MITOMYCIN ANALOGUES

Abstract: Compounds of the general formula: {wherein X represents a group [in which R₃ represents a cycloalkyl or straight chain or branched alkyl group having up to 7 carbon atoms, said alkyl or cycloalkyl group optionally carrying 1 to 3 amino groups and/or 1 to 3 hydroxyl groups; a -(CH₂) n CO₂R₄ group (in which n is the integer 1, 2 or3, and R₄ represents a methyl or ethyl group); a pyridyl group; or a group of the formula: and R₁ and R₂ which may be the same or different, each represents a hydrogen atom or a methyl group, and indicates α or β bonding] possess good antibacterial and anti-tumor activity. The compounds of formula I may be prepared for example by reaction of mitomycin A, B, F or J with the appropriate amine.

Description: Mitomycin Analogues The present invention relates to mitomycin analogues, processes for their preparation, pharmaceutical compositions containing them and their use as anti-tumour and antibacterial agents. Certain mitomycin compounds are known as antibiotics having antibacterial and antitumour activities, and are exemplified by mitomycin A, mitomycin B, mitomycin C and porfiromycin, which are referred to in the Merck Index, 9th Edition, as well as by mitomycin D and mitomycin E which are disclosed in Japanese Patent Application as laid open to public inspection as Kokai Koho 122797/79, mitomycin F (Japanese Patent Application as laid open to public inspection as Kokai Koho 45322/80) and mitomycin J (Shirahata et. al., 23rd symposium the chemistry of natural products Nagoya 608, 1980). These compounds may be obtained by culturing a microorganism of Streptococcus caespitosus and have the following chemical structures: EMI1.1 EMI1.2 <tb> <SEP> XA <SEP> 9 <SEP> vvlo <SEP> RA <SEP> RB <tb> Mitomycin <SEP> A <SEP> OCH3 <SEP> """" <SEP> CH3 <SEP> H <tb> <SEP> B <SEP> OCH3 <SEP> ¯¯ as <SEP> H <SEP> CH3 <tb> <SEP> C <SEP> NH <SEP> 2 <SEP> ''''' <SEP> CH3 <SEP> H <tb> <SEP> D <SEP> NH2 <SEP> H <SEP> CH3 <tb> <SEP> " <SEP> NH2 <SEP> CH3 <SEP> CH3 <tb> <SEP> " <SEP> E <SEP> 2 <SEP> CH3 <SEP> CH3 <tb> <SEP> F <SEP> F <SEP> SOCH3 <SEP> "'""" <SEP> CH3 <SEP> CH3 <tb> <SEP> J <SEP> J <SEP> OCH3 <SEP> ¯¯ sa <SEP> CH3 <SEP> CH3 <tb> Porfiromycin <SEP> NH2 <SEP> ""''"' <SEP> CH3 <SEP> CH3 <tb> Various derivatives of the above-mentioned mitomycin compounds are also known. For example, certain derivatives of mitomycin C, in which the 7-amino group is substituted with various different groups have been described in U.S. Patent No. 4,268,676, in J. Med. Chem. 24, 975 (1981) and in a Japanese Patent Application laid open to public inspection as Kokai Koho 188590/82. U.S. Patent 4,268,676 and J. Med. Chem., 24, 975 (1981) disclose the presence of 2-thiazolylamino, furfurylamino, 2-propenylamino, 2-propynylamino, 2-thienylmethylamino and carbamoylmethylamino groups at the 7-position. Japanese Patent Application as laid open to public inspection as Kokai Koho 188590/82 discloses mitomycin derivatives, in which the 7-amino group is substituted with various heterocyclic groups (quinolinyl, pyrazolyl, thiazolyl, etc.) or 7-position is substituted with various heterocyclic groups containing a nitrogen atom (l-pyrrolinyl, l-indolinyl, etc.), the 2-mercaptoethylamino group (Examples 16 and 33) or the 2-(ethylthio)ethylamino group (Example 32). The present invention is based on the discovery that mitomycin analogues having a 7-amino group substituted by certain groups comprising the disulfide linkage -S-Spossess good antibacterial and antitumour activity and have not hitherto been reported. Thus according to one feature of the present invention there are provided- compounds of the general formula: EMI2.1 {wherein X represents a EMI2.2 or R3-S-S-CH2-CH2- group tin which R3 represents a cycloalkyl or straight chain or branched alkyl group having up to 7 carbon atoms, said alkyl or cycloalkyl group optionally carrying 1 to 3 amino groups and/or 1 to 3 hydroxyl groups; a -(CH2)nCO2R4 group (in which n is the integer 1, 2 or 3, and R4 represents a methyl or ethyl group); a pyridyl group; or a group of the formula: EMI3.1 and R1 and R2 which may be the same or different, each represents a hydrogen atom or a methyl group, and vvv¯ > indicates a or ss bonding). With regard to the definition of R3 in general formula (I), the cycloalkyl or straight chain or branched alkyl groups having up to 7 carbon atoms optionally substituted by 1 to 3 hydroxyl groups and/or 1 to 3 amino groups,. are exemplified by C1 4, e.g. C13, straight chain or branched alkyl groups optionally carrying 1, 2 or 3 hydroxy groups and/or 1, 2 or 3 amino groups e.g. a methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, 2-hydroxyethyl, 3-hydroxypropyl, 2, 3-dihydroxypropyl , 2aminoethyl, 3-aminopropyl, 2-amino-1-methylethyl or 4aminobutyl group; or a C5 or C6 cycloalkyl group optionally carrying 1 to 3 hydroxy groups and/or 1 to 3 amino groups such as a cyclopentyl, cyclohexyl or 4-hydroxycyclohexyl group. With regard to the definition of R3 as a -(CH2)nCO2R4 group such groups may be exemplified by the ethoxycarbonylmethyl and methoxycarbonylethyl group. Pyridyl groups are exemplified by the 2-pyridyl and 4pyridyl groups. The following compounds are especially excellent in chemotherapeutic index onanti-tumour activity and low toxicity against bone marrow, namely, compounds of formula I having mitomycin C or D structure wherein X represents the group EMI4.1 or the group R3-S-S-CH2CH2- in which R3 represents straight chain or branched alkyl group having 1 to 4 carbon atoms optionally substituted by 1, 2 or 3 hydroxyl groups and/or 1, 2 or 3 amino groups (for example, an ethyl, n-propyl, 2-aminoethyl, 2-hydroxyethyl, 2,3dihydroxypropyl group), (CH2)nCO2R4 wherein n and R4 are as hereinbefore defined (for example, methoxycarbonylmethyl group), or a group of the formula: EMI4.2 wherein R1 and R2 are as hereinbefore defined. Specifically, the following compounds are mentioned as such excellent compounds 7-N,7 '-N'-dithiodiethylenedimitomycin D; 7-N- t2- (2-aminoethyl)dithioethyllmitomycin D; 7-N- (2-ethyldithioethyl)mitomycin C; 7-N-[ 2-(2-hydroxyethyl)dithioethyl)mitomycin C; 7-N- t2-(2-aminoethyl)dithioethyl]mitomycin C; 7-N, 7 1-N' -dithiodiethylenedimitomycin C; 7-N-(1,2-dithiolan-4-yl)mitomycin C; 7-N- (l,2-dithiolan-4-yl)mitomycin D; 7-N- [2- (2, 3-dihydroxypropyl) dithioethyl] mitomycin C; 7-N-(2-methoxycarbonylmethyldithioethyl)mitomycin C; and 7-N,7'-N'-dithiodiethylenediporfiromycin. The compounds of formula I as hereinbefore defined may, if desired, be prepared by either of the following processes, which processes constitute further features of the present invention: a) The reaction of a compound of the formula: EMI5.1 (wherein R1 and R2, which may be the same or different, are as hereinbefore defined) with a compound of the formula: X-NH2 (III) (wherein X is as hereinbefore defined) or a salt thereof; and b) For the preparation of compounds of formula I as hereinbefore defined [wherein X represents the group R3'-S-S-CH2-CH2- in which R3' represents a cycloalkyl or straight chain or branched alkyl group with up to 7 carbon atoms said alkyl or cycloalkyl group optionally carring 1 to 3 amino groups and/or 1 to 3 hydroxy groups; or R3' represents a -(CH2)nCO2R4 group (in which n is the integer 1, 2 or 3 and R4 represents a methyl or ethyl group)l, the reaction of a compound of the formula: EMI5.2 (wherein Rl and R2, which may be the same or different, are as hereinbefore defined) with a compound of the formula: R31 SH (V) (wherein R3' is as hereinbefore defined) or, where appropriate, a base addition salt thereof. Process (a) is conveniently effected in the presence of an inert solvent, advantageously under basic conditions (e.g. in the presence of a base) and preferably at a temperature of from OOC to ambient temperature. The compound of formula (III) may, if desired, be used in the form of an acid addition salt (e.g. the hydrochloride, sulfate or nitrate) and where 4-amino-1,2-dithiolane is used, conveniently the hydrochloride thereof. Where more than 2 mols of the compound of formula III wherein R3 represents a cycloalkyl or a straight chain or branched alkyl group, having 2-7 carbon atoms and substituted an amino group (hereinafter referred to as formula III') is used per mol of the compound of formula II, the resultant product is formed by reaction of the compound of formula (II) with the compound of formula (III') in a ratio of 1 : 1 as exemplified in Example 3 hereinafter, and where about 0.5 mol of the compound of formula (III') is used per mol of the compound of formula (II), the resultant. product is obtained by reaction of the compound of formula (II) with the compound of formula (III') in a ratio of 2 : 1 as exemplified in Example 1 hereinafter. Methanol, ethanol, isopropanol, methylene chloride, chloroform, acetonitrile, tetrahydrofuran, dioxan and/or dimethylformamide may for example be used either alone or in combination as the inert solvent. The reaction may for example be effected in the presence of a tertiary amine such as triethylamine or pyridine in order to ensure basic conditions. Although the reaction time may vary with solvents used and with the compounds (II) and (III) used, the reaction is usually completed within a period of from scores of minutes to several hours, and where 4-amino-l,2-dithiolane is used, the reaction is usually complete within"a period of from several hours to several days. After completion of the reaction, water may be poured into the reaction mixture which may then be extracted with for example chloroform or ethyl acetate. After concentrating the extracted solution in vacuo, the concentrated solution may be purified, for example by column chromatography, preparative thin layer chromatography and/or recrystallization. The synthesis of 4-amino-1,2-dithiolane hydrochloride is described in Chemical Abstracts, 63, 18061 (1965). With regard to process (b) the reaction may if desired be effected using a compound of formula V in the form of a salt (e.g. abase addition salt) for example with an alkali metal or alkaline earth metal e.g. the potassium or sodium salt. The reaction is conveniently effected in the presence of an inert solvent, advantageously at a temperature of from OOC to ambient temperature. The reaction (b) may be effected, for example, by using as the inert solvent, methanol, ethanol, isopropanol, acetonitrile, dimethylformamide, dimethylsulfoxide or another organic solvent and/or water. These solvents may be used alone or in combination. The reaction time may vary, depending upon the kind of the compound (V) used, although the reaction is usually complete within a period of from several minutes to several hours. After completion of the reaction, water is poured into the reaction mixture which is then extracted with chloroform or ethyl acetate. The extracted solution is conveniently concentrated in vacuo and, if desired, purified by, for example, column chromatography, preparative thin layer chromatography, and/or recrystallization. The synthesis of a disulfide by the use of a 2-pyridyldisul fide and its uses are described, for example, in Biochem. J., 173, 723 (1978). Biochem. Biophy. Res. Comm., 101, 599 (1981); Cancer Res., 42, 457 (1982) and Nature, 290, 145 (1981). Minimum growth inhibiting concentrations of various compounds (I) [ug/ml; agar dilution method; pH = 7.0] are shown in the following Table I in which the various compounds are indicated by the following abbreviations: a. 7-N, 7 '-N' -dithiodiethylenedimitomycin D EMI8.1 b. 7-N,7'-N'-dithiodiethylenedimitomycin E EMI8.2 c. 7-N-[2-(2-aminoethyl)dithioethyl]mitomycin D EMI8.3 d. 7-N-[2-(2-pyridyldithio)ethyl]mitomycin C EMI8.4 e. 7-N-[2-(2-pyridyldithio)ethyl]porfiromycin EMI9.1 f. 7-N-[2-(2-pyridyldithio)ethyl]mitomycin D EMI9.2 g. 7-N-(2-ethyldithioethyl)mitomycin C EMI9.3 h. 7-N-(2-propyldithioethyl)mitomycin C EMI9.4 i. 7-N-[2-(2-hydroxyethyl)dithioethyl]mitomycin C EMI9.5 j. 7-N-(1,2-dithiolan- 4-yl)mitomycin C EMI10.1 k. 7-N-(1,2-dithiolan- 4 -yl) porfiromycin EMI10.2 1. 7-N-(1,2-dithiolan- 4-yl)mitomycin D EMI10.3 m. 7-N-(1,2-dithiolan- 4-yl)mitomycin E EMI10.4 n. 7-N- [2-(2-pyridyldithio)ethyl]mitomycin E EMI10.5 o. 7-N-[2-(2,3-dihydroxypropyl)dithioethyl]mitomycin C EMI11.1 p. 7-N- (2-methoxycarbonylmethyldithioethyl)mitomycin C EMI11.2 q. 7-N-(2-cyclohexyldithioethyl)mitomycin C EMI11.3 r. 7-N- [2- (2-aminoethyl)dithioethyl)mitomycin C EMI11.4 s. 7-N-, 7'-N'-dithiodiethylenedimitomycin C EMI11.5 t. 7-N, 7'-N'-dithiodiethylenediporfiromycin EMI12.1 u. 7-N-[2-(2-aminoethyl)dithioethyl)porfiromycin EMI12.2 Table 1 A ... Mitomycin derivatives, B ... Microorganisms* EMI13.1 <tb> B <tb> <SEP> CA <SEP> SF <SEP> SA <SEP> EC <SEP> BS <SEP> PV <SEP> SS <SEP> ST <SEP> KP <tb> A <tb> <SEP> a <SEP> - <SEP> 20 <SEP> 20 <SEP> - <SEP> 5 <SEP> - <SEP> - <SEP> - <SEP> <tb> <SEP> b <SEP> - <SEP> > 20 <SEP> 5 <SEP> - <SEP> 1.3 <SEP> - <SEP> - <SEP> - <SEP> <tb> <SEP> c <SEP> - <SEP> 20 <SEP> 20 <SEP> - <SEP> 5 <SEP> - <SEP> - <SEP> - <SEP> <tb> <SEP> d <SEP> > 20 <SEP> 0.039 <SEP> 0.039 <SEP> 20 <SEP> < 0.0098 <SEP> 1.3 <SEP> 10 <SEP> 20 <SEP> 0.31 <tb> <SEP> e <SEP> > 20 <SEP> 1.3 <SEP> 0.31 <SEP> - <SEP> 0.078 <SEP> 20 <SEP> > 20 <SEP> > 20 <SEP> 10 <tb> <SEP> f <SEP> - <SEP> 1.3 <SEP> 1.3 <SEP> - <SEP> 0.31 <SEP> 10 <SEP> - <SEP> - <SEP> <tb> <SEP> g <SEP> - <SEP> < 0.0098 <SEP> < 0.0098 <SEP> - <SEP> < 0.0098 <SEP> 0.31 <SEP> > 20 <SEP> - <SEP> 0.16 <tb> <SEP> h <SEP> - <SEP> 0.039 <SEP> 0.020 <SEP> - <SEP> < 0.0098 <SEP> 0.63 <SEP> > 20 <SEP> > 20 <SEP> 0.63 <tb> <SEP> i <SEP> - <SEP> 0.039 <SEP> 0.16 <SEP> - <SEP> 0.078 <SEP> 2.5 <SEP> > 20 <SEP> - <SEP> 0.31 <tb> <SEP> j <SEP> - <SEP> < 0.0098 <SEP> < 0.0098 <SEP> 20 <SEP> < 0.0098 <SEP> 0.31 <SEP> 2.5 <SEP> 10 <SEP> 0.039 <tb> <SEP> k <SEP> - <SEP> 0.039 <SEP> 0.020 <SEP> - <SEP> < 0.0049 <SEP> 10 <SEP> - <SEP> - <SEP> 1.3 <tb> <SEP> 1 <SEP> - <SEP> 5 <SEP> 1.3 <SEP> - <SEP> 0.31 <SEP> 5 <SEP> - <SEP> - <SEP> 5 <tb> <SEP> m <SEP> - <SEP> > 20 <SEP> 1.3 <SEP> - <SEP> 0.16 <SEP> > 20 <SEP> - <SEP> - <SEP> 20 <tb> <SEP> n <SEP> - <SEP> 20 <SEP> 0.63 <SEP> - <SEP> 0.078 <SEP> 10 <SEP> - <SEP> - <SEP> > 20 <tb> <SEP> o <SEP> - <SEP> > 20 <SEP> > 20 <SEP> - <SEP> > 20 <SEP> 20 <SEP> - <SEP> - <SEP> 2.5 <tb> <SEP> P <SEP> - <SEP> > 20 <SEP> > 20 <SEP> > 20 <SEP> > 20 <SEP> 2.5 <SEP> 20 <SEP> 20 <SEP> 0.16 <tb> <SEP> q <SEP> - <SEP> > 20 <SEP> 1.3 <SEP> - <SEP> 20 <SEP> 10 <SEP> - <SEP> - <SEP> 2.5 <tb> <SEP> r <SEP> - <SEP> 1.3 <SEP> 0.63 <SEP> - <SEP> 0.16 <SEP> 5 <SEP> - <SEP> - <SEP> 2.5 <tb> <SEP> s <SEP> - <SEP> 1.3 <SEP> 0.63 <SEP> - <SEP> 0.16 <SEP> 10 <SEP> - <SEP> - <SEP> 2.5 <tb> <SEP> t <SEP> - <SEP> 2.5 <SEP> 0.31 <SEP> - <SEP> 0.039 <SEP> - <SEP> - <SEP> - <SEP> 5 <tb> <SEP> u <SEP> ¯ <SEP> 2.5 <SEP> 0.63 <SEP> - <SEP> 0.039 <SEP> > 10 <SEP> - <SEP> - <SEP> 5 <tb> MM-C <SEP> - <SEP> 0.039 <SEP> 0.020 <SEP> 2.5 <SEP> < 0.0049 <SEP> 0.020 <SEP> 1.3 <SEP> 1.3 <SEP> < 0.0049 <tb> * Notes: : A -C Mitomycin C CA Candida albicans ATCC 10231 SF Streptococcus faecalis ATCC 10541 SA Staphylococcus aureus ATCC 6538P EC Escherichia coli ATCC 26 BS Bacillus subtilis 10707 PV Proteus vulgaris ATCC 6897 SS Shigella sonnei ATCC 9290 ST Salmonella typhosa ATCC 9992 KP Klebsiella pneumoniae ATCC 10031 The following examples illustrate the invention. Example 1: Preparation of 7-N, 7'-N'-dithiodiethylenedimitomycin D Cystamine dihydrochloride (12.9 mg) is dissolved in methanol (3 ml). To the solution is added triethylamine (50 p1) with stirring. Then mitomycin B (40 mg in total) is added in several portions to the solution and the mixture is stirred at ambient temperature for 12 hours. Water is added to the reaction solution which is then extracted with chloroform. The extracted solution is dried by using anhydrous sodium sulfate and the solvent is removed by distillation in vacuo. The resultant oily substance is purified by silica gel column chromatography. The elution is effected by using a solvent systemof.a mixture of chloroform/methanol (4 :1; v/v). By concentrating the fractions, green crystals (42 mg) having the following characteristics are obtained in a yield of 93%: Melting point: decomposed at above 2200C Elemental analysis (%) as C34H42N8010S2 Found: H 5.43; C 51.94; N 14.02 Calculated: H 5.37 C 51.90 N 14.24 H-NMR spectrum (py-d5): 62.10(3H, s), 2.13(3H, s), 2.22(lH, d), 2.47(lH, d), 2.91(2H, t), 3.66(lH, d), 3.87(2H, q), 4.23(lH, dd), 4.44(lH, d), 5.21(lah, t), 5.47(1H, dd), 7.26(1H, t), 7.46(2H, br.s). IR spectrum (KBr method): -1 3420, 3250, 1703, 1543, 1503, 1453, 1342 cm Example 2: Preparation of 7-N,7'-N'-dithiodiethylenedimitomycin E To cystamine dihydrochloride (12.4 mg) dissolved in methanol (2 ml), triethylamine (50 Frl) is added with stirring. To the mixture mitomycin J (40 mg in total) is added in several portions and the mixture is stirred for 10 hours at ambient temperature. Water is added to the reaction solution which is then extracted with chloroform. The extracted solution is dried by using anhydrous sodium sulfate and the solvent is removed by distillation in vacuo. The resultant oily substance is purified by silica gel chromatography. The elution is effected by using a solvent system of a mixture of chloroform/methanol (95 :5; v/v) to give active fractions which are concentrated to give a black powder (43 mg) with a yield of 96%. The product has the following characteristics: Melting point: 132.5 - 1340C Elemental analysis (%): as C36H46N8OloS2 Found: H 5.74; C 53.21; N 13.47 Calculated: H 5.69 C 53.06 N 13.75 1 spectrum (CDC13): 62.01(3H, s), 2.22(1H, d), 2.31(3H, s), 2.37(1H, dd), 2.85(2B, t), 3.30(3H, s), 3.57(1H, dd), 3.86(2H, q), 4.02(1K, d), 4.45(1H, dd), 4.74(2H, br.s), 4.80(1H, dd), 6.47(1H, t) IR spectrum (KBr method): 3300, 2930, 1716, 1553, 1510, 1445, 1333, 1050 cm Example 3: Preparation of 7-N- [2- (2-aminoethyl) dithioethyl] - mitomycin D Cystamine dihydrochloride (103 mg) is dissolved in methanol (2.5 ml), to which triethylamine (0.4 ml) is then added dropwise with stirring. To the mixture is added mitomycin B (40 mg in total) in several portions, and the mixture is stirred for 40 minutes at ambient temperature. Water is added to the solution which is then extracted with chloroform. The extracted solution is dried over anhydrous sodium sulfate and the solvent is removed by distillation in vacuo. The resultant oily substance is purified by column chromatography using Diaion HP-20 (a resin commercially available from Mitsubishi Kasei Kogyo K.K., Tokyo). The elution is effected by using a solvent system of a mixture of water/methanol (1 :4; v/v) to give active fractions which are concentrated to obtain a dark green paste (23 mg) having the following characteristics (yield 43%):- Elemental analysis (%): as CLgH27N505S2 Found: H 5.82; C 48.67; N 14.70 Calculated: H 5.80 C 48.60 N 14.91 H-NMR spectrum (py-d5): 62.08(3H, s), 2.13(3H, s), 2.23(111, dd), 2.47(111, d), 2.78 -3.17(6H, m), 3.66(1H, d), 3.86(2H, q), 4.21(1H, dd), 4,43(1H, d), 5,19flH, dd), 5.46(1H, dd), 7.23(1H, t), 7.45(2H, br.s) IR spectrum (KBr method): 3280, 1707, 1629, 1547, -l 1511, 1451, 1332, 1071 cm Example 4: Preparation of 7-N-[2-(2-pyridyldithio)ethyl]mitomycin C 50 mg of 2-pyridyldithioethylamine dihydrochloride (disclosed in Japanese Patent Application as laid open to public inspection as Kokai Koho 136,261/80) is dissolved in methanol (2.5 ml), to which triethylamine (0,2 ml) is added dropwise while stirring. Mitomycin A (40 mg in total) is added in several portions to the mixture which is then stirred at ambient temperature for 5 hours. Water is added to the reaction solution and the extraction is effected by using chloroform. The extracted solution is dried over anhydrous sodium sulfate and distilled in vacuo to remove the solvent. The resultant oily substance is purified by silica gel column chromatography. The elution is effected by using a solvent system of a mixture of ethyl acetate/ methanol (95 :5, v/v) to give active fractions which are concentrated to obtain a blackish purple powder (54 mg) having the following characteristics (yield 94%): Elemental analysis (%): as C22H25N505S2 Found: H 5.06 C 52.58 N 13.63 Calculated: H 5.00 C 52.47 N 13.91 1.H-NMR spectrum (py-d5): 62.06(3H, s), 2.76(1H, br), 3.08(2H, t), 3.14(1H, br), 3.60(111, dd), 3.90 (1H, q), 4.00(1H, dd), 4.53(1H, d), 5.06(1H, t), 5.40(1H, dd), 7.06(2H, m), 7.61(2B, m), 8.66 (1H, m) IR spectrum (KBr method): 3290, 2930, 1713, 1632, 1553, 1505, 1444, 1414, 1330, 1061, 755 cm 1 Example 5: Preparation of 7-N-[2-(2-pyridyldithio)ethyl]- porfiromycin A similar procedure to that described in Example 4 is effected by using 2-pyridyldithioethylamine dihydrochloride (50 mg) and mitomycin F (40 mg) to obtain a blackish purple powder having the following characteristics (56 mg: yield 98%): Elemental analysis (%) as C23H27N505S2 Found: H 5.30 C 53.41 N 13.32 Calculated: H 5.26 C 53.37 N 13.53 H-NMR spectrum (CDC13): #1.94(3H, s), 2.27(3H, s), 2.27(2H, m), 2.96(2H, t) , 3.18(3H, s), 3.45(1H, dd), 3.57(1H, dd), 3.86(2H, q), 4.24(1H, d), 4.35(1H, dd), 4.72(1H, dd), 4.73(2H, br.s), 7.10 (1H, br.), 7.13(1H, m), 7.50-7.72(2H, m), 8.59 (1H, m) IR spectrum (KBr method): 3290, 2930, 1719, 1632, 1557, 1508, 1445, 1326, 1060, 758 cm Example 6: Preparation of 7-N-[2-(2-pyridyldithio)ethyl]mitomycin D A similar procedure to that described in Example 4 is carried out by using 2-pyridylthioethylamine dihydrochloride (50 mg) and mitomycin B (40 mg) to obtain 57 mg of a dark green powder having the following characteristics (yield: 99%): Elemental analysis (%): as C22H25H505S2 Found: H 5.03 C 52.51 N 13.69 Calculated: H 5.00 C 52.47 N 13.91 1H-NMR spectrum (CDC13): 61.91(3H, s), 2.27(3H, s), 2.27(2H, m), 2.96(2H, t), 3.49(1H, br.d), 3.71 (1H, t), 3.84(2H, q), 4.14(1H, d), 4.48(1H, br.), 4.72(2B, d), 4.81(2B, br.), 7.02(1H, br.), 7.10 (1H, m), 7.50 -7.70(2H, m), 8.56(1H, m) IR spectrum (KBr method): 3270, 1713, 1631, 1601, 1548, 1510, 1450, 1414, 1332, 1113, 1058, 758 cm 1 Example 7: Preparation of 7-N-(2-ethyldithioethyl)mitomycin C 7-N-(2-pyridyldithioethyl)mitomycin C prepared by the method of Example 4 (50 mg) is dissolved in methanol (2.5 ml),-to which ethanethiol (8iil) is then added. The mixture is stirred at ambient temperature for 10 minutes, and a saturated aqueous solution of sodium hydrogen carbonate is poured into the mixture. The mixture is extracted with chloroform and the extracted solution is dried over anhydrous sodium sulfate. The dried material is distilled in vacuo to remove the solvent. The resultant oily substance is purified by silica gel column chromatography. The elution is effected by using a solvent system of a mixture of chloroform/methanol (96 : 4; v/v) to give active fractions which are concentrated to obtain a residue which is then dissolved in chloroform. This solution is dropwise added to cyclohexane, from which a greyish blue powder (43 mg) having the following characteristics is recovered (Yield 96%): Elemental analysis (%): as C19H26N4O5S2 Found: H 5.79 C 50.29 N 12.16 Calculated: H 5.76 C 50.20 N 12.33 H-NMR spectrum (CDC13): #1.33(3H, t), 2.03(3H, s), 2.67(2H, q). 2.84(2H, t), 2.85(2H, m), 3,21(3H, s), 3.51(1H, dd), 3.62(1H, dd), 3.87(2H, q), 4.28 (1H, d), 4.50(1H, dd), 4.68(2H, br.s), 4.71(1H, dd), 6.49(1H, br.t) IR spectrum (KBr method): 3270, 1718, 1633, 1554, 1507, 1447, 1328, 1061 cm Example 8: Preparation of 7-N- (2-propyldithioethyl)mitomycin C 7-N-(2-pyridyldithioethyl)mitomycin C (50 mg) and propanethiol (9 p1) are treated in a similar manner to that described in Example 7 to obtain 29 mg of a greyish blue powder having the following characteristics with a yield of 62%: Elemental analysis (%): as C20H28N405S2 Found: H 6.03 C 51.32 N 11.75 Calculated: H 6.02 C 51.26 N 11.96 1K-NMR spectrum (CDC13): #0.99(3H, t), 1.71(2H, sextet), 2.03(3H, s), 2.68(2H, t), 2.83(2H, t), 2.85(2B, m), 3.21(3H, s), 3.51(1H, dd), 3.60(1H, dd), 3.84(2H, q), 4.28(1H, d), 4.50(1H, dd), 4.68(2H, br.s), 4.71(1H, dd), 6.48(1H, br.t) IR spectrum (KBr method) : 3290, 1721, 1634, 1558, -l 1509, 1448, 1327, 1060 cm Example 9: : Preparation of 7-N-[2-(2-hydroxyethyl)dithioethyll mitomycin C A similar procedure to that described in Example 7 is carried out by using 7-N-(2-pyridyldithioethyl)mitomycin C (50 mg) and 2-mercaptoethanol (7 p1) to obtain a greyish blue powder (41 mg) having the following characteristics with a yield of 88%: Elemental analysis (%): as C19H26N4O6S2 Found: H 5.60 C 48.12 N 11.62 Calculated: H 5.57 C 48.50 N 11.91 H-NMR spectrum (CDC13): 62.02(3H, s), 2.80-2.97(2H, m), 2.86(2H, t), 2.90(2H, t), 3.21(3H, s), 3.51 (1H, dd), 3.59(1H, dd), 3.87(2H, q), 3.88(2H, t), 4.27(1H, d), 4.50(1H, dd), 4.70(1H, dd), 4.78 (2H, br.s), 6.49(1, br.t) IR spectrum (KBr method): 3430, 3280, 1712, 1632, -1 1551, 1510, 1448, 1328, 1060 cm Example 10: Preparation of 7-N-(1,2-dithiolan- 4 -yl)mitomycin C 4-amino-1,2-dithiolane hydrochloride (14 mg) is added to a mixture (3 ml) of dimethylformamide and methanol (4 :1; v/v), which is then stirred at room temperature with addition of triethylamine (0.1 ml). Mitomycin A (30 mg) is added to the mixture, and the mixture is stirred at room temperature for 3 days. Water is poured into the reaction solution which is then extracted with chloroform. Anhydrous sodium sulfate is used to remove the solvent from the reaction solution which is then distilled in vacuo to give an oily substance. This substance is purified by silica gel column chromatography using a solvent system of a mixture of ethyl acetate and acetone (7 :3; v/v) to obtain a blackish brown paste (32 mg) having the following characteristics with a yield of 858: Elemental analysis (%): as C18H22N405S2 Found: H 5.09 C 49.42 N 12.51 Calculated: H 5.07 C 49.30 N 12.78 MS (EI-MS) m/z 438 (M+), 406, 395, 377, 273 H-NMR spectrum (CDCl3): 62.01(3H, s), 2.82(1H, dd), 2.91(111, d), 3.11-3.38(411, m), 3.21(3H, s), 3.51(1H, dd), 3.61(1H, dd), 4.24 (1H, d), 4.50 (1H, dd), 4.72(1H, dd), 4.73(2H, dd), 5.24(1H, m), 6.38(1H, br.d) IR spectrum (KBr method): 3280, 2930, 1718, 1633, -l 1561, 1501, 1447, 1338, 1059, 758 cm Example 11: Preparation of 7-N-(1,2-dithiolan- 4 -yl) porfiromycin A similar procedure to that described in Example 10 is carried out by using 4-amino-1,2-dithiolane hydrochloride (13 mg) and mitomycin F (30 mg) to obtain a blackish brown powder (28 mg) having the following charac teristics with a yield of 75%: Elemental analysis (%): as C19H24N4O5S2 Found: H 5.37 C 50.49 N 12.20 Calculated: H 5.35 C 50.43 N 12.38 MS (FD-MS) m/z 453 (M +H) H-NMR spectrum (CDC13): 62.00(3H, s), 2.27(3H, s) 2.27(2H, m), 3.05-3.35(4H, m), 3.18(3H, s), 3.45(1H, dd), 3.56(1H, dd), 4.20(1H, d), 4.34 (1H, dd), 4.70(1H, dd), 4.71(2B, br.s), 5.24 (1H, m), 6.39(1H, br.d) IR spectrum (KBr method) : : 3450, 3350, 3250, 2960, 1722, 1699, 1639, 1566, 1508, 1341, 1055, 744 cm Example 12 Preparation of 7-N-(1,2-dithiolan-4-yl)mitomycin D A similar procedure to that described in Example 10 is carried out by using 4-amino-1,2-dithiolane hydrochloride (14 mg) and mitomycin B (30 mg) to obtain a brown powder (32 mg) having the following characteristics with a yield of 85%: Elemental analysis (%): as C18H22N405S2 Found: H 5.08 C 49.36 N 12.59 Calculated: H 5.07 C 49.30 N 12.78 MS (FD-MS) m/z 439 (M+H) + 1H-NMR spectrum (CDC13): #1.99(3H, s), 2.27(3H, s), 3.05-3.40(4H, m), 3.50(1H, dd), 3.70(1H, t), 4.12(1H, d), 4.49(1H, br.s), 4.71(2H, d), 4.77 (2H, br.s), 5.24(1H, m), 6.39(1H, br.d) IR spectrum (KBr method): 3350, 2960, 1713, 1660, 1631, 1553, 1501, 1342, 1052 cm 1 Example 13 Preparation of 7-N-(1,2-dithiolan-4-yl)mitomycin E A similar procedure to that described in Example 10 is carried out by using 4-amino-1,2-dithiolane hydrochloride (13 mg) and mitomycin J (30 mg) to obtain a blackish brown powder (27 mg) having the following characteristics with a yield of 72%: Elemental analysis (%): as C19H24N405S2 Found: H 5.36 C 50.44 N 12.09 Calculated: H 5.35 C 50.43 N 12.38 H-NMR spectrum (CDC13): #1.99(3H, s), 2.22(1H, d), 2.32(3H, s), 2.38(1H, dd), 3.04 -3.39(4H, m), 3.31(38, s), 3.58(1H, dd), 3.81(1H, dd), 3.99 (1H, d), 4,45(1H, dd), 4.67(2H, br.s), 4.79(1H, dd), 5.24(1H, m), 6.34(1H, br.d) IR spectrum (KBr): 3360, 2950, 1717, 1631, 1557, 1501, 1444, 1333, 1048, 750 cm Example 14: Preparation of 7-N- [2-(2-pyridyldithio)ethyl]mitomycin E A similar procedure to that described in Example 4 is carried out by using 2-pyridyldithioethylamine dihydrochloride (50 mg) and mitomycin J (40 mg) to obtain a blackish purple powder (55 mg) having the following characterist-ics with a yield of 96%: Elemental analysis (%): as C23H27N505S2 Found: H 5.28 C 53.47 N 13.26 Calculated: H 5.26 C 53.37 N 13.53 1H-NMR spectrum (CDCl3): #1,93(3H, s), 2.21(1H,d), 2.32(311, S), 2.37(111, dd), 2.96(2H, t), 3.31(3H, s), 3.57(1H, dd), 3.81(1H, dd), 3.85(2H, q), 4.02(1H, d), 4.45(1H, dd), 4.66(2H, br.s), 4.82 (111, dd), 6.99(1H, br.t), 7.11(1H, m), 7.58(2H, m), 8.57(111, m) IR spectrum (KBr method): 3280, 2950, 1717, 1631, 1551, 1507, 1445, 1413, 1332, 1112, 1047, 757 cm 1 Example 15: Preparation of 7-N-[2-(2,3-dihydroxypropyl)dithioethyl)- mitomycin C A similar procedure to that described in Example 7 is carried out by using 7-N-(2-pyridyldithioethyl)mitomycin C (40 mg) and 1-mercapto-2,3-propanediol (7.1 p1) to obtain black paste, which is then freeze-dried to obtain a black powder having the following characteristics (33 mg; yield 83%): Elemental analysis (%): as C20H28N407S2 Found: H 5.62 C 47.96 N 11.01 Calculated: H 5.64 C 47.99 N 11.19 1H-NMR spectrum (py-d5): 62.13(3H, s), 2.73(1H, m), 3.03(2H, t), 3.12(1H, d), 3.22(3H, s), 3.37(2H, d), 3.59(1H, dd), 3.83- 4.11(3H, m), 4.08(2H, d), 4.44(1H, m), 4.52(1H, d), 5.03(1H, m), 5.38(1H, dd), 7.28(1H, br), 7.57(2H, br) IR spectrum (KBr method): 3430, 3280, 2930, 1701, 1632, 1553, 1510, 1449, 1332, 1064, 755 cm Example 16: Preparation of 7-N-(2-methoxycarbonylmethyldithioethyl) mitomycin C A similar procedure to that described in Example 7 is carried out by using 7-N- (2-pyridyldithioethyl)mitomycin C (50 mg) and methyl thioglycolate (8.8 p1) to obtain a greyish blue powder (34 mg) having the following characteristics with a yield of 69%: Elemental analysis (%): as C20H26N407S2 Found: H 5.28 C 48.21 N 10.97 Calculated: H 5.26 C 48.18 N 11.24 H-NMR spectrum (CDC13): 62.02(3H, s), 2.84(2H, br.s), 2.95(2B, t), 3.21(3H, s), 3.51(2B, s), 3.52(1H, br.d), 3.60(111, dd), 3.76(3H, s), 3.89(2H, q), 4.28(1H, d), 4.50(1H, dd), 4.73(1H, dd), 4.74(2H, br.s), 6.47(1H, br.t) IR spectrum (KBr method): 3280, 2930, 1723, 1554, 1508, 1445, 1330, 1060 cm Example 17: Preparation of 7-N-(2-cyclohexyldithioethyl)mitomycin C 7-N-(2-pyridyldithioethyl)mitomycin C (50 mg) is dissolved in methanol (2.5 ml), to which is then added cyclohexanethiol (12.1 p1). The mixture is stirred at ambient temperature for 12 hours under nitrogen stream and is then treated in a similar manner to that described in Example 7 to obtain a greyish blue powder (49.5 mg) having the following characteristics with a yield of 98%: Elemental analysis (%): as C23H32N405S2 Found: H 6.33 C 54.33 N 10.76 Calculated: H 6.34 C 54.31 N 11.01 111-NMR- spectrum (CDCl3): 61.02 -2.20(1OH, m), 2.03 -(3H, s), 2.68(1H, br), 2.82(4H, m), 3.20(3K, s), 3.51(111, dd), 3.61(1H, dd), 3,86(2H, q), 4.28 (1H, d), 4.50(1H, dd), 4.72(1H, dd), 4.83(2H, br.s), 6.49(111, br.t) IR spectrum (KBr method): 3300, 2930, 2850, 1718, 1633, 1558, 1509, 1448, 1329, 1062 cm 1 Example 18: Preparation of 7-N-[2-(2-aminoethyl)dithioethyl]- mitomycin C Cystamine dihydrochloride (103 mg) is dissolved in methanol (2.5 ml), to which triethylamine (0.4 ml) is added dropwise with stirring, followed by addition of mitomycin A (40 mg in total) in several portions After stirring for 40 minutes at ambient temperature, water is added to the reaction mixture, followed by extraction with chloroform. Anhydrous sodium sulfate is used to dry the extracted solution, from which the solvent is then removed by distillation in vacuo. The resultant oily substance is purified by column chromatography using Diaion HP-20. The elution is effected by using a mixture of water/methanol (1 :4; v/v) to give the active fractions which are then concentrated to obtain a blackish purple paste (21 mg) having the following physical characteristics (yield 41%):- Elemental analysis (%): as C19H27N505S2 Found: H 5.86 C 48.72 N 14.66 Calculated: H 5.80 C 48.60 N 14.91 1H-NMR spectrum (d, py-d5): 2.14(3H, s), 2.76(1H, br), 2.87 -3,19(7H, m), 3.22(3H, s), 3.59(1H, br.d), 3.85 -4.06(3H, m), 4,52(1H, d), 5.03(1K, t), 5.38 (1H, dd), 7,31(1H, t), 7.58(2H, br) IR spectrum (KBr method) : 3280, 2920, 1712, 1632, -1 1552, 1508, 1449, 1330, 1061 and 752 cm Example 19: Preparation of 7-N,7'-N'-dithiodiethylenedimitomycin C Cystamine dihydrochloride (12.9 mg) is dissolved in methanol (2.5 ml), to which is then added triethylamine (50 pl) with stirring. To this mixture is added mitomycin A (40 mg in total) in several portions, and the mixture is stirred at room temperature for 10 hours. After addition of water, the reaction mixture is extracted with chloroform. The extracted solution is dried by using anhydrous sodium sulfate, followed by removal of the solvent by distillation in vacuo. The resultant oily substance is purified by silica gel column chromatography. The elution is effected by using a mixture of chloroform/methanol (9 :1; v/v) as developer to give active fractions which are then concentrated to obtain a blackish purple powder (44 mg) having the following characteristics (yield: 98%): Elemental analysis ( & : as C341142N8O4S2 Found: H 5.41 C 51.93 N 14.01 Calculated: H 5.37 C 51.90 N 14.24 H-NMR spectrum (6, py-d5): 2.14(3H, s), 2.75(1H, dd), 3.00(2H, t), 3.13(1H, d), 3.22(3H, s), 3.59(1H, dd), 3.95(2B, q), 3.99(1H, dd), 4.52(1H, d), 5.02(1H, t), 5.36(1H, dd), ?.27(111, t), 7.58(2H, br) 13C-NMR spectrum: (6, py-d5) 10.0; 32.7; 36.6; 38.6; 43.8; 44.3; 49.7; 50.5; 62.4; 104.5; 106.8; 110.8; 147.1; 155.7; 158.0; 176.7; 179.1 IR spectrum (KBr method): 3290, 2920, 1714, 1632, 1554, 1507, 1448, 1325, 1217, 1062 and 752 cm 1 Example 20: Preparation of 7-N, 7'-N'-dithiodlethylenediporfiromycin To cystamine dihydrochloride (12.4 mg) dissolved in methanol (2 ml) is added triethylamine (50 p1). To this solution mitomycin F (40 mg in total ) is added in several portions and the mixture is stirred at room temperature for 8 hours. After addition of water, the reaction mixture is extracted with chloroform. Anhydrous sodium sulfate is used to dry the extracted solution, from which the solvent is removed by distillation in vacuo. The resultant oily substance is purified by silica gel column chromatography. The solution is effected by using a solvent system of chloroform/methanol (95 :5; v/v) to give the active fractions which are then concentrated to obtain a black powder (43.5 mg) having the following characteristics (yield: 97%): Melting point: 67.5 - 70 C Elemental analysis (%): as C36H46N8OloS2 Found: H 5.72 C 53.17 N 13.50 Calculated: H 5.69 C 53.06 N 13.75 H-NMR spectrum (pud5): 62.15(3H, s), 2.15(111), 2.25(3he s), 2.53(1K, d), 3.00(2H, t), 3.20 (3H, s), 3.51(lH, d), 3.95(3H, m), 4.45(1H, d), 4.77(1H, t), 5.30(1H, dd), 7.25(1H, t), 7.58 (2H, br.s) IR spectrum (KBr method): 3280, 2920, 1721, 1633, 1568, 1510, 1447, 1327, 1060 cm Example 21: Preparation of 7-N-2- (2-aminoethyl)dithioethyl)- porfiromycin To cystamine dihydrochloride (100 mg) dissolved in methanol (2.5 ml), triethylamine (0.4 ml) is added with stirring. Mitomycin F (40 mg in total) is added in several portions to this solution and the mixture is stirred at room temperature for 15 minutes. After this, water is added to the reaction mixture which is extracted with chloroform. Anhydrous sodium sulfate is used to dry the extracted solution, from which the solvent is then removed by distillation in vacuo. The resultant oily substance is purified by silica gel column chromatography. The elution is effected by using a solvent system of chloroform/methanol (3 :2; v/v) to give the active fractions which are concentrated to yield a black paste (12 mg) having the following characteristics (yield: 23%): Elemental analysis (%): as C20H29N505S2 Found: H 6.07 C 49.76 N 14.23 Calculated: H 6.04 C 49.67 N 14.48 1H-NMR spectrum (py-d5): 62.14(3H, s), 2.16(1H, m), 2.24(3H, s), 2.53(1H, d), 2.80-3.19(6H, m), 3.19(3H, s), 3.52(1H, dd), 3.94(1H, dd), 3.94(2H, q), 4.45(1H, d), 4,77(1H, dd), 5.31(1H, dd), 7.27(1H, br.t), 7.64(2H, br.s) IR spectrum (KBr method): 3360, 1714, 1633, 1554, 1510, 1459, 1328, 1062 cm According to a further feature of the present invention, there is provided a pharmaceutical composition, comprising as active ingredient at least one compound of formula I as hereinbefore defined in association with a physiologically acceptable carrier or excipient. The carrier or excipient may take various forms depending upon the desired formulation. Thus, for example, one or more compounds of general formula (I) as hereinbefore defined may, for example, be dissolved in a physiological solution of sodium chloride, or a solution of glucose, lactose and/or mannitol in order to formulate a pharmaceutical composition suitable for injection. Alternatively, it is possible to freeze-dry the compounds or compound of the present invention, to which sodium chloride is added to prepare a powderly injection agent according to the Pharmacopoeia of Japan. The composition may, if desired, comprise conventional additives or excipients such as for example pharmaceutically acceptable salts which are well known in the pharmaceutical art. The dosage units may contain any appropriate amount of active ingredient, for example, an amount of 0.02 to 1 mg/kg/day, although the daily dose may vary with differring conditions. The administration may be effected, for example, by intravenous injection and may be administered, for example, from 1 to 3 times per week. The present invention thus includes compositions of the present invention in sterile form. If desired, oral administration may be possible. Dosage unit forms suitable for oral administration may, for example, include tablets, powders, granules and ampoules and may further contain appropriate excipients well known in the pharmaceutical art. If desired, the composition may be administered, for example, into the artery, abdominal cavity or thorax. Formulations of the compounds of the present invention are illustrated in the following non-limiting Examples. Example A: 7-N, 7'.-N 'dithiodiethylenediporfiromycin prepared by the method of Example 20 (10 g) is dissolved in ethanol (1000 ml) and sterilized by filtering under pressure by the use of Millipore Filter (commercial product of Millipore Corpn., U.S.A.) having a pore size of 0.22 p. The resultant sterilized filtrate (1.0 ml) is poured into brown vials (10 mg/vial) and frozen at -500C for 2 hours. After confirming that the temperature of the ingredient in the vial reaches the atmospheric temperature, the material is further dried in vacuo (0.1 mm Hg) at an atmospheric temperature of 200C for 4 hours, and the vial is sealed with a rubber plug In use, a sterilized physiological sodium chloride solution (5 ml) containing a dissolution aid is added to the ingredient and well stirred to obtain an injecting solution. Example B: 7-N-(2-hydroxyethyldithioethyl)mitomycin C (3 g) prepared by the method of Example 9 is dissolved in distilled water (1000 ml) and treated in a smilar manner to that described in Example A with the exception that the second drying is effected at an atmospheric temperature of 300C. Example C: 7-N-(2-aminoethyldithioethyl)mitomycin D (10 mg), prepared by the method of Example 3, lactose (90 mg), corn starch (40 mg), polyvinyl alcohol (4 mg), Avicel (28 mg; microcrystalline cellulose, commercially available from FMC Corpn., U.S.A.) and magnesium stearate (1 mg) are used to prepare a tablet in conventional manner. The following experiment illustrates the antitumour activities, acute toxicities (LD50) and toxicities against bone marrow of certain compounds of the present invention : - Experiment: (1) Effect on Sarcoma 180 solid tumour: 5 x 106 cells of Sarcoma 180 solid tumour were innoculated into the abdominal cavities of groups of ddy mice, each group consisting of 5 mice. 7.days after this, on each occasion, the tumour cells were collected from the ascites of the mouse. The cells were washed with a sterilized physiological sodium chloride solution and used to 7 prepare a cell suspension containing 5 x 10 cells per ml of a sterilized physiological solution of sodium chloride, of which 0.1 ml was injected under the skin of the right armpit of a ddy male mouse (body weight 20 +2 g). A test compound was dissolved in a physiological solution of sodium chloride or a similar solution containing Tween 80 (a surfactant commercially available from Atlas Chemical Industries, Inc., U.S.A.). 24 hours after the implantation of the tumour cells, the test compound (0.1 to 0.2 ml) was injected into the test mice intraperitoneally. In order to determine the antitumour activity of the test compound, 7 days after the implantation of the tumour cells, on each occasion, the major axis (a) and minor axis (b) of the tumour were measured to calculate the volume of the tumour ['a' x 'b'/2]. The anti-tumour effect was evaluated by the ratio of the tumour volume in the test animals (T) to the corresponding volume of the control (untreated) animals (C). (2) Determination of ED50: A dose capable of reducing the volume of a Sarcoma 180 solid tumour to 50% of the corresponding volume of the untreated group on average was defined as the ED50. T/C ratios and the doses were respectively plotted on the ordinate in arithmetic scale and abscissa in logarithmic scale on graph paper, from which the relationship between the doses and the T/C ratios was calculated as a straight line by the least square method. From the straight tropic line thus-obtained, the dose corresponding to a T/C of 0.5 was determined. (3) Acute toxicity (LD50): On each occasion, the test compound was given to the test animal. After this, the death ratio of the animals of the test group was observed for 14 days, from which LD50 was calculated by Behrens-Körber's method. (4) Chemotherapeutic Index (C.I.): The ratio of LD50 to ED50 was defined as C.I. A greater C.I. suggests a greater effective range of the drug. (5) Effect upon the number of peripheral leukocytes: 5 x 106 cells of Sarcoma 180 solid tumour were implanted under the skin of each mouse at the right armpit. 24 hours after this, venous blood (0.02 ml) was collected from the eyepit of the mouse and suspended in Cell-Kit Seven solution (10 ml; commercially available from Toa Iryo Denshi R.K., Japan). To the suspension, a drop of saponin solution was added to dissolve the red cells and the number of leukocytes were counted using a microcell counter. The number of leukocytes and the corresponding dose were respectively plotted on the ordinate in arithmetic scale and on the abscissa in logarithmic scale on graph paper to investigate the relationship between dosage and the number of peripherical leukocytes. A dose capable of giving 4000 leukocytes/mm was defined as WBC 4000, which corresponded to about 1/2 the number of peripherical leukocytes in normal mice. (6) WBC 4000/ED50: The greater the ratio of WBC 4000 to ED50 the smaller the decrease in the number of peripherical leukocytes viz. the lower the toxicity against bone marrow in the area of the effective dose. The results obtained from the experiments are shown in the following Table 2. Table 2 A ... Anti-tumour activity B ... Toxicity against bone marrow EMI31.1 <tb> A <SEP> B <tb> <SEP> Com- <SEP> LD50 <SEP> liD <SEP> <tb> <SEP> pound <SEP> 50 <SEP> *1 <SEP> WBC <SEP> 4000/ <SEP> *2 <tb> <SEP> ED50 <tb> <SEP> a <SEP> > 60 <SEP> > 2.99 <SEP> 1.4 <SEP> 2.29 <SEP> 3.8 <tb> <SEP> c <SEP> 74.3 <SEP> 3.11 <SEP> 1.5 <SEP> 1.87 <SEP> 3.1 <tb> <SEP> g <SEP> 5.4 <SEP> 1.64 <SEP> 0.8 <SEP> 3.76 <SEP> 4.7 <tb> <SEP> i <SEP> #11.25 <SEP> <SEP> #2.12 <SEP> #1 <SEP> 2.13 <SEP> 2.7 <tb> <SEP> j <SEP> 5.25 <SEP> - <SEP> <SEP> 1.3-0.7 <SEP> - <SEP> <SEP> 4.1-8.1 <tb> <SEP> 1 <SEP> 35.6 <SEP> - <SEP> 1.2 <SEP> - <SEP> 1.4 <tb> <SEP> o <SEP> 22.5 <SEP> - <SEP> <SEP> 1.4 <SEP> - <SEP> <SEP> 3.9 <tb> <SEP> P <SEP> 25 <SEP> -12.5 <SEP> - <SEP> 1.6-0.9 <SEP> - <SEP> 0.9 <SEP> 3.2 <tb> <SEP> r <SEP> 13.5 <SEP> 0.73 <SEP> ¯ <SEP> 0.6 <SEP> 1.25 <SEP> 3.0 <tb> <SEP> s <SEP> 18.8 <SEP> 2.98 <SEP> 1.6 <SEP> 2.63 <SEP> 3.0 <tb> <SEP> t <SEP> 33.8 <SEP> 2.15 <SEP> 1.0 <SEP> 1.34 <SEP> 2.2 <tb> Notes:- * Comparison with mitomycin C *1 ... C.I./C.I. of mitomycin C *2 ... [WBC 4000/ED50]/[WBC 4000/ED50 of mitomycin C].

Claims: Claims 1. Compounds of the general formula: EMI32.1 wherein X represents a EMI32.2 or R3-S-S-CH2-CH2- group [in which R3 represents a cycloalkyl or straight chain or branched alkyl group having up to 7 carbon atoms, said alkyl or cycloalkyl group optionally carrying 1 to 3 amino groups and/or I to 3 hydroxyl groups; a (C112)nC02R4 group (in which n is the integer 1, 2 or 3, and R4 represents a methyl or ethyl group); a pyridyl group; or a group of the formula: EMI32.3 and R1 and R2, which may be the same or different, each represents a hydrogen atom or a methyl group, and indicates CL or ss bonding}. 2. Compounds as claimed in claim 1 having mitomycin C or D structure wherein R3 represents straight chain or branched alkyl group having I to 4 carbon atoms optionally substituted by 1, 2 or 3 hydroxyl group and/or 1, 2 or 3 amino group, -(CH2)nCO2R4 wherein n and R4 are as hereinbefore defined, or a group of the formula: EMI33.1 wherein R1 and R2 are as defined in claim 1. 3. A compound as claimed in claim 1 selected from: 7-N,7'-N'-dithiodiethylenedimitomycin D; 7-N-(2-aminoethyldithioethyl)mitomycin D; 7-N-ethyldithioethylmitomycin C; 7-N-(2-hydroxyethyldithioethyl)mitomycin C; 7-N-(2-aminoethyldithioethyl)mitomycin C; 7-N,7'-N'-dithiodiethylenedimitomycin C; 7-N-(1,2-dithiolan-4-yl)mitomycin C; 7-N-(1,2-dithiolan-4-yl)mitomycin D; 7-N- [2- (2, 3-dihydroxypropyl) dithioethylimitomycin C; 7-N- (2-methoxycarbonylmethyldithioethyl)mitomycin C; and 7-N, 7 '-N'-dithiodiethylenediporfiromycin. 4. Compounds as claimed in claim 1 wherein R3 represents a 2-pyridyl group. 5. A process for the preparation of compounds as claimed in claim 1 selected from a) the reaction of Åa compound of the formula: EMI33.2 (wherein R1 and R2, which may be the same or different, are as defined in claim 1) with a compound of the formula: X-NH2 ( III) (wherein X is as defined in claim 1) or a salt thereof; and b) for the preparation of compounds of formula I as defined in claim 1 [wherein X represents the group R3'-S-S- CH2-CH2 - in which R3' represents a cycloalkyl or straight chain or branched alkyl group with up to 7 carbon atoms, said alkyl or cycloalkyl group optionally carrying I to 3 amino groups and/or I to 3 hydroxy groups; or R3' represents a -(CE2)nCO2Ro group (in which n is the integer 1, 2 or 3 and R4 represents a methyl or ethyl group)3, the reaction of a compound of the formula: EMI34.1 (wherein R1 and R2, which may be the same or different, are as defined in claim 1) with a compound of the formula: R31 SH (V) (wherein R3, is as herein defined) or, where appropriate, a base addition salt thereof. 6. A pharmaceutical composition comprising as active ingredient at least one compound of formula I as defined in claim 1 in association with a physiologically acceptable carrier or excipient. 7. A compound of formula I as defined in claim 1 for use as an anti-tumour agent. 8. A compound of formula I as defined in claim I for use as an antibacterial agent.

Inventors: ASHIZAWA, TADASHI, GOTO, JYOJI, KONO, MOTOMICHI, MORIMOTO, MAKOTO, SAITO, YUTAKA, SHIRAHATA, KUNIKATSU
Applicants: KYOWA HAKKO KOGYO CO., LTD.
Application year: 1983
Main classification: C07D487
IPC codes: C07D519, C07D487