ANTI-TUMOUR AGENTS

Abstract: The invention concerns anti-tumour agents of formula (I), wherein each of R<1>, R<2> and R<3> has the meanings defined in the specification including hydrogen, (1-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl and (1-4C)alkoxy; each of R<4> and R<5> is (1-4C)alkyl; each of R<6> and R<7> is hydrogen or (1-4C)alkyl; X is <u>N</u>-(1-4C)alkylimino, <u>N</u>-(3-4C)alkenylimino or <u>N</u>-(3-4C)alkynylimino; m is 1 or 2 and each R<8> is as defined in the specification; each of Y<1> and Y<2> is halogeno, (1-4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl-(1-4C)alkanesulphonyloxy; or a pharmaceutically acceptable salt thereof; provided that at least one of R<1>, R<2> and R<3> is other than hydrogen; a process for their preparation, pharmaceutical compositions containing them and their use in the production of an anti-proliferative effect.

Description: - 1 - ANTI-TUMOUR AGENTS The invention relates to cytotoxic anti-tumour agents. More particularly the invention relates to novel (l,4-benzoquinonyl)alkanoic acid derivatives which bear a substituent comprising a cytotoxic nitrogen mustard moiety. The invention also relates to processes for the preparation of said (l,4-benzoquinonyl)alkanoic acid derivatives, to pharmaceutical compositions containing them and to their use in the production of an anti-tumour effect in a warm-blooded animal such as man. Many of the current treatments for cell proliferation diseases such as cancer and psoriasis utilise cytotoxic agents which inhibit DNA synthesis or cell division. Such compounds tend to lack specificity and can be toxic to cells generally as neoplastic cells are usually only slightly different from normal cells. The toxic effect of the cytotoxic agent on rapidly dividing tumour cells can be beneficial but normal cells in which continual cell division occurs such as bone marrow cells and gut epithelial cells can also be adversely affected. There are particular difficulties in obtaining an effective treatment of solid tumours using either chemotherapy with cytotoxic agents or radiotherapy as, within the inner hypoxic regions of the tumour mass where the network of blood capillaries is deficient, cell division is slow or absent. Such hypoxic regions exist in most major classes of solid tumours, for example in bladder, breast, cervical, colorectal, head and neck, lung, ovarian, pancreatic, prostate and stomach tumours. In particular it has been shown by analysis of clinical samples that a significant proportion of most head and neck, breast and cervical tumours, for example between 10% and 30% of the tumour mass, is severely hypoxic with an oxygen tension below 5mm Hg (0.0066 bar). It has been recognised that the presence of such hypoxic regions within solid tumours could present an opportunity to allow a more selective cytotoxic drug therapy based on either a prodrug or double-prodrug approach. For example, a prodrug approach is disclosed by B.D. Palmer et al, J. Med. Chem.. 1992, 35, 3214-3222, and in International Patent Application WO 93/11099 concerning a nitro-substituted anilino-mustard compound which may be capable of reduction to a more potent amino-substituted anilino-mustard. A problem with this approach was that those additional substituents which were necessary to allow rapid - 2 - enzymatic reduction of the nitro group tended to diminish the cytotoxic potency of the resultant amino-substituted compound. The double-prodrug approach was taken up to address this problem. For example, it is disclosed by G. J. Atwell et aL, J. Med. Chem.. 1994, 37, 371-380, and B. M. Sykes et al, J. Chem. Soc. Perkin Transact. II. 1995, 337-342, that certain N-{4-[bis(2-chloroethyl)amino]phenyl}-2-nitrophenylacetamide derivatives could be reduced to the corresponding 2-arninophenylacetamide derivatives which could cyclise to release the anilino mustard 4-[bis(2-chlorocthyl)amino]aniline. An alternative double-prodrug approach involves the interconversion in biological systems of quinone and hydroquinone moieties. For example, it is disclosed by L. A. Carpino et al.. J. Org. Chem.. 1989, 54, 3303-3310, that certain (1 ,4-benzoquinonyl)alkanoic acid derivatives could provide a feasible approach for the delivery of a cytotoxic agent. Model compounds which were prepared included N,N-di-(2-chloroethyl)-3-(2-methoxy-3,5-dimethyl-l,4-benzoquinonyl)-3-methylbutyramide and N,N-di-(2-chloroethyl)-3-(2,3-dimethoxy-5-methyl-l,4-benzoquinonylj- 3-methylbutyramide which were designed to release the simple mustard bis(2-chloroethyl)amine. It is further known from Proceedings of the American Association for Cancer Research. 1997, 38, 433-434 (Abstract No. 2894) that the cytotoxic mustard drug melphalan can be linked to a (l,4-benzoquinonyl)alkanoic acid. It was noted that the fastest in vitro bio-reductive activation of certain prodrugs was of the order of 25% per hour i.e. a tι /2 of approximately 2.5 hours and this was linked to reduction potentials in the range -480 to -520 mV. In contrast a slower in vitro bio-reductive activation of other prodrugs of the order of 10% per hour e. a tγ 2 of approximately 6 hours was linked to a reduction potential of the order of -730 mV. It is an object of the present invention to provide double-prodrug quinone compounds which on reduction to the hydroquinone form rapidly break down to release the cytotoxic agent. According to the present invention there is provided an anti-tumour agent of the formula I - 3 - O ° R S A c V R 3 O wherein R 1 is hydrogen, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, (1 -4C)alkoxy-(l -4C)alkyl, amino-(l -4C)alkyl, (1 -4C)alkylamino-(l -4C)alkyl, di-[( 1 -4C)alkyl]amino-( 1 -4C)alkyl, pyrrolidin- 1 -yl-( 1 -4C)alkyl, piperidino-( 1 -4C)alkyl, moφholino-(l-4C)alkyl, piperazin- l-yl-(l-4C)a!kyl, 4-(l-4C)alkylpiperazin-l-yl-(l-4C)alkyl, carboxy-( 1 -4C)alkyl, ( 1 -4C)alkoxycarbonyl-( 1 -4C)alkyl, carbamoyl-( 1 -4C)alkyl, N-(l-4C)alkylcarbamoyl-(l-4C)alkyl, N,N-di-[(l-4C)alkyl]carbamoyl-(l-4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino-(2-4C)alkoxy, (l-4C)alkylamino-(2-4C)alkoxy, di-[(l-4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, morpholino-(2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy, 4-( 1 -4C)alkylpiperazin- 1 -yl-(2-4C)alkoxy , ( 1 -4C)alkylthio, (l-4C)alkylsulphinyl or (l-4C)alkylsulphonyl; R 2 is hydrogen, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, ( 1 -4C)alkylamino-( 1 -4C)alkyl, di-[(l-4C)alkyl]amino-(l-4C)alkyl, pyrrolidin- l-yl-(l-4C)alkyl, piperidino-(l-4C)alkyl, moφholino-( 1 -4C)alkyl, piperazin- 1 -yl-( 1 -4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alkyl, carboxy-( 1 -4C)alkyl, ( 1 -4C)alkoxycarbonyl-( 1 -4C)alkyl, carbamoyl-( 1 -4C)alkyl, N-(l -4C)alkylcarbamoyl-(l -4C)alkyl, N,N-di-[(l -4C)alkyl]carbamoyl-(l -4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino- (2-4C)alkoxy, (l-4C)alkylamino-(2-4C)alkoxy, di-[(l-4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino-(2-4C)alkoxy, piperazin- l-yl-(2-4C)alkoxy or 4-(l-4C)alkylpiperazin-l-yl-(2-4C)alkoxy; R 3 is hydrogen, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, ( 1 -4C)alkylamino-( 1 -4C)alkyl, - 4 - di-[(l-4C)alkyl]amino-(l-4C)alkyl, pyrrolidin-l-yl-(l-4C)alkyl, piperidino-(l-4C)alkyl, moφholino-( 1 -4C)alkyl, piperazin- 1 -yl-( 1 -4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alky 1, carboxy-( 1 -4C)alkyl, ( 1 -4C)alkoxycarbonyl-( 1 -4C)alkyl, carbamoyl-( 1 -4C)alkyl, N-(l-4C)alkylcarbamoyl-(l-4C)alkyl, N,N-di-[(l-4C)alkyl]carbamoyl-(l-4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino- (2-4C)alkoxy, (1 -4C)alkylamino-(2-4C)alkoxy, di-[(l -4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino- (2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy, piperazin- l-yl-(2-4C)alkoxy or 4-(l-4C)alkylpiperazin-l-yl- (2-4C)alkoxy; R 4 is (l-4C)alkyl; R 5 is (l-4C)alkyl; R 6 is hydrogen or (l-4C)alkyl; R 7 is hydrogen or (l-4C)alkyl; X is N-(l-4C)alkylimino, N-(3-4C)alkenylimino or N-(3-4C)alkynylimino; m is 1 or 2 and each R 8 is independently hydrogen, halogeno, hydroxy, (l-4C)alkoxy, (2-4C)alkenyloxy, (2-4C)alkynyloxy, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, amino, (l-4C)alkylamino, di-[(l-4C)alkyl]amino, cyano, (2-4C)alkanoylamino, carboxy, (l-4C)alkoxycarbonyl, carbamoyl, N-(l-4C)alkylcarbamoyl or N,N-di-[(l-4C)alkyl]carbamoyl; Y 1 is halogeno, (l-4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl- (l-4C)alkanesulphonyloxy; and Y 2 is halogeno, (l-4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl- ( 1 -4C)alkanesulphonyloxy ; and wherein any heterocyclic group in R 1 , R 2 or R 3 is optionally substituted with 1, 2 or 3 (l-4C)alkyl substituents, and wherein any phenyl group in Y 1 or Y 2 when Y 1 and Y 2 is benzenesulphonyloxy or phenyl-(l-4C)alkanesulphonyloxy is optionally substituted with 1, 2 or 3 substituents selected from halogeno, nitro, cyano, trifluoromethyl, hydroxy, amino, (l-4C)alkyl, (l-4C)alkoxy, (l-4C)alkylamino and di-[(l-4C)alkyl] amino; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. - 5 - Within the present invention it will be observed that an anti-tumour agent of the invention may possess one or more asymmetric carbon atoms and it can therefore exist in diastereoisomeric, racemic and optically active forms. It is to be understood that the invention encompasses any such form which possesses anti-tumour activity, it being a matter of common general knowledge how various diastereoisomeric forms may be separated and how a racemic compound may be separated into its optically-active forms. It is also to be understood that the compounds of the invention can exist in solvated as well as unsolvated forms such as, for example, hydrated forms. It is to be understood that the invention encompasses all such solvated forms which possess anti-tumour activity. Suitable values for the generic groups mentioned above are set out below. The term 'alkyl' includes both straight- and branched-chain alkyl groups but references to individual alkyl groups such as 'propyl' are specific for the straight chain version only. An analogous convention applies to other generic terms . A suitable value for each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 when it is (l-4C)alkyl or for a (l-4C)alkyl substituent on a phenyl or heterocyclic group is, for example, methyl, ethyl, propyl, isopropyl, butyl or isobutyl. A suitable value for each of R 1 , R 2 , R 3 and R 8 when it is (l-4C)alkoxy or for a (l-4C)alkoxy substituent on a phenyl group is, for example, methoxy, ethoxy, propoxy, butoxy or isobutoxy. A suitable value for R 8 when it is (l-4C)alkylamino or for a (l-4C)alkylamino substituent on a phenyl group is, for example, methylamino, ethylamino, propylamino, isopropylamino, butylamino or isobutylamino. A suitable value for R 8 when it is di-[(l-4C)]alkyl]amino or for a di-[(l-4C)alkyl]amino substituent on a phenyl group is, for example, dimethylamino, diethylamino, N-ethyl-N-methylamino, dipropylamino or di-isopropylamino. Suitable values for each R ! , R 2 or R 3 group include, for example:- for (3-4C)alkenyl: allyl, methylallyl, 2-butenyl and 3-butenyl; for (3-4C)alkynyl: 2-propynyl and 2-butynyl; for hydroxy-(l-4C)alkyl: hydroxymethyl, 1 -hydroxy ethyl, 2 -hydroxy ethyl and 3-hydroxypropyl; for ( 1 -4C)alkoxy-( 1 -4C)alkyl : methoxymethyl, ethoxymethyl, 1 -methoxy ethyl, - 6 - 2-methoxy ethyl, 2-ethoxy ethyl and 3-methoxypropyl; for amino-( 1 -4C)alkyl : aminomethyl, 1 -aminoethyl, 2-aminoethyl and 3-aminopropyl; for ( 1 -4C)alkylamino-( 1 -4C)alky 1 : methylaminomethyl, ethylaminomethyl, 1 -methylaminoethyl, 2-methylaminoethyl, 2-ethylamimoethyl and 3-methylaminopropyl; for di-[(l-4C)alkyl]amino- (l-4C)alkyl: dimethylaminomethyl, diethylaminomethyl, 1-dimethylaminoethyl, 2-dimethylaminoethyl and 3-dimethylaminopropyl; for pyrrolidin- 1 -y l-( 1 -4C)alkyl : pyrrolidin- 1-ylmethyl and 2-(pyrrolidin-l-yl)ethyl; for piperidino-(l-4C)alkyl: piperidinomethyl and 2-piperidinoethyl; for moφholino-(l-4C)alkyl: moφholinomethyl and 2-moφholinoethyl; for piperazin- 1 -yl-(l -4C)alkyl: piperazin- 1-ylmethyl and 2-(piperazin-l-yl)ethyl; for 4-(l -4C)alkylpiperazin- l-yl-(l-4C)alkyl: 4-methylpiperazin- 1 -ylmethyl, 4-ethylpiperazin- 1 -ylmethyl, 2-(4-methylpiperazin- 1 -yl)ethyl and 2-(4-ethylpiperazin- 1 -yl)ethyl; for carboxy-(l-4C)alkyl: carboxymethyl, 1 -carboxyethyl, 2-carboxyethyl and 3-carboxypropyl; for (l-4C)alkoxycarbonyl- (l-4C)alkyl: methoxycarbonylmethyl, ethoxycarbonylmethyl, tejt-butoxycarbonylmethyl, 1 -methoxycarbonylethyl, 1 -ethoxycarbonylethyl, 2-methoxycarbonylethyl, 2-ethoxycarbonylethyl, 3-methoxycarbonylpropyl and 3-ethoxycarbonylpropyl; for carbamoyl-(l-4C)alkyl: carbamoylmethyl, 1-carbamoyl ethyl, 2-carbamoylethyl and 3-carbamoylpropyl; for N-(l-4C)alkylcarbamoyl- (l-4C)alkyl: N-methylcarbamoylmethyl, N-ethylcarbamoylmethyl, - 7 - N-propylcarbamoylmethyl, 1 -(N-methylcarbamoyl)ethyl, 1 -(N-ethylcarbamoyl)ethyl, 2-(N-methylcarbamoyl)ethyl, 2-(N-ethylcarbamoyl)ethyl and 3 -(N-methylcarbamoyl)propyl; for N,N-di-[(l -4C)alkyl]carbamoyl- (l-4C)alkyl: N,N-dimethylcarbamoylmethyl, N-ethyl-N-methylcarbamoylmethyl, N,N-diethy lcarbamoy lmethy 1 , 1 -(N,N-dimethylcarbamoyl)ethyl, 1 -(N,N-diethylcarbamoyl)ethyl, 2-(N,N-dimethylcarbamoyl)ethyl, 2-(N,N-diethylcarbamoyl)ethyl and 3 -(N,N-dimethylcarbamoy l)propy 1 ; for hydroxy-(2-4C)alkoxy: 2-hydroxyethoxy, 3-hydroxypropoxy and 4-hy droxybutoxy ; for (l-4C)alkoxy-(2-4C)alkoxy: 2-methoxyethoxy, 2-ethoxyethoxy, 3-methoxypropoxy and 3-ethoxypropoxy; for amino-(2-4C)alkoxy: 2-aminoethoxy and 3-aminopropoxy; for (l-4C)alkylamino- (2-4C)alkoxy: 2-methylaminoethoxy, 2-ethylaminoethoxy, 2-propylaminoethoxy, 3-methylaminopropoxy and 3 -ethylaminopropoxy ; for di-[(l-4C)alkyl]amino- (2-4C)alkoxy: 2-dimethylaminoethoxy, 2-(N-ethyl-N-methylamino)ethoxy, 2-diethylaminoethoxy, 2-dipropylaminoethoxy, 3-dimethylaminopropoxy and 3-diethylaminopropoxy; for pyrrolidin- l-yl-(2-4C)alkoxy: 2-(pyrrolidin-l-yl)ethoxy and 3 -(pyrrolidin- 1 -yl)propoxy; for piperidino-(2-4C)alkoxy: 2-piperidinoethoxy and 3-piperidinopropoxy; for moφholino-(2-4C)alkoxy: 2-moφholinoethoxy and 3-moφholinopropoxy; - 8 - for piperazin- l-yl-(2-4C)alkoxy: 2-(piperazin-l-yl)ethoxy and 3-(piperazin-l-yl)propoxy; for 4-(l-4C)alkylpiperazin- 1 -yl-(2-4C)alkoxy : 2-(4-methylpiperazin- 1 -yl)ethoxy and 3-(4-methylpiperazin-l-yl)propoxy. A suitable value for R 8 , Y 1 or Y 2 when it is halogeno or for a halogeno substituent on a phenyl group is, for example, fluoro, chloro, bromo or iodo. A suitable value for X when it is N-(l-4C)alkylimino is, for example, N-methylimino (i.e. a bivalent group of formula -N(Me)-), N-ethylimino or N-propylimino; when it is N-(3-4C)alkenylimino is, for example, N-allylimino (i.e. a bivalent group of formula -N(CH 2 -CH=CH 2 )-), N-methylallylimino or N-(2-butenyl)imino; and when it is N-(3-4C)alkynylimino is, for example, N-(2-propynyl)imino ( e. a bivalent group of formula -N(CH 2 -C≡CH)-) or N-(2-butynyl)imino. Suitable values for each R 8 group include for example:- for (2-4C)alkenyloxy: vinyloxy, allyloxy, methylallyoxy and 2-butenyloxy; for (2-4C)alkynyloxy: ethynyloxy and 2-propynyloxy; for (3-4C)alkenyl: allyl, methylallyl, 2-butenyl and 3-butenyl; for (3-4C)alkynyl: 2-propynyl and 2-butynyl; for (2-4C)alkanoyl: acetyl, propionyl and butyryl; for (l-4C)alkoxycarbonyl: methoxycarbonyl, ethoxycarbonyl and tert-butoxy carbonyl ; for N-(l-4C)alkylcarbamoyl: N-methylcarbamoyl and N-ethylcarbamoyl; for N,N-di-[(l -4C)alkyl]carbamoyl: N,N-dimethylcarbamoyl and N,N-diethylcarbamoyl. A suitable value for Y 1 or Y 2 when it is (l-4C)alkanesulphonyloxy is, for example, methanesulphonyloxy, ethanesulphonyloxy or propanesulphonyloxy; when it is, for example, phenyl-(l-4C)alkanesulphonyloxy is, for example, phenylmethanesulphonyloxy or 2-phenylethanesulphonyloxy. It will be appreciated that, when it is stated that a heterocyclic group in R 1 , R 2 or R 3 may optionally be substituted, the heterocyclic groups include those specified in the definitions of R 1 , R 2 and R 3 such as, for example, a pyrrolidin- 1-yl, moφholino, piperidino- (l-4C)alkyl or 4-(l-4C)alkylpiperazin-l-yl-(2-4C)alkoxy group. - 9 - A suitable pharmaceutically-acceptable salt of an anti-tumour agent of the invention is, for example, an acid-addition salt of an anti -tumour agent of the invention which is sufficiently basic, for example, an acid-addition salt with, for example, an inorganic or organic acid, for example hydrochloric, hydrobromic, sulphuric, phosphoric, trifluoroacetic, citric or maleic acid. In addition a suitable pharmaceutically-acceptable salt of an anti-tumour of the invention which is sufficiently acidic is an alkali metal salt, for example a sodium or potassium salt, an alkaline earth metal salt, for example a calcium or magnesium salt, an ammonium salt or a salt with an organic base which affords a physiologically-acceptable cation, for example a salt with methylamine, dimethylamine, trimethylamine, piperidine, moφholine or tris-(2-hydroxyethyl)amine. Particular novel anti -tumour agents of the invention include, for example, compounds of the formula I, or pharmaceutically-acceptable salts thereof, wherein: (a) R 1 , R 2 or R 3 is independently hydrogen, (1 -4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-( 1 -4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, (l-4C)alkylamino-(l-4C)alkyl, di-[(l-4C)alkyl]amino-(l-4C)alkyl, pyrrolidin- 1-yl- (l-4C)alkyl, piperidino-(l-4C)alkyl, moφholino-(l-4C)alkyl, piperazin- l-yl-(l-4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alkyl, carboxy-( 1 -4C)alkyl, ( 1 -4C)alkoxycarbonyl- (l-4C)alkyl, carbamoyl-(l-4C)alkyl, N-(l-4C)alkylcarbamoyl-(l-4C)alkyl or N,N-di-[(l-4C)alkyl]carbamoyl-(l-4C)alkyl, provided that at least one of R 1 , R 2 or R 3 is other than hydrogen; and each of R 4 , R 5 , R 6 , R 7 , R 8 , m, X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti-tumour agents of the invention; (b) R 1 , R 2 or R 3 is independently (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (1 -4C)alkoxy-(2-4C)alkoxy, amino-(2-4C)alkoxy, (1 -4C)alkylamino-(2-4C)alkoxy, di-[(l-4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino-(2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy or 4-(l-4C)alkylpiperazin-l-yl- (2-C)alkoxy; and each of R 4 , R 5 , R 6 , R 7 , R 8 , m, X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti-tumour agents of the invention; (c) each of R 4 and R 5 is independently methyl, ethyl, propyl or isopropyl and each of R 1 , R 2 , R 3 , R 6 , R 7 , R 8 , m, X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti-tumour agents of the invention; - 10 - (d) R 6 is hydrogen, methyl, ethyl, propyl or isopropyl and R 7 is hydrogen or methyl; and each of R 1 , R 2 , R 3 , R\ R 5 , R 8 , m, X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti -tumour agents of the invention; (e) X is N-(l -4C)alkylimino or N-(3-4C)alkenylimino; and each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , m,Y' and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti -tumour agents of the invention; (f) m is 1 or 2 and each R 8 is independently hydrogen, halogeno, hydroxy, (l-4C)alkoxy, (l-4C)alkyl, amino, (l-4C)alkylamino, di-[(l-4C)alkyl]amino or cyano; and each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti-tumour agents of the invention; (g) m is 1 and R 8 is hydrogen, halogeno, hydroxy, (l-4C)alkoxy, (l-4C)alkyl, amino, (l-4C)alkylamino, di-[(l-4C)alkyl]amino or cyano; and each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , X, Y 1 and Y 2 has any of the meanings defined hereinbefore or in this section relating to particular novel anti -tumour agents of the invention; (h) each of Y 1 and Y 2 is halogeno or each of Y 1 and Y 2 is (1 -4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl-(l-4C)alkanesulphonyloxy; and each of R 1 , R 2 , R 3 ,R 4 , R 5 , R 6 , R 7 , R 8 , m and X, has any of the meanings defined hereinbefore or in this section relating to particular novel anti -tumour agents of the invention. A preferred compound of the invention is an anti-tumour agent of the formula I wherein each of R 1 , R 2 and R 3 is independently hydrogen, methyl, ethyl, propyl, allyl, methylallyl, 2-hydroxy ethyl, 3-hydroxypropyl, 2-methoxy ethyl, 2-ethoxy ethyl, 3-methoxypropyl, 3-ethoxypropyl, 2-carboxyethyl, 3-carboxypropyl, 2-methoxycarbonyethyl, 2-ethoxycarbonylethyl, 3-methoxycarbonylpropyl, 3 -ethoxy carbonylpropyl, 2-(N-methylcarbamoyl)ethyl, 3 -(N-methylcarbamoyl)propyl, 2-(N,N-dimethylcarbamoyl)ethyl, 3-(N,N-dimethylcarbamoyl)propyl, methoxy or ethoxy; each of R 4 and R 5 is independently hydrogen, methyl, ethyl, propyl or isopropyl; R 6 is hydrogen, methyl, ethyl, propyl or isopropyl; R 7 is hydrogen or methyl; X is N-methylimino, N-efhylimino, N-propylimino or N-allylimino; m is 1 or 2 and each R 8 is independently hydrogen, fluoro, chloro, bromo, methoxy, ethoxy, methyl, ethyl, propyl, isopropyl or cyano; and - 11 - each of Y 1 and Y 2 is independently chloro, bromo, iodo, methanesulphonyloxy, benzenesulphonyloxy or phenylmethanesulphonyloxy; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. A further preferred compound of the invention is an anti-tumour agent of the formula I wherein R 1 is hydrogen, methyl, ethyl, propyl, allyl, methylallyl, methoxy or ethoxy; R 2 is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, allyl, methylallyl, methoxy or ethoxy; R 3 is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, allyl, methylallyl, methoxy or ethoxy; R 4 is methyl, ethyl, propyl or isopropyl; R 5 is methyl, ethyl, propyl or isopropyl; R 6 is hydrogen, methyl, ethyl, propyl or isopropyl; R 7 is hydrogen or methyl; X is N-methylamino, N-ethylimino, N-propylimino or N-allylimino; m is 1 or 2 and each R 8 is independently hydrogen, fluoro, chloro, bromo, methoxy, ethoxy, methyl, ethyl, propyl or isopropyl; Y 1 is chloro, bromo, iodo or methanesulphonyloxy; and Y 2 is chloro, bromo, iodo or methanesulphonyloxy; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. A further preferred compound of the invention is an anti -tumour agent of the formula I wherein R 1 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 2 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 3 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 4 is methyl or ethyl; R 5 is methyl or ethyl; R 6 is hydrogen, methyl or ethyl; R 7 is hydrogen X is N-methylimino, N-ethylimino, N-propylimino or N-allylimino; m is 1, R 8 is located meta to X and R 8 is hydrogen, fluoro, chloro, methyl, ethyl, propyl or isopropyl; and each of Y 1 and Y 2 is chloro, bromo or iodo; - 12 - or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. A further preferred compound of the invention is an anti-tumour agent of the formula I wherein R 1 is hydrogen, methyl or methoxy; R 2 is hydrogen, methyl, allyl or methoxy; R 3 is methyl, ethyl, propyl or allyl; each of R 4 and R 5 is methyl; each of R 6 and R 7 is hydrogen; X is N-methylimino; m is 1 and R 8 is hydrogen; and each of Y 1 and Y 2 is chloro; or a pharmaceutically-acceptable salt thereof. A specific preferred compound of the invention is the following anti -tumour agent of the formula I:- N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(5-methyl-3-propyl-l,4-benzoquinon-2-yl)- 3 -methy 1-N-methy lbutyramide . 3-(3-allyl-2,5-dimethyl-l,4-benzoquinonyl)-N-{4-[bis(2-chloroethyl)amino]phenyl}- 3 -methy 1-N-methy lbutyramide ; N- { 4- [bis(2-chloroethyl)amino]phenyl } -3 -(2,5 -dimethyl- 1 ,4-benzoquinonyl)-3 -methyl - N-methylbutyramide; 3-(3-allyl-5-methyl-l,4-benzoquinon-2-yl)-N-{4-[bis(2-chloroethyl)amino]phenyl}-3-methyl- N-methylbutyramide; N r {4-[bis(2-chloroethyl)amino]phenyl}-3-methyl-N-methyl-3-(2,3,5-trimethyl- 1 ,4-benzoquinonyl)butyramide, N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,3-dimethoxy-5-methyl-l,4-benzoquinonyl)- 3 -methy 1-N-methy lbutyramide or N-allyl-N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,3-dimethoxy-5-methyl- 1 ,4-benzoquinonyl)-3 -methy lbutyramide; or a pharmaceutically-acceptable salt thereof. It is an object of a further aspect of the present invention to provide a group of novel (l,4-benzoquinonyl)alkanoic acid derivatives which possesses balanced reduction potentials - 13 - i.e. reduction potentials which are neither too low such that the rate of reduction of the 1 ,4-benzoquinonyl group is substantially slowed and nor are they too high such that a significant amount of reduction occurs outwith the hypoxic region of the tumour mass. According to this aspect of the present invention there is provided an anti -tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as defined hereinbefore wherein the reduction potential of the compound is in the range, for example, of -300 to -600 mV, preferably in the range -300 to -500 mV, more preferably in the range, for example, -300 to -475 mV. The methodology used to measure the reduction potentials of the compounds of the invention is described in detail hereinafter. An anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, may be prepared by any process known to be applicable to the preparation of chemically related compounds. According to a further feature of the invention there are provided the processes defined hereinafter for the preparation of an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, in which, unless otherwise stated, each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , m, X, Y 1 and Y 2 have any of the meanings defined hereinbefore. Necessary starting materials may be obtained by standard procedures of organic chemistry. The preparation of such starting materials is described hereinafter within the accompanying Examples. Alternative necessary starting materials are obtainable by analogous procedures to those illustrated and such analogous procedures are achievable using the ordinary skill of an organic chemist. According to this aspect of the invention there is provided a process for the preparation of an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as defined hereinbefore which comprises :- the reaction of an acid of the formula II OH II - 14 - wherein each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 has any of the meanings defined hereinbefore, or a reactive derivative thereof, with a compound of the formula III ( R 8 )r πι wherein each of X, R 8 , m, Y 1 and Y 2 has any of the meanings defined hereinbefore. A suitable reactive derivative of an acid of the formula II is, for example, an acyl halide, for example an acyl chloride formed by the reaction of the acid and an inorganic acid chloride, for example thionyl chloride; a mixed anhydride, for example an anhydride formed by the reaction of the acid and a chloroformate such as isobutyl chloroformate; an active ester, for example an ester formed by the reaction of the acid and a phenol such as pentafluorophenol, an ester such as pentafluorophenyl trifluoroacetate, an alcohol such as 1-hydroxybenzotriazole or a uranium salt such as 2-(l-benzotriazolyl)-l,l,3,3- tetramethyluronium hexafluorophosphate(V); an acyl azide, for example an azide formed by the reaction of the acid and an azide such as diphenylphosphoryl azide; an acyl cyanide, for example a cyanide formed by the reaction of an acid and a cyanide such as diethylphosphoryl cyanide; or the product of the reaction of the acid and a carbodiimide such as N,N'-dicyclohexylcarbodiimide or 1 -(3-dimethylaminopropyl)-3-ethylcarbodiimide. The reaction is preferably carried out in the presence of a suitable base such as, for example, an alkali or alkaline earth metal carbonate, alkoxide, hydroxide or hydride, for example sodium carbonate, potassium carbonate, sodium hydride or potassium hydride, or an organometallic base such as an alkyl-lithium, for example lithium di-isopropylamide, or, for example, an organic amine base such as, for example, pyridine, 2,6-lutidine, collidine, 4-dimethylaminopyridine, triethylamine, moφholine or diazabicyclo-[5.4.0]undec-7-ene. The reaction is also preferably carried out in a suitable inert solvent or diluent, for example methylene chloride, acetonitrile, tetrahydrofuran, 1 ,2-dimethoxyethane, N,N-dimefhylformamide, N,N-dimefhylacetamide, N-methylpyrrolidin-2-one, dimethylsulphoxide or acetone, and at a temperature in the range, for example, -78° to 150°C, conveniently at or near ambient temperature. - 15 - Optionally, when there is an amino, alkylamino, hydroxy or carboxy group in R 1 , R 2 , R 3 or R 8 , any such group may be protected by a conventional protecting group which may be removed when so desired by conventional means. A suitable protecting group for an amino or alkylamino group is, for example, an acyl group, for example an alkanoyl group such as acetyl, an alkoxycarbonyl group, for example a methoxycarbonyl, ethoxycarbonyl or tert-butoxycarbonyl group, an arylmethoxycarbonyl group, for example benzyloxycarbonyl, or an aroyl group, for example benzoyl. The deprotection conditions for the above protecting groups necessarily vary with the choice of protecting groups. Thus, for example, an acyl group such as an alkanoyl or alkoxycarbonyl group or an aroyl group may be removed, for example, by hydroylsis with a suitable base such as an alkali metal hydroxide, for example lithium or sodium hydroxide. Alternatively an acyl group such as a tert-butoxycarbonyl group may be removed, for example, by treatment with a suitable acid such as hydrochloric, sulphuric or phosphoric acid or trifluoroacetic acid and an arylmethoxycarbonyl group such as a benzyloxycarbonyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon, or by treatment with a Lewis acid for example boron tris(trifluoroacetate). A suitable alternative protecting group for a primary amino group is, for example, a phthaloyl group which may be removed by treatment with an alkylamine, for example dimethylaminopropylamine, or with hydrazine. A suitable protecting group for a hydroxy group is, for example, an acyl group, for example benzoyl, or an arylmethyl group, for example benzyl. The deprotection conditions for the above protecting groups will necessarily vary with the choice of protecting group. Thus, for example, an acyl group such as an alkanoyl or an aroyl group may be removed, for example, by hydrolysis with a suitable base such as an alkali metal hydroxide, for example lithium or sodium hydroxide. Alternatively an arylmethyl group such as a benzyl group may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon. A suitable protecting group for a carboxy group is, for example, an esterifying group, for example a methyl or an ethyl group which may be removed, for example, by hydrolysis with a base such as sodium hydroxide, or for example a tert-butyl group which may be removed, for example, by treatment with an acid, for example an organic acid such as trifluoroacetic acid, or for example, a benzyl group which may be removed, for example, by hydrogenation over a catalyst such as palladium-on-carbon. - 16 - The starting materials of the formula II and III are either commercially available or they may be prepared by standard procedures of organic chemistry. For example, the starting material of the formula II may be prepared by the hydrolysis of a 3,4-dihydrocoumarin of the formula IN. IV wherein each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 has any of the meanings defined hereinbefore, and the subsequent oxidation of the hydroquinone so formed. Suitable conditions for the hydrolysis and subsequent oxidation reactions for use in the preparation of the starting material of the formula II from a 3,4-dihydrocoumarin of the formula IV include, for example, any agents known in the art for such conversions. For example, the hydrolysis step may be carried out using a suitable base such as an alkali metal hydroxide, for example lithium or sodium hydroxide. If the hydrolysis step is carried out under an atmosphere of air or oxygen, oxidation of the hydroquinone occurs spontaneously. Alternatively the 3,4-dihydrocoumarin may be hydrolysed with water in the presence of an oxidising agent such as an iron halide, for example ferric chloride. In general the reaction is carried out in a suitable inert solvent or diluent, for example water, acetonitrile, Ν,Ν-dimethylformamide, methanol or ethanol, and at a temperature in the range, for example, 15° to 100°C, conveniently in the range, for example, 20° to 80°C. When a pharmaceutically-acceptable salt of a compound of the formula I is required, it may be obtained, for example, by reaction of said compound with a suitable acid or base using a conventional procedure. When an optically active form of a compound of the formula I is required, it may be obtained by earring out the aforesaid process using an optically active starting material, or by resolution of a racemic form of said compound using a conventional procedure. As stated hereinbefore the compounds of the formula I of the present invention possess anti-tumour activity, in particular activity by virtue of release of a cytotoxic agent in a hypoxic region of a tumour mass. The cytotoxic and anti-tumour activities of the compounds - 17 - of the invention may be assessed using, for example, one or more of the procedures set out below. (a) An in vitro assay which determines the ability of a test compound to cause cross- linking of a piece of DNA using a procedure adapted from the work of Sunter et al. , 5 Biochemical Pharmacology. 1992, 44, 59-64. The effects of test compounds were assessed by their ability to cross-link the DNA strands of a linearised P 32 labelled plasmid. Cross linking was detected by denaturing the DNA and measuring its mobility by gel electrophoresis on a neutral agarose gel. Double- and single-stranded pieces of DNA were separated by molecular size. The detailed methodology was as follows :- 10 PBR322 circular plasmid DNA (Pharmacia Biotech., St. Albans, Hertfordshire, UK) was linearised using Hind III restriction endonuclease and after end-dephosphorylation with alkaline phophatase, T4 polynucleotide kinase (Biolabs, Hitchin, Hertfordshire, UK) was used to add [γ- 32 P]ATP to the 5' ends of the DNA. Each test compound was dissolved in DMSO and added to a mixture of the plasmid 15 DNA (12.5 ng per assay) and a pH7.2 buffer comprising 25mM triethanolamine buffer and ImM EDTA. Treatments were either carried out under aerobic conditions (solutions gassed with air) or hypoxic conditions (solutions degassed by overnight bubbling with nitrogen and then maintained in an anaerobic chamber with the addition of a 3- to 10-fold excess of the reducing agent sodium dithionite) for up to 3 hours at a temperature in the range of 30° to 20 37°C. The reaction was stopped by the addition of an ice-cold mixture of 0.6M sodium acetate, 20mM EDTA and 100 μg/mg tRNA (Sigma, Poole, Dorset, UK). The DNA was precipitated by the addition of 95% ethanol, isolated and stored at -20°C overnight. Each plasmid DNA sample was re-suspended in a mixture of 30% aqueous DMSO and ImM EDTA and denatured by heating to 90°C for 2 minutes. The denatured DNA sample 25 was mixed with a pH8.0 buffer comprising 20% Ficoll 400 (Sigma, Poole, Dorset, UK), 0. IM EDTA and 0.25% bromophenol blue and applied to an electrophoresis gel (0.8%> agarose in pH8.2 tris-borate-EDTA buffer). Each gel was polarised at 30 volts (3 v/cm) for 3 hours or until the bromophenol dye reached the end of the gel. The gel was dried and the single- and double-stranded DNA was quantified using a phosphoimager (Molecular Dynamics Limited, 30 Kemsing, England). Standard samples of single- and double-stranded DNA were run on each gel and the percentage of double-stranded DNA in the test sample was calculated. Dose - 18 - response curves were constructed using various concentrations of each test compound to allow the determination of the test dose that produced 50% of double-stranded DNA. (b) An in vitro assay which determines the ability of a test compound to inhibit the growth of T18 murine breast cancer cells in cell culture under oxic conditions. The cells were grown in monolayer in 96 well plates and treated with compounds for 2 hours under an atmosphere of 90%) air and 10%> CO 2 . The cells were then grown on for 6 days at which time the extent of proliferation was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) endpoint. The test is similar to that described in J. Immunological Methods. 1983, 65, 55-63. The detailed methodology was as follows :- Tl 8 murine breast tumour cells (derived from a spontaneous mammary tumour in the Balb/c mouse colony at Zeneca Pharmaceuticals, Mereside, Macclesfield, UK) were harvested from an exponentially growing monolayer culture. The cells were counted, diluted in RPMI 1640 culture medium (Gibco BRL, Life Technologies, Paisley, UK; supplemented with 15% foetal calf serum, glutamine, pyruvate, penicillin and streptomycin), and transferred to 96 well plates at 500 cells per 50 μl per well. The cells were incubated at 37°C in a CO 2 incubator (i.e. under an atmosphere of 90%) air and 10% CO 2 ) for 2 days. Further fresh culture medium (125 μl) was added to each well. Each test compound was dissolved in DMSO and diluted to the required test concentration in water. A 25 μl portion of each test solution was added to each well. The plates were then returned to the incubator for 2 hours. At the end of this time, the supernatant culture medium containing the test compound was removed. The residual cells in each well were washed once with 200 μl of phosphate buffered saline (PBS A) and fresh culture medium (200 μl) was added. The plates were then returned to the CO 2 incubator and grown on for 6 days. A 50 μl portion of MTT (5 mg/ml) was added to each well and the plates were incubated for a further 4 hours, during which time viable cells converted MTT into an insoluble, intracellular deposit of blue formazan, the extent of conversion being proportional to the number of viable cells in the well. The supernatant culture medium containing excess MTT was removed and DMSO (100 μl) was added to solubilise the formazan, the concentration of which was measured by determining the optical density at 540nM. Various concentrations of each test compound were assayed to allow the determination of the concentration causing 50% inhibition (IC 50 ). - 19 - (c) An in vitro assay which determines the ability of a test compound to inhibit the growth in an oxygenated culture medium of spheroidal aggregates (-400 microns in diameter) of EMT6 murine breast cancer cells. As the oxygen diffusion distance through tissue is approximately 120-150 microns, such spheroids have a chronically hypoxic central population 5 of cells and a well oxygenated outer layer of cells. The multicellular spheroids were treated with test compounds for 2 hours as a well oxygenated suspension culture. The spheroids were subsequently washed free of test compound and selected spheroids were transferred to static culture so that the effect of treatment on volume growth could be measured. The detailed methodology was as follows :- 10 EMT6 murine breast cells (obtained from P.R. Twentyman, MRC Oncology and Radiotherapeutics Unit, Cambridge, UK) were harvested from exponentially growing monolayer cultures and approximately lxl 0 6 cells were used to inoculate a 500 ml spinner culture vessel containing Eagles minimal essential medium (200 ml; supplemented with 10%> foetal calf serum, glutamate, non-essential amino acids, penicillin and streptomycin). The 15 spinner vessel was gassed with a mixture of 90% air and 10% CO 2 , sealed, and incubated at 37°C for 4-5 days with slow stirring (50 φm for the first 24 hours and thereafter 40 φm). The cells aggregated into clumps which grew into tight spheroids with a mean diameter of about 400 microns. Aliquots (5 ml) of spheroid-containing culture medium were transferred to conical flasks (siliconised, 25 ml) which were gassed with a mixture of 90%> air and 10%) 20 CO 2 and sealed with a rubber stopper. The flasks were placed in an orbital shaker in a CO 2 incubator at 37°C and gently agitated for at least 15 minutes. Each test compound was dissolved in DMSO and diluted to the required test concentration in water. A 200 μl portion of each test solution was added by syringe to each sealed flask. The resultant mixtures were incubated for 2 hours, each transferred to a centrifuge tube and allowed to settle. The 25 supernatant culture medium containing the test compound was decanted and fresh culture medium (5 ml) was added to each tube The contents of each tube were then transferred to plastic petri dishes (35 mm diameter) and observed under a dissecting microscope with a calibrated graticule. From each treatment group, 6 spheroids of uniform shape and approximately 400 micron diameter were selected and transferred to separate wells in a 30 24-well plate, to each well of which had been added 1% agar (0.3 ml; to create a base layer that prevents spheroid attachment) and 1 ml of culture medium. The area of each spheroid - 20 - was measured using an image analyser and the 24-well plates were transferred to a CO 2 incubator at 37°C. The spheroids were then re-measured every 2-3 days for up to 21 days, with fresh culture medium (250 μl) being added to each well every 3 days. The spheroid volumes were calculated from the area measurements (assuming spherical shape) and volume growth curves were constructed from which the effect of treatment could be assessed. The test dose which caused stasis (no growth or regression of spheroid size) during a period of 2-3 weeks was noted. (d) An in vivo assay in a group of Balb/c mice which determines the ability of a test compound to delay the growth of T18 murine breast tumours. The detailed methodology was as follows :- T18 murine breast tumour tissue was routinely maintained by animal to animal passage. To prepare a batch of tumours for an experiment, tumour tissue was removed from several donor Balb/c mice and placed in saline. Outer tissue was removed and healthy looking regions of tumour were cut into approximately 1 mm 3 pieces and implanted subcutaneously by trocar into the left flanks of anaesthetised female Balb/c mice. After 2-3 weeks, most of the implants had grown to approximately 8 mm in diameter. The animals were placed randomly into groups of 6-7, rejecting any with very large, or small, tumours. Each test compound was dissolved in DMSO and diluted with Cremophor EL followed by saline, to give a 1 : 1 :3 mixture of DMSO, Cremophor EL and saline. Each test compound was administered by the intraperitoneal route as a single bolus dose (0.1 ml per 10 g body weight of each animal). Control animals received vehicle alone. All mice were weighed daily and the dimensions (length and width) of each tumour were measured every 2-3 days using vernier calipers. The measurements were used to estimate the volume of each tumour assuming a prolate elipsoid shape (volume = π/6 x Length x Width 2 ). Growth curves were constructed and the effect of treatment was assessed using a growth delay endpoint. Although the pharmacological properties of the compounds of the formula I vary with structural change as expected, in general activity possessed by compounds of the formula I may be demonstrated at the following concentrations or doses in one or more of the above test procedures:- Test (a):- under hypoxic conditions, IC 50 in the range, for example l-20μM; under oxic conditions, IC 50 generally greater than three-fold higher; - 21 - Test (b):- IC 50 in the range, for example, l-30μM; Test (c):- for stasis; ED 50 in the range, for example, l-16μM; and Test (d):- a dose in the range, for example, 30-100 mg/kg intraperitoneally gives a growth delay of, for example, 4 to 15 days. Thus, by way of example, the compound of Example 1 hereinafter has a stasis ED 50 dose of approximately 4μM in Test (c) and a growth delay of approximately 9 days from a single bolus dose of 20 mg/kg intraperitoneally in Test (d). As stated hereinbefore it is an object of one aspect of the present invention to provide double-prodrug compounds which rapidly release a cytotoxic drug when they encounter a region of low oxygen tension such as in the hypoxic region of a solid tumour. This property may be assessed, for example, using the following test procedure: Each test compound was dissolved in acetonitrile (approximately 2 mg/ml) and diluted in pH7.4 phosphate buffer (if solubility difficulties were encountered, the minimum additional quantity of acetonitrile was added) to give a test concentration of approximately 5 x 10 "5 M. Each test solution was thoroughly degassed under helium and warmed to a thermostatically- controlled reaction temperature of 37°C. A sodium dithionite (Na 2 S 2 O 4 ) solution (100 μl of a 100 mg/ml solution in degassed water) was added to a portion (1.4 ml) of each test solution. Aliquots of the reaction solution were taken at regular intervals and analysed by high performance liquid chromatography (HPLC) for release of the cytotoxic drug moiety and formation of the appropriate 3,4-dihydrocoumarin. Typical HPLC conditions involved use of a S5ODS1 reversed-phase column (250 by 4.6 mm, packed with 5 micron octadecylsilane- coated Spherisorb particles from Jones Chromatography, Hengoed, Glamorgan, UK) using a 75:25:0.1 mixture of acetonitrile, water and trifluoroacetic acid as eluent and a flow rate of 1.5 ml per minute. In general, it was found that, under reductive conditions, the compounds of the invention of the formula I rapidly released the cytotoxic drug moiety with a t^ of less than 2 hours, preferably less than 1 hour, more preferably less than 20 minutes and especially less than 10 minutes. In general, for many of the compounds of the invention of the formula I wherein X is an alkylimino group, it was found that reductive conditions caused the release of the cytotoxic drug moiety so rapidly that the hydroquinone product of the reduction step could - 22 - not be detected. In such instances the t^* of cytotoxic drug release was substantially less than 10 minutes. As stated hereinbefore it is a further object of another aspect of the present invention to provide double-prodrug compounds which possess a balanced reduction potential e. a reduction potential that is not so high that a significant proportion of reduction occurs outwith areas of low oxygen tension, nor so low that a significant proportion of reduction does not occur even in an area of low oxygen tension. The reduction potential of the compounds of the present invention may be assessed, for example, using the following test procedure :- Each test compound (2 mg) was dissolved in DMF and cyclic voltammetry was carried out using a Luggin Cell fitted with platinum working and secondary electrodes and a standard saturated calomel reference electrode (SCE) and tetra-butylammonium bromide (0.1 moles per litre in DMF) as electrolyte (see, for example, G.A. Mabbott, J Chem. Ed.. 1983, 60, 697 and J.G. Dick et ah, Metrohm Monographs, Electrode Reaction Kinetics determined by Cyclic Sweep Triangular Wave Voltammetry, 1983). In a typical experiment, for example, the potential of the working electrode, controlled relative to the reference electrode, was scanned at 100 mV per second from the starting potential to the switching potential and back to the initial potential. The current produced was plotted as a function of potential and the cathodic peak potential (Epc) was taken as a measure of the reduction potential in DMF solution. An Eaq value for each test compound in aqueous solution was determined by way of a calibration plot based on measured Epc values of DMF solutions of a group of standard quinone compounds for which the pH7 Eaq values in aqueous solutions were known (P. Wardman, J. Phys. Chem. Ref. Data, 1989 18, 1637). The calibration plot allowed the following equation to be determined :- Eaq (V) = 1.23 Epc (V) + 0.62 In general, the compounds of the invention of the formula I have a calculated Eaq value in the range, for example, -300 to -600 mV, preferably in the range, for example, -300 to -500 mV, more preferably in the range, for example, -300 to -475 mV. According to a further aspect of the invention there is provided a pharmaceutical composition which comprises an anti-tumour agent of the formula I, or a pharmaceutically- acceptable salt thereof, as defined hereinbefore in association with a pharmaceutically- acceptable diluent or carrier. - 23 - The composition may be in a form suitable for oral administration, for example as a tablet or capsule, for parental injection (including intraveous, subcutaneous, intramuscular, intravascular or infusion) as a sterile solution, suspension or emulsion, for topical administration as an ointment or cream or for rectal administration as a suppository. In general the above compositions may be prepared in a conventional manner using conventional excipients. The anti-tumour agent will normally be administered to a warm-blooded animal at a unit dose within the range 50-10000 mg per square meter body area of the animal, Le. approximately 1-200 mg/kg, and this normally provides a therapeutically-effective dose. A unit dose form such as a tablet or capsule will usually contain, for example 1-250 mg of active ingredient. Preferably a daily dose in the range of 1-50 mg/kg is employed. However the daily dose will necessarily by varied depending upon the host treated, the particular route of administration, and the severity of the illness being treated. Accordingly the optimum dosage may be determined by the practitioner who is treating any particular patient. According to a further aspect of the present invention there is provided an anti-tumour agent of the formula I as defined hereinbefore for use in a method of treatment of the human or animal body by therapy. We have found that the compounds of the present invention possess anti-poliferative properties such as anti-tumour properties which are believed to arise from the hypoxia- selective release of a cytotoxic agent from the double-prodrug of the formula I. Accordingly the compounds of the present invention are expected to be useful in the treatment of tumours of sufficient size to possess hypoxic regions such that reduction of the 1 ,4-benzoquinonyl moiety occurs and the cytotoxic moiety is thereafter rapidly released. It will be appreciated by the person skilled in the art that the above-mentioned anti- proliferative activity of the compounds of the present invention against spheroidal aggregates of EMT6 murine breast cancer cells demonstrates not only that the compounds of the present invention are hypoxia-selective prodrugs of a cytotoxic agent but also that the cytotoxic agent, once released, can diffuse into nearby oxic regions of the celluar aggregate to continue the destruction of cancer cells. Hence sufficient cytotoxic activity can be released to cause stasis of the growth of the spheroidal aggregate of cancer cells. - 24 - Thus according to this aspect of the invention there is provided the use of an anti- tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as defined hereinbefore in the manufacture of a medicament for use in the production of an anti- proliferative effect in a warm-blooded animal, such as man. According to a further feature of this aspect of the invention there is provided a method for producing an anti-proliferative effect in a warm-blooded animal, such as man, in need of such treatment which comprises administering to said animal an effective amount of an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as defined hereinbefore. As stated above the size of the dose required for the therapeutic or prophylactic treatment of a particular proliferative disease will necessarily by varied depending on the host treated, the route of administration and the severity of the illness being treated. A unit dose in the range, for example, 1-200 mg/kg, preferably 1-100 mg/kg, more preferably 1-10 mg/kg is envisaged. The anti-tumour effect of the compounds of the present invention may be applied as a sole therapy or may involve, in addition, one or more other substances and/or treatments. Such conjoint treatment may be achieved by way of the simultaneous, sequential or separate administration of the individual components of the treatment. In the field of medical oncology it is normal practice to use a combination of different forms of treatment to treat each patient with cancer such as a combination of surgery, radiotherapy and/or chemotherapy. In particular, it is known that irradiation or treatment with antiangiogenic and/or vascular permeability reducing agents can enhance the amount of hypoxic tissue within a tumour. Therefore the effectiveness of the compounds of the present invention is expected to be improved by conjoint treatment with radiotherapy and/or with an antiangiogenic agent. In general such chemotherapy may cover three main categories of therapeutic agent:- (i) antiangiogenic agents including those believed to act by way of inhibition of vascular endothelial growth factor (VEGF) such as the compounds disclosed in International Patent Applications WO 97/22596, WO 97/30035 and WO 97/32856 and antiangiogenic agents that work by different mechanisms, for example linomide, inhibitors of integrin αvβ3 function, angiostatin, razoxin and thalidomide; - 25 - (ii) cytostatic agents such as antioestrogens (for example tamoxifen, toremifene, raloxifene, droloxifene and iodoxyfene), progestogens (for example megestrol acetate), aromatase inhibitors (for example anastrozole, letrazole, vorazole and exemestane), antiprogestogens, antiandrogens (for example flutamide, nilutamide, bicalutamide and cyproterone acetate), LHRH agonists and antagonists (for example goserelin acetate, luprolide and buserelin), inhibitors of testosterone 5α-dihydroreductase (for example finasteride), anti- invasion agents (for example metalloproteinase inhibitors like marimastat and inhibitors of urokinase plasminogen activator receptor function) and inhibitors of growth factors (for example inhibitors of epidermal growth factor (EGF), fibroblast growth factor (FGF), platelet derived growth factor and hepatocyte growth factor such as EGF receptor tyrosine kinase inhibitors and serine/threonine kinase inhibitors); and (iii) antiproliferative, antineoplastic drugs and combinations thereof, as used in medical oncology, such as antimetabolites (for example antifolates like methotrexate and raltitrexed, fluoropyrimidines like 5-fluorouracil, purine and adenosine analogues and cytosine arabinoside); antitumour antibiotics (for example the bleomycins and anthracyclines like doxorubicin, daunomycin, epirubicin and idarubicin, mitomycin-C, dactinomycin and mithramycin); platinum derivatives (for example cisplatin and carboplatin); alkylating agents (for example nitrogen mustard, melphalan, chlorambucil, busulphan, cyclophosphamide, ifosfamide, nitrosoureas and thiotepa); antimitotic agents (for example vinca alkaloids like vincrisitine and taxoids like taxol and taxotere); topoisomerase inhibitors (for example epipodophyllotoxins like etoposide and teniposide, amsacrine and topotecan). The invention will now be illustrated in the following non-limiting Examples in which, unless otherwise stated: - (i) evaporations were carried out by rotary evaporation in vacuo and work-up procedures were carried out after removal of residual solids such as drying agents by filtration; (ii) unless otherwise stated, operations were carried out at ambient temperature, that is in the range 18-25°C and under an atmosphere of an inert gas such as argon; (iii) column chromatography (by the flash procedure) and medium pressure liquid chromatography (MPLC) were performed on Merck Kieselgel silica (Art. 9385) or Merck - 26 - Lichroprep RP-18 (Art. 9303) reversed-phase silica obtained from E. Merck, Darmstadt, Germany; (iv) yields are given for illustration only and are not necessarily the maximum attainable; (v) melting points were determined using a Mettler SP62 automatic melting point apparatus, an oil-bath apparatus or a Koffler hot plate aparatus. (vi) the structures of the end-products of the formula I were confirmed by nuclear (generally proton) magnetic resonance (NMR) and mass spectral techniques; proton magnetic resonance chemical shift values were measured on the delta scale and peak mutiplicities are shown as follows: s, singlet; d, doublet; t, triplet; m, multiplet, unless otherwise stated end- products of the formula I were dissolved in CD 3 SOCD 3 for the determination of NMR values; (vii) intermediates were not generally fully characterised and purity was assessed by thin layer chromatography (TLC), infra-red (IR) or NMR analysis; (viii) the following abbreviation have been used:- DMF N,N-dimethylformamide; DMA N,N-dimethylacetamide; DMSO dimethylsulphoxide; EDTA ethylenediaminetetracetic acid. - 27 - Example 1 l-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (0.185 g) was added to a stirred mixture of 3-(5-methyl-3-propyl-l,4-benzoquinon-2-yl)-3-methylbutyric acid (0.17 g), 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride (Chem. Abs., 73. 5 120373 and J. Chem. Soc. Perkin Trans. I. 1973, 2397-2402; 0.17 g), 1-hydroxybenzotriazole (0.087 g), triethylamine (0.277 ml) and methylene chloride (7 ml). The resultant mixture was stirred at ambient temperature for 16 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 4:1 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 0 N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(5-methyl-3-propyl-l ,4-benzoquinon-2-yl)- 3 -methyl-N-methy lbutyramide (0.105 g); NMR Spectrum: (CDC1 3 ) 0.97 (t, 3H), 1.32 (s, 6H), 1.46 (m, 2H), 1.98 (s, 3H), 2.52 (m, 2H), 2.78 (m, 2H), 3.12 (s, 3H), 3.67 (t, 4H), 3.77 (t, 4H), 6.52 (s, IH), 6.68 (d, 2H), 7.03 (d, 2H); Mass Spectrum: (M + Na + ) 519, 517, 515. 5 The 3 -(5 -methyl-3 -propyl- 1 ,4-benzoquinon-2-yl)-3 -methy lbutyric acid used as a starting material was obtained as follows :- A mixture of 6-hydroxy-4,4,7-trimethyl-3,4-dihydrocoumarin (J. Amer. Chem. Soc. 1983, 105, 2752-2760; 10 g), allyl bromide (12.6 ml), potassium carbonate (20 g) and DMF (100 ml) was stirred at ambient temperature for 2 hours. The mixture was partitioned between 0 diethyl ether and water. The organic phase was washed with a saturated aqueous chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 6-allyloxy-4,4,7-trimethyl- 3,4-dihydrocoumarin (12 g); NMR Spectrum: (CDC1 3 ) 1.32 (s, 6H), 2.22 (s, 3H), 2.58 (s, 2H), 4.53 (m, 2H), 5.35 (m, 2H), 6.05 (m, 2H), 6.71 (s, IH), 6.85 (s, IH). A mixture of a portion (6 g) of the material so obtained and N,N-dimethylaniline 5 (96 ml) was stirred and heated to 200°C for 5 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 4:1 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 5-allyl-6- hydroxy-4,4,7-trimethyl-3,4-dihydrocoumarin (3.7 g); NMR Spectrum: (CDCL,) 1.42 (s, 6H), 2.22 (s, 3H), 2.56 (s, 2H), 3.58 (m, 2H), 4.87 (s, IH), 5.2 (m, 2H), 6,08 (m, IH), 6.8 (s, IH). 0 A mixture of a portion (1 g) of the material so obtained, 10% palladium-on-charcoal catalyst (0.15 g) and ethanol (60 ml) was stirred under 3 atmospheres pressure of hydrogen for - 28 - 30 minutes. The mixture was filtered and the filtrate was evaporated to give 6-hydroxy- 5-propyl-4,4,7-trimethyl-3,4-dihydrocoumarin (1 g); NMR Spectrum: (CDC1 3 ) 1.06 (t, 3H), 1.46 (s, 6H), 1.66 (m, 2H), 2.21 (s, 3H), 2.56 (s, 2H), 2.72 (m, 2H), 4.57 (s, IH), 6.72 (s, IH). 5 A solution of the material so obtained in acetonitrile (12 ml) was stirred and heated to reflux. A solution of ferric chloride hexahydrate (2.18 g) in a mixture of acetonitrile (10 ml) and water (10 ml) was added portionwise during 2 hours. The mixture was cooled to ambient temperature and partitioned between diethyl ether and a 5% aqueous sodium bicarbonate solution. The aqueous phase was acidified by the addition of 2N aqueous 10 hydrochloric acid and extracted with diethyl ether. The resultant organic phase was dried (MgSO 4 ) and evaporated. There was thus obtained 3-(5-methyl-3-propyl-l,4-benzoquinon- 2-yl)-3-methylbutyric acid as an oil (0.335 g); NMR Spectrum: (CDC1 3 ) 0.99 (t, 3H), 1.42 (m, 2H), 1.46 (s, 6H), 1.97 (s, 3H), 2.6 (m, 2H), 3.03 (s, 2H), 6.45 (s, IH). 15 Example 2 A mixture of 3-(3-allyl-2,5-dimethyl-l,4-benzoquinonyl)-3-methylbutyric acid (1.38 g), 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride (1.6 g), 2-(l-benzotriazolyl)-l,l,3,3-tetramethyluronium hexafluorophosphate(V) (1.99 g), triethylamine (1.52 g) and acetonitrile (30 ml) was stirred at ambient temperature for 20 18 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 17:3 mixture of hexane and ethyl acetate as eluent. There was thus obtained 3-(3-allyl-2,5-dimethyl-l,4-benzoquinonyl)-N-{4-[bis(2-chloroethyl)amino]phenyl}- 3-methyl-N-methylbutyramide (0.88 g); 25 NMR Spectrum: (CDC1 3 ) 1.3 (s, 6H), 2.0 (s, 3H), 2.1 (s, 3H), 2.73 (s, 2H), 3.1 (s, 3H), 3.2 (d, 2H), 3.62-3.82 (m, 8H), 5.04 (m, 2H), 5.8 (m, IH), 6.65-7.1 (m, 4H); Mass Spectrum: (M + H + ) 509, 507, 505. The 3-(3-allyl-2,5-dimethyl-l,4-benzoquinonyl)-3-methylbutyric acid used as a starting material was obtained as follows :- 30 Allyl bromide (8.45 g) was added to a mixture of 6-hydroxy-4,4,5,8-tetramethyl- 3,4-dihydrocoumarin (J. Org. Chem.. 1989, 54, 3303-3310; 5 g), potassium carbonate (9.4 g) - 29 - and DMF (50 ml). The resultant mixture was stirred at ambient temperature for 2 hours. The mixture was partitioned between diethyl ether and water. The organic phase was washed with water and with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 6-allyloxy-4,4,5,8-tetramethyl-3,4-dihydrocoumarin (5.2 g); NMR Spectrum: (CDC1 3 ) 1.48 (s, 6H), 2.28 (s, 3H), 2.34 (s, 3H), 2.57 (s, 2H), 4.5 (m, 2H), 5.36 (m, 2H), 6.07 (m, IH), 6.63 (s, IH). A mixture of a portion (3 g) of the material so obtained and N,N-diethylaniline (40 ml) was stirred and heated to 180°C for 18 hours. The mixture was cooled to ambient temperature, acidified by the addition of 5N aqueous hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with water and with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 7-allyl-6-hydroxy- 4,4,5,8-tetramethyl-3,4-dihydrocoumarin (2.9 g); NMR Spectrum: (CDC1 3 ) 1.48 (s, 6H), 2.24 (s, 3H), 2.37 (s, 3H), 2.58 (s, 2H), 3.44 (d, 2H), 4.84 (broad s, IH), 5.12 (m, 2H), 5.98 (m, IH). A mixture of a portion (2.6 g) of the material so obtained, IN aqueous sodium hydroxide solution (17.5 ml) and acetonitrile (50 ml) was stirred at ambient temperature in air for 4 days. The mixture was acidified by the addition of 5N aqueous hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 3-(3-allyl- 2,5-dimethyl-l ,4-benzoquinonyl)-3-methylbutyric acid as an oil (2.7 g); NMR Spectrum: (CDC1 3 ) 1.44 (s, 6H), 1.95 (s, 3H), 2.14 (s, 3H), 3.0 (s, 2H), 3.19 (d, 2H), 5.0 (m, 2H), 5.77 (m, IH). Example 3 A mixture of 3-(2,5-dimethyl-3-propyl- 1 ,4-benzoquinonyl)-3-methylbutyric acid (0.65 g), 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride (0.716 g), 2-(l-benzotriazolyl)-l,l,3,4-tetramethyluronium hexafluorophosphate(V) (0.935 g), triethylamine (0.709 g) and acetonitrile (15 ml) was stirred at ambient temperature for 40 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 17:3 mixture of hexane and ethyl acetate as eluent. There - 30 - was thus obtained N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,5-dimethyl-3-propyl- l,4-benzoquinonyl)-3-methyl-N-methy lbutyramide as a gum (0.464 g); NMR Spectrum: (CDC1 3 ) 0.97 (t, 3H), 1.32 (s, 6H), 1.47 (m, 2H), 2.01 (s, 3H), 2.1 (s, 3H), 2.4 (t, 2H), 2.75 (s, 2H), 3.1 (s, 3H), 3.64-3.82 (m, 8H), 6.7 (d, 2H), 7.06 (d, 2H); Mass Spectrum: (M + HO 511. 509. 507. The 3-(2,5-dimethyl-3-propyl-l,4-benzoquinonyl)-3-methylbutyric acid used as a starting material was obtained as follows :- A mixture of 7-allyl-6-hydroxy-4,4,5,8-tetramethyl-3,4-dihydrocoumarin (3 g), 10%) palladium-on-charcoal catalyst (0.5 g) and methanol (75 ml) was stirred under an atmosphere of hydrogen for one hour. The mixture was filtered and the filtrate was evaporated. There was thus obtained 6-hydroxy-4,4,5,8-tetramethyl-7-propyl- 3,4-dihydrocoumarin (1.06 g); NMR Spectrum: (CDC1 3 ) 1.03 (t, 3H), 1.46 (s, 6H), 1.57 (s, 2H), 2.23 (s, 3H), 2.36 (s, 3H), 2.6 (m, 4H), 4.58 (s, IH). A mixture of the material so obtained, IN aqueous sodium hydroxide solution (4.5 ml) and acetonitrile (15 ml) was stirred at ambient temperature in air for 4 days. The mixture was acidified by the addition of 2N aqueous hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 3-(2,5-dimethyl-3-propyl- l,4-benzoquinonyl)-3-methylbutyric acid as an oil (1.12 g); NMR Spectrum: (CDC1 3 ) 0.93 (t, 3H), 1.38-1.5 (m, 8H), 1.95 (s, 3H), 2.14 (s, 3H), 2.39 (m, 2H), 3.0 (s, 2H). Example 4 N,N'-dicyclohexylcarbodiimide (0.285 g) was added to a stirred mixture of 3-(2,5-dimethyl-l,4-benzoquinonyl)-3-methylbutyric acid (0.297 g), N-hydroxybenzotriazole (0.02 g) and methylene chloride (20 ml) which had been cooled in an ice-bath and the resultant mixture was stirred for 5 minutes. Triethylamine (0.267 g) and 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride (0.423 g) were added in turn and the reaction mixture was stirred at 0°C for 1.5 hours and then at ambient temperature for 4 hours. The mixture was evaporated and the residue was purified by column chromatography on alumina using increasingly polar mixtures of hexane and ethyl acetate as eluent. There was thus obtained N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,5-dimethyl- - 31 - l,4-benzoquinonyl)-3-methyl-N-methylbutyramide as a gum (0.028 g); NMR Spectrum: (CDC1 3 ) 1.3 (s, 6H), 2.05 (d, 3H), 2.08 (s, 3H), 2.75 (s, 2H), 3.1 (s, 3H), 3.65-3.85 (m, 8H), 6.4 (d, IH), 6.7 (d, 2H), 7.05 (d, 2H); Mass Spectrum: (M + H 465. The 3-(2,5-dimethyl-l,4-benzoquinonyl)-3-methylbutyric acid used as a starting material was obtained as follows :- A mixture of 6-hydroxy-4,4,5,8-tetramethyl-3,4-dihydrocoumarin (J. Org. Chem.. 1989, 54, 3303-3310; 2.2 g), IN aqueous sodium hydroxide solution (10 ml) and acetonitrile (20 ml) was stirred at ambient temperature in air for 2 days. The mixture was acidified by the addition of 5N aqueous hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with v/ater and with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained the required starting material (1.8 g) which was used without further purification; NMR Spectrum: (CDC1 3 ) 1 44 (s, 6H), 2.12 (s, 3H), 2.4 (s, 3H), 3.02 (d, 2H), 7.25 (s, IH). Example 5 A solution of l-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (0.126 g) in methylene chloride (2 ml) was added to a stirred mixture of 3-(3-allyl-5-methyl- 1 ,4-benzoquinon-2-yl)-3 -methy lbutyric acid (0.115 g), 4-[bis(2-chloroethyl)amino]- N-methylaniline dihydrochloride (0.146 g), triethylamine (0.13 ml) and methylene chloride (4 ml). The resultant mixture was stirred at ambient temperature for 16 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 4:1 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 3-(3-allyl-5-methyl-l,4-benzoquinon-2-yl)-N-{4-[bis(2-chloroethyl)amino]phenyl}- 3-methyl-N-methylbutyramide (0.06 g); NMR Spectrum: (CDC1 3 ) 1.32 (s, 6H), 1.99 (s, 3H), 2.78 (s, 2H), 3.12 (s, 3H), 3.43 (m, 2H), 3.67 (t, 4H), 3.77 (t, 4H), 5-5.8 (m, 3H), 5.87 (m, IH), 6.56 (s, IH), 6.68 (d, 2H), 7.04 (d, 2H). The 3-(3-allyl-5-methyl-l,4-benzoquinon-2-yl)-3-methylbutyric acid used as a starting material was obtained as follows :- A mixture of 6-hydroxy-4,4,7-trimethyl-3,4-dihydrocoumarin (J. Amer. Chem. Soc. 1983, 105, 2752-2760; 10 g), allyl bromide (12.6 ml), potassium carbonate (20 g) and DMF - 32 - (100 ml) was stirred at ambient temperature for 2 hours. The mixture was partitioned between diethyl ether and water. The organic phase was washed with a saturated aqueous chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 6-allyloxy-4,4,7-trimethyl- 3,4-dihydrocoumarin (12 g); NMR Spectrum: (CDC1 3 ) 1.32 (s, 6H), 2.22 (s, 3H), 2.58 (s, 2H), 4.53 (m, 2H), 5.35 (m, 2H), 6.05 (m, 2H), 6.71 (s, IH), 6.85 (s, IH). A mixture of a portion (6 g) of the material so obtained and N,N-dimethylaniline (96 ml) was stirred and heated to 200°C for 5 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 4:1 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 5-allyl-6- hydroxy-4,4,7-trimethyl-3,4-dihydrocoumarin (3.7 g); NMR Spectrum: (CDC1 3 ) 1.42 (s, 6H), 2.22 (s, 3H), 2.56 (s, 2H), 3.58 (m, 2H), 4.87 (s, IH), 5.2 (m, 2H), 6.08 (m, IH), 6.8 (s, IH). A solution of a portion (3 g) of the material so obtained in acetonitrile (30 ml) was stirred and heated to reflux. A solution of ferric chloride hexahydrate (13 g) in a mixture of acetonitrile (60 ml) and water (60 ml) was added portionwise during 2 hours. The mixture was cooled to ambient temperature and partitioned between diethyl ether and a 5% > aqueous sodium bicarbonate solution. The aqueous phase was acidified by the addition of 2N aqueous hydrochloric acid and extracted with diethyl ether. The resultant organic phase was washed with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained 3-(3-allyl-5-methyl-l,4-benzoquinon-2-yl)-3-methylbutyric acid (0.97 g); NMR Spectrum: (CDC1 3 ) 1.47 (s, 6H), 1.99 (s, 3H), 3.04 (s, 2H), 3.48 (m, 2H), 5.02 (m, 2H), 5.85 (m, IH), 6.49 (s, IH). Example 6 Using an analogous procedure to that described in Example 2, 3-(2,3,5-trimethyl- 1 ,4-benzoquinonyl)-3-methylbutyric acid was reacted with 4-[bis(2-chloroethyl)amino]- N-methylaniline dihydrochloride. The product was purified by column chromatography on silica using a 9:1 mixture of hexane and ethyl acetate as eluent. There was thus obtained N-{4-[bis(2-chloroethyl)amino]phenyl}-N-methyl-3-methyl-3-(2,3,5-trimethyl- 1 ,4-benzoquinonyl)butyramide as a solid in 30% yield; NMR Spectrum: (CDC1 3 ) 1.32 (s, 6H), 1.95 (s, 3H), 2.0 (s, 3H), 2.1 (s, 3H), 2.75 (s, 2H), 3.1 (s, 3H), 3.64-3.82 (m, 8H), 6.66-7.1 (m, 4H); - 33 - Mass Spectrum: (M + H 479. The 3-(2,3,5-trimethyl-l,4-benzoquinonyl)-3-methylbutyric acid used as a starting material was obtained as follows :- Methyl 3,3-dimethylacrylate (6 g) was added to a stirred mixture of 2,3,5-trimethylhydroquinone (7.6 g) and methanesulphonic acid (40 ml) which had been heated to 75 °C and the mixture was stirred at 75 °C for 1 hour. The mixture was poured onto a mixture of ice and water and the resultant mixture was extracted with ethyl acetate. The organic phase was washed with a 5%> aqueous sodium bicarbonate solution, dried (MgSO 4 ) and evaporated. There was thus obtained 6-hydroxy-4,4,5,7,8-pentamethyl- 3,4-dihydrocoumarin (10.7 g); NMR Spectrum: (CDC1 3 ) 1.48 (s, 6H), 2.18 (s, 3H), 2.22 (s, 3H), 2.37 (s, 3H), 2.55 (s, 2H), 4.6 (s, IH). A mixture of a portion (5.85 g) of the material so obtained, 0.5N aqueous sodium hydroxide solution (50 ml) and acetonitrile (100 ml) was stirred at ambient temperature in air for 18 hours. The mixture was acidified by the addition of 5N aqueous hydrochloric acid and extracted with ethyl acetate. The organic phase was washed with water and with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. There was thus obtained the required starting material (4.1 g) which was used without further purification; NMR Spectrum: (CDC1 3 ) 1 46 (s, 6H), 1.93 (s, 3H), 1.96 (s, 3H), 2.15 (s, 3H), 3.02 (s, 2H). Example 7 Using an analogous procedure to that described in Example 4, 3-(2,3-dimethoxy- 5-methyl-l,4-benzoquinonyl)-3-methylbutyric acid (J. Org. Chem.. 1989, 54, 3303-3310) was reacted with 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride. The product was purified by column chromatography on silica using increasingly polar mixtures of hexane and ethyl acetate as eluent. There was thus obtained N-{4-[bis(2-chloroethyl)amino]phenyl}- 3-(2,3-dimethoxy-5-methyl-l,4-benzoquinonyl)-3-methyl-N-methylbutyramide as an oil in 7% yield; NMR Spectrum: (CDC1 3 ) 1.31 (s, 6H), 2.1 (s, 3H), 2.78 (s, 2H), 3.11 (s, 3H), 3.67-3.82 (m, 8H), 3.95 (s, 3H), 3.99 (s, 3H), 6.72 (d, 2H), 7.06 (d, 2H); Mass Spectrum: (M + U + ) 511. - 34 - Example 8 Using an analogous procedure to that described in Example 5, 3-(5-allyl-2,3-dimethoxy-l,4-benzoquinonyl)-3-methylbutryric acid was reacted with 4-[bis(2-chloroethyl)amino]-N-methylaniline dihydrochloride. The product was purified by column chromatography on silica using increasingly polar mixtures of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 3-(5-allyl-2,3-dimethoxy- l,4-benzoquinonyl)-N-{4-[bis(2-chloroethyl)amino]phenyl}-3-methyl-N-methylbutyramide as an oil in 29%> yield; NMR Spectrum: (CDC1 3 ) 1.32 (s, 6H), 2.76 (s, 2H), 3.11 (s, 3H), 3.39 (d, 2H), 3.68 (t, 4H), 3.77 (t, 4H), 3.96 (s, 3H), 3.97 (s, 3H), 5.02-5.06 (m, 2H), 5.76-5.86 (m, IH), 6.69 (d, 2H), 7.04 (d, 2H); Mass Spectrum: (M + NaO 559, 561 & 563. The 3-(5-allyl-2,3-dimethoxy-l,4-benzoquinonyl)-3-methylbutryric acid used as a starting material was obtained as follows :- Sodium hydrosulphite (Na 2 S 2 O 4 , 26 g) was added portionwise to a stirred solution of 2,3-dimethoxy-l,4-benzoquinone (J. Med. Chem.. 1971, 14, 45; 5 g) in a mixture of methanol (50 ml) and water (100 ml). The resultant mixture was stirred at ambient temperature for 1 hour. The mixture was partitioned between ethyl acetate and water. The organic phase was dried (MgSO 4 ) and evaporated to give 2,3-dimethoxyhydroquinone (2 g); NMR Spectrum: (CD 3 SOCD 3 ) 3.71 (s, 6H), 6.37 (s, 2H), 8.47 (s, 2H). A mixture of 2,3-dimethoxyhydroquinone (3.6 g), methyl 3,3-dimethylacrylate (3.2 ml) and methanesulphonic acid (36 ml) was stirred and heated to 70°C for 2 hours. The mixture was poured onto a mixture of ice and water and the resultant mixture was extracted with ethyl acetate. The organic phase was washed with a 5%> aqueous sodium bicarbonate solution, dried (MgSO 4 ) and evaporated. The residue was purified by column chromatography on silica using a 3:2 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained 6-hydroxy-7,8-dimethoxy-4,4-dimethyl- 3,4-dihydrocoumarin (2.3 g); NMR Spectrum: (CDC1 3 ) 1.3 (s, 6H), 2.59 (s, 2H), 3.95 (s, 6H), 5.58 (s, IH), 6.64 (s, IH). A mixture of 6-hydroxy-7,8-dimethoxy-4,4-dimethyl-3,4-dihydrocoumarin (1.6 g), allyl bromide (1.65 ml), potassium carbonate (2.63 g) and DMF (15 ml) was stirred and - 35 - heated to 70°C for 1 hour. The mixture was partitioned between diethyl ether and water. The organic phase was washed with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. The residue was purified by column chromatography on silica using a 3:2 mixture of petroleum ether (b.p. 40 to 60°C) and diethyl ether as eluent. There was thus obtained 6-allyloxy-7,8-dimethoxy-4,4-dimethyl-3,4-dihydrocoumarin (1.51 g); NMR Spectrum: (CDC1 3 ) 1.31 (s, 6H), 2.59 (s, 2H), 3.9 (s, 3H), 3.95 (s, 3H), 4.57 (d, 2H), 5.37 (m, 2H), 6.08 (m, IH), 6.58 (s, IH). A mixture of the material so obtained and N,N-dimethylaniline (20 ml) was stirred and heated to 200°C for 4 hours. The mixture was evaporated and the residue was purified by column chromatography on silica using a 1 :1 mixture of petroleum ether (b.p. 40 to 60°C) and diethyl ether as eluent. There was thus obtained 5-allyl-6-hydroxy-7,8-dimethoxy- 4,4-dimethyl-3,4-dihydrocoumarin (1.4 g); NMR Spectrum: (CDC1 3 ) 1.44 (s, 6H), 2.56 (s, 2H), 3.58 (m, 2H), 3.91 (s, 3H), 3.97 (s, 3H), 5.02 (m, 2H), 5.73 (s, IH), 6.02 (m, IH). A mixture of a portion (0.65 g) of the material so obtained, 2N aqueous sodium hydroxide solution (1 ml) and water (25 ml) was stirred at ambient temperature in air for 1.5 hours. The mixture was extracted with diethyl ether. The organic phase was washed with water and with a saturated aqueous sodium chloride solution, dried (MgSO 4 ) and evaporated. The residue was purified by column chromatography on silica using a 50:50:0.1 mixture of petroleum ether (b.p. 40 to 60°C), diethyl ether and acetic acid as eluent. There was thus obtained the required starting material (0.112 g); NMR Spectrum: (CDC1 3 ) 1.46 (s, 6H), 3.03 (s, 2H), 3.44 (s, 2H), 3.9 (s, 3H), 3.95 (s, 3H), 5.02 (m, 2H), 5.83 (m, IH). Example 9 Ethyl chloroformate (0.060 ml) was added to a stirred mixture of 3-(2,3-dimethoxy- 5-methyl-l,4-benzoquinonyl)-3-methylbutyric acid (0.14 g), triethylamine (0.087 ml) and methylene chloride (5 ml) which had been cooled to 0°C and the mixture was stirred for 30 minutes. N-Allyl-4-[bis(2-chloroethyl)amino]aniline dihydrochloride (0.173 g) and triethylamine (0.14 ml) were added in turn and the resultant mixture was stirred at ambient temperature for 3 days. The mixture was evaporated and the residue was purified by column chromatography on silica using a 19:1 mixture of methylene chloride and diethyl ether as - 36 - eluent. There was thus obtained N-allyl-N-{4-[bis(2-chloroethyl)amino]phenyl}- 3-(2,3-dimethoxy-5-methyl-l,4-benzoquinonyl)-3-methylbutyramide (0.11 g); NMR Spectrum: (CDC1 3 ) 1.31 (s, 6H), 2.09 (s, 3H), 2.77 (s, 2H), 3.67 (t, 4H), 3.77 (t, 4H), 3.93 (s, 3H), 3.98 (s, 3H), 4.13 (d, 2H), 5.04 (m, 2H), 5.73 (m, IH), 6.67 (d, 2H), 7.01 (d, 2H). The N-allyl-4-[bis(2-chloroethyl)amino]aniline dihydrochloride used as a starting material was obtained as follows :- 2-(tert-Butoxycarbonyloxyimino)phenylacetonitrile (BOC-ON; 13.5 g) was added to a mixture of 4-[bis(2-hydroxyethyl)amino]aniline [10 g; prepared by neutralising the corresponding dihydrochloride salt (J. Org. Chem., 1961, 26, 1933)], acetone (100 ml) and water (100 ml) and the resultant mixture was stirred at ambient temperature for 16 hours. The mixture was extracted with ethyl acetate. The organic phase was extracted with 2N aqueous hydrochloric acid solution. The aqueous phase was neutralised by the addition of 2N aqueous sodium hydroxide solution and extracted with ethyl acetate. The organic phase was evaporated and the residue was purified by column chromatography on silica using ethyl acetate as eluent. There was thus obtained 4-[bis(2-hydroxyethyl)amino]- N-(tert-butoxycarbonyl)aniline (11.84 g); NMR Spectrum: (CDC1 3 ) 1.59 (s, 9H), 3.56 (t, 4H), 3.84 (t, 4H), 6.5 (broad s, IH), 6.71 (d, 2H), 7.24 (d, 2H). A mixture of a portion (2 g) of the material so obtained, tert-butyldimethyl sily 1 chloride (2.5 g), imidazole (2.3 g) and DMF (20 ml) was stirred at ambient temperature for 2 days. Water was added and the mixture was extracted with ethyl acetate. The organic extract was evaporated and the residue was purified by column chromatography on silica using a 19:1 mixture of methylene chloride and diethyl ether as eluent. There was thus obtained 4- [bis(2-tert-butyldimethylsilyloxyethyl)amino] -N-(tert-butoxycarbonyl)aniline (3.86 g); NMR Spectrum: (CDC1 3 ) 0.0 (s, 12H), 0.85 (s, 18H), 1.47 (s, 9H), 3.42 (t, 4H), 3.69 (t, 4H), 6.18 (broad s, IH), 6.58 (d, 2H), 7.13 (d, 2H). Sodium hydride (60% dispersion in mineral oil; 0.265 g) was added to a stirred solution of 4- [bis(2-tert-butyldimethylsilyloxyethyl)amino] -N-(tert-butoxycarbonyl)aniline (3.15 g) in DMF (20 ml) which had been cooled to 0°C. The resultant mixture was stirred at ambient temperature for 1 hour. Allyl bromide (0.625 ml) was added and the mixture was stirred at ambient temperature for 12 hours. Water (5 ml) was added and the mixture was partitioned between diethyl ether and water. The organic phase was dried (MgSO 4 ) and - 37 - evaporated to give N-allyl-4-[bis(2-tert-butyldimethylsilyloxyethyl)amino]- N-(tert-butoxycarbonyl)aniline (3.5 g); NMR Spectrum: (CDC1 3 ) 0.0 (s, 12H), 0.81 (s, 9H), 0.82 (s, 9H), 1.4 (s, 9H), 3.43 (t, 4H), 3.71 (t, 4H), 4.11 (d, 2H), 5.07 (m, 2H), 5.87 (m, IH), 6.58 (d, 2H), 6.93 (d, 2H). A mixture of the material so obtained and tetra-n-butylammonium fluoride (1.IM in THF; 55 ml) was stirred at ambient temperature for 30 minutes. The solvent was evaporated and the residue was purified by column chromatography on silica using ethyl acetate as eluent. There was thus obtained N-allyl-4-[bis(2-hydroxyethyl)amino]- N-(tert-butoxycarbonyl)aniline(2.09 g); NMR Spectrum: (CDC1 3 ) 1.44 (s, 9H), 3.55 (t, 4H), 3.83 (t, 4H), 4.13 (d, 2H), 5.11 (m, 2H), 5.89 (m, IH), 6.61 (d, 2H), 7.04 (d, 2H). A mixture of the material so obtained, carbon tetrachloride (12 ml), triphenylphosphine (4.92 g) and acetonitrile (40 ml) was stirred at ambient temperature for 30 minutes. The solvent was evaporated and the residue was purified by column chromatography on silica using a 17:3 mixture of petroleum ether (b.p. 40 to 60°C) and ethyl acetate as eluent. There was thus obtained N-allyl-4-[bis(2-chloroethyl)amino]- N-(tert-butoxycarbonyl)aniline (1.49 g); NMR Spectrum: (CDC1 3 ) 1.44 (s, 9H), 3.61 (t, 4H), 3.7 (t, 4H), 4.14 (d, 2H), 5.12 (m, 2H), 5.88 (m, IH), 6.61 (d, 2H), 7.08 (d, 2H). A saturated solution of hydrogen chloride gas in ethyl acetate (6.5 ml) was added to a solution of the material so obtained in ethyl acetate (5 ml) and the mixture was stirred at ambient temperature for 30 minutes. The precipitate was isolated. There was thus obtained N-allyl-4-[bis(2-chloroethyl)amino]aniline dihydrochloride (0.56 g); NMR Spectrum: (CD 3 SOCD 3 ) 3.75 (s, 8H), 3.87 (d, 2H), 5.37 (d, IH), 5.45 (d, IH), 5.95 (m, IH), 6.86 (d, 2H), 7.37 (d, 2H). Example 10 Pharmaceutical compositions The following illustrate representative pharmaceutical dosage forms of the invention as defined herein (the active ingredient being termed "Compound X"), for therapeutic or prophylactic use in humans: - 38 - (a) Tablet I mg/tablet Compound X 100 Lactose Ph.Eur 182.75 Croscarmellose sodium 12.0 Maize starch paste (5%> w/v paste) 2.25 Magnesium stearate 3.0 (b) Tablet II mg/tablet Compound X 50 Lactose Ph.Eur 223.75 Croscarmellose sodium 6.0 Maize starch 15.0 Polyvinylpyrrolidone (5% w/v paste) 2.25 Magnesium stearate 3.0 (c) Tablet III mg/tablet Compound X 1.0 Lactose Ph.Eur 93.25 Croscarmellose sodium 4.0 Maize starch paste (5% w/v paste) 0.75 Magnesium stearate 1.0 (d) Capsule mg/capsule Compound X 10 Lactose Ph.Eur 488.5 Magnesium 1.5 (e) Injection I (50 mg/ml) Compound X 5.0% w/v IM Sodium hydroxide solution 15.0% v/v - 39 - 0.1M Hydrochloric acid (to adjust pH to 7.6) Polyethylene glycol 400 4.5%) w/v Water for injection to 100%) (f) Injection II (10 mg/ml) Compound X 1.0% w/v Sodium phosphate BP 3.6%> w/v 0.1M Sodium hydroxide solution 15.0%) v/v Water for inj ection to 100%> (g) Injection III (1 mg/ml, buffered to pH6) Compound X 0.1%) w/v Sodium phosphate BP 2.26% w/v Citric acid 0.38% w/v Polyethylene glycol 400 3.5% w/v Water for injection to 100%) (h) Aerosol I mg/ml Compound X 10.0 Sorbitan trioleate 13.5 Trichlorofluoromethane 910.0 Dichlorodifluoromethane 490.0 (i) Aerosol II mg/ml Compound X 0.2 Sorbitan trioleate 0.27 Trichlorofluoromethane 70.0 Dichlorodifluoromethane 280.0 Dichlorotetrafluoroethane 1094.0 - 40 - (j) Aerosol III mg/ml Compound X 2.5 Sorbitan trioleate 3.38 Trichlorofluoromethane 67.5 Dichlorodifluoromethane 1086.0 Dichlorotetrafluoroethane 191.6 (k) Aerosol IV mg/ml Compound X 2.5 Soya lecithin 2.7 Trichlorofluoromethane 67.5 Dichlorodifluoromethane 1086.0 Dichlorotetrafluoroethane 191.6 (1) Ointment ml Compound X 40 mg Ethanol 300 μl Water 300 μl l-Dodecylazacycloheptan-2-one 50 μl Propylene glycol to 1 ml Note The above formulations may be obtained by conventional procedures well known in the pharmaceutical art. The tablets (a)-(c) may be enteric coated by conventional means, for example to provide a coating of cellulose acetate phthalate. The aerosol formulations (h)-(k) may be used in conjunction with standard, metered dose aerosol dispensers, and the suspending agents sorbitan trioleate and soya lecithin may be replaced by an alternative suspending agent such as sorbitan monooleate, sorbitan sesquioleate, polysorbate 80, polyglycerol oleate or oleic acid.

Claims: - 41 CLAIMS 1. An anti -tumour agent of the formula I I wherein R 1 is hydrogen, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, ( 1 -4C)alkylamino-( 1 -4C)alkyl, di- [( 1 -4C)alkyl]amino-( 1 -4C)alkyl, pyrrolidin- 1 -yl-( 1 -4C)alkyl, piperidino-( 1 -4C)alkyl, moφholino-( 1 -4C)alkyl, piperazin- 1 -yl-( 1 -4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alkyl, carboxy-( 1 -4C)alkyl, ( 1 -4C)alkoxycarbonyl-( 1 -4C)alkyl, carbamoyl-( 1 -4C)alkyl, N-( 1 -4C)alkylcarbamoyl-( 1 -4C)alkyl, N,N-di- [( 1 -4C)alkyl]carbamoyl-( 1 -4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino-(2-4C)alkoxy, (l-4C)alkylamino-(2-4C)alkoxy, di-[(l-4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino-(2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy , 4-( 1 -4C)alkylpiperazin- 1 -yl-(2-4C)alkoxy , ( 1 -4C)alkylthio, (l-4C)alkylsulphinyl or (l-4C)alkylsulphonyl; R 2 is hydrogen, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, ( 1 -4C)alkylamino-( 1 -4C)alkyl, di- [( 1 -4C)alkyl]amino-( 1 -4C)alkyl, pyrrolidin- 1 -yl-( 1 -4C)alkyl, piperidino-( 1 -4C)alkyl, moφholino-( 1 -4C)alkyl, piperazin- 1 -yl-( 1 -4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alkyl, carboxy-(l-4C)alkyl, (l-4C)alkoxycarbonyl-(l-4C)alkyl, carbamoyl-(l-4C)alkyl, N-( 1 -4C)alkylcarbamoyl-( 1 -4C)alkyl, N,N-di-[( 1 -4C)alkyl]carbamoyl-( 1 -4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino- (2-4C)alkoxy, (1 -4C)alkylamino-(2-4C)alkoxy, di-[(l -4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino-(2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy or 4-( 1 -4C)alkylpiperazin- 1 -yl-(2-4C)alkoxy ; - 42 - R 3 is hydrogen, ( C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, hydroxy-(l-4C)alkyl, ( 1 -4C)alkoxy-( 1 -4C)alkyl, amino-( 1 -4C)alkyl, ( 1 -4C)alkylamino-( 1 -4C)alkyl, di- [( 1 -4C)alkyl]amino-( 1 -4C)alkyl, pyrrolidin- 1 -yl-( 1 -4C)alkyl, piperidino-( 1 -4C)alkyl, moφholino-( 1 -4C)alkyl, piperazin- 1 -yl-( 1 -4C)alkyl, 4-( 1 -4C)alkylpiperazin- 1 -yl-( 1 -4C)alkyl, carboxy-(l-4C)alkyl, (l-4C)alkoxycarbonyl-(l-4C)alkyl, carbamoyl-(l-4C)alkyl, N-(l-4C)alkylcarbamoyl-(l-4C)alkyl, N,N-di-[(l-4C)alkyl]carbamoyl-(l-4C)alkyl, hydroxy, (l-4C)alkoxy, hydroxy-(2-4C)alkoxy, (l-4C)alkoxy-(2-4C)alkoxy, amino- (2-4C)alkoxy, (l-4C)alkylamino-(2-4C)alkoxy, di-[(l-4C)alkyl]amino-(2-4C)alkoxy, pyrrolidin- 1 -yl-(2-4C)alkoxy, piperidino-(2-4C)alkoxy, moφholino- (2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy, piperazin- 1 -yl-(2-4C)alkoxy or 4-( 1 -4C)alkylpiperazin- 1 -yl- (2-4C)alkoxy; R 4 is (l-4C)alkyl; R 5 is (l-4C)alkyl; R 6 is hydrogen or (l-4C)alkyl; R 7 is hydrogen or ( 1 -4C)alkyl; X is N-(l-4C)alkylimino, N-(3-4C)alkenylimino or N-(3-4C)alkynylimino; m is 1 or 2 and each R 8 is independently hydrogen, halogeno, hydroxy, (l-4C)alkoxy, (2-4C)alkenyloxy, (2-4C)alkynyloxy, (l-4C)alkyl, (3-4C)alkenyl, (3-4C)alkynyl, amino, (l-4C)alkylamino, di-[(l-4C)alkyl]amino, cyano, (2-4C)alkanoylamino, carboxy, (l-4C)alkoxycarbonyl, carbamoyl, N-(l-4C)alkylcarbamoyl or N,N-di-[(l-4C)alkyl]carbamoyl; Y 1 is halogeno, (l-4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl - (l-4C)alkanesulphonyloxy; and Y 2 is halogeno, (l-4C)alkanesulphonyloxy, benzenesulphonyloxy or phenyl- (l-4C)alkanesulphonyloxy; and wherein any heterocyclic group in R 1 , R 2 or R 3 is optionally substituted with 1, 2 or 3 (l-4C)alkyl substituents, and wherein any phenyl group in Y 1 or Y 2 when Y 1 and Y 2 is benzenesulphonyloxy or phenyl-(l-4C)alkanesulphonyloxy is optionally substituted with 1, 2 or 3 substituents selected from halogeno, nitro, cyano, trifluoromethyl, hydroxy, amino, (l-4C)alkyl, (l-4C)alkoxy, (l-4C)alkylamino and di-[(l-4C)alkyl]amino; - 43 - or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. 2. An anti -tumour agent of the formula I as claimed in claim 1 wherein each of R 1 , R 2 and R 3 is independently hydrogen, methyl, ethyl, propyl, allyl, methylallyl, 2-hydroxyethyl, 3-hydroxypropyl, 2 -methoxy ethyl, 2-ethoxy ethyl, 3-methoxypropyl, 3-ethoxypropyl, 2-carboxyethyl, 3-carboxypropyl, 2-methoxycarbonyethyl, 2-ethoxycarbonylethyl, 3-methoxycarbonylpropyl, 3-ethoxycarbonylpropyl, 2-(N-methylcarbamoyl)ethyl, 3-(N-methylcarbamoyl)propyl, 2-(N,N-dimethylcarbamoyl)ethyl, 3-(N,N-dimethylcarbamoyl)propyl, methoxy or ethoxy; each of R 4 and R 5 is independently hydrogen, methyl, ethyl, propyl or isopropyl; R 6 is hydrogen, methyl, ethyl, propyl or isopropyl; R 7 is hydrogen or methyl; X is N-methylimino, N-ethylimino, N-propylimino or N-allylimino; m is 1 or 2 and each R 8 is independently hydrogen, fluoro, chloro, bromo, methoxy, ethoxy, methyl, ethyl, propyl, isopropyl or cyano; and each of Y 1 and Y 2 is independently chloro, bromo, iodo, methanesulphonyloxy, benzenesulphonyloxy or phenylmethanesulphonyloxy; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. 3. An anti-tumour agent of the formula I as claimed in claim 1 wherein R 1 is hydrogen, methyl, ethyl, propyl, allyl, methylallyl, methoxy or ethoxy; R 2 is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, allyl, methylallyl, methoxy or ethoxy; R 3 is hydrogen, methyl, ethyl, propyl, isopropyl, butyl, allyl, methylallyl, methoxy or ethoxy; R 4 is methyl, ethyl, propyl or isopropyl; R 5 is methyl, ethyl, propyl or isopropyl; R 6 is hydrogen, methyl, ethyl, propyl or isopropyl; R 7 is hydrogen or methyl; X is N-mefhylamino, N-ethylimino, N-propylimino or N-allylimino; m is 1 or 2 and each R 8 is independently hydrogen, fluoro, chloro, bromo, methoxy, ethoxy, methyl, ethyl, propyl or isopropyl; Y 1 is chloro, bromo, iodo or methanesulphonyloxy; and - 44 - Y 2 is chloro, bromo, iodo or methanesulphonyloxy; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. 4. An anti -tumour agent of the formula I as claimed in claim 1 wherein R 1 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 2 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 3 is hydrogen, methyl, ethyl, propyl, allyl, methoxy or ethoxy; R 4 is methyl or ethyl; R 5 is methyl or ethyl; R 6 is hydrogen, methyl or ethyl; R 7 is hydrogen X is N-methylimino, N-ethylimino, N-propylimino or N-allylimino; m is 1, R 8 is located meta to X and R 8 is hydrogen, fluoro, chloro, methyl, ethyl, propyl or isopropyl; and each of Y 1 and Y 2 is chloro, bromo or iodo; or a pharmaceutically-acceptable salt thereof; provided that at least one of R 1 , R 2 and R 3 is other than hydrogen. 5. An anti -tumour agent of the formula I as claimed in claim 1 wherein R 1 is hydrogen, methyl or methoxy; R 2 is hydrogen, methyl, allyl or methoxy; R 3 is methyl, ethyl, propyl or allyl; each of R 4 and R 5 is methyl; each of R 6 and R 7 is hydrogen; X is N-methylimino; m is 1 and R 8 is hydrogen; and each of Y 1 and Y 2 is chloro; or a pharmaceutically-acceptable salt thereof. 6. An anti-tumour agent of the formula I as claimed in claim 1 selected from :- N- { 4- [bis(2-chloroethyl)amino]phenyl } -3 -(5 -methyl-3 -propyl- 1 ,4-benzoquinon-2-yl)- 3-methyl-N-methylbutyramide. 3 -(3 -allyl-2, 5 -dimethyl- 1 ,4-benzoquinonyl)-N- { 4- [bis(2-chloroethyl)amino]phenyl } - - 45 - 3-methyl-N-methylbutyramide; N- { 4- [bis(2-chloroethyl)amino]phenyl } -3 -(2,5 -dimethyl- 1 ,4-benzoquinonyl)-3 -methyl- N-methy lbutyramide ; 3 -(3 -allyl-5 -methyl- 1 ,4-benzoquinon-2-yl)-N- { 4- [bis(2-chloroethyl)amino]phenyl } -3 -methyl- N-methy lbutyramide; N = {4-[bis(2-chloroethyl)amino]phenyl}-3-methyl-N-methyl-3-(2,3,5-trimethyl- 1 ,4-benzoquinonyl)butyramide, N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,3-dimethoxy-5-methyl-l,4-benzoquinonyl)- 3-methyl-N-methylbutyramide and N-allyl-N-{4-[bis(2-chloroethyl)amino]phenyl}-3-(2,3-dimethoxy-5-methyl- l,4-benzoquinonyl)-3-methylbutyramide; or a pharmaceutically-acceptable salt thereof. 7. An anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as claimed in any of claims 1 to 6 wherein the reduction potential of the compound is in the range -300 to -475 mV. 8. A process for the preparation of an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as claimed in claim 1 which comprises :- the reaction of an acid of the formula II o " wherein each of R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 has any of the meanings defined in claim 1, or a reactive derivative thereof, with a compound of the formula III ( R 8 )m Y 1 HX N / >v γ / 2 2 in - 46 - wherein each of X, R 8 , m, Y 1 and Y 2 has any of the meanings defined in claim 1; and when a pharmaceutically-acceptable salt of a compound of the formula I is required, it may be obtained by reaction of said compound with a suitable acid or base using a conventional procedure and when an optically active form of a compound of the formula I is required, it may be obtained by earring out the aforesaid process using an optically active starting material, or by resolution of a racemic form of said compound using a conventional procedure. 9. A pharmaceutical composition which comprises an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as claimed in claim 1 in association with a pharmaceutically- acceptable diluent or carrier. 10. The use of an anti-tumour agent of the formula I, or a pharmaceutically-acceptable salt thereof, as claimed in claim 1 in the manufacture of a medicament for use in the production of an anti -proliferative effect in a warm-blooded animal.

Inventors: BOYLE FRANCIS THOMAS, BOYLE, FRANCIS, THOMAS
Applicants: BOYLE FRANCIS THOMAS, ZENECA LTD, BOYLE, FRANCIS, THOMAS, ZENECA LIMITED
Application year: 1999
Main classification: C07C235
IPC codes: A61K31, A61P35, C07C235