EP-A-214,632 discloses quinoxaline 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 the priority date 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 a hydroxyalkyl group; a group of formula (II)

0

/\

-(C(R) ₂ ) _a CR-C(R) ₂ (II)

wherein a is from 1 to 4, the groups R are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms such that the group of formula (II) contains in total from 1 to 10 carbon atoms; a group of formula (III)

-R ⁴ -Am (III)

wherein R ⁴ is -(C(R) ₂ ) _b - or -(C(R) ₂ ) _b CROHC(R) ₂ -, b is from 1 to 4, the groups R are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, such that R ⁴ is an alkylene or hydroxyalkylene group containing from 1 to 10 carbon atoms, and Am is alkylamino or dialkylamino or a heterocyclic group which is an aziridino group, unsubstituted or substituted by one or more alkyl substituents or a 1-piperazino group, unsubstituted or substituted in the 2- or 3-position of the piperazine ring by alkyl, hydroxyl or halogen, and in the 4-position of the piperazine ring by an alkyl, cycloalkyl of 5 to 7 carbon atoms, phenyl or pyridyl; a group of formula (IV)

-R-^-Het ¹ ( IV)

wherein R ⁵ is -(C(R) ₂ ) _C - where c is from 1 to 4 or R ⁵ is -C(R ₂ ) _d CROH(C(R) ₂ ) _c -, where d is from 1 to 4, and e is from 1 to 4 , at least one of d and e being 1, the groups R are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, such the R ⁵ is an alkylene or hydroxyalkylene group containing from 1 to 10 carbon atoms, and Het ¹ is 2- nitroimidazolyl, optionally further substituted by one or more alkyl, haloalkyl, halogen, hydroxy, alkoxy or nitro substituents; or a group of formula (V) :-

-(C(R) ₂ ) _f -Het ² (V)

wherein f is from 1 to 6, the groups R are the same or different and each is hydrogen or alkyl of 1 to 4 carbon atoms, such that the group -(C(R) ₂ ) _f - contains from 1 to 10 carbon atoms and Het ² is a 5-nitrofuryl group, optionally further substituted by one or more alkyl, haloalkyl, halogen, hydroxy, alkoxy or nitro 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; the groups R ³ are the same or different and each is hydrogen, alkyl, or hydroxy;

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 unless specified otherwise and the said haloalkyl groups contain one or more halogen atoms; or a pharmaceutically acceptable salt thereof. According to further features the present invention provides processes for producing the compounds of the present invention and pharmaceutical compositions comprising them.

In the compounds of formula (I) , the alkyl 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 one embodiment of the compounds of the invention R ¹ is other than hydroxyalkyl. ^" Where the group R ¹ is a group of formula (II) preferably the groups R are all hydrogen, i.e. the group of formula (II) is unbranched. Where a group R is other than

hydrogen, preferably R is methyl or ethyl, more preferably methyl. Preferably there is no more than one group R which is other than hydrogen. Preferably the group of formula (II) contains from 1 to 8, more preferably 1 to 6 carbon atoms. Preferably a is 1 or 2, more preferably 1.

Where the group R ¹ is a group of formula (III) , preferably all the groups R are hydrogen, i.e. R ⁴ is straight chain alkylene or hydroxyalkylene. Where a group R is other than hydrogen, preferably R is methyl or ethyl, more preferably methyl. Preferably there is no more than one group R which is other than hydrogen. Preferably R ⁴ contains from 1 to 8, more preferably 1 to 6 carbon atoms. Preferably R ⁴ is a group -(C(R) ₂ ) _b CROHC(R) ₂ and preferably b is 1 or 2, more preferably 1. When Am is unsubstituted or substituted, 1- pyrrolidino, l-piperidino, or 1-morpholino preferably the group is unsubsituted. 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.

When Am is a 1-piperazino group, preferably the piperazinyl ring is unsubstituted in the 2- and 3- posάtions. In the 4-position the piperazinyl ring is preferably unsubstituted or N-substituted by alkyl, cyclohexyl or 2-pyridyl, more preferably alkyl and most preferably methyl.

Preferably Am is unsubstituted aziridino. Where Am is substituted aziridino, preferred substituents as wethyl and ethyl, more preferably methyl.

Where the group R ¹ is a group of formula (IV) , preferably the groups R are all hydrogen, i.e. the group R ⁵ is straight chain alkylene or hydroxyalkylene. Where a group R is other than hydrogen, preferably R is methyl or ethyl, more preferably methyl. Preferably there is no more than one group R which is other than hydrogen. Preferably R ³ contains from 1 to 8, more preferably 1 to 6 carbon atoms. Preferably R ^s is a group -(C(R) ₂ ) _d CROH(C(R),) _e -, more preferably d and e are the same or different and each is 1 or 2, and still more preferably both d and e are 1. Where R ⁵ is -(C(R) ₂ ) _C - preferably c is 1 or 2. Preferably Het ¹ is a 2-nitroimidazolyl group, which does not bear any further substituents and most preferably the group of formula (IV) is a group of formula (IVA)

N _N ¹ (CH . _CHOHCH--- (IVA)

NC- 2 1-2 2

When R ¹ is a group of formula (V) preferably the groups R are all hydrogen, so that -(C(R) ₂ ) _f - is straight chain alkylene. Where a group R is other than hydrogen, preferably R is methyl or ethyl, more preferably methyl other than hydrogen. Preferably -(C(R) ₂ ) _f . contains from 1

to 8, more preferably 1 to 6 carbon atoms. Preferably f is 1 or 2.

Preferably the group Het ² is unsubstituted 5- nitrofuryl (bearing no further substituents) and most preferably the group Het ² is a group of formula (VA):-

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 tri luoromethyl, 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.

Preferably each of the groups R ³ is hydrogen. Where R ³ is other than hydrogen, preferably it is hydroxyl or alkyl, preferably ethyl or methyl and more preferably methyl. 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:-

l _jt. 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,

1, 2-Di ^' hydro-8-( (4-oxiranylmethyl)piperazin-1-yl) -4- phenylimidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide,

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

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

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

l,2-Dihydro-8-( (4-(3-(aziridinyl)-2- hydroxypropyl)piperazin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide,

l,2-Dihydro-8-(4-(3-(2-nitro-l-imidazolyl)-2- hydroxypropyl)piperazinyl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide,

l,2-Dihydro-8-(4-(3-(2-nitro-l-imidazolyl)-2- hydroxypropyl)piperazinyl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide,

1,2_-Dihydro-8-(4-(2-(5-nitrofuryl)methyl)piperazinyl)-4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide, and

1,2-Dihydro-8-(4-(2-hydroxyethyl)piperazinyl)-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.

Compounds of formula (I) in which R ¹ is a group of formula (II) may be prepared by reacting a compound of formula (VI) :-

O in which R ² , R ³ , X and X ¹ are as hereinbefore defined, with a compound of formula (VII):-

O Y-(C(R) ₂ ) _a CR-C(R) ₂ (VII) where R and a are as hereinbefore defined and Y is a readily displaceable group such as halogen or an alkyl or aryl ester group such as tosylate, mesylate or triflate.

The reaction may be performed in an organic solvent, such as dichloromethane or DMF at ambient temperature.

Compounds of formula (VI) may be obtained by reacting a compound of formula (VIII):-

(VIII)

in which R ² , X and X ¹ are as hereinbefore defined and Z is halogen, with piperazine or a derivative thereof. This reaction is generally carried out in an organic solvent as reaction medium, such as an alcohol, for example ethanol or propan-2-ol, at a temperature from 60 to 110°C.

Compounds of formula (I) in which R ¹ is a group of formula (III) and R ⁴ is -(C(R) ₂ ) _b CR0HC(R) ₂ - may be obtained by reacting a corresponding compound of formula (I) in which R ¹ is a group of formula (II) with an amine Am-H, in which Am is as hereinbefore defined.

The reaction may be performed in an organic solvent, such as an alcohol for example ethanol or 2-propanol, at a temperature from 60 to 110°C. Compounds of formula (I) in which R ¹ is a group of formula (III) and R ⁴ is -(C(R) ₂ ) _b - may be obtained by reacting an amine Am-H with a compound of formula (IX)

. wherein X, X, R, R ² , and b are as hereinbefore defined and Y ¹ is a readily displaceable group, such as halogen or an alkyl or aryl sulphonate ester group, e.g.,

mesylate, tosylate or triflate.

The reaction may be performed at ambient temperature, in an aprotic solvent, such as DMF, under basic conditions. Compounds of formula (I) wherein R ¹ is hydroxyalkyl may be obtained by conventional methodology from compounds of formula (VI) by reacting with a compound of formula (X)

Z ² -(C(R) ₂ ) _b -0H (X)

wherein Z ² is halogen, and R and c are as hereinbefore defined. The reaction may be performed in an alcohol, as reaction solvent, for example ethanol or 2- propanol at a temperature from 60 to 110°C.

Alternatively, compounds of formula (I) wherein R ¹ is hydroxylalkyl may be obtained by reacting a compound of formula (VIII) as hereinbefore defined with a hydroxyalkyl piperazine. This reaction is generally carried out in an organic solvent as reaction medium, such as an alcohol, for example ethanol or propan-2-ol, at a temperature from 60 to 110°C.

Compounds of formula (I) wherein R ¹ is hydroxyalkyl may be converted to a compound of formula (IX) , for example by reaction within an alkyl or aryl sulphonic acid at room temperature in basic conditions (to yield a compound in which Y ¹ is a sulphonate ester group) optionally followed by reaction with halide, e.g. lithium halide to provide a compound of formula (IX) in which Y ¹ is halogen.

Compounds of formula (I) in which R ¹ is a group of formula (IV) and R ⁵ is -(C(R) ₂ ) _d CROH(C(R) ₂ ) _e - and d is 1 may be obtained by reacting a compound of formula (VI) with a compound of formula (XI):-

C(R) ₂ -CR-(C(R) ₂ ) _e -Het' (XI) in which Het ¹ , R and e are as hereinbefore defined.

The reaction may be performed in an organic solvent, such as an alcohol for example ethanol or 2-propanol, at a temperature from 60 to 110°C.

Compounds of formula (XI) in which e is 1 may be prepared using conventional methodology from a halohydroxy compound of formula (XII) ,

Z ³ C(R) ₂ CR0HC(R) ₂ -Het' (XII)

in which Z ³ is halogen and R and Het ¹ are as hereinbefore defined. Generally this is performed under basic conditions, eg. using sodium hydroxide as a base. Compounds of formula (XII) may be obtained by reacting an imidazole Het'-H with an epichlorohydrin or a derivative thereof of formula (XIII) .

Z ³ C(R) ₂ CRC(R) ₂ (XIII)

in which Z ³ and R are as hereinbefore defined. This may be performed in known and conventional manner.

Compounds of formula (XI) including those where e is not 1 may be prepared alternatively by epoxidation, in conventional manner, e.g. using meta-chloroperbenzoic acid, of a compound of formula (XIV)

C(R) ₂ =CR-(C(R) ₂ ) _C -Het ¹ (XIV)

in which R and Het ¹ are as hereinbefore defined.

Compounds of formula (XIV) may be obtained by reacting an imidazole Het'-H with a compound (XV)

C(R),=CR-(C(R) ₂ ) _C -Z ⁴ (XV)

in which R is as hereinbefore defined and Z ⁴ is halogen, in conventional manner.

Compounds of formula (I) in which R ¹ is a group of formula (IV) and R ⁵ is -(C(R) ₂ ) _d CR0H(C(R) ₂ ) _e - and e is 1 may be obtained by reacting an imidazolide anion Het ^1" with a corresponding compound of formula (I) in which R ¹ is a group of formula (II) . Preferably the reaction is performed in an aprotic solvent, such as DMF using a salt of the imidazole, such as the potassium salt.

Compounds of formula (I) wherein R ¹ is a group of formula (IV) where R ⁵ is -(C(R) ₂ ) _C - or when R ¹ is a group of formula (V) , may be obtained by reacting a compound of formula (VI) with a compound of formula (XVI) or (XVII):-

Het'- ( C (R) ₂ ) _C - Y ² ( XVI )

Het ² - (C (R) ₂ ) _f - Y ² (XVII )

wherein Het ¹ , Het ² , R, c and f are as hereinbefore defined and Y ² is a readily displaceable group such as halogen or an alkyl or aryl sulphonate ester group for example tosylate, mesylate or triflate.

The reaction may for example be performed in basic conditions and in an aprotic organic solvent, for example dichloromethane or DMF, at ambient temperature.

Compounds of formula (I) thus obtained may be purified by chromatography, for example or 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 (VII) , (VIII) , (X) , (XIII) , (XV) , (XVI) , and (XVII) are compounds which may be prepared using known methods. In particular compounds of formula (VIII) may be prepared 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- reatable 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(l-(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 for use in the treatment of the human or animal body in a method of therapy and the use of compound of formula (I) and pharmaceutically acceptable salts thereof 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.

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

Under an argon atmosphere, 1,2-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 Et0Ac/CH ₂ Cl ₂ to yield 4.2g (72%) of 1,2- dihydro-8-(piperazine-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%).

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

Reference - 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-1-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 ₁₉ N ₂₀ N ₆ 0.0.33H ₂ 0 requires C; 64.4, H; 5.8, N; 23.7%)

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

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

Glycidyl tosylate (l.Og, 4.4 mmol) was stirred in 10 ml anhydrous DMF with 1,2-dihydro-8-piperazin-l-yl) -4- phenylimidazo[l,2-a] pyrido [3,2-e] pyrazine 5-oxide (1.5g, 4.3 mmol), together with 1.5 ml Et ₃ N for 24h at ambient temperature. The solvent was removed under reduced pressure at 35°C and the residue purified on silica, eluting with MeOH. The resulting solid was recrystallised from 2-propanol to afford 1,2-dihydro-8-( (4- oxiranylmethyl)piperazin-1-yl) -4-phenylimidazo[1,2-a] pyrido [3,2-e] pyrazine 5-oxide (55%) as orange crystals, mp=104-107°C, Η-NMR (CDC1 ₃ ) δ 2.3 (t,2H,J=6Hz) , 2.8 (m,6H), 3.5 (m,4H), 4.1 (s,4H), 6.1 (d, 1H,J=2.4Hz) , 6.6

(dd,lH,J=2.4 and 9.6Hz) , 7.3 (m,3H), 7.8 (m,2H) and 8.1 (d,lH,J=8.4Hz) ppm. (Found : C; 66.7, H; 6.4, N; 16.7%,

C ₂₃ H ₂₅ N ₅ 0 ₂ . 0 . 5H ₂ 0 requires C ; 66 . 8 , H ; 6 . 3 , N ; 16 . 9% ) .

EXAMPLE 4 l,2-Dihydro-8-( (4-oxiranylmethyl)piperazin-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 3 to yield 1,2-dihydro-8-( (4- oxiranylmethyl)piperazin-l-yl) -4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (60%) as an orange solid, mp=196-197°C, ^! H-NMR (CDC1 ₃ ) <S 2.4 (t,2H,J=6Hz) , 2.7 (m,7H), 3.8 (m,4H) , 4.1 (s4H) , 6.2 (d, 1H,J=8.4Hz) , 7.4 (m,3H), 7.8 (m,2H) and 8.2 (d, 1H,J=8.4Hz) ppm.

EXAMPLE 5 1,2-Dihydro-8-(4-(3-(cis-2,3-dimethylaziridinyl)-2- hydroxypropyl)piperazin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide l,2-Dihydro-8-( (4-oxiranylmethyl)piperazin-l-yl) -4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (0.25g, 0.62 mmol) was dissolved in 1.5 ml EtOH (1% Et ₃ N) together with cis-2, 3-dimethylaziridine (0.25 ml, ca. 5 mmol) , and the reaction mixture heated under reflux for 3h. The solution was cooled and evaporated, and the residue purified on silica, eluting with CHCl ₃ /Me0H/Et ₃ N (90:9:1) to give l ^" ,2-dihydro-8-(4-(3-(cis-2,3-dimethylaziridinyl) -2- hydroxypropyl)piperazin-l-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (52%) as orange crystals,

mp=73-76°C, ¹ H-NMR (CDC1 ₃ ) δ 1.1 (d, 6H, J=4.8Hz) , 1.45 (m,2H) , 2.4-2.8, (m,8H) , 3.5 (m,5H) , 4.1 (s,4H) , 6.2 (d,lH,J=8.4Hz) , 7.35 (m,3H) , 7.7 (m,2H) and 8.1 (d,lH,J=8.4Hz) ppm.

EXAMPLE 6 l,2-Dihydro-8-(4-(3-aziridinyl) -2-hydroxypropyl)piperazin-

1-yl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5- oxide This compound was prepared in accordance with the procedure of Example 5 but using aziridine and with a reaction time of 0.3h. The residue obtained after evaporation of the solvents was purified on neutral alumina, eluting with MeOH/Et ₃ N (99:1) to give 1,2-dihydro- 8-( (4-(3-aziridinyl) -2-hydroxypropyl)piperazin-1-yl) -4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (35%) as an orange waxy solid ^■ H-NMR (CDC1 ₃ ) δ 1.3 (m,2H), 1.8 (m,2H) , 2.5-2.8 (m,8H) , 3.5 (m,lH), 3.6 (m,4H), 4.15 (s,4H) , 6.2 (d,lH,J=8.4Hz) , 7.4 (m,3H), 7.8 (m,2H) and 8.2 (d,lH,J=8.4Hz) ppm.

EXAMPLE 7 l,2-Dihydro-8-( (4-(3-(aziridinyl)-2- hydroxypropyl)piperazin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide

This compound was prepared in accordance with the procedure of Example 6 using 1,2-dihydro-8-( (4-

oxiranylmethyl)piperazin-l-yl) -4-phenylimidazo[l, 2-a] pyrido [3,2-e] pyrazine 5-oxide as starting material to afford 1,2-dihydro-8-(4-(3-(aziridinyl) -2- hydroxypropyl)piperazin-l-yl)-4-phenylimidazo [1,2-a] quinoxaline 5-oxide (32%) as an orange solid, mp=124-128°C, Η-NMR (CDC1 ₃ ) δ 1.2 (m,2H), 1.8 (m,2H), 2.2-2.5 (m,8H), 3.3 (m,5H), 4.0 (s,4H), 6.0 (d, 1H,J=2.4Hz) , 6.6 (dd, 1H,J=2.4 and 9.6Hz), 7.3 (m,3H), 7.7 (m,2H) and 8.1 (d, 1H,J=8.4Hz) ppm.

EXAMPLE 8 l,2-Dihydro-8-(4-(3-(2-nitro-l-imidazolyl)-2- hydroxypropyl) iperazinyl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide l-0xiranylmethyl-2-nitroimidazole (0.l5g, 0.83 mmol) and l,2-dihydro-8-(piperazin-l-yl) -4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (0.15g, 0.43 mmol) were refluxed for 1.5h in 5m EtOH. The cooled solution was evaporated and purified on silica, eluting with MeOH/CHCl ₃ (1:9) to give 1, 2-dihydro-8-(4-(3-(2-nitro-l-imidazolyl) -2- hydroxypropyl)piperazinyl) -4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (68%) as an orange solid, mp=158- 160°C (dec) , Η-NMR (CDC1 ₃ ) δ 2.5 (m,2H) , 2.6 (m,4H) , 3.55 (m,4H) , 4.1 (s,4H) , 4.5 (m,3H) , 6.3 (d, 1H,J=8.4Hz) , 7.2 (S,1H) , 7.25 (S,1H) , 7.3 (m,3H) , 7.8 (m,2H) and 8.2 (d,1H,J=8.4Hz) ppm. The product was converted to a bishydrochloride by dissolving in Et0Ac/CH ₂ Cl ₂ , and treating

with 1.0M HC1 in Et ₂ 0. The resulting solid was triturated and washed with Et ₂ 0, to yield the bishydrochloride as an orange solid, mp=>200°C (dec) , (Found : C; 45.2 H; 5.3, N; 18.7%, C ₂₅ H ₂₈ N ₉ 0 ₄ .2HC1.4H ₂ 0 requires C; 45.3, H; 5.7, N; 19.0%) . EXAMPLE 9

1,2-Dihydro-8-(4-(3-(2-nitro-l-imidazolyl)-2- hydroxypropyl)piperazinyl) -4-phenylimidazo [1,2-a] quinoxaline 5-oxide This compound was prepared in accordance with the procedure of Example 8 to afford 1,2-dihydro-8-(4-(3-(2- nitro-l-imidazolyl) -2-hydroxypropyl)piperazinyl) -4- phenylimidazo [1,2-a] quinoxaline 5-oxide (69%) , as an orange crystalline solid, mp=220-221°C (dec) , (Found : C; 59.4, H; 5.4, N; 21.0%, C ₂₆ H ₂₈ N ₈ 0 ₄ .0.5H ₂ 0 requires C; 59.4, H; 5.5, N; 21.3%) .

EXAMPLE 10 (4-(2-(5-nitrofuryl)methyl)ρiperazinyl) -4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide

5-Nitrofuran-2-methanol (0.5g, 3.5 mmol) in 2 ml anhydrous CH ₂ C1 ₂ was added slowly with stirring at 0°C to 4- toluenesulphonyl chloride (3.3g, 17.5 mmol) in 3 ml anhydrous CH ₂ C1, containing Et ₃ N (0.4g, 5.25 mmol). The solution was stirred for 2.5h and then allowed to reach room temperature, diluted with 50 ml CH ₂ C1 ₂ and washed with 2 x 50 ml H ₂ 0. The solvent was removed under reduced

pressure and the residue purified on silica, eluting with CH ₂ C1 ₂ to afford 0.35g (34%) of 5-nitrofuran-2-methyl 4- toluenesulphonate as a white solid, mp=97-98°C, Η-NMR (CDC1 ₃ ) 2.4 (s,3H) , 5.0 (s,2H), 6.55 (d, 1H,J=4Hz) , 7.1 (d, 1H,J=4H ₃ ) 7.3 (d,2H,J=8.4Hz) and 7.7 (d,2H,J=8.4Hz) ppm. 5-Nitrofuran-2-methyl 4-toluenesulphonate (0.25g, 0.85 mmol) was added slowly, with stirring, to a solution of l,2-dihydro-8-(piperazin-l-yl) -4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (0.2g, 0.575 mmol) in anhydrous CH ₂ C1 ₂ (2ml) containing Et ₃ N (0.5 ml) . Stirring was continued for lh, and the solution washed with 2 x 10 ml NaHC0 ₃ (aq) , dried (Na ₂ S0 ₄ ) and evaporated. The residue was purified on silica, eluting with MeOH, to afford 1,2- dihydro-8-(4-(2-(5-nitrofuryl)methyl)piperazinyl) -4- phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (57%) as a dark orange solid recrystallised from EtOH, mp=107- 109°C, ¹ H-NMR (CDC1 ₃ ) δ 2.6 (m,4H), 3.7 (m,6H) , 4.2 (s,4H) , 6.3 (d,lH,J=8.4Hz) , 6.5 (d, 1H,J=4Hz) , 7.4 (m.4H) , 7.8 (m,2H) and 8.15 (d, 1H,J=8.4Hz) ppm.

EXAMPLE 11

1,2-Dihydro-8-(4-(2-hydroxyethy1)piperaziny1) -4- phenylimidazo [l,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) and 4- hydroxyethylpiperazine (3.9mL, ca.30mmol) were heated at 90°C in 2-propanol (5mL) for 2h. The solution was colled

to 0°C filtered and the solid washed with cold 2-propanol. The mateial obtained was recrystallised from ethanol to give l,2-dihydro-8-(4-(2-hydroxyethyl)piperazinyl) -4- phenylimidazo [1,2-a]pyrido [3,2-e]pyrazine 5-oxide as an orange solid, mp 200-201.5°C.

EXAMPLE 12

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. OPhys. 15 973-976) . 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