AU3123400A - 2,3,4,4a-tetrahydro-1h-pyrazino(1,2-a)quinoxalin-5(6h)one derivates being 5ht2c agonists - Google Patents

Description

WO 00/35922 PCT/US99/29894 -1 2

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3

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4 ,4A-TETRAHYDRO-1H-PYRAZINO(1,2-A)QINOXALIN-5(6H)ONE DERIVATES BEING 5HT2C AGONISTS BACKGROUND OF THE INVENTION 5 The present invention relates to derivatives of 2,3,4,4a-tetrahydro-lH pyrazino[1,2,-a]quinoxalin-5(6H)ones which are serotonin 5-hydroxytryptamine 2 c (5HT2c) receptor agonists useful for the treatment of disorders such as obsessive compulsive disorder, depression, anxiety, schizophrenia, migraine, sleep disorders, 10 eating disorders, obesity, type II diabetes, and epilepsy. Obesity is a medical disorder characterized by an excess of body fat or adipose tissue. Comorbidities associated with obesity are Type II diabetes, cardiovascular disease, hypertension, hyperlipidemia, stroke, osteoarthritis, sleep 15 apnea, gall bladder disease, gout, some cancers, some infertility, and early mortality. As the percentage of obese individuals continues to rise both in the U.S. and abroad, obesity is expected to be a major health risk in the 21"s Century. The serotonin 5 hydroxytryptamine (5-HT) receptor is a G-protein coupled receptor which is expressed in neurons in many regions of the human central nervous system. 20 [Wilkinson, L. O. and Dourish, C. T. in Serotonin Receptor Subtypes: Basic and Clinical Aspects (ed. Peroutka, S. J. ) 147-210 (Wiley-Liss, New York, 1991).] The 5HTC receptor (formerly called the 5HTC receptor) is a prominent subtype of the serotonin receptor found in the central nervous system of both rats and humans. It is expressed widely in both cortical and subcortical regions. [Julius, D. MacDermott, A. 25 B., Axel, R. Jessell, T. M. Science 241:558-564 (1988).] Studies in several animal species and in humans have shown that the non-selective 5HT 2 c receptor agonist, meta-chlorophenylpiperazine (MCPP) decreases food intake. [Cowen, P.J., Clifford, E. M. , Williams, C., Walsh, A. E. S., Fairburn, C. G. Nature 376: 557 (1995).] Tecott, et al have demonstrated that transgenic mice lacking the 5HT 2 c receptor eat 30 more and are heavier than Wild Type mice. [Tecott, L. H., Sun, L. M., Akana, S. F., Strack, A. M., Lowenstein, D. H., Dallman, M. F., Jullus, D. Nature 374: 542-546 (1995).] Compounds of this invention are 5HT 2 c receptor subtype selective agonists which are selective over other monoamine receptors, causes a reduction in food WO 00/35922 PCT/US99/29894 -2 intake and result in a reduction in weight gain. Other therapeutic indications for 5HT 2 c agonists are obsessive compulsive disorder, depression, panic disorder, schizophrenia, sleep disorders, eating disorders, and epilepsy. United States Patent 4,032,639; 4,089,958; and 4,203,987 describe 2,3,4,4a 5 Tetrahydro- 1 H-pyrazino[1,2-a]quinoxalin-5(6)-ones and derivatives thereof as antihypertensive agents. In contrast, compounds of this invention bind to and activate the 5HT 2 C receptors in the CNS and are useful for the treatment of CNS disorders. Indian J. Chem. 17B, 244-245 (1979) discloses 3-Substituted 2,3,4,4a,5,6 Hexahydro-l(H)-pyrazino[1,2-a]quinoxalines which exhibit no anorexigenic or 10 stimulant activity at 60 mg/kg i.p. dose. Weak CNS depressant activity and significant hypotensive activity in anaesthetized animals. Tachyphylaxis was observed. DESCRIPTION OF THE INVENTION 15 This invention provides compounds of formula I having the structure R2N R3 N R4 R' I wherein R is hydrogen or alkyl of 1-6 carbon atoms; 20 R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl;

R

1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, 25 trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5

R

6 or a carbonyl group;

R

5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; WO 00/35922 PCT/US99/29894 -3 or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 ,

R

2 , R 3 , or R 4 are not hydrogen; which are 5HT 2 C receptor agonists useful for the treatment of disorders involving the central nervous system such as obsessive-compulsive disorder, depression, anxiety, 5 panic disorder, schizophrenia, migraine, sleep disorders, eating disorders, obesity, type II diabetes, and epilepsy. The compounds of this invention may contain an asymmetric carbon atom and some of the compounds of this invention may contain one or more asymmetric 10 centers and may thus give rise to optical isomers, enantiomers and diastereoisomers. While shown without respect to stereochemistry in Formula I, the present invention includes such optical isomers and diastereoisomers; as well as the racemic and resolved, enantiomerically pure R and S stereoisomers; as well as other mixtures of the R and S stereoisomers and pharmaceutically acceptable salts thereof. 15 The term "alkyl" includes both straight- and branched-chain saturated aliphatic hydrocarbon groups. Preferred alkyl groups are methyl, ethyl, propyl or butyl, most preferably methyl. The term "aroyl" is defined as an aryl ether, where aryl is defined as an aromatic system of 6-14 carbon atoms, which may be a single 20 ring or multiple aromatic rings fused or linked together as such that at least one part of the fused or linked rings forms the conjugated aromatic system. Preferred aryl groups include phenyl, naphthyl, biphenyl, anthryl, tetrahydronaphthyl, phenanthryl groups. Halogen is defined as Cl, Br, F, and I, preferably chlorine or fluorine. 25 Pharmaceutically acceptable salts can be formed from organic and inorganic acids, for example, acetic, propionic, lactic, citric, tartaric, succinic, fumaric, maleic, malonic, mandelic, malic, phthalic, hydrochloric, hydrobromic, phosphoric, nitric, sulfuric, methanesulfonic, napthalenesulfonic, benzenesulfonic, toluenesulfonic, camphorsulfonic, and similarly known acceptable acids. 30 Preferred compounds of this invention are those in which at least one of R 1 ,

R

2 , R 3 , or R 4 are not hydrogen, and the non-hydrogen substituents of R 1 , R 2 , R 3 , and

R

4 are halogen or trifluoromethyl.

WO 00/35922 PCT/US99/29894 -4 Preferred enantiomerically pure compounds of formulas IA and IB are provided as follows: R2 RR R2 R

R

3 R N 0 H

R

3 H R4

R

4 IA IB 5 wherein R, R 1 , R 2 , R 3 , and R 4 are as described above. The compounds of this invention can be prepared according to the following schemes from commercially available starting materials or starting materials which 10 can be prepared using literature procedures. These schemes show the preparation of representative compounds of this invention.

WO 00/35922 PCT/US99/29894 -5 Scheme 1 'Pbz R1 N R2 R2 Cbz N COOH + R 0 2 R3 N02 OH H R4 4 I II III 1 rN-Cbz KN-Cbz R2 R3, Y R3!N

R

4 H

R

4 R' IV V i (^'N-H R 1 <N-H R2 R2#

R

4 H R4 R' R R N

R

4 R' VII R2, N R rN

R

4 R'

R

4 R VIII IX In Scheme 1, the symbol Cbz represents a carbobenzyloxy group and Y stands for chlorine, fluorine, or bromine. A solution of 4 -carbobenzyloxypiperazine 5 2-carboxylic acid (I) is allowed to react with a substituted ortho-nitrohalobenzene (II) to give a 4-carbobenzyloxy-1-(o-nitro-substituted-phenyl)-piperazine-2-carboxylic acid (III). The reaction is carried out in an inert organic solvent, such as dimethylsulfoxide, in the presence of a base, such as triethylamine, at a temperature above ambient temperature, such as 50-150oC.

WO 00/35922 PCT/US99/29894 -6 The intermediate (III) is cyclized by a process involving reduction of the nitro group to an amino group, preferably by reaction of a metal, such as iron, in an acid, such as acetic acid, followed by heating at elevated temperature, such as 50 100oC, to effect cyclization to (IV). Removal of the Cbz protecting group using boron 5 tribromide, catalytic reduction or a base, such as potassium hydroxide, gives products of this invention (IVa). Or treatment of (IV) with a base, such as sodium hydride, followed by reaction with an alkyl halide, such as methyl iodide, give intermediates (V). Removal of the Cbz group with boron tribromide or potassium hydroxide give compounds of this invention (VI) where R' is lower alkyl. 10 Compounds (VI) can also be alkylated a second time using a base, such as sodium hydride, and an alkyl halide, such as methyl iodide, to give compounds of this invention (VIII). Alternatively, compounds (VI) can be reduced with a reducing agent, such as borane in THF, to compounds of this invention (VII). Compounds (VIII) can also be reduced with borane in THF to give (IX) which are compounds of 15 this invention. The amide of compounds (V) can also be reduced to amines (VII) using a reducing agent, such as borane in tetrahydrofuran, at 0-50oC. Compounds (VII) are also compounds of this invention. 20 Likewise, the amide of compounds (VI) can be reduced to amines (VIII) which are compounds of this invention. In compounds (VI) where R' is acyl this group is put on, as already described, after reduction of amides (VI) where R' is hydrogen.

WO 00/35922 PCT/US99/29894 -7 Scheme 2 Rl -R R, -R

R

2 0 'OH R2 I -OMe 03 0

N

2 R 3 #NO IV Ix R3 0

NHN

2 R2

RO

2 -R RR N)JRR -R R3# H N R I N R H4

R

3 NO R 6 4R4 1 ( N-R 1 y R R , f N<X

H

3 N3N R 4 R R R' II R5I __ R WO 00/35922 PCT/US99/29894 -8 In Scheme 2, the carboxylic acids of intermediate (IV) are converted to the corresponding N-methoxy-N-methyl amides (IX) by reaction of the corresponding acids (IV) with N,O-dimethylhydroxylamine hydrochloride in the presence of a base, 5 such as pyridine, and a coupling reagent, such as dicyclohexylcarbodiimide (DCC) in an organic solvent, such as methylene chloride at a temperature between 0-50oC. Treatment of intermediates (IX) with Grignard reagents or organolithium reagents, such as methyl lithium, gives ketones (X). Reduction of the nitro group in intermediates (X) with a reducing agent, such as iron in acetic acid, gives the 10 corresponding amines (XI) which cyclize at elevated temperatures, such as 50-150 0 C, in the presence of an acid, such as p-toluenesulfonic acid, in an inert organic solvent, such as benzene, to give compounds of this invention (XII). Alkylation of (XII) with an alkyl halide, such as methyl iodide, or an acyl halide such as acetyl chloride, gives compounds of this invention (XIII). Treatment of intermediates (X) with a Grignard 15 reagent, such as methylmagnesium chloride, give tertiary alcohols (XIV). Reduction of the nitro group in intermediates (XIV) with a metal, such as iron, in an acid, such as acetic acid, followed by heating at a temperature from 50-150 0 C, gives (XV) which are compounds of this invention. Reaction of compounds (XV) with an alkyl halide, such as methyl iodide, or an acyl halide, such as acetyl chloride, gives (XVI) 20 which are compounds of this invention. The enantiomerically pure compounds of this invention can be prepared according to the following Scheme 3 from commercially available starting materials or starting materials which can be prepared using literature procedures. This scheme 25 shows the preparation of representative (R)-compounds of formula IA of this invention, starting with the known 2 -(R)-piperazinecarboxylic acid (reference below). Starting from the known 2 -(S)-piperazinecarboxylic acid gives the (S)-compounds of formula IB of this invention.

WO 00/35922 PCT/US99/29894 -9 Scheme III H NH -. Cbz HN HN CO2H

CO

2 H 2-(R)-PIPERAZINE CARBOXYLIC ACID XVII R2 , F R N Cbz R F2 R N R3 / "NO2 R2" N =

R

3 N0 2 R

R

4

CO

2 H

R

3

NO

2 4 XVIII , N Cbz R, O NH R2N R2N R3 N OR 3 N O H H

R

4 R4 XIX IA 5 In Scheme 3, the (R)-2-piperazinecarboxylic acid (prepared according to the references below) was converted by standard methods to the N-protected amino-acid (XVII); the symbol Cbz represents a carbobenzyloxy group. A solution of (R)-4 carbobenzyloxypiperazine-2-carboxylic acid (XVII) is allowed to react with a substituted ortho-nitrofluorobenzene to give a 4-carbobenzyloxy-l-(o-nitro 10 substituted-phenyl)-(R)-piperazine-2-carboxylic acid (XVIII). The reaction is carried out in an inert organic solvent, such as dimethylformamide, in the presence of a base, such as triethylamine, at a temperature above ambient temperature, such as 50-70 0

C.

WO 00/35922 PCT/US99/29894 -10 The intermediate (XVIII) is cyclized by a process involving reduction of the nitro group to an amino group, preferably by reaction of a metal, such as iron, in an acid, such as acetic acid, followed by heating at elevated temperature, such as 50 70 0 C, to effect cyclization to (XIX). Removal of the Cbz protecting group using 30% 5 HBr in acetic acid, boron tribromide, or catalytic reduction, gives chiral products of this invention (IA). Processes for the preparation of the compounds of formula I, IA and IB form further aspects of the present invention. 10 The ability of the compounds of this invention to act as 5HT 2 c agonists was established is several standard pharmacological test procedures; the procedures used and results obtained are provided below. 15 Test Procedures 5HT2C Receptor Binding Test Procedure To evaluate high affinity for the 5HT 2 c receptor, a CHO (Chinese Hamster Ovary) cell line transfected with the cDNA expressing the human 5-hydroxy tryptamine 2 C (h5HT 2 c) receptor was maintained in DMEM (Dulbecco's Modified 20 Eagle Media) supplied with fetal calf serum, glutamine, and the markers: guaninephosphoribosyl transferase (GTP) and hypoxanthinethymidine (HT). The cells were allowed to grow to confluence in large culture dishes with intermediate changes of media and splitting. Upon reaching confluence, the cells were harvested by scraping. The harvested cells were suspended in half volume of fresh 25 physiological phosphate buffered saline (PBS) solution and centrifuged at low speed (900 x g). This operation was repeated once more. The collected cells were then homogenized with a polytron at setting #7 for 15 sec in ten volumes of 50 mM Tris.HC1, pH 7.4 and 0.5 mM EDTA. The homogenate was centrifuged at 900 x g for 15 min to remove nuclear particles and other cell debris. The pellet was discarded 30 and the supernatant fluid recentrifuged at 40,000 x g for 30 min. The resulting pellet was resuspended in a small volume of Tris.HCI buffer and the tissue protein content was determined in aliquots of 10-25 microliter (ptl) volumes. Bovine Serum Albumin WO 00/35922 PCT/US99/29894 -11 (BSA) was used as the standard in the protein determination by the method of Lowry et al., (J. Biol. Chem., 193:265 (1951). The volume of the suspended cell membranes was adjusted with 50 mM Tris.HCI buffer containing: 0.1% ascorbic acid, 10 mM pargyline and 4 mM CaCI, to give a tissue protein concentration of 1-2 mg per ml of 5 suspension. The preparation membrane suspension (many times concentrated) was aliquoted in 1 ml volumes and stored at -70oC until used in subsequent binding experiments. Binding measurements were performed in a 96 well microtiter plate format, in a total volume of 200 pl. To each well was added: 60 pal of incubation buffer made 10 in 50 mM Tris.HCI buffer, pH 7.4 and containing 4 mM CaCl,; 20 Pal of [125I] DOI (S.A., 22(00 Ci/mmol, NEN Life Science). The dissociation constant, KD of [125I] DOI at the human serotonin 5HT 2 C receptor was 0.4 nM by saturation binding with increasing concentrations of [125I] DOI. The reaction was initiated by the final addition of 100.0 Pl of tissue suspension 15 containing 50 ptg of receptor protein. Nonspecific binding is measured in the presence of 1 pM unlabeled DOI added in 20.0 [l volume. Test compounds were added in 20.0 ml. The mixture was incubated at room temperature for 60 min. The incubation was stopped by rapid filtration. The bound ligand-receptor complex was filtered off on a 96 well unifilter with a Packard® Filtermate 196 Harvester. The 20 bound complex caught on the filter disk was dried in a vacuum oven heated to 60oC and the radioactivity measured by liquid scintillation with 40 pl Microscint-20 scintillant in a Packard TopCount® equipped with six (6) photomultiplier detectors. Specific binding is defined as the total radioactivity bound less the amount bound in the presence of 1 [M unlabeled DOI. Binding in the presence of varying 25 concentrations of test drugs is expressed as percent of specific binding in the absence of drug. These results are then plotted as log % bound vs log concentration of test drug. Non linear regression analysis of data points yields both the IC50 and the Ki values of test compounds with 95% confidence limits. Alternatively, a linear regression line of decline of data points is plotted, from which the IC50 value can be 30 read off the curve and the Ki value determined by solving the following equation: WO 00/35922 PCT/US99/29894 - 12 Ki = IC50 1 +L/KD 5 where L is the concentration of the radioactive ligand used and the KD is the dissociation constant of the ligand for the receptor, both expressed in nM. The following Ki's are provided for various reference compounds: Ki value and 95% confidence interval. 10 Ritanserin 2.0 (1.3 - 3.1) nM Ketanserin 94.8 (70.7 - 127.0) nM Mianserin 2.7 (1.9 - 3.8) nM Clozapine 23.2 (16.0 - 34.0) nM Methiothepin 4.6 (4.0 - 6.0) nM 15 Methysergide 6.3 (4.6 - 8.6) nM Loxapine 33.0 (24.0 - 47.0) nM mCPP 6.5 (4.8 - 9.0) nM DOI 6.2 (4.9 - 8.0) nM 20 Stimulation of [ 3 HI Inositol Monophosphate production by 5HT_ agonists CHO cells transfected with the cDNA expressing the human 5-HTc receptor were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum and non-essential amino acids. Upon reaching confluence the cells were harvested using PBS/EDTA and plated in 24 well plates at an initial 25 density of 2.5 x 105 cells per well. One (1) ml of maintenance medium containing 1 PCi/ml myo-[ 3 H] inositol was added to each well. After 48 hours labeling, the cells were washed once with 0.5 ml DMEM containing 25 mM HEPES and 10 mM LiC1, then preincubated with the medium for 30 min (antagonists were included in this period if tested). At the end of the preincubation, the medium was removed, the cells 30 were then incubated with test compounds (in presence of antagonists if needed) for 30 min. The reaction was terminated by removal of the incubation solution and addition of 0.5 ml ice-cold 5% PCA, followed by 15 to 30 min incubation on ice. 200 pl of 0.5 M Tes/1.5 M K 2

CO

3 was added to each well to neutralize to pH 7, and plates were WO 00/35922 PCT/US99/29894 - 13 left on ice for another 15 to 30 min to precipitate all salts. The liquid and solid phases were separated by centrifugation. A portion (350apl) of the upper aqueous phase was applied to Dowex AG-1X8 5 (formate form, 100-200 mesh) columns. The columns were then washed stepwise with 10 ml of water and 10 ml of 25 mM ammonium formate to remove free myo [3H]inositol and deacylated phosphoinositol, respectively. Finally 10 ml of 0.2 M ammonium formate solution was applied to the columns to elute [ 3 H] inositol monophosphate ([ 3 H] IP,) directly into scintillation vials. Of this eluate, I ml was 10 used to determine radioactivity by scintillation counting. Agonist-stimulated levels of [ 3 H]inositol monophosphate (IP 1 ) is expressed as a percentage of the response observed with a maximally effective concentration of 5-HT (10pM). A 3-parameter logistic function is used to generate estimate of 15 ECJICo. Antagonists are tested in the presence of 10 piM 5-HT. The following data are provided for various reference compounds: 5-HT 15.1 nM

EC

50 so 20 mCPP 46.8 nM

EC

50 so 60% Em x (relative to 5-HT) SB200646 286 nM IC 5 0 (10pM 5-HT as agonist) 25 Effects of compounds on feeding behavior in rats Eight (8) male Sprague-Dawley rats weighing 150-180g were separated into individual cages and acclimated to a powdered diet for 2 weeks. During this period and throughout the test procedure, the food cup and the animals were weighed daily. Following the acclimation period, animals were fasted for 24 hours and then injected 30 with either vehicle or one of 4 doses of the test compound. Food intake was assessed at 2 and 24 hours following compound administration. Compounds to be evaluated were injected 1 -2 x per week until all animals had received all doses of the test compound. The order of doses were chosen using to a modified Latin Square design.

WO 00/35922 PCT/US99/29894 - 14 Additional studies may be conducted in satiated rats at the start of the dark cycle. Compounds were injected i.p, s.c. or p.o. At the end of the study effects of the test compound on food intake was evaluated using a repeated measures ANOVA. Data were collected were 2 hour food intake (g). Data were subjected to one-way ANOVA 5 with posthoc t-tests to assess group differences. Where appropriate, ED50 values were calculated. The ED50 value is the dose that produces a 50% reduction in food intake during the test period. Results 10 Results from in vitro Test Procedures 5HT 2 C Affinity 5HT 2 C Stimulation of IP3 DOI/Agonist binding (Ki, nM) % Emax (EC50, nM) Compound (5HT, 100%) Example 1 4.33 107.50 12.00 Example 2 4.18 112.50 7.92 Example 3 66.40 89.00 289.50 Example 4 1.00 99.00 7.32 Example 5 7.00 100.00 33.80 Example 6 8.00 77.00 23.20 Example 7 8.00 100.00 97.30 Example 8 516.00 85.00 2607.00 Example 9 25.00 100.00 18.80 Example 10 1036.00 ND* ND Example 11 19.79 73% @ 1 gM ND Example 12 9.00 95.00 30.00 Example 13 91.00 ND ND * ND = Not determined.

WO 00/35922 PCT/US99/29894 - 15 Results from in vivo 5HT 2 C Food Intake in Rats (24 hr fast) Compound Route of Admin. ED50 (mg/kg) Example 1 ip 1.91 po 9.73 Example 2 ip 1.99 Example 11 ip 9.99 5 The results obtained in this standard pharmacological test procedures demonstrate that the compounds of this invention are 5HT 2 C receptor agonists useful for the treatment of diseases involving the central nervous system such as obsessive compulsive disorder; depression; anxiety; panic disorder; schizophrenia; migraine; sleep disorders, such as sleep apnea; eating disorders, such as hyperphagia; obesity; 10 type II diabetes; and epilepsy. The compounds are for treatment of diseases of a mammal, preferably a human. The compounds of this invention can be formulated neat or with a pharmaceutical carrier for administration, the proportion of which is determined by 15 the solubility and chemical nature of the compound, chosen route of administration and standard pharmacological practice. The pharmaceutical carrier may be solid or liquid. A solid carrier can include one or more substances which may also act as 20 flavoring agents, lubricants, solubilizers, suspending agents, fillers, glidants, compression aids, binders or tablet-disintegrating agents; it can also be an encapsulating material. In powders, the carrier is a finely divided solid which is in admixture with the finely divided active ingredient. In tablets, the active ingredient is mixed with a carrier having the necessary compression properties in suitable 25 proportions and compacted in the shape and size desired. The powders and tablets preferably contain up to 99% of the active ingredient. Suitable solid carriers include, for example, calcium phosphate, magnesium stearate, talc, sugars, lactose, dextrin, starch, gelatin, cellulose, methyl cellulose, sodium carboxymethyl cellulose, polyvinylpyrrolidine, low melting waxes and ion exchange resins. 30 Liquid carriers are used in preparing solutions, suspensions, emulsions, syrups, elixirs and pressurized compositions. The active ingredient can be dissolved WO 00/35922 PCT/US99/29894 - 16 or suspended in a pharmaceutically acceptable liquid carrier such as water, an organic solvent, a mixture of both or pharmaceutically acceptable oils or fats. The liquid carrier can contain other suitable pharmaceutical additives such as solubilizers, emulsifiers, buffers, preservatives, sweeteners, flavoring agents, suspending agents, 5 thickening agents, colors, viscosity regulators, stabilizers or osmo-regulators. Suitable examples of liquid carriers for oral and parenteral administration include water (partially containing additives as above, e.g. cellulose derivatives, preferably sodium carboxymethyl cellulose solution), alcohols (including monohydric alcohols and polyhydric alcohols, e.g. glycols) and their derivatives, lecithins, and oils (e.g. 10 fractionated coconut oil and arachis oil). For parenteral administration, the carrier can also be an oily ester such as ethyl oleate and isopropyl myristate. Sterile liquid carriers are useful in sterile liquid form compositions for parenteral administration. The liquid carrier for pressurized compositions can be halogenated hydrocarbon or other pharmaceutically acceptable propellant. 15 Liquid pharmaceutical compositions which are sterile solutions or suspensions can be utilized by, for example, intramuscular, intraperitoneal or subcutaneous injection. Sterile solutions can also be administered intravenously. The compounds of this invention can also be administered orally either in liquid or solid composition form. 20 The compounds of this invention may be administered rectally or vaginally in the form of a conventional suppository. For administration by intranasal or intrabronchial inhalation or insufflation, the compounds of this invention may be formulated into an aqueous or partially aqueous solution, which can then be utilized in the form of an aerosol. The compounds of this invention may also be administered 25 transdermally through the use of a transdermal patch containing the active compound and a carrier that is inert to the active compound, is non toxic to the skin, and allows delivery of the agent for systemic absorption into the blood stream via the skin. The carrier may take any number of forms such as creams and ointments, pastes, gels, and occlusive devices. The creams and ointments may be viscous liquid or semisolid 30 emulsions of either the oil-in-water or water-in-oil type. Pastes comprised of absorptive powders dispersed in petroleum or hydrophilic petroleum containing the active ingredient may also be suitable. A variety of occlusive devices may be used to release the active ingredient into the blood stream such as a semipermeable membrane covering a reservoir containing the active ingredient with or without a 35 carrier, or a matrix containing the active ingredient. Other occlusive devices are known in the literature.

WO 00/35922 PCT/US99/29894 - 17 The dosage requirements vary with the particular compositions employed, the route of administration, the severity of the symptoms presented and the particular subject being treated. Based on the results obtained in the standard pharmacological test procedures, projected daily dosages of active compound would be 0.02 ptg/kg 5 750 pg/kg. Treatment will generally be initiated with small dosages less than the optimum dose of the compound. Thereafter the dosage is increased until the optimum effect under the circumstances is reached; precise dosages for oral, parenteral, nasal, or intrabronchial administration will be determined by the administering physician based on experience with the individual subject treated. 10 Preferably, the pharmaceutical composition is in unit dosage form, e.g. as tablets or capsules. In such form, the composition is sub-divided in unit dose containing appropriate quantities of the active ingredient; the unit dosage forms can be packaged compositions, for example, packaged powders, vials, ampoules, pre filled syringes or sachets containing liquids. The unit dosage form can be, for example, a capsule or 15 tablet itself, or it can be the appropriate number of any such compositions in package form. The following provides the preparation of a representative compound of this invention. 20 Example 1 8,9-Dichloro-2.3,4,4a-Tetrahvdro- I H-Pvrazino r 1.2-a] Ouinoxalin- 5 (6H)-One A. 4 -Carbobenzyloxypiperazine-2-Carboxylic Acid, Copper Chelate To a solution of 10 g of piperazine-2-carboxylic acid in 40 mL of HO is 25 added 39 mL of 2.5 N NaOH. A solution of 6.5 g of CuSO 4 *5H 2 O in 80 mL of H,O is then introduced and the resulting deep blue solution is cooled to 0OC. To this cooled solution is added 5 g of solid NaHCO 3 in one portion followed by the dropwise addition of a solution of 7.7 mL of benzylchloroformate in 40 mL of dioxane over 10 minutes. The pH is monitored and NaHCO 3 is added as needed to 30 maintain a basic solution. The ice bath is then removed and the reaction mixture is stirred overnight at ambient temperature. The blue precipitate is filtered and the solid is washed with cold H,O (20 mL), EtOH (20 mL), and EtOAc (20 mL) to give 10.4 g of a light blue solid.

WO 00/35922 PCT/US99/29894 - 18 B. 4-Carbobenzyloxy- 1-( 4 ,5-Dichloro-2-Nitrophenyl)Piperazine-2-Carboxylic Acid A mixture of 10.4 g of 4 -carbobenzyloxypiperazine-2-carboxylic acid, copper chelate and 7.9 g of ethylenediaminetetraacetic acid, disodium salt in 800 mL of H 2 0 5 is heated to 80oC for 3 hours. After cooling to room temperature, the mixture is concentrated to dryness. A mixture of this solid, 7.3 g of 1,2-dichloro-4-fluoro-5 nitrobenzene, and 20 mL of triethylamine in 100 mL of dimethylsulfoxide is heated to 60oC for 12 hours. After cooling to ambient temperature, the resulting mixture is treated with HCI to pH 3. The mixture is then diluted with H,O and extracted with 10 ethyl acetate. The combined extracts are dried over MgSO, and concentrated to give 16 g of crude product. C. 3 -Carbobenzyloxy-8,9-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[1,2-a] Quinoxalin-5(6H)-One 15 A rapidly stirred solution of 16 g of 4 -carbobenzyloxy-1-(4,5-dichloro-2 nitrophenyl)piperazine-2-carboxylic acid in 200 mL of acetic acid is heated to 60oC and then 16 g of iron powder is added in portions. The reaction mixture is stirred at 60oC for 3 hours and then allowed to cool to room temperature. The mixture is diluted with 1 N HCI and the resulting precipitate is collected. The solid is washed 20 with water and ether to give 11 g of product. The crude 'H NMR is consistent. A small amount (1 g) of the product is purified by flash column chromatography (gradient elution with 25% ethyl acetate-hexanes to 100% ethyl acetate) to give an analytically pure sample. 'H NMR (400 MHz, d 6 -DMSO) 6 10.8 (s, 1H); 7.39-7.31 (m, 5H); 7.04 (s, 1H); 6.96 25 (s, 1H); 5.12 (s, 2H); 4.38 (d, 1H, J = 13.0 Hz); 4.06 (d, 1H, J = 13.1 Hz); 3.71 (d, 1 H, J = 11.5 Hz); 3.63 (dd, 1H, J = 11.2, 3.7 Hz); 2.99 (brs, 2H); 2.68 (dt, 1H, J = 12.1, 3.6 Hz). IR (KBr) 3400, 3250, 2800, 1690, 1500, 1370, 1240, 1130, 860, 770, 730 cm'. MS (ESI, m/e (%)) 406 (100, [M+H]*), 408 (65, [M+H]+). 30 Anal. Calc'd for C19H17C1 2 N303: C, 56.17; H, 4.22; N, 10.34. Found: C, 55.95; H, 3.88; N, 10.29.

WO 00/35922 PCT/US99/29894 - 19 D. 8,9-Dichloro-2,3,4,4a-Tetrahydro- I 1H-Pyrazino[ 1,2-a]Quinoxalin-5(6H)-One A solution of 20 g of KOH in 50 mL of H,O is added to a solution of 4.2 g of 3-carbobenzyloxy-8,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2-a]quinoxalin 5(6H)-one in 50 mL of methanol. The resulting reaction mixture is heated to reflux 5 for 3 hours and then is allowed to cool to ambient temperature. The solution is concentrated and the crude solid is partitioned between water and ethyl acetate. The phases are separated and the aqueous phase is extracted with ethyl acetate. The combined organic phases are concentrated. The crude solid is dissolved in a minimum amount of hot ethanol and then a solution of HCI in ethanol is added to 10 pH 3. The solid is collected and dried in a vacuum oven at 80oC to give 2.4 g of product as its hydrochloride salt. H NMR (400 MHz, d 6 -DMSO) 5 11.0 (s, 1H); 9.51 (br s, 2H); 7.12 (s, 1H); 7.02 (s, 1H); 4.02 (dd, 1H, J = 11.5, 3.4 Hz); 3.88 (d, 1H, J = 11.0 Hz); 3.61 (m, 1 H); 3.41 (d, 1H, J = 9.8 Hz); 3.15-2.98 (m, 3H). 15 IR (KBr) 3420, 3200, 3020, 2970, 2800, 1695, 1500, 1460, 1430, 1395, 1375, 1290, 1140 cm

-

'. MS (APCI, m/e (%)) 272 (100, [M+H]), 274 (65, [M+H]*). Anal. Calc'd for C1 1H12C1 3 N30: C, 42.81; H, 3.92; N, 13.62. Found: C, 42.66; H, 3.75; N, 13.33 20 Example 2 (R)-8.9-Dichloro-2.3.4.4a-Tetrahydro-1H-Pyrazino[ 1.2-al] Ouinoxalin-5(6H)-One Method A (Separation Method) The enantiomers of the compound of Example 1 were separated by HPLC 25 using a Chiracel AD column with 100% ethanol at a flow rate of 0.5 mL/min to provide the compounds of Example 2 and 3. The first enantiomer (Example 2) elutes at 10.4 min ([a] 2 5 D+27.8) and the second (Example 3) at 13.7 min ([Cu]21D-25.5).

WO 00/35922 PCT/US99/29894 - 20 Method B (Chiral Synthesis) A. (R)-4-Carbobenzyloxypiperazine-2-Carboxylic Acid. To a solution of 5.0 g of (R)-piperazine-2-carboxylic acid' in 30 mL of water is added 5.0 g CuSO 4 .5H 2 0 dissolved in 60 mL of HO. The solution is cooled to 0 5 5 0 C and 10.0 g of NaHCO 3 is added followed by the addition of 5.3 g of benzyl chloroformate in 40 mL of acetone over 90 minutes. The mixture is warmed to ambient temperature and stirred for 24 h. The blue precipitate is filtered and the solid is washed with cold water. The solids are slurried in 100 mL of 1:1 methanol : water mixture and the pH adjusted to < 4 by the addition of 2.5 N HC1. The solution is 10 applied to a column of 400 g of AG 50W-8X resin that had been pre-washed with a mixture of 1:16:16 pyridine : methanol : water. The product was eluted with the same solvent mixture and the combined product fractions are concentrated under reduced pressure (< 50oC) to give a semi-solid residue. This material is slurried with 50 mL of ethanol to obtain crystalline solid. The solids are collected and dried to 15 give 6.0 g (59.5%) of white solid, mp 246-8oC decomposed. H' NMR (400 Hz, d 6 -DMSO) 8 7.37-7.30 (m, 5H); 5.08 (s, 2H); 4.19 (d, 1H, J = 12.1 Hz); 3.89 (d, 1H, J = 13.8); 3.27 (dd, 1H, J = 11.0, 4.0 Hz); 3.08 (m, 3H); 2.82 (dt, 1H, J = 12.2, 3.6 Hz). IR (KBr) 3050, 1700, 1620, 1430, 1400, 1235, 1150 cm' 1 . 20 MS (ESI(+), m/e (%)) 265 (100, [M+H]*). Anal. Calc'd for C3H,N,04: C, 59.08; H, 6.10; N, 10.60. Found: C, 59.04; H, 6.09; N, 10.40. Chiral Purity = 99.99% (HPLC: Chiralcel WH, 4.6 X 25 mm). [ot]D = -38.770 (c = 1, H20O). 25 B. (R)-4-Carbobenzyloxy- 1-(4,5-Dichloro-2-Nitrophenyl)-Piperazine-2 Carboxylic Acid. To a slurry containing 5.0 g of (R)-4-carbobenzyloxypiperazine-2-carboxylic acid, 4.2 g of 1,2-dichloro-fluoro-5-nitrobenzene, 85 mL of water and 170 mL of 30 dimethylformamide is added slowly 5.3 mL of triethylamine. The solution is heated to 50'C for 5 hours, then at ambient temperature overnight. The dark orange solution WO 00/35922 PCT/US99/29894 -21 is concentrated under reduced pressure (1 - 2 mrm, < 50 0 C) to an orange oily residue. This oil is dissolved in 400 mL of ethyl acetate and washed with 100 mL of 1 N HCI (2X), with 150 mL of water (2X), and 100 mL of brine. The organic layer is dried over MgSO 4 , filtered and concentrated to give 8.1 g ( 94.2%) of title compound as an 5 orange solid foam. MS (ESI(+), m/e (%)) 454 (40, [M+H]), 456 (35, [M+H]'), 471 (100, [M+NH 4 ]) and 473 (100, [M+NH 4 ). Chiral Purity = 99.99% (HPLC: Whelk-O, 4.6 X 250 mm). 10 C. (R)-Carbobenzyloxy-8,9-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2a] Quinoxalin-5(6H)-One. To a solution of 8.0 g (R)- 4 -carbobenzyloxy-l-(4,5-dichloro-2-nitrophenyl) piperazine-2-carboxylic acid in 200 mL of acetic acid is added 6.0 g of iron powder. With good stirring, the mixture is heated at 60oC for 2 hours, followed by 15 concentrated under reduced pressure (1-2mm, < 40oC) to a gray-black residue. This material was slurried with 400 mL of ethyl acetate and filtered. This process was repeated. The combined ethyl acetate filtrates are washed with 150 mL of 1N HC1, 200 mL of water (2X), 200 mL of brine and dried over MgSO 4 . Filtration and concentration of the solvent gave a semi-solid material that is crystallized from ethyl 20 acetate-hexane to afford 5.44 g (76.1%) of title compound as a white solid, mp 136 138 0 C.

H

1 NMR (400 Hz, d 6 -DMSO) 6 10.81 (s, 1H); 7.38-7.31 (m, 5H); 7.04 (s, 1H); 6.95 (s, 1H); 5.11 (s, 2H); 4.37 (d, 1H, J = 12.5 Hz); 4.05 (d, 1H, J = 13.4 Hz); 3.70 (d, 1H, J = 11.2 Hz); 3.63 (dd, 1H, J = 3.6, 10.8 Hz); 3.00 (bs, 2H); 2.66 (dt, 1H, J = 3.6, 25 12.2 Hz). IR (KBr) 3240, 1710, 1675, 1500, 1300, 1245, 1130 cm 1 . MS (APCI, m/e (%)) 406 (100, [M+H]') and 408 (90, [M+H]+). Anal. Calc'd for C 1 9

H,

17 C1,N 3 0 3 : C, 56.17; H, 4.27; N, 10.34. Found: C, 55.97; H, 4.33; N, 9.90. 30 Chiral Purity = 99.99% (HPLC: Chiralcel AD, 4.6 X 250 mm). [1a]D = +23.890 (c = 1, CHCl 3 ). 1 E. Felder, S. Maffei, S. Pietra, D. Pitre, HeIv. Chim. Acta. 1960, 888-896.

WO 00/35922 PCT/US99/29894 - 22 D. (R)- 8 ,9-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2a]Quinoxalin-5(6H) One. To a solution of 5.0 g of (R)-carbobenzyloxy-8,9-dichloro-2,3,4,4a-tetrahydro-1H 5 pyrazino-[1,2a]quinoxalin-5(6H)-one in 100 mL of acetic acid is added dropwise 15 mL of 30% HBr in acetic acid. The solution is stirred at ambient temperature for 5 hour and concentrated under reduced pressure ( 1 mm, < 40oC) to give solid residue. The residue is dissolved in 300 mL of ethyl acetate and washed with 100 mL of 1 N NaOH, 200 mL of water (2X) and 300 mL of brine and dried over MgSO 4 . Filtration 10 and concentration of the solvent affords 3.59 g (99%) of crude free base. Purification by column chromatography (265 g of silica gel, 9:1 ethylacetate: 2M NH 3 in methanol) gives 1.8 g (54.9%) of product as a yellowish solid, mp 203oC decomposed. The solid (1.6 g) was dissolved in 50 mL of methanol and treated with an excess of 1 M HCl in ether to afford 1.6 g (88.2%) of the hydrochloride salt as an 15 off-white solid, mp >290'C. H' NMR (400 Hz, d 6 -DMSO) 5 11.00 (s, 1H); 9.58 (s,2H); 7.12 (s, 1H); 7.02 (s, 1H); 4.03 (dd, 1H, J = 11.6, 3.6 Hz); 3.87 (d, 1H, J = 10.7 Hz); 3.61 (dd, 1H, J = 12.9, 2.0 Hz); 3.41 (d, 1H, J = 9.5 Hz); 3

.

4 2 -2.99(m, 3H). IR (KBr) 2950, 2700, 1700, 1590, 1500 cm-'. 20 MS (APCI, m/e (%)) 272 (100, [M+H]* ) and 274 (65, [M+H]+). Anal. Calc'd for C,,H,C1,N 3 0 * HCL: C, 42.81; H, 3.92; N, 13.62. Found: C, 42.45; H, 3.78; N, 13.43. Chiral Purity = 99.99% (HPLC: Chiralcel AD, 4.6 X 250 mm). [o]D = +27.720 (c = 1, DMSO). 25 Example 3 (S)-8.9-Dichloro-2,3,4.4a-Tetrahvdro- IH-Pvrazino[ 1.2-a] Ouinoxalin-5(6H)-One Method A (Separation Method) The enantiomers of the compound of Example 1 were separated by HPLC 30 using a Chiracel AD column with 100% ethanol at a flow rate of 0.5 mL/min to provide the compounds of Example 2 and 3. The first enantiomer (Example 2) elutes at 10.4 min ([ot] 25 D+27.8) and the second (Example 3) at 13.7 min ([a] 2 5 D-25.5).

WO 00/35922 PCT/US99/29894 - 23 Method B (Chiral Synthesis) A. (S)- 4 -Carbobenzyloxypiperazine-2-Carboxylic Acid. To a solution of 4.0 g of (S)-piperazine-2-carboxylic acid' in 70 mL of water is added 5 4.2 g of CuCI,. The pH of the blue solution is adjusted to 10 by the addition of 2.5 N NaOH and 70 mL of acetone is added. The solution is cooled to 0-50C and 5.3 g of benzylchloroformate in 40 mL of acetone is added over 90 minutes. The pH is monitored and maintained by the addition of I N NaOH. The mixture is warmed to ambient temperature and stirred overnight. The blue precipitate is filtered and the 10 solid is washed with cold water. The solids are slurried in 100 mL of 1:1 methanol : water mixture and the pH adjusted to < 4 by the addition of 2.5 N HC1. The solution is applied to a column of 400 g of AG 50W-8X resin that had been pre-washed with a mixture of 1:16:16 pyridine : methanol : water. The product was eluted with the same solvent mixture and the combined product fractions are concentrated under 15 reduced pressure (< 50oC) to give a semi-solid residue. This material is slurried with 50 mL of methanol to obtain crystalline solids. The solids are collected and dried to give 4.0 g (50%) of white solid, mp 247oC decomposed. H' NMR (400 Hz, d 6 -DMSO) 6 7.37-7.30 (m, 5H); 5.08 (s, 1H); 4.19 (d, 1H, J = 12.1 Hz); 3.89 (d, 1H, J = 13.8); 3.27 (dd, 1H, J = 11.0, 4.0 Hz); 3.08 (m, 3H); 2.82 (dt, 20 1H, J = 12.2, 3.6 Hz). IR (KBr) 3200, 1700, 1620, 1430, 1400, 1235, 1150 cm 1 . MS (APCI, m/e (%)) 263 (100, [M-H]). Anal. Calc'd for C 1 3HI N,204: C, 59.08; H, 6.10; N, 10.60. Found: C, 58.90; H, 6.20; N, 10.58. 25 Chiral Purity = 99.88% (HPLC: Chiralcel WH, 4.6 X 25 mm). B. (S)-4-Carbobenzyloxy- 1-( 4 ,5-Dichloro-2-Nitrophenyl)-Piperazine-2 Carboxylic Acid. To a slurry containing 1.5 g of (S)- 4 -carbobenzyloxypiperazine-2-carboxylic 30 acid, 1.25 g of 1, 2 -dichloro-fluoro-5-nitrobenzene, 25 mL of water and 50 mL of dimethylformamide is added slowly 1.6 mL of triethylamine. The solution is heated to 50oC for 5 hours, then at ambient temperature over night. The dark orange WO 00/35922 PCT/US99/29894 - 24 solution is concentrated under reduced pressure (1 - 2 mm, < 50 0 C) to an orange oily residue. This oil is dissolved in 100 mL of ethyl acetate and washed with 20 mL of I N HCI (2X), with 100 mL of water (2X), and 100 mL of brine. The organic layer is dried over MgSO 4 , filtered and concentrated to give 2.5 g (99%) an orange solid 5 foam. MS (APCI, m/e (%)) 452 (100, [M-H]) and 454 (75, [M-H]). Anal. Calc'd for C,

,H

1 7 C1,N 3 0 6 * 0.5 H,O: C, 49.26; H, 3.92; N, 9.07. Found: C, 48.90; H, 3.80; N, 8.74. Chiral Purity = 99.99% (HPLC: Whelk-O, 4.6 X 250 mm). 10 [x]D = -64.2o (c = 1, MeOH). C. (S)-Carbobenzyloxy-8,9-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2a] Quinoxalin-5(6H)-One. To a solution of 1.5 g (S)- 4 -carbobenzyloxy-l-(4,5-dichloro-2-nitrophenyl) 15 piperazine-2-carboxylic acid in 40 mL of acetic acid is added 1.2 g of iron powder. With good stirring, the mixture is heated at 60 0 C for 2 hours, then concentrated under reduced pressure (1-2mm, < 40 0 C) to a gray-black residue. This material was slurried with 100 mL of ethyl acetate (2X). The combined ethyl acetate filtrates are washed with 100 mL of IN HCI, 200 mL of water (2X), 100 mL of brine and dried 20 over MgSO 4 . Filtration and concentration of the solvent gave a semi-solid material that is crystallized from hexane to afford 1.08 g (80.6%) of title compound as a white solid, mp 174-6'C. H' NMR (400 Hz, d 6 -DMSO) 8 10.93 (s, 1H); 7.41-7.31 (m, 5H); 7.04 (s, 1H); 6.95 (s, 1H); 5.11 (s, 1H); 4.37 (d, 1H, J = 12.5 Hz); 4.05 (d, 1H, J = 13.4 Hz); 3.70 (d, 25 1H, J = 11.2 Hz); 3.63 (dd, 1H, J = 3.6, 10.8 Hz); 3.00 (bs, 2H); 2.66 (dt, 1H, J = 3.6, 12.2 Hz). IR (KBr) 3240, 1710, 1675, 1500, 1300, 1245, 1130 cm'. MS (APCI, m/e (%)) 406 (70, [M+H]*) and 408 (45, [M+H] ). Anal. Calc'd for C1 H 1Cl2 303: C, 56.17; H, 4.27; N, 10.34. 30 Found: C, 56.26; H, 4.18; N, 10.37. Chiral Purity = 99.9% (HPLC: Chiralcel AD, 4.6 X 250 mm).

WO 00/35922 PCT/US99/29894 - 25 D. (S)-8,9-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2a]Quinoxalin-5(6H) One. To a solution of 0.155 g of (S)-carbobenzyloxy-8,9-dichloro-2,3,4,4a tetrahydro-1H-pyrazino-[1,2a]quinoxalin-5(6H)-one in 8 mL of acetic acid is added 5 dropwise 1.5 mL of 30% HBr in acetic acid. The solution is stirred at ambient temperature for 2.5 hour and concentrated under reduced pressure (1 mm, < 4(0) C) to afford 0.18 g of tan solid. The solids dissolved in 50 mL of ethyl acetate and washed with 10 mL of 1 N NaOH, 20 mL of water (2X) and 30 mL of brine and dried over MgSO 4 . Filtration and concentration of the solvent affords 0.056 g (53.8%) of title 10 compound as a white solid.

H

1 NMR (400 Hz, d 6 -DMSO) 5 10.63 (s, 1H); 6.96 (s, 1H); 6.92 (s, 1H); 3.49 (bd, 1H, J = 10.0 Hz); 3.41 (dd, 1H, J = 10.5, 3.5 Hz); 3.29 (min, 1H); 2.94 (bd, 1H, J = 9.9 Hz) 2.67-2.53 (min, 4H). MS (APCI, m/e (%)) 272 (100, [M+H]') and 274 (55, [M+H]*). 15 Chiral Purity = 99.9% (HPLC: Chiralcel AD, 4.6 X 250 mm). [o]D= -25.50 (c = 1, DMSO). Example 4 8.9-Dichloro-2,3.4.4a.5.6-Hexahvdro- 1H-Pvrazino[ I ,2-a] Quinoxaline, 20 dihydrochloride A solution of 5 mL of 1 M BH 3 *THF in THF was added to a cooled (0OC) solution of 0.43 g of 8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[1,2-a] quinoxalin-5(6H)-one in 20 mL of THF. The resulting solution was allowed to gradually warm to room temperature overnight. The reaction was quenched with 25 methanol and concentrated. The crude material was dissolved in methanol and again concentrated. The product was purified by flash column chromatography through silica gel (elution with 40% ethyl acetate-hexanes) to afford 0.30 g (73%). The material was dissolved in ethanol and HCl in EtOH was added until the solution was acidic. Diethyl ether was then added until a precipitate formed. The solid was 30 collected and dried under vacuum to give 68 mg of product as the dihydrochloride salt.

WO 00/35922 PCT/US99/29894 - 26 'H NMR (400 MHz, d 6 -DMSO) 6 9.44-9.35 (m, 2H); 6.86 (s, 1H); 6.59 (s, 1H); 3.78 (d, 1H, J = 11.8 Hz); 3.37-3.24 (m, 4 H); 3.07-2.89 (m, 3H); 2.69 (m, 1 H). IR (KBr) 3380, 3190, 2970, 2810, 2750, 2400, 1600, 1500, 1450, 1380, 1270, 1140, 1110 cm". 5 MS (APCI, m/e (%)) 258 (100, [M+H]'), 260 (65, [M+H]+). Example 5 (R)-8.9-Dichloro-2,3.4.4a.5.6-Hexahydro- I H-Pvrazinof[ 1.2-alOuinoxaline, dihydrochloride 10 By the same procedure described for Example 4, 1.8 g of (R)-8,9-dichloro 2,3,4,4a-tetrahydro- I H-pyrazino[1, 2 -a]quinoxalin-5(6H)-one was reduced to give 0.77 g of product. The enantiomers were be separated by HPLC using a Chirapak AD column with 100% methanol at a flow rate of 0.8 mL/min. The first enantiomer eluted at 7.2 min 15 and the second at 8.9 min. HPLC analysis indicated an ee of >99% (7.2 min retention time). 'H NMR (400 MHz, d 6 -DMSO) 5 9.44-9.35 (m, 2H); 6.86 (s, 1H); 6.59 (s, 1H); 3.78 (d, 1H, J = 11.8 Hz); 3.37-3.24 (m, 4 H); 3.07-2.89 (m, 3H); 2.69 (m, 1 H). IR (KBr) 3380, 3190, 2970, 2810, 2750, 2400, 1600, 1500, 1450, 1380, 1270, 1140, 20 1110 cm-'. MS (APCI, m/e (%)) 258 (100, [M+H]+), 260 (65, [M+H]+). Example 6 25 (S)-8,9-Dichloro-2,3,4,4a.5,6-Hexahydro- 1H-Pyrazino[ 1.2-a] Ouinoxaline, dihydrochloride By the same procedure described for Example 4, 0.80 g of (S)-8,9-dichloro 2,3,4,4a-tetrahydro- 1 H-pyrazino[1,2-a]quinoxalin-5(6H)-one was reduced to give 0.31 g of product. 30 The enantiomers were separated by HPLC using a Chirapak AD column with 100% methanol at a flow rate of 0.8 mL/min. The first enantiomer eluted at 7.2 min (Example 5) and the second at 8.9 min (Example 6). HPLC analysis indicated an ee of >99% (8.9 min retention time).

WO 00/35922 PCT/US99/29894 - 27 [c] 5 +4.35 1 H NMR (400 MHz, d 6 -DMSO) 6 9.44-9.35 (m, 2H); 6.86 (s, 1H); 6.59 (s, 1H); 3.78 (d, 1H, J = 11.8 Hz); 3.37-3.24 (m, 4 H); 3.07-2.89 (m, 3H); 2.69 (m, 1 H). IR (KBr) 3380, 3190, 2970, 2810, 2750, 2400, 1600, 1500, 1450, 1380, 1270, 1140, 5 1110 cm-. MS (APCI, m/e (%)) 258 (100, [M+H]'), 260 (65, [M+H]+). Anal. Calc'd for C 1 ,HI4C1 3 3: C, 44.85; H, 4.79; N, 14.26 Found: C, 44.48; H, 4.84; N, 13.71 10 Example 7 9-Chloro-8-Trifluoromethvl-2,3,4.4a-Tetrahydro- I1H-Pvrazino[ 1.2-a] Quinoxalin-5(6H)-One, Hydrochloride A. 4-Carbobenzyloxy- 1- (5-Chloro-2-Nitrophenyl-4-Trifluoromethyl)Piperazine 2-Carboxylic Acid 15 A mixture of 0.98 g of 4-carbobenzyloxypiperazine-2-carboxylic acid, 1.0 g of 2,4-dichloro-5-nitrobenzotrifluoride, and 0.99 mL of diisopropylethylamine in 35 mL of dimethylsulfoxide is heated to 60oC for 72 hours. After cooling to ambient temperature, the resulting mixture is treated with HCI to pH 3. The mixture is then diluted with HO and extracted with ethyl acetate. The combined extracts are dried 20 over MgSO 4 and concentrated to give the crude product. B. 3-Carbobenzyloxy-9-Chloro-8-Trifluoromethyl-2,3,4,4a-Tetrahydro- 1H Pyrazino [1,2-a]Quinoxalin-5(6H)-One Iron powder, 0.64 g, was added in portions to a rapidly stirred solution of 25 1.8 g of 4-carbobenzyloxy-1-(5-chloro-2-nitrophenyl-4-trifluoromethyl)-piperazine 2-carboxylic acid in 35 mL glacial acetic acid at 50oC. The resulting mixture was stirred overnight at 50oC. After cooling to ambient temperature, the reaction mixture was poured into 20 mL of HO and filtered. The solid was washed with 1 N HCI and diethyl ether to give 0.59 g of the desired product as a brown solid. 30 WO 00/35922 PCT/US99/29894 - 28 C. 9 -Chloro-8-Trifluoromethyl-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2-a] Quinoxalin-5(6H)-One, Hydrochloride A mixture of 0.58 g of 3 -carbobenzyloxy-9-chloro-8-trifluoromethyl-2,3,4,4a tetrahydro-lH-pyrazino-[1,2-a]quinoxalin-5(6H)-one and 2.3 g of potassium 5 hydroxide in 12 mL of 50% aqueous methanol was heated to reflux for 2 h. The reaction mixture was concentrated under reduced pressure to approximately half its original volume. The crude material was diluted with 100 mL of ethyl acetate and 100 mL of saturated aqueous sodium bicarbonate. The phases were separated and the aqueous phase was extracted with ethyl acetate. The combined organic phases were 10 dried over MgSO 4 , filtered, and concentrated. The crude material was dissolved in ethanol and a solution of HCI in ethanol was added until acidic. The resulting mixture was filtered and the solid was washed with ether. The solid was then dried in a vacuum oven to give 0.21 g (48%) of the desired product as its hydrochloride salt. 15 'H NMR (400 MHz, d 6 -DMSO) 8 11.0 (s, 1H); 9.47 (br s, 2H); 7.22 (s, 1H); 7.18 (s, 1H); 4.19 (dd, 1H, J = 11.6, 3.2 Hz); 4.01 (d, 1H, J = 11.8 Hz); 3.62 (d, 1 H, J = 11.7 Hz); 3.41 (d, 1H, J = 10.1 Hz); 3.14-3.01 (m, 3H). IR (KBr) 3460, 3170, 3020, 2970, 2800, 1700, 1620, 1505, 1450, 1400, 1370, 1300, 1230, 1160, 1110 cm-. 20 MS (APCI, m/e 306 (100, [M+H]'), 308 (33, [M+H]+). Anal. Calc'd for C12H12C1F 3 N30: C, 42.13; H, 3.54; N, 12.28. Found: C, 41.88; H, 3.71; N, 11.81. The enantiomers were separated by HPLC using a Chirapak AD column with 85:15 methanol:water (+0.1% diethylamine) at a flow rate of 0.5 mL/min. The first 25 enantiomer (Example 9) eluted at 17.5 min ([o] 2 5 D+ 43) and the second (Example 8) at 22.0 min ([o] 25

D

-40).

WO 00/35922 PCT/US99/29894 - 29 Example 8

(S)-

9 -Chloro-8-Trifluoromethyl-2,3,4.4a-Tetrahydro- I H-Pvrazino[ 1.2-al Quinoxalin-5(6H)-One. Hydrochloride The enantiomers were separated by HPLC using a Chirapak AD column with 5 85:15 methanol:water (+0.1% diethylamine) at a flow rate of 0.5 mL/min. The first enantiomer (Example 9) eluted at 17.5 min ([c]2 5 D+ 43) and the second (Example 8) at 22.() rmin ([a]21D -40). 'H NMR (400 MHz, d 6 -DMSO) 5 11.0 (s, 1H); 9.47 (br s, 2H); 7.22 (s, 1H); 7.18 (s, 1H); 4.19 (dd, 1H, J = 11.6, 3.2 Hz); 4.01 (d, 1H, J = 11.8 Hz); 3.62 (d, 1 H, J = 11.7 10 Hz); 3.41 (d, 1H, J = 10.1 Hz); 3.14-3.01 (m, 3H). IR (KBr) 3460, 3170, 3020, 2970, 2800, 1700, 1620, 1505, 1450, 1400, 1370, 1300, 1230, 1160, 1110 cm-'. MS (APCI, m/e 306 (100, [M+H]'), 308 (33, [M+H] ). []25 D - 40 15 Anal. Calc'd for C12H12C1F 3 N30: C, 42.13; H, 3.54; N, 12.28. Found: C, 41.59; H, 3.61; N, 12.07. Example 9

(R)-

9 -Chloro-8-Trifluoromethyl-2,3,4,4a-Tetrahydro- I H-Pvrazino[ 1,2-al 20 Ouinoxalin-5(6H)-One. Hydrochloride The enantiomers were separated by HPLC using a Chirapak AD column with 85:15 methanol:water (+0.1% diethylamine) at a flow rate of 0.5 mL/min. The first enantiomer (Example 9) eluted at 17.5 rmin ([X]25D+ 43) and the second (Example 8) at 22.0 min ([a]" 2 5 D -40). 25 HPLC analysis indicated an ee of 96% (17.5 min retention time). []2 D + 43 'H NMR (400 MHz, d 6 -DMSO) 6 11.0 (s, 1H); 9.47 (br s, 2H); 7.22 (s, 1H); 7.18 (s, 1H); 4.19 (dd, 1H, J = 11.6, 3.2 Hz); 4.01 (d, 1H, J = 11.8 Hz); 3.62 (d, 1 H, J = 11.7 Hz); 3.41 (d, 1H, J = 10.1 Hz); 3.14-3.01 (m, 3H). 30 IR (KBr) 3460, 3170, 3020, 2970, 2800, 1700, 1620, 1505, 1450, 1400, 1370, 1300, 1230, 1160, 1110 cm-'. MS (APCI, m/e 306 (100, [M+H]+), 308 (33, [M+H]j).

WO 00/35922 PCT/US99/29894 - 30 Anal. Calc'd for C12H12C1F 3

N

3 0: C, 42.13; H, 3.54; N, 12.28. Found: C, 41.83; H, 3.49; N, 12.01. Example 10 5 9.10-Dichloro-2.3,4.4a-Tetrahydro- I H-Pyrazino [ 1,2-a] -Ouinoxalin- 5 (6H)-One, Hydrochloride A. 4-Carbobenzyloxy- 1-(5, 6 -Dichloro- 2 -Nitrophenyl)Piperazine-2-Carboxylic Acid By the same procedure described for Example 7 A, from 0.86 g of 2,3,4-tri 10 chloronitro-benzene and 1.0 g of 4 -carbobenzyloxypiperazine-2-carboxylic acid, there was obtained 0.75 g of the desired product as a brown oil. B. 3-Carbobenzyloxy-9,10-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[1,2-a] Quinoxalin-5(6H)-One 15 By the same procedure described for Example 7 B, from 0.75 g of 4-carbo benzyloxy- I -(5, 6 -dichloro- 2 -nitrophenyl)piperazine-2-carboxylic acid and 0.28 g of iron powder, there was obtained 0.34 g (49%) of the desired product as a brown solid. C. 9,10-Dichloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[1,2-a]-Quinoxalin-5(6H) 20 One, Hydrochloride By the same procedure described for Example 7, from 0.34 g of 4-carbo benzyloxy-l-(5, 6 -dichloro-2-nitrophenyl)piperazine-2-carboxylic acid and 1.5 g of potassium hydroxide, there was obtained 18 mg of product isolated as its hydrochloride salt. 25 'H NMR (400 MHz, d 6 -DMSO) 8 11.1 (s, 1H); 9.05 (br s, 2H); 7.45 (d, 1H, J = 8.8 Hz); 6.97 (d, 1H, J = 8.8 Hz); 4.06 (d, 1H, J = 3.7 Hz); 3.84 (d, 1H, J = 13.2 Hz); 3.29-3.12 (m, 4 H); 2.77 (m, 1H). IR (KBr) 3440, 3160, 3020, 2970, 1695, 1570, 1470, 1390, 1280 cm-'. MS (EI, m/e (%) 271 (55, M'), 273 (35, M'). 30 Anal. Calc'd for C11H12C 3 N30: C, 42.81; H, 3.92; N, 13.62. Found: C, 42.40; H, 3.98; N, 12.82.

WO 00/35922 PCT/US99/29894 -31 Example 11 7.9-Dichloro-2,3.4.4A-Tetrahydro- I H-Pyrazinof 1,2-alOuinoxalin-5 (6H)-One, Hydrochloride 5 The title compound was synthesized according to the method of Example 1, substituting 2

,

4 -dichloro-6-fluoronitrobenzene [Clark, J. H. ; Nightengale, D. J. . J. Fluorine Chem. (1996) 78 (1), 91-93.] for 1, 2 -dichloro-4-fluoro-5-nitrobenzene. The melting point of the title compound is 308-311 C. 10 Example 12 (R)-9-Chloro-2.3.4,4a-Tetrahydro- I H-Pyrazino [ 1 2a] Ouinoxalin-5(6H)-One A. (R)-4-Carbobenzyloxy- 1-(5-Chloro- 2 -Nitrophenyl)-Piperazine-2-Carboxylic Acid. By the same procedure described for example 2 method 2B, from 0.95 g of (R)-4 15 carbobenzyloxypiperazine-2-carboxylic acid, there was obtained 1.2 g (85.7%) of title compound as a orange solid, mp 145-155oC. MS (ESI, m/e (%)) 420 (100, [M+H]') and 422 (40, [M+H]*). [ot], = +196.00 (c = 1, MeOH). 20 B. (R)-Carbobenzyloxy-9-Chloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[1,2a] Quinoxalin-5(6H)-One. By the same procedure described for example 2 method 2C, from 1.12 g (R) 4-carbobenzyloxy-l-(5-chloro- 2 -nitrophenyl)-piperazine-2-carboxylic acid, there was obtained 0.80 g (80.8%) of title compound as a white solid, mp 139-141 0 C. 25 H' (NMR (400 Hz, d 6 -DMSO) 8 10.73 (s,1H); 7.38-7.30 (m, 5H); 6.87-6.78 (m, 3H); 5.11 (s, 2H); 4.38 (d, 1H, J = 13.0 Hz); 4.06 (d, 1H, J = 13.0 Hz); 3.70 (d, 1H, J = 11.4 Hz); 3.57 (dd, 1H, J = 11.0, 3.7 Hz); 2.97 (bs, 2H); 2.65 (dt, 1H, J = 11.3, 3.5 Hz). MS (APCI, m/e (%)) 372 (100, [M+H]') and 374 (40, [M+H]'). 30 Anal. Calc'd for C19H, 8 C1N 3 0 3 : C,61.38; H,4.88; N, 11.30. Found: C, 61.46; H, 4.76; N, 11.27.

WO 00/35922 PCT/US99/29894 - 32 C. (R)-9-Chloro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2a]-Quinoxalin-5(6H)-One. By the same procedure described for example 2 method 2D, from 0.50 g (R) carbobenzyloxy-9-chloro-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2a]-quinoxalin-5(6H) one, there was obtained 0.27 g (87.1%) of title compound as a white solid, mp 146 5 149 0 C. MS ((+)ESI, m/e (%)) 238 (85, [M+H]). Anal. Calc'd for CI 1

H

1 2 C1N 3 0: C, 55.59; H, 5.09; N, 17.68. Found: C, 55.59; H, 4.98; N, 17.40.

[]

2 5 D = + 28.90 (c = 1, MeOH). 10 Chiral Purity = 99.9% (Chiralpak AD, 4.6 X 250 mm). The hydrochloride salt was prepared from HCI and MeOH as a light green solid, mp decomposed 270-280 0 C. H' NMR (400 Hz, d 6 -DMSO) 8 10.90 (s, 1H); 9.53 (s,2H); 6.94 (bs, 1H); 6.90-6.84 (m, 2H); 3.96 (dd, 1H, J = 13.1, 3.4 Hz); 3.86 (d, 1H, J = 11.0 Hz); 3.62 (bd, 1H, J = 15 12.0 Hz); 3.42 (d, 1H, J = 10.6 Hz); 3.10-2.97 (m, 3H). MS (APCI, m/e (%)) 238 (100, [M+H]*) and 240 (40, [M+H]+). Anal. Calc'd for CIHC1N 3 0 * HCl: C, 48.19; H, 4.78; N, 15.33. Found: C,48.38; H, 5.06; N, 14.91. Chiral Purity = 99.9% (Chiralpak AD, 4.6 X 250 mm). 20 [O]D = +7.00 (c = 1, MeOH). Example 13 8,9-Difluoro-2,3,4.4a-Tetrahydro- 1H-Pvrazino[ 1,2-a] Quinoxalin-5(6H)-One A. 4-Carbobenzyloxy- 1- ( 4 ,5-Difluoro-2-Nitrophenyl)-Piperazine-2-Carboxylic 25 Acid. By the same procedure described for example 2 method 2B, from 1.5 g of racemic 4-carbobenzyloxypiperazine-2-carboxylic acid and 1,2,4-trifluoro-5-nitro benzene, there was obtained 0.4 g (16.7%) of title compound as an orange-red residue. 30 MS (APCI, m/e (%)) 422 (45, [M+H]*).

WO 00/35922 PCT/US99/29894 - 33 B. 3-Carbobenzyloxy-8,9-Difluoro-2,3,4,4a-Tetrahydro- 1 H-Pyrazino[1,2-a] Quinoxalin-5(6H)-One. By the same procedure described for example 2 method 2C, from 0.29g of 4 carbobenzyloxy-l1-( 4 ,5-difluoro- 2 -nitrophenyl)-piperazine-2-carboxylic acid, there 5 was obtained 0.17 g (66.0%) of title compound as a white solid, mp 226-8 0 C. H' NMR (400 MHz, d 6 -DMSO) 8 10.70 (s, 1H); 7.39-7.30 (m, 5H); 6.98-6.92 (m, 1H); 6.82-6.77 (m, 1H); 5.11 (s, 2H); 4.38 (d, 1H, J = 13.0 Hz); 4.06 (d, 1H, J = 13.0 Hz); 3.62 (d, 1H, J = 11.0 Hz); 3.52 (dd, 1H, J = 11.0, 4.0 Hz); 2.98 (bs, 2H); 2.65 (dt, IH, J = 11.0, 4.0 Hz). 10 MS (APCI, m/e (%)) 374 (100, [M+H]*). Anal. Calc'd for C,,H1 7

F

2

N

3 03: C, 61.12; H, 4.59; N, 11.25. Found: C, 60.79; H, 4.54; N, 10.95. C. 8,9-Difluoro-2,3,4,4a-Tetrahydro- 1H-Pyrazino[ 1,2-a] Quinoxalin-5(6H)-One 15 By the same procedure described for example 2 method 2D, from 0.28 g 3 -carbobenzyloxy-8,9-difluoro-2,3,4,4a-tetrahydro- 1 H-pyrazino[ 1,2-a]quinoxalin 5(6H)-one there was obtained 0.14 g (78.1%) of title compound as a white solid. The hydrochloride salt of this material, prepared from an excess of hydrogen chloride in ethanol, was obtained as a white solid, mp >280 0 C. 20 H' NMR (400 MHz, d 6 -DMSO) 8 10.89 (s, 1H); 9.57 (s, 2H); 7.07-7.02 (m, 1H); 6.90-6.86 (m, 1H); 3.93 (dd, 1H, J = 11.0, 3.0 Hz); 3.77 (d, 1H, J = 11.0 Hz); 3.62 (m, 1H); 3.62 (m, 1H); 3.42 (d, 1H, J = 10.0 Hz); 3.10-2.95 (m, 3H). MS ((+)APCI, m/e (%)) 240 (75, [M+H] ). Anal. Calc'd for C,,H,FN 3 0: C, 47.92; H, 4.39; N, 15.24. 25 Found: C, 47.96; H, 4.37; N, 14.86.

Claims (17)

1. A compound of formula I having the structure R2NR R3 NX N R4 R I wherein 5 R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 10 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least two of R 1 , 15 R 2 , R 3 , or R 4 are not hydrogen.

2. The compound according to claim 1, wherein the non-hydrogen substituents of R 1 , R 2 , R 3 , or R 4 are halogen or trifluoromethyl. 20

3. The compound of claim 1, having the structure R2 1 2 R1 N ' N R4 R

4 IA IB or a pharmaceutically acceptable salt thereof. WO 00/35922 PCT/US99/29894 - 35 4. The compound of claim 1, which is a) 8,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]quinoxalin-5(6H) 5 one or a pharmaceutically acceptable salt thereof; b) 8,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2-a]quinoxalin-5(6H) one hydrochloride salt; 10 c) (R)-8,9-dichloro-2,3,4,4a-tetrahydro-1H-pyrazino[ 1,2-a]quinoxalin 5(6H)-one or a pharmaceutically acceptable salt thereof; d) (R)-8,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]quinoxalin 5(6H)-one hydrochloride salt; 15 e) (S)-8,9-dichloro-2,3,4,4a-tetrahydro- I H-pyrazino[ 1,2-a]quinoxalin 5(6H)-one or a pharmaceutically acceptable salt thereof; f) (S)-8,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]quinoxalin 20 5(6H)-one hydrochloride salt; g) 8,9-dichloro-2,3,4,4a,5,6-hexahydro- 1H-pyrazino[1,2-a]quinoxaline or a pharmaceutically acceptable salt thereof; 25 h) 8,9-dichloro-2,3,4,4a,5,6-hexahydro- 1H-pyrazino[ 1,2-a]quinoxaline dihydrochloride salt; i) (R)-8,9-dichloro-2,3,4,4a,5,6-hexahydro- 1H-pyrazino[1,2 a]quinoxaline or a pharmaceutically acceptable salt thereof; 30 j) (R)-8,9-dichloro-2,3,4,4a,5,6-hexahydro- 1H-pyrazino[1,2 a]quinoxaline dihydrochloride salt; k) (S)-8,9-dichloro-2,3,4,4a,5,6-hexahydro- 1H-pyrazino[1,2 35 a]quinoxaline or a pharmaceutically acceptable salt thereof; 1) (S)-8,9-dichloro-2,3,4,4a,5,6-hexahydro-1H-pyrazino[1,2 a]quinoxaline dihydrochloride salt; 40 m) 9-chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2 a]quinoxalin-5(6H)-one or a pharmaceutically acceptable salt thereof; n) 9-chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2 a]quinoxalin-5(6H)-one hydrochloride salt; 45 WO 00/35922 PCT/US99/29894 - 36 o) (S)- 9 -chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- I H-pyrazino[ 1,2 a]quinoxalin-5(6H)-one or a pharmaceutically acceptable salt thereof; p) (S)-9-chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2 5 a]quinoxalin-5(6H)-one hydrochloride salt; q) (R)- 9 -chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2 a]quinoxalin-5(6H)-one or a pharmaceutically acceptable salt thereof; 10 r) (R)- 9 -chloro-8-trifluoromethyl-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2 a]quinoxalin-5(6H)-one hydrochloride salt; s) 9,10-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2-a]-quinoxalin 5(6H)-one or a pharmaceutically acceptable salt thereof; 15 t) 9,10-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]-quinoxalin 5(6H)-one hydrochloride salt; u) 7,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]quinoxalin-5(6H) 20 one or a pharmaceutically acceptable salt thereof; v) 7,9-dichloro-2,3,4,4a-tetrahydro- 1H-pyrazino[1,2-a]quinoxalin-5(6H) one hydrochloride salt; 25 w) (R)-9-chloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2a]quinoxalin-5(6H) one or a pharmaceutically acceptable salt thereof; x) (R)-9-chloro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2a]quinoxalin-5(6H) one hydrochloride salt 30 y) 8,9-difluoro-2,3,4,4a-tetrahydro-1H-pyrazino[ 1,2-a]quinoxalin-5(6H) one or a pharmaceutically acceptable salt thereof; or z) 8,9-difluoro-2,3,4,4a-tetrahydro- 1H-pyrazino[ 1,2-a]quinoxalin-5(6H) 35 one hydrochloride salt. WO 00/35922 PCT/US99/29894 - 37

5. A method of treating obsessive-compulsive disorder, depression, anxiety, panic disorder, or schizophrenia in a mammal, which comprises administering to said mammal a compound of formula I having the structure 1 , R R2 N N R4 R' I 5 R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 10 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , 15 R 2 , R 3 , or R 4 are not hydrogen.

6. A method of treating migraine in a mammal, which comprises administering to said mammal a compound of formula I having the structure RI R R2 R3 N X I 20 wherein R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; WO 00/35922 PCT/US99/29894 - 38 R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, 5 trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , R 2 , R 3 , or R 4 are not hydrogen. 10

7. A method of treating sleeping disorders in a mammal, which comprises administering to said mammal a compound of formula I having the structure R2Y R3 N R4 R I 15 wherein R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide 20 of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; 25 or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , R 2 , R 3 , or R 4 are not hydrogen. WO 00/35922 PCT/US99/29894 - 39

8. A method of treating eating disorders in a mammal, which comprises administering to said mammal a compound of formula I having the structure 1 ,R R2 or" N R3 \ N R4R' I wherein 5 R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 10 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , 15 R 2 , R 3 , or R 4 are not hydrogen.

9. A method of treating obesity in a mammal, which comprises administering to said mammal a compound of formula I having the structure RI rN"R R2 3 N I R 4 R', 20 wherein R is hydrogen or alkyl of 1-6 carbon atoms; WO 00/35922 PCT/US99/29894 - 40 R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 5 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , 10 R 2 , R 3 , or R 4 are not hydrogen.

10. A method of treating type II diabetes in a mammal, which comprises administering to said mammal a compound of formula I having the structure RI R R2N RRX 3 N R4 R' I 15 wherein R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide 20 of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; 25 or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , R 2 , R 3 , or R 4 are not hydrogen. WO 00/35922 PCT/US99/29894 -41

11. A method of treating epilepsy in a mammal, which comprises administering to said mammal a compound of formula I having the structure 1 , RR R2~R N I wherein 5 R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 10 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , 15 R 2 , R 3 , or R 4 are not hydrogen.

12. A pharmaceutical composition which comprises a compound of formula I having the structure Rz R R2 NY R3 N R4 R' I 20 wherein R is hydrogen or alkyl of 1-6 carbon atoms; WO 00/35922 PCT/US99/29894 - 42 R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 5 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least one of R 1 , 10 R 2 , R 3 , or R 4 are not hydrogen; and a pharmaceutical carrier.

13. A compound of formula I having the structure R, r N' R R2 R3 N R4 R I wherein 15 R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 20 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least two of R 1 , 25 R 2 , R 3 , or R 4 are not hydrogen, for use as a medicament.

14. A compound for use as a medicament according to claim 13, in which the use comprises treatment of diseases involving the central nervous system such as obsessive-compulsive disorder; depression; anxiety; panic disorder; schizophrenia; WO 00/35922 PCT/US99/29894 - 43 migraine; sleep disorders, such as sleep apnea; eating disorders, such as hyperphagia; obesity; type II diabetes; and epilepsy.

15. A process for the preparation of a compound of formula I having the structure R Ri q R2 N R3 X R4 1 5 I wherein R is hydrogen or alkyl of 1-6 carbon atoms; R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, 10 alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; 15 R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least two of R 1 , R 2 , R 3 , or R 4 are not hydrogen, which comprises reacting a compound of formula Cbz I N C _COOH N H 20 in which Cbz represents a carbobenzyloxy group and Y stands for chlorine, fluorine or bromine, with a compound of formula WO 00/35922 PCT/US99/29894 - 44 R R2 R 3 " NO 2 R4 in which R,, R,, R 3 and R 4 are as previously defined above, in the presence of a base, and at a temperature above ambient, to form a compound of formula R, 0 5 R 4 which is cyclized by reduction of the NO, group to an amino group followed by heating at an elevated temperature to form the compound of formula: RI N-Cbz R2 N R3N 0 H R4 10 and then removing the Cbz group to give the compound of formula I where R' is H, and optionally treating with a reducing agent to form the compound of formula I wherein X is CR 5 R 6 ; or treating with a base and an alkyl or acyl halide followed by removing the Cbz group to give the compound of formula R, N-H R2 N R N 0 151 15 R4 R' and optionally treating with a reducing agent to form the compound of formula I wherein X is CR 5 R 6 ; WO 00/35922 PCT/US99/29894 - 45 or alkylating using a base and an alkyl halide to give the compound of formula I where R is alkyl of 1-6 carbon atoms, and optionally treating with a reducing agent to form the compound of formula I wherein X is CR 5 R 6 . 5

16. A process for the preparation of a compound of formula I having the structure R Ri R2., N R3 X R4 I wherein R is hydrogen or alkyl of 1-6 carbon atoms; 10 R' is hydrogen, alkyl of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; R 1 , R 2 , R 3 , and R 4 are each, independently, hydrogen, alkyl of 1-6 carbon atoms, alkoxy of 1-6 carbon atoms, halogen, trifluoroalkyl, -CN, alkyl sulfonamide of 1-6 carbon atoms, alkyl amide of 1-6 carbon atoms, amino, alkylamino of 1-6 carbon atoms, dialkylamino of 1-6 carbon atoms per alkyl moiety, 15 trifluoroalkoxy of 1-6 carbon atoms, acyl of 2-7 carbon atoms, or aroyl; X is CR 5 R 6 or a carbonyl group; R 5 and R 6 are each, independently, hydrogen or alkyl of 1-6 carbon atoms; or a pharmaceutically acceptable salt thereof, with the proviso that at least two of R 1 , R 2 , R 3 , or R 4 are not hydrogen, which comprises reacting a compound of formula 20 R, N-R R 3 NO 2 OH R4 by reaction with N,O-dimethylhydroxylamine hydrochloride in the presence of a base and a coupling reagent to form a compound of formula WO 00/35922 PCT/US99/29894 - 46 R 1 R2 N-R NO 2 N- OMe R3 NO R40 and treating this compound with a Grignard reagent or organolithium reagent to give a compound of formula R, R2 N-R R 3 NO2 5 0 R4 5 and then either (a) reducing with a reducing agent to a compound of formula R R2 N-R R 3 NH 2 OH 0 R4 which is then cyclised at an elevated temperature in the presence of an acid to give compounds of formula I in which R' is hydrogen, and optionally alkylating or 10 acylating with an corresponding alkyl or acyl halide to give compounds of formula I in which R' is other than hydrogen, and optionally forming a pharmaceutical salt thereof ; or (b) treating with a Grignard reagent to give a tertiary alcohol of formula 15 R4 HO R 6 WO 00/35922 PCT/US99/29894 - 47 which is then reduced with a metal in acid followed by heating at an elevated temperature to give compounds of formula I in which R' is hydrogen, and optionally alkylating or acylating with an corresponding alkyl or acyl halide to give compounds of formula I in which R' is other than hydrogen, and optionally forming a 5 pharmaceutical salt thereof.

17. A process for the preparation of compounds of formula IA or IB R2 N R2 N R 3 N R 3 N 0 H * H R4 R 4 IA IB 10 in which R, R, R 2 , R 3 , and R 4 have the meanings defined in claim I or a pharmaceutically acceptable salt thereof, which comprises starting from the relevant (S) or (R)-piperazinecarboxylic acid and converting to the corresponding N protected compound of formula H N-Cbz HN 15 0co 2 H in which Cbz represents a carbobenzyloxy group, and then reacting with a substituted ortho-nitrofluorobenzene to give a corresponding (S) or (R) compound of formula R1 N-R R2 NCO 2 H RR 3 NO 2 WO 00/35922 PCT/US99/29894 - 48 which is cyclised by reducing the nitro group to an amino group and then heating at elevated temperatures, followed by removal of the Cbz protecting group to form the compound of IA or IB, and optionally forming a pharmaceutical salt thereof.