EP-A-214,632 discloses guinoxaline and pyridopyrazine derivatives which are useful as anti-anaerobic agents, for the treatment of diseases related to anaerobic bacteria. Such diseases include for example, post-operative sepsis following lower gastrointestinal surgery or female urinogenital surgery, pelvic inflammatory disease, ulcers, gangrene, trichomonal vaginitis, non-specific vaginitis, amoerbiasis, giardiasis, periodontal disease, acne, and the like. O-A-93/00900 which was published after both the priority dates of the present case, discloses that the compounds disclosed in EP-A-214,632 and pharmaceutically acceptable salts thereof are useful in the treatment of tumours and particularly hypoxic tumours.

The present invention provides a quinoxaline or pyridopyrazine derivative of formula (I)

(I)

wherein R ¹ is : hydrogen, alkyl, alkoxy, alkylamino, dialkylamino, aminoalkylamino unsubstituted or substituted on the terminal amino group by one or two alkyl groups or by a divalent group which forms a saturated heterocyclic ring together with the amino nitrogen atom to which it is attached optionally containing a further oxygen or nitrogen atom and optionally being substituted by one or more alkyl, hydroxyl or halogen substituents, aminoalkyl(N-alkyl)amino unsubstituted or substituted on the terminal amino group by one or ^" two alkyl groups or by a divalent group which forms a saturated heterocyclic ring together with the amino nitrogen atom to which it is attached optionally containing a further oxygen or nitrogen atom and optionally being substituted by one or more alkyl, hydroxyl or halogen substituents, aminoalkoxy unsubstituted or substituted on the amino group by one or two alkyl groups or by a divalent which forms a saturated heterocyclic ring together with the amino nitrogen atom to which it is attached optionally containing a further oxygen or nitrogen atom and optionally being substituted by one or more alkyl, hydroxyl or halogen substituents, hydroxyalkylamino, hydroxyalkyl(N- alkyl)amino, hydroxyalkyloxy, haloalkylamino, haloalkyl(N- alkyl)amino, or haloalkyloxy; a heterocyclic group which is a 1-pyrrolidino, 1-piperidino or l-morpholino group, unsubstituted or substituted by one or more alkyl, hydroxy or halogen substituents, or an aziridino group unsubstituted or substituted by one or more or alkyl substituents; or

a 1-piperazino-group which is unsubstituted or substituted by one or more alkyl, hydroxy or halogen substituents in the 2- or 3- position and in the 4-position is unsubstituted or N-substituted by haloalkyl, cycloalkyl of 5 to 7 carbon atoms (unsubstituted or substituted by one or more alkyl, hydroxy or halogen substituents), or pyridyl (unsubstituted or substituted by one or more alkyl, haloalkyl, hydroxy, alkoxy, nitro or halogen substituents) or phenyl (unsubstituted or substituted by one or more alkyl, haloalkyl, hydroxy, alkoxy, nitro or halogen substituents) ;

R ² is a hydrocarbyl or heterocyclyl aromatic group unsubstituted or substituted by one or more substituents selected from halogen, haloalkyl, alkyl, nitro, hydroxy, alkoxy and alkylenedioxy;

X is -CH= or -N=; and

X ^I is hydrogen or halogen; wherein the said alkyl groups and moieties incorporating alkyl groups contain from 1 to 6 carbon atoms and the said haloalkyl groups contain one or more halogen atoms; or a pharmaceutically acceptable salt thereof; with the exclusion of (a) the compounds of formula (I) where R ¹ is hydrogen, X is -N=, X ¹ is hydrogen and R ² is unsubstituted phenyl or 3-pyridyl, and R ¹ is hydrogen, X is -CH=, -X ¹ is hydrogen and R ² is 4-fluorophenyl, 3,4- dimethoxyphenyl, 3,4-ethylenedioxy or 3,4,5- trimethoxyphenyl and (b) the compound of formula (I) which is l,2-dihydro-8-(piperazin-l-yl) -4-phenylimidazo [1,2a]

quinoxaline 5-oxide.

According to further features the present invention provides processes for producing the compounds of the present invention and pharmaceutical compositions comprising compounds of formula (I) (including exclusions (a) and (b) from the compounds of the invention) .

In the compounds of formula (I), the alkyl, haloalkyl and alkoxy groups may be either straight or branched. It is preferred that any alkyl groups in the compounds of formula (I) (including alkyl groups which form part of alkoxy groups) be alkyl groups of 1 to 4 carbon atoms, i.e. methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl. Particularly preferred alkyl substituents are methyl, and ethyl, most preferably methyl. In the compounds of formula (I) halogen atoms present as halogen substituents or in haloalkyl substituents may for example be fluorine, chlorine or bromine atoms.

In a first embodiment the group R ¹ is hydrogen or an alkyl group. Preferably R ¹ is other than hydrogen. In a second embodiment the group R ¹ is an alkylamino, dialkylamino or alkoxy group, for example an alkylamino or dialkylamino group.

In a third embodiment the group R ¹ is an aminoalkylamino, aminoalkyl(N-alkyl)amino or aminoalkoxy group, substituted or unsubstituted on the terminal amino group, a hydroxyalkylamino, hydroxyalkyl(N-alkyl)amino or hydroxyalkoxy group or a haloalkylamino, haloalkyl(N-

alkyl)amino or haloalkoxy group.

R ¹ may for example be aminoalkylamino unsubstituted or substituted on the terminal amino group by one or two alkyl groups, amino(N-alkyl)amino unsubstituted or substituted on the terminal amino group by one or two alkyl groups, hydroxyalkylamino, hydroxyalkyl(N- alkyl)amino, haloalkylamino, or haloalkyl(N-alkyl)amino.

Preferably when R ¹ is an aminoalkylamino, aminoalkyl(N-alkyl)amino or aminoalkoxy group or a substituted derivative thereof, it is a group of formula (II):-

R ³ R ⁴ N(CH ₂ ) _a Y- (II) wherein Y is -O- or -NR ⁵ -, preferably -NR ⁵ -, R ³ , R ⁴ and R ⁵ are the same or different and each is hydrogen or alkyl of 1 to 6 carbon atoms, preferably hydrogen or methyl, and a is 2 or 3, preferably 2. Alternatively R ³ and R ⁴ may, together with the nitrogen atom to which they are attached form a heterocyclic ring, preferably containing 5 to 7 atoms, such as a pyrrolidino or piperidino ring, or which may contain an extra nitrogen or oxygen atom, such as a piperazino or morpholino ring. Such a ring may be unsubstituted or substituted by one or more alkyl, hydroxyl or halogen substituents and/or in the case of a heterocyclic ring containing an additional nitrogen atom unsubstituted at the nitrogen atom or N-substituted by alkyl, haloalkyl, cycloalkyl of 5 to 7 carbon atoms, pyridyl or phenyl. Such N-substituents may themselves be

unsubstituted or substituted as hereinbefore defined in relation N-substituted piperazino groups R ¹ .

Preferably when R ¹ is a haloalkylamino, haloalkyl(N- alkyl)amino or haloalkoxy or hydroxyalkyla ino hydroxyalkyl(N-alkyl)amino group, or hydroxyalkoxy it is a group of formula (III):-

Y ² (CH ₂ ) _b Y'- (III) wherein Y ¹ is -O- or -NR ⁶ -, preferably -NR ⁶ -, R ⁶ is hydrogen or alkyl of 1 to 6 carbon atoms, preferably hydrogen or methyl, Y ² is halogen or hydroxyl, preferably hydroxyl and b is 2 or 3, preferably 2. R ¹ may for example be haloalkylamino or haloalkyl(N-alkyl)amino or hydroxyalkylamino or hydroxyalkyl(N-alkyl)amino group. In a fourth embodiment R ¹ is an unsubstituted or substituted, preferably unsubstituted, 1-pyrrolidino, 1-piperidino, l-morpholino or aziridino group. 1- Morpholino groups are most preferred. When such a group is substituted it is preferably substituted by a single substituent. Preferred substituents include hydroxyl and alkyl, preferably methyl or ethyl, more preferably methyl, for pyrrolidino, piperadino and morpholino groups and methyl and ethyl, more preferably methyl, for aziridino groups.

In a fifth embodiment R ¹ is an unsubstituted or substituted 1-piperazino group. Preferably the group is unsubstituted in the 2- and 3-positions. Where there is such substitution, there is preferably a single

substituent, and preferred substituents include hydroxyl and alkyl, preferably methyl or ethyl, more preferably methyl.

Preferably the 1-piperazino is N-substituted in the 4-position by a haloalkyl, cycloalkyl, pyridyl or phenyl group.

Preferred haloalkyl substituents are fluoroalkyl substituents preferably containing more than one fluorine atom, for example 2,2,2-trifluoroethyl or trifluoromethyl, preferably 2,2,2-trifluoroethyl.

Preferred cycloalkyl substituents are cyclohexyl substituents. Preferably such a cycloalkyl substituent is itself unsubstituted. When such a cycloalkyl group is substituted it is preferably substituted by a single substituent and preferred substituents include hydroxyl and alkyl, preferably methyl or ethyl, more preferably methyl.

Of pyridyl or phenyl substituents, pyridyl substituents are preferred and may be 2- or 3-, preferably 2-pyridyl. Such phenyl and pyridyl groups are preferably themselves unsubstituted. When such a group is itself substituted preferred substituents are as defined in relation to R ² below.

In the compounds of formula (I) R ² may be unsubstituted or substituted, preferably unsubstituted. Hydrocarbyl aromatic groups may for example be phenyl or

naphthyl, preferably phenyl, and heterocyclyl aromatic groups may for example be pyridyl or thiophenyl, preferably pyridyl. Most preferably R ² is unsubstituted or substituted phenyl. Pyridyl groups may be 2- or 3-, preferably 3-, pyridyl. Naphthyl groups may be 1- or 2-, preferably 2-, naphthyl. Thiophenyl groups may be 2- or 3- thiophenyl.

Where the group R ² is substituted it is preferably substituted by 1 or 2 substituents, chosen from halogen, haloalkyl, alkyl, nitro, hydroxy, alkoxy and alkylenedioxy. Preferred substituents include halogen, for example fluorine, chlorine or bromine, haloalkyl, for example trifluoromethyl, nitro, and alkoxy, for example methoxy and ethoxy, preferably methoxy. Where R ² is substituted phenyl, preferably it is 4-substituted phenyl, more preferably 4-halophenyl and most preferably 4-fluorophenyl. In the compounds of formula (I) X is preferably -N=. Preferably X ¹ is hydrogen.

Salts of the compounds of formula (I) may be any pharmaceutically acceptable acid addition salts of the compounds of formula (I) . Examples of suitable salts include, salts of inorganic acids such as chlorides, bromides, iodides, phosphates and sulphates and salts of organic acids such as acetates, citrates, lactates and tartrates. Salts of inorganic acids are preferred, hydrochlorides, hydrobromides and hydroiodides are more preferred. Hydrochlorides are most preferred.

Particular examples of the compounds of formula (I) are:-

1,2-Dihydro-8-(piperazin-1-yl)-4-phenylimidazo[1,2- a]quinoxaline 5-oxide,

l,2-Dihydro-8-(piperazin-l-yl)-4-phenylimidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-4-(4-fluorophenyl)imidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(1-methyl-l-(N,N-dimethylaminoethy1)amino)- 4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(l-methyl-1-hydroxyethylamino)-4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l _i 2-Dihydro-8-(1-aminopropyl)amino-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-8-(morpholin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-8-(4-cyclohexylpiperazin-l-yl)-4-phenylimidaz o [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(2-methylaziridin-l-yl)-4-phenylimidazo [1,2- a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(piperidin-1-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(4-(2,2,2-trifluoroethyl)piperazin-1- yl)imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-8-(4-(2-pyridyl)piperazin-l-yl)-4-phenylimida zo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(morpholin-1-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide,

1,2-Dihydro-8-(pipiridin-1-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide,

lj.2-Dihydro-8-(pyrrolidin-1-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide,

1,2-Dihydro-8-(1-methyl-l-(N,N-dimethylaminoethyl)amino)- 4- phenylimidazo [1,2-a] quinoxaline 5-oxide,

l,2-Dihydro-4-(3-pyridyl)-imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

1,2-Dihydro-8-(aziridin-1-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-8-methoxy-4-phenylimidazo [1,2-a] pyrido [3,2- e] pyrazine 5-oxide, and

1,2-Dihydro-8-(1-(dimethylamino)ethoxy)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide.

These compounds may be in the form of a free base or of salts, and in particular hydrochloride salts. The compounds of formula (I) may be produced, by reacting a compound of formula (IV) :

in which R ² is as hereinbefore defined, with a compound of formula (V)

in which Z is halogen and R ¹ , X and X ¹ are as hereinbefore defined.

The reaction is generally carried out under basic conditions in an organic solvent as reaction medium, such as acetonitrile or an alcohol, for example 2-propanol. Generally the reaction is carried out at from 50 to 110°C, preferably about 80°C.

Compounds of formula (I) where R ¹ is other than hydrogen or alkyl, alkoxy, unsubstituted or substituted aminoalkoxy, hydroxyalkoxy or haloalkoxy, may alternatively be produced by reacting a compound of formula (VI):-

R'-H (VI)

wherein R ¹ is as hereinbefore defined with a compound of formula (VII)

wherein R ² , X and X ¹ are as hereinbefore defined and Z ¹ is halogen.

Generally reaction with a compound (VI) is carried out in an organic solvent, such as an alcohol, for example propan-2-ol at a temperature from 60 to 110°C.

Compounds of formula (I) where R ¹ is alkoxy, unsubstituted or substituted aminoalkoxy, hydroxyalkoxy or haloalkoxy may be produced by reacting a metal alkoxide,

(VIA) R ¹ -M (VIA)

in which R ¹ is alkoxy, unsubstituted or substituted aminoalkoxy, hydroxyalkoxy or haloalkoxy, and M is a metal, for example an alkali metal, with a compound of formula (VII) as hereinbefore defined. Generally reaction with an alkoxide (VIA) is performed in an alcoholic solution of alkoxide, for example in the corresponding alcohol as solvent or in methanol or ethanol, at a temperature from 50 to 80°C.

The compound of formula (I) thus obtained may be purified by chromatography, for example on silica gel, or recrystallised using an appropriate solvent.

Compounds of formula (I) may be converted into pharmaceutically acceptable salts in conventional manner for the formation of acid addition salts. For example, the salts of the present invention may be produced by reaction with an organic acid, or more preferably an inorganic acid such as hydrochloric acid, in an organic reaction medium.

The compounds of formulae (IV) , (V) , (VI) , (VIA) and (VII) are compounds which may be prepared using known methods. In particular compounds of formula (IV) may be obtained by reacting an acetonitrile derivative R ² CH ₂ CN in ethylenediamine at elevated temperature, e.g. about 200°C for 24 to 48 hours. Compounds of formula (VII) may be obtained according to procedures described in EP-A-214,632. The compounds of formula (I) and salts thereof are useful in increasing the sensitivity of tumour cells to

radiation in radiotherapy and as bioreductive agents. A compound is administered to a patient having a radiation- treatable cancer, prior to or after, more typically shortly after irradiation of the tumour, in an amount effective to increase the sensitivity of the tumour cells to the effects of the irradiation.

Any solid tumour, which may have regions where cells are radiobiologically hypoxic and become resistant to ionising radiation, may be treated. Examples of such tumours are epithelial tumours of the head, neck, thorax and abdomen, soft tissue sarcomas and brain tumours. The compounds of formula (I) and salts thereof can therefore be employed in the radiotherapy of all such solid tumours where hypoxic cells are known or suspected to exist. The compounds of formula (I) and salts thereof may also be used where an agent having differential hypoxic cytotoxicity is required. The compounds can be employed for chemopotentiation of a chemotherapeutic agent or as a chemotherapeutic by administration of a compound to a patient having a localised or metastatic cancer.

Administration is carried out prior to, simultaneously with or after administration of, typically prior to or simultaneously with, a chemotherapeutic agent such as melphalan, cyclophosphamide, 5-fluorouracil, adriamycin, CCNU(r-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea) or tumour necrosis factor (TNF) . Any solid tumours, such as above, which are primary or secondary deposits, where it is

known or suspected that hypoxic cells are present can therefore benefit from treatment employing a compound of formula (I) or a salt thereof.

The compounds of formula (I) and salts thereof are useful in particular for the treatment of hypoxic tumours. However they may also be useful in the treatment of other tumours rich in enzymes required to activate them as bioreductive agents or radiosensitisers. Such enzymes may include cytochrome P450, NADPH dependent cytochrome P450 reductase, DT-diaphorase and xanthine oxidase.

The compounds of formula (I) and salts thereof may be administered orally or parenterally. The amount administered depends on factors such as the cancer, the condition of the patient and the body weight of the patient. Typically, however, doses of 50 to 1000mg/m ² of a patient's body area may be employed.

Accordingly, the present invention further provides a pharmaceutical composition comprising a compound of formula (I) , as hereinbefore defined or a pharmaceutically acceptable salt thereof, in association with a pharmaceutically acceptable carrier or diluent.

The compounds of formula (I) and salts thereof may be formulated in a manner appropriate to the treatment for which it is to be used by bringing it into association with a pharmaceutically acceptable carrier or diluent.

Preferably the composition is in a form suitable for parenteral administration. The compound may be included in

a dosage form suitable for bolus injection or such as a tablet or capsule, for example a capsule comprising known formulation components. The compound may also be formulated for intravenous administration e.g. in a saline drip solution.

Suitable carrier or diluent materials for inclusion in the compositions of the present invention include organic or inorganic inert carrier or diluent material for example, water, gelatin, lactose, starch, magnesium stearate, talc, vegetable oils, gum arabic, polyalkylene- glycols, petroleum jelly and the like. The pharmaceutical compositions may be sterilised, pyrogen-free and isotonic. The compositions may contain adjuvants such as preserving, stabilising, wetting or emulsifying agents, salts for varying the osmotic pressure or buffers. The pharmaceutical compositions may contain other therapeutically valuable substances.

The present invention further provides compounds of formula (I) , as hereinbefore defined, and pharmaceutically acceptable salts thereof with the exclusion of (a) the compounds of formula (I) where R ¹ is hydrogen, X is -N=, X ¹ is hydrogen and R ² is unsubstituted phenyl or 3-pyridyl, and R ¹ is hydrogen, X is -CH=, X ¹ is hydrogen and R ² is 4- fluorophenyl, 3,4-dimethoxyphenyl, 3,4-ethylenedioxy or 3,4,5-trimethoxyphenyl (but including 1,2-dihydro-8- (piperazin-1-yl)-4-phenylimidazo [1,2a] quinoxaline 5- oxide) for use in the treatment of the human or animal body

in a method of therapy, for example treatment of a hypoxic tumour.

The invention further provides use of the compounds of formula (I) and pharmaceutically acceptable salts thereof (including compounds excluded by (a) and (b) , from the compounds of the invention) in the manufacture of a medicament for use in the treatment of a tumour, for example a hypoxic tumour.

The following Examples illustrate the invention. EXAMPLE 1 l,2-Dihydro-8-(piperazin-l-yl)-4-phenylimidazo[1,2- a]quinoxaline 5-oxide.

Under an argon atmosphere, l,2-dihydro-8-fluoro-4- phenylimidazo [1,2-a] quinoxaline 5-oxide (4.0g, 14.2 mmol) and piperazine (12.2g, 0.142 mmol) were heated at 90°C in 2-propanol (20 ml) for 3.5h. The solvent was removed under reduced pressure and the residue dissolved in CH ₂ C1 ₂ (50 ml), washed with H ₂ 0 (50 ml)) and dried (MgS0 ₄ ) and concentrated. The resulting orange solid was recrystallised from EtOAc/CH ₂ Cl ₂ to yield 4.2g (72%) of 1,2- dihydro-8-(piperazin-1-yl)-4-phenylimidazo[1,2 a]quinoxaline 5-oxide, mp-212-214°C (Found : C; 68.2, H; 6.0, N; 19.6%, C ₂₀ H ₂₁ N ₅ 0.0.33H ₂ 0 requires C; 68.0, H; 6.1, N; 19.8%).

^" i,2-Dihydro-8-fluoro-4-phenylimidazo[1,2- a]quinoxaline 5-oxide may be prepared as disclosed in EP-A- 214632.

EXAMPLE 2 l,2-Dihydro-8-(piperazin-l-yl)-4-phenylimidazo[1,2-a] pyrido [3,2-e] pyrazine 5-oxide.

1,2-Dihydro-8-chloro-4-phenylimidazo[1,2-a] pyrido [3,2-e] pyrazine 5-oxide (O.lg, 0.335 mmol) and piperazine (0.288g, 3.35 mmol) were heated at 60°C in 2-propanol for 0.5h under an argon atmosphere. The solution was cooled, evaporated and redissolved in 50ml CH ₂ C1 ₂ , washed with H ₂ 0 (50 ml) , dried and evaporated to afford, after recrystallisation from EtOAc/CHCl ₃ l,2-dihydro-8-

(piperazin-l-yl)-4-phenylimidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide (72%) as an orange solid, mp=177-178°C (Found : C; 64.7, H; 5.7, N; 23.8%, C _I9 N ₂₀ N ₆ O.0.33H ₂ O requires C; 64.4, H; 5.8, N; 23.7%) The product was converted to a bis-hydrochloride by reaction with 2.2 equivalents of HCl, using the procedure described in Example 4, (m.p.: greater than 250°C) .

1,2-Dihydro-8-chloro-4-phenylimidazo[1,2-a] pyrido [ _. 3,2-e] pyrazine 5-oxide may be prepared as disclosed in EP-A-214632.

EXAMPLE 3 l,2-Dihydro-4-(4-fluorophenyl)imidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide. A mixture of 2-chloro-3-nitropyridine (0.44g, 2.8 mmol) and 2-(4-fluorobenzyl)-2-imidazoline (0.5g, 2.79 mmol) in CH ₃ CN (8 ml) was heated at 80°C for 12 h in a

nitrogen atmosphere. The solution was then left at room temperature overnight, evaporated and the residue purified on silica (MeOH/EtOAc, 1:10) to give 0.38g (48%) of 1,2- dihydro-4-(4-fluorophenyl)imidazo[1,2-a] pyrido [3,2-e] pyrazine 5-oxide after recrystallisation from MeOH, mp=213- 215°C, Η-NMR (CDClj) δ 4.1 (s,4H), 6.8 (dd,lH,J=8 and 8Hz) , 7.0 (d,2H,J=9.6Hz) , 7.9 (d,2H,J=9.6Hz) and 8.2 (m,2H) ppm.

EXAMPLE 4 l,2-Dihydro-8-(1-methyl-l-(N,N-dimethylaminoethyl)amino)-4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide bishydrochloride

8-Chloro-l,2-dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (l.Og, 3.36 mmol) and N,N,N'- trimethylethylenediamme (3.4g, 33.6 mmol) were heated at 90°C in 2-propanol (5 ml) for 3.5h. The solution was then evaporated and the residue purified on silica (Me0H/CH ₂ Cl ₂ , 1:10) to afford an orange foam (65%), of which 437 mg (1.0 minol) was redissolved in 4 ml Et0Ac/CH ₂ Cl ₂ (1:1), and 2.2ml of a 1.0M solution of HCl in Et ₂ 0, filtered and washed again with cold Et ₂ 0 to give 1,2-dihydro-8-(l-methyl-l- (N,N-dimethylaminoethyl)amino)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide bishydrochloride mp=205- 208°C (dec.) Η-NMR (CDC1 ₃ ) 2.3 (s,6H) 2.5 (t,2H,J=7.2Hz) , 3.1 (s ^" ,3H), 3.75 (t,2H,J=7.2Hz) , 4.1 (s,4H), 6.1 (d,lH.J=8.4 Hz), 7.4 (m,3H), 7.8 (m,2H) and 8.05 (d,lH,J=8.4Hz) ppm. (Found : C; 49.7, H; 6.4, N; 17.0%,

C ₂₀ H ₂₄ N ₆ O . 2HC1 . 2 . 5H ₂ O requires C ; 49 . 8 , H ; 6 . 3 , N ; 17 . 4 % )

EXAMPLE 5

1,2-Dihydro-8-(1-methyl-l-hydroxyethylamino)-4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide hydrochloride

This compound was prepared in accordance with the procedure of Example 4 using 2-(methylamino)ethanol as nucleophile and with a reaction time of 1.5h and converted to a hydrochloride to afford l,2-dihydro-8-(l-methyl-l- hydroxyethylamino)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide hydrochloride (63%) as a yellow solid, mp=228-230°C (dec.) (Found : C; 57.8, H; 5.3, N; 18.9%, C, ₈ H ₁₉ N ₅ θ ₂ .HCl requires C; 57.8, H; 5.3, N; 18.7%).

EXAMPLE 6 l,2-Dihydro-8-(l-aminopropyl)amino-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

This compound was prepared in accordance with the procedure of Example 4 above using 1,3-diaminopropane as nucleophile and a reaction time of l.5h. The residue after evaporation was triturated with EtOAc and the solid filtered and recrystallised from EtOAc to afford 1,2- dihydro-8-(l-aminopropyl)amino-4-phenylimidazo [1,2-a] pyrido ^" [3,2-e] pyrazine 5-oxide (57%) as orange crystals, mp=179-180°C (Found : C; 62.4, H; 6.0, N; 24.4%, C ₁₈ H ₂₀ N ₆ 0.0.5H ₂ 0 requires C; 62.6, H; 6.1, N; 24.4%).

EXAMPLE 7 l,2-Dihydro-8-(morpholin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide bishydrochloride

This compound was prepared in accordance with the procedure of Example 4 above at 80°C for 2.5h using morpholine as the nucleophile, and the orange crystals which appeared upon cooling were filtered, washed with EtOH and recrystallised from 2-propanol, and converted to the hydrochloride using the procedure described above to yield l,2-dihydro-8-(morpholin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide bishydrochloride (74%), mp=224-226°C, (Found, C; 54.3, H; 5.3, N; 16.6%, C ₁₉ H ₁₉ N _s θ ₂ .2HCl requires C; 54.0, H; 5.0, N; 16.6%).

EXAMPLE 8 l,2-Dihydro-8-(4-cγclohexylpiperazin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

This compound was prepared in accordance with the procedure of Example 4 above using 4-cyclohexylpiperazine as the nucleophile, and the orange crystals formed on cooling were collected and washed with 2-propanol. The product was recrystallised from 2-propanol to afford 1,2- dihydro-8-(4-cyclohexylpiperazin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (78%), mp=188- 189°C, ^" (Found : C; 69.7, H; 7.0, N; 19.5%, C ₂₅ H ₃₀ N ₆ O requires C; 69.8, H; 7.0, N; 19.5%).

EXAMPLE 9 l,2-Dihydro-8-(2-methylaziridin-l-yl)-4-phenylimidazo [1,2- a] pyrido [3,2-e] pyrazine 5-oxide

8-Chloro-l,2-dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (0.25g, 0.84 mmol) was dissolved in 1.5 ml benzene and 0.3 ml Et ₃ N, and 2-methylaziridine (0.2g, 3.5 mmol) were added and the solution stirred at 70- 80°C for 1.5h. The solution was cooled and evaporated and the residue purified on silica (MeOH/CH ₂ Cl ₂ ,1:10) to afford l,2-dihydro-8-(2-methylaziridin-l-yl)-4-phenylimidazo [1,2- a] pyrido [3,2-e] pyrazine 5-oxide (42%) as an orange waxy solid. The compound was analysed as the ring-opened hydrobromide, prepared by treating with 48% HBr in Me ₂ CO, filtering and washing with cold Me ₂ CO to give the ring- opened monohydrobromide, mp=200-201°C (dec), (Found : C; 45.2, H; 4.1, N; 14.6%, C _lg H _I8 N ₅ OBr.HBr requires C; 44.9, H; 4.0, N; 14.6%) .

EXAMPLE 10 l,2-Dihydro-8-(piperidin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

This compound was prepared in accordance with the reaction conditions described for Example 4, using piperidine as nucleophile and at a reaction temperature of 60°C for 0.5h. Recrystallisation from 2-propanol afforded 1,2-dihydro-8-(piperidin-1-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (68%) as an orange solid,

mp=185-187°C (Found : C; 69.1, H; 6.1, N; 20.2%, C ₂ H ₂₁ N ₅ O requires C; 69.2, H; 6.1, N; 20.2%).

EXAMPLE 11 1, 2-Dihydro-8- (4- (2,2 , 2-trif luoroethyl) piperazin-1- yl) imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

This compound was prepared in accordance with the procedure of Example 4, using N- ( 2,2,2- trifluoroethyl) piperazine as nucleophile to afford 1,2- dihydro-8- (4- (2, 2, 2-trif luoroethyl) piperazin-1-yl) imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (68%) as an orange solid after recrystallisation from ethanol, mp=221-222°C (Found : C; 58.7, H; 4.9, N; 19.6%, C ₂₁ H _2I N ₆ OF ₃ required C; 58.6, H; 4.9, N; 19.5%) .

EXAMPLE 12 l,2-Dihydro-8-(4-(2-pyridyl)piperazine-l-yl)-4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

This compound was prepared in accordance with the procedure of Example 4, except that the cooled reaction mixture was left at -18°C for lh, and the orange crystals filtered and washed with 2-propanol to yield, after recrystallisation from 2-propanol, 1,2-dihydro-8-(4-(2- pyridyl)piperazine-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e ^" ] pyrazine 5-oxide (55%), mp=201.5-202.5°C, Η-NMR

(CDC1 ₃ ) <S 3.8 (m,8H), 4.2 (s,4H), 6.3 (d,1H,J=8.4Hz) , 6.75 (m,2H), 7.4 (m,3H), 7.8 (m,3H), 8.3 (m,lH), 8.35

(d , lH , J=8 . 4Hz ) ppm .

The product was converted to a bishydrochloride as described for Example 4, mp=232-235°C (dec.)

EXAMPLE 13 l,2-Dihydro-8-(morpholin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide l,2-Dihydro-8-fluoro-4-phenylimidazo [1,2-a] quinoxaline 5-oxide (0.5g, 1.54 mmol) in 5 ml 2-propanol, was heated at 100°C for 8h with morpholine (1.5 ml,ca. 16.8 mmol) . The solution was then cooled and evaporated, and the residue purified on silica gel, eluting with EtOAc/MeOH (5:1), to yield l,2-dihydro-8-(morpholin-l-yl)-4- phenylimidazo [1,2-a] quinoxaline 5-oxide (65%) as an orange solid, mp=232-233°C (dec.)

The product was converted to a monohydrochloride as described for Example 4 using 1.1 equivalents of HCl.

EXAMPLE 14 l,2-Dihydro-8-(pipiridin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide

This compound was prepared in accordance with the procedure of Example 13 to afford 1,2-dihydro-8-(pipiridin- 1-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide (71%) as an ora ^' hge solid, mp=230-231°C (dec), monohydrochloride mp=246-247°C (dec.) Η-NMR (CDCl ₃ ) <S 1.8 (m,6H), 3.4 (m,4H), 4.05 (s,4H), 6.0 (d,lH,J=2.4Hz) , 6.5 (dd,lH,J=2.4 and

9.6Hz), 7.3 (m,3H), 7.8 (m,2H) and 8.0 (d,1H,J=8.4Hz) ppm.

EXAMPLE 15 l,2-Dihydro-8-(pyrrolidin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide

This compound was prepared in accordance with the procedure of Example 13, to afford, as an orange solid, 1,2-dihydro-8-(pyrrolidin-1-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide, mp=246-247°C (dec), monohydrochloride mp>=275°C (dec) Η-NMR δ 2.0 (m,4H), 3.35 (m,4H), 4.0

(s,4H), 5.6 (d,lH,J=2.4Hz) , 6.2 (dd,lH,J=2.4 and 9.6Hz), 7.3 (m,3H), 7.75 (m,2H) and 8.0 (d,1H,J=8.4Hz)ppm.

EXAMPLE 16 1,2-Dihydro-8-(1-methyl-l-(N,N-dimethylaminoethyl)amino)-4- phenylimidazo [1,2-a] quinoxaline 5-oxide bishydrochloride

1,2-Dihydro-8-fluoro-4-phenylimidazo [1,2-a] quinoxaline 5-oxide (0.5g, 1.7 mmol) and N,N,N'- trimethylethylenediamine (1.7g, ca.17 mmol) were heated at 95°C for 24h, cooled and evaporated. The residue was purified on silica gel eluting with 10% MeOH/CH ₂ Cl ₂ to afford an orange waxy solid (62%) , which was converted into the bishydrochloride as described in Example 4 to give 1,2- dihydro-8-(1-methyl-l-(N,N-dimethylaminoethyl)amino)-4- phenylimidazo [1,2-a] quinoxaline 5-oxide bishydrochloride, mp=> 250°C (dec) Η-NMR (CDC1 ₃ ) δ 2.3 (s,6H), 2.6 (t,2H,J=7.2Hz) , 3.05 (s,3H), 3.5 (t,2H,J=7.2Hz) , 4.0

(S,4H) , 5.8 (d,lH,J=2.4Hz) , 6.4 (dd,lH,J=2.4 and 9.6Hz) , 7.35 (m,3H), 7.7 (m,2H) , and 8.0 (d, 1H, J=8.4Hz) ppm.

EXAMPLE 17 i,2-Dihydro-4-(3-pyridyl)-imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

2-Chloro-3-nitropyridine (0.22g, 1.4 mmol) and 2-(3- pyridyl)methyl-imidazoline (0.23g, 1.42 mmol) were heated at 85°C in acetonitrile for 4.5h. The solution was cooled, evaporated and the residue purified on silica, eluting with EtOAc/MeOH (10:1) to yield 1,2-dihydro-4-(3-pyridyl)- imidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (50%) as deep yellow crystals after recrystallisation from EtOAc, mp=128-130°C, monohydrochloride mp=214-216°C (dec.) Η-NMR δ 3.6 (s,2H), 3.8 (s,2H), 6.7 (dd,lH,J=4.8 and 9.6Hz), 7.3 (m,lH), 7.6 (m,lH) and 8.4 (m,4H) ppm.

EXAMPLE 18

1^2-Dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide hydrochloride

This compound was prepared in accordance with the procedure of Example 17 using tolazoline in place of 2-(3- pyridyl)methyl-imidazoline and with a reaction time of 12h. Deep yellow crystals of the free base were obtained (63%) and recrystallised from MeOH, mp=194-195°C Η-NMR (CDC1 ₃ ) δ 3.6 (s,2H) 3.9 (s,2H), 6.6 (dd,lH,J=8 and 8Hz) and 8.3 (m,2H) ppm. This material was converted into the

monohydrochloride salt as described in Example 4, using 1.1 equivalents of HCl, to afford, as a yellow solid, 1,2- dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5- oxide hydrochloride, mp=238-240°C (dec).

EXAMPLE 19 l,2-Dihydro-8-(aziridin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

8-Chloro-l,2-dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (l.Og, 3.36 mmol) was stirred with aziridine 3.5g (81.4 mmol) at 25°C for 2h. The excess aziridine was evaporated at room temperature and the residue purified on silica eluting with ethyl acetate: triethylamine (99:1) to afford l,2-dihydro-8-(aziridin-l- yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide as a deep yellow solid, recrystallised from ethyl acetate mp = 168-170°C Η-NMR (CDC1 ₃ ) δ 2.2 (s,4H), 4.0 (bs,4H), 6.4 (d,lH,J=8.4Hz) , 7.2 (m,3H), 7.6 (m,2H), and 8.0 (d,lH,J=8.4Hz) ppm. (Found: C; 66.8, H; 4.6, N; 22.7%, C ₁₇ H _I5 N ₅ 0 requires C; 66.9, H; 4.9, N; 22.9%).

EXAMPLE 20 l,2-Dihydro-8-methoxy-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide A. solution of sodium methoxide in methanol (25%, lmL) was stirred at room temperature together with 8-chloro-l,2- dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-

oxide (O.lg, 0.34 mmol) for 2 hours. The solution was then heated for 1 hour at 80°C, cooled and water (l L) added. The solution was evaporated, and redissolved in chloroform (25mL) , then washed with water (25mL) . The organic layer was dried and evaporated, and the residue purified on silica gel, eluting with ethyl acetate/hexane (1:1) to afford l,2-dihydro-8-methoxy-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (75mg, 75%) as an orange solid which was recrystallised from mp 194-195°C. The product was converted to a monohydrochloride using the method described in Example 4, mp 223-224°C(dec) . Found: C; 64.8, H; 4.8, N; 19.2%, C ₁₆ H ₁₄ N ₄ 0 ₂ requires C; 65.3, H; 4.8, N; 19.0%. EXAMPLE 21 l-2-Dihydro-8-(l-dimethylamino)ethoxy-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

8-Chloro-l,2-dihydro-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (l.Og, 3.4 mmol) was added slowly to a cooled solution of sodium N,N-dimethylethanolamine (6mL, 30% in N,N-dimethylethanolamine) and the solution stirred at room temperature for 12 hours, followed by 2 hours at 50°C. Water (50mL) was added and the solution extracted with ethyl acetate (3xl00mL) , dried and evaporated. The residue was purified on silica, eluting with ethyl acetate: methanol: ammonium hydroxide (47.5:47.5:5) to afford l-2-dihydro-8-(1- dimethylamino)ethoxy-4-phenylimidazo [1,2-a] pyrido [3,2-e]

pyrazine 5-oxide as an orange solid (0.7g, 69%) recrystallised from ethyl acetate:methanol, mp 158-161°C, (Found C; 61.0, H; 5.9, N; 18.8%, C ₁₉ H ₂₁ N ₅ 0 ₂ 1.25 H ₂ 0 requires C; 61.0, H; 6.3, N; 18.7%) EXAMPLE 22

The toxicity of compounds prepared in the foregoing Examples towards aerobic or hypoxic V79 Chinese hamster cells in vitro is shown in Table 1. Toxicity was determined by the use of the modified MTT assay (Stratford and Stephens (1989), Int. J. Radiat- Oncol. Biol. Phys. JL6 _. 973-976) . Values quoted represent concentration of drug required to reduce proliferation of treated cultures by 50%. Cells are treated with various drug doses for 3 hours at 37°C under aerobic or hypoxic conditions, following drug removal cells are allowed to proliferate for 3 days prior to assay.

TABLE 1

Compound C air C N ₂ Ratio

* tested as free base.

EXAMPLE 23

C3H mice in which the transplantable rodent tumour RIF-1 had been implanted subcutaneously were administered the compound of Example 2 (hydrochloride salt) [100 mg/kg] mtraperitoneally immediately after irradiation with 25 Gy X-rays. The time for the tumour to increase in size to four times its original volume was 44 days compared with the corresponding time where no treatment was applied to the tumour (5 days) and where the tumour was treated by irradiation with 25 Gy X-rays alone (35 days) .

The results show that the use of the compound immediately after irraditation to kill viable cells which were hypoxic at the time of irradiation, leads to a significant slowing in the growth of the tumour.