8-substituted derivative 2d proved much more active than
MAO Inhibition. The findings described above are impor-
tant, especially with respect to validation of previously reported
structure-activity relationships.5,7,8 In view of this, we have
determined the MAO-A and MAO-B inhibitory properties of

3746 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 12
Brief Articles
mmol; 500 mg) and benzyl bromide (1.59 g; 10 mmol) in 10 mL
of anhydrous DMF. The mixture was stirred at room temperature
under an inert atmosphere for 5 h. The crude suspension was then
filtered and washed with ethyl acetate. The filtrate was evaporated
to dryness under vacuum (0.5 mmHg) and the residue purified twice
on a silica gel column (100% EtOAc) to yield a yellow solid (26
mg, 40% yield). TLC: Rf 0,7 (AcOEt); mp: 168 °C. Calcd for
C19H14N2O2: C, H, N.
6-Hydroxy-1-indanone 6h1. A solution of dimethyl diselenide
(347 mg, 1.84 mmol) in anhydrous DMF (3 mL) was added
dropwise to a suspension of NaH (110 mg, 3.69 mmol) in anhydrous
DMF (1 mL). After stirring for 45 min at room temperature under
an argon atmosphere, a solution of 6-methoxy-1-indenone (500 mg,
3.08 mmol) in anhydrous DMF (10 mL) was added and the resulting
mixture stirred vigorously for 2 h at 130 °C. After cooling, the
solution was poured into 10% hydrochloric acid (20 mL), extracted
with chloroform (3 × 50 mL), dried over magnesium sulfate,
filtered, and evaporated. The residue was purified by column
chromatography over silica gel and eluted with CH2Cl2/AcOEt (3:
1) to give 6h1 (317 mg, 70%). TLC: Rf 0,2 (Pentane/AcOEt 7:3);
mp 146 °C.
4,4,4-Trifluoromethylbutoxy-1-indanone 6f. 1-Tosyl-4,4,4-
trifluorobutane (3.56 g, 12.6 mmol) was added to in a solution of
6h (1.7 g, 11.4 mmol) in acetonitrile (15 mL) in which potassium
carbonate (3.46 g, 25.08 mmol) is suspended. The resulting mixture
was stirred for 4 h at 90 °C under an argon atmosphere and then
cooled to room temperature. After evaporation of the solvents, the
residue was poured into ethyl acetate, washed with water, dried
over magnesium sulfate, filtered, and evaporated to dryness. The
residue was purified by column chromatography over silica gel and
eluted with pentane/AcOEt (7:3) to give 6f (2.53 g, 86%). TLC:
Rf 0,4. (pentane/AcOEt 7:3); mp 96 °C.
5-Trifluorobutoxyninhydrin 3f. 6f (1.8 g, 6.97 mmol) was
added to a suspension of selenium dioxide (3.87 g, 34.8 mmol) in
dioxane (10 mL). The suspension was then stirred for 4 h to reflux
under an argon atmosphere and filtered, and the solvents were
evaporated. The residue was poured into dichloromethane (30 mL)
into which the unreacted SeO2 precipitated. The SeO2 was filtered
off and the filtrate evaporated to dryness. The residue was purified
by column chromatography over silica gel eluted with CH2Cl2/
AcOEt (3:1) to give 3f (1.56 g, 74%). TLC: Rf (CH2Cl2/AcOEt
7:3) 0.3.
3-Methyl-8-[4,4,4-trifluorobutoxy]-5H-indeno[1,2-c]pyridazin-
5-one 2f. Acetone (572 mg, 9.8 mmol) was added to a solution of
3f (1 g, 3.2 mmol) in glacial acetic acid (5 mL) which was then
stirred under reflux for 2.5 h. After cooling, the solution was
concentrated and hydrazine monohydrate (494 mg, 9.8 mmol)
added. After stirring vigorously at room temperature for 24 h, the
precipitate was filtered and washed with pentane (3x) to give 2f
(420 mg, 40%). TLC: Rf 0,5 (CH2Cl2/AcOEt 3:1); mp 116 °C.
Calcd for C16H13F3N2O2: C, H, N.
MAO Inhibition. Intact mitochondria prepared from human
placenta and baboon liver served as sources for MAO-A and MAO-
B, respectively. Mitochondria were prepared as described by Salach
and Weyler18 and stored in aliquots containing the equivalent of
5-12 mg protein at -70 °C in Eppendorf tubes. Before use, the
original mitochondrial isolate was suspended in 200 µL of sodium
phosphate buffer (100 mM, pH 7.4 containing 50% glycerol, w/v),
and the protein concentration was determined by the method of
Bradford.19 The inhibition of MAO by the test compounds was
evaluated by incubating the nonselective substrate 1-methyl-4-(1-
methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine20 (MMTP; 70 µM)
with the mitochondrial homogenate (0.15 mg of protein/mL) and
various concentrations of the test compounds. The Km values of
MMTP for MAO-A and MAO-B are 52.0 and 60.9 µM, respec-
tively, in human placental and baboon liver tissue. The test
compounds were dissolved in DMSO and added to the buffered
incubation mixture such that the final DMSO concentration was
4%. The final volume of the incubation mixtures was 500 µL (in
sodium phosphate buffer, pH 7.4), and the samples were incubated
at 37 °C for 25 min. All samples were protected from light by
its 7-regioisomer 1d. These findings are of value when attempt-
ing to document the structure-activity relationships in these
series and to rationalize the design of new potent and selective
reversible MAO-B inhibitors.
Finally, as the demethylation-alkylation sequence was the
weaker point in the synthesis of 2 from 3, we have designed a
novel synthetic strategy which efficiently allowed the synthesis
of the trifluorobutyloxy analogue 2f, which is expected to be
widely applicable for the synthesis of the most biologically
active 8-alkoxy-5H-indeno[1,2-c]pyridazin-5-ones.
Experimental Section
1H and 13C NMR spectra were obtained from a JEOL JNM EX
1
400 spectrometer (400 MHz for H or 100.4 MHz for 13C). The
spectra were measured in CDCl3 with TMS as internal standard
(δ: 0.00 ppm). IR data reported in cm-1 were obtained using a
BIO-RAD FTS 165 spectrophotometer. Those data are given as
Supporting Information. Elemental analysis (C,H,N) were performed
on a ThermoFinnigan flash EA112 analyzer and were within (0.4%
of the theoretical values. Analytical thin-layer chromatography
(TLC) were performed on prefabricated, glass-backed plates SiO2,
60PF254, 250 µm (Merck 5719). Compounds were visualized by
UV illumination and by heating to 150 °C after spraying with
phosphomolybdic acid/ethanol. All the reactions were performed
in two necked round-bottomed flasks equipped with a septum
stopper and an argon-filled balloon. Glassware were warmed prior
to use and degassed at 0.1 mmHg. All transfers of reagents were
performed via syringes.
3-Methyl-8-methoxy-5H-indeno[1,2-c]pyridazin-5-one 2g. A
solution of methoxyninhydrin (500 mg, 2.4 mmol) and acetone (278
mg, 4.8 mmol, 2 equiv) in glacial acetic acid (6 mL) was heated to
reflux at 120 °C over a period of 2 h. The mixture was evaporated
in order to eliminate the excess of acetone. Upon cooling to room
temperature, the orange mixture was diluted in glacial acetic acid
(2 mL) and stirred with hydrazine hydrate 98% (209 mg, 4.2 mmol)
for 2 h at room temperature under an inert atmosphere. The yellow
solid which precipitates was collected after filtration, washed with
pentane, and dried under vacuum (385 mg; 71% yield). TLC: Rf
(100% AcOEt) 0.4. mp 175 °C. Calcd for C13H10N2O2: C, H, N.
3-(3-Trifluoromethyl)phenyl-8-methoxy-5H-indeno[1,2-c]py-
ridazin-5-one 2d and 3-(3-Trifluoromethyl)phenyl-7-methoxy-
5H-indeno[1,2-c]pyridazin-5-one 1d. A solution of ninhydrin
(0.178 g, 1 mmol) and (m-trifluoromethyl)phenyl methyl ketone
(0.118 g, 1 mmol) in glacial acetic acid (5 mL) was heated at 110
°C for 2 h and then allowed to cool to room temperature. Addition
of hydrazine hydrate (98%, 0.075 g, 1.5 mmol.) proceeded slightly
exothermically and, after 4 h at 20 °C, yielded a precipitate which
was collected after filtration, washed quickly with pentane (2 × 5
mL), and then dried under vacuum to afford 0.220 g of a solid..
The latter was purified by silica gel column chromatography and
eluted with dichloromethane to produce small amounts of regio-
isomeric 2d (Rf: 0.7) and 1d (Rf: 0.66). The intermediate fraction
containing a mixture of the two regioisomers was purified by three
consecutive column chromatography runs on silica gel and finally
led to the isolation of a yellow solid 2d (0.172 g, 47%, mp 214
°C) and an orange solid 1d (0.013 g, 3.5%, mp 204 °C). Calcd for
C19H11F3N2O2: C, H, N. Calcd for C19H11F3N2O2: C, H, N.
3-Methyl-8-ol-5H-indeno[1,2-c]pyridazin-5-one 2h. A solution
of 3-methyl-8-methoxy-5H-indeno[1,2-c]pyridazin-5-one (385 mg;
1.7 mmol) in 10 mL of aqueous HBr (47%)/glacial acetic acid (50:
50) was refluxed at 120 °C for 24 h under an inert atmosphere.
The mixture was then diluted in 80 mL of water and concentrated
under vacuum. The residue was again diluted in 50 mL of water
and concentrated under vacuum. The dark brown solid formed was
dried under vacuum (0.5 mmHg) and used without any further
purification in the next step of the synthesis.
3-Methyl-8-benzyloxy-5H-indeno[1,2-c]pyridazin-5-one 2e.
Silver oxide (2.32 g, 10 mmol) was added at room temperature to
a solution of 3-methyl-8-ol-5H-indeno[1,2-c]pyridazin-5-one 2h (2.4

Brief Articles
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 12 3747
(4) Kneubu¨hler, S.; Carta, V.; Altomare, C.; Carotti, A.; Testa, B.
Synthesis and monoamine oxidase inhibitory activity of 3-subsituted
5H-indeno[1,2-c]pyridazines. HelV. Chim. Acta 1993, 76, 1956-1963.
(5) Kneubu¨hler, S.; Thull, U.; Altomare, C.; Carta, V.; Gaillard, P.;
Carrupt, P.-A.; Carotti, A.; Testa, B. Inhibition of monoamine
oxidase-B by 5H-indeno[1,2-c]pyridazines: biological activities,
quantitative structure-activity relationships (QSARs) and 3D-
QSARs. J. Med. Chem. 1995, 38, 3874-3883.
(6) Wouters, J. Structural Aspects of Monoamine Oxidase and its
Reversible Inhibition. Curr. Med. Chem. 1998, 5, 137-162.
(7) Ooms, F. Rational approach of the reversible inhibition of type A
and B MAO. Design and synthesis of original 5H-indeno[1,2-c]-
pyridazin-5-one derivatives. Ph.D. Thesis, FUNDP, Namur, Belgium,
2000.
covering the incubation tubes (1.5 mL microcentrifuge tubes) with
aluminum foil. The reactions were terminated by the addition of
20 µL perchloric acid (70% v/v) and centrifuged (16000g for 5
min), and the concentrations of the enzyme-generated dihydropy-
ridinium metabolite MMDP+ in the supernatant fractions were
estimated spectrophotometrically at 420 nm (ꢀ ) 25000 M-1 cm-1).
These data were used to determine the velocity (V) of the MAO-
catalyzed oxidation of MMTP. IC50 values were calculated from a
sigmoidal dose-response nonlinear regression equation using
GraphPad Prism version 3.02 (GraphPad software).
X-ray Diffraction. CCDC 282947 and CCDC 2828948 contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data_re-
quest/cif, or by e-mailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(8) Ooms, F.; Fre´de´rick, R.; Durant, F.; Petzer, J. P.; Castagnoli, N.;
Van der Schyf, C. J.; Wouters, J. Rational approaches towards
reversible inhibition of type B monoamine oxidase. Design and
evaluation of a novel 5H-Indeno[1,2-c]pyridazin-5-one derivative.
Bioorg. Med. Chem. Lett. 2003, 13, 69-73.
Single crystals of compounds 2e and 2g were obtained by slow
evaporation of concentrated solutions of acetonitrile. In both case,
a suitable crystal was mounted on a quartz fiber on the goniometer
head of a CAD4 Nonius diffractometer. After determination of the
cell parameter using 25 well-centered reflections, complete dif-
fraction data sets were collected. The structure was solved using
direct methods and refined by full matrix least squares on F2 using
the program Shelxl97.21 All non-hydrogen atoms were treated
anisotropically while a riding model was applied for the hydrogens.
Analytical and psi-scan corrections for absorption were introduced
for 2e and 2g, respectively. Compound 2g: monoclinic, P21/c, a
) 3.899(1) Å, b ) 26.078(1) Å, c ) 10.481(1) Å, R ) 90.00°, â
) 95.097 (7)°, γ ) 90.00°, V ) 1061.5(3) Å3, Z ) 4 (four
molecules in the asymmetric unit), µ ) 0.802 mm-1, Dx ) 1.416
g cm-3, λ (Cu KR) ) 1.54178 Å, F(000) ) 472, T ) 293 K, 1319
unique reflections (Rint ) 0.0458), R1 ) 0.0467 for 1319 Fo >
2σ(Fo), R1 ) 0.0920 for all data (2083) and wR2 ) 0.1100, GOF
) S ) 1.039. Compound 2e: Orthorhombic, P 21 21 21, a ) 4.061-
(1) Å, b ) 9.890(1) Å, c ) 36.633(4) Å, R ) 90.00°, â ) 90.00°,
γ ) 90.00°, V ) 1471.3(4) Å3, Z ) 4 (four molecules in the
asymmetric unit), µ ) 0.726 mm-1, Dx ) 1.365 g cm-3, λ (Cu
KR) ) 1.54178 Å, F(000) ) 632, T ) 293 K, 1744 unique
reflections (Rint ) 0.0184), R1 ) 0.0528 for 1744 Fo > 2σ(Fo), R1
) 0.0931 for all data (1744) and wR2 ) 0.1209, GOF ) S ) 1.076.
(9) Fre´de´rick, R.; Norberg, B.; Durant, F.; Ooms, F.; Wouters, J. Three
5H-indeno[1,2-c]pyridazin-5-one derivatives, potent type-B monoam-
ine oxidase inhibitors. Acta Crystallogr. C 2004, 60, o623-626.
(10) Weyler, W.; Hsu, Y.-P. P.; Breakefield, O. Biochemistry and genetics
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Supporting Information Available: Microanalytical data for
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Crystallographic parameters for the structure of compounds 2e and
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