A compound represented by formula (I): ##STR1## or a pharmaceutically acceptable salt thereof is provided, which has an excellent antitumor activity.

FIELD OF THE INVENTION 
This invention relates to a novel compound UCE6 which has an antitumor 
activity and is useful as an antitumor agent. 
BACKGROUND OF THE INVENTION 
It is reported in the literature that several antibiotics, such as 
anthracycline, have an anthraquinone skeleton [CRC Handbook of Antibiotic 
Compounds, CRC Press, U.S.A. (1981)]. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a compound having an 
excellent antitumor activity. 
The present inventors found that a substance having an antitumor activity 
is produced in a culture obtained by incubating a microorganism 
(hereinafter referred to as strain UOE6) separated from soil in a medium. 
The active substance was isolated and purified from the medium. The 
investigation of the physicochemial properties of the purified active 
substance revealed that the purified active substance is a novel compound. 
The novel compound is named UCE6. 
According to the present invention, a novel compound UCE6 which is 
represented by the following formula (I): 
##STR2## 
or a pharmaceutically acceptable salts thereof. 
UCE6 provides antitumor activity. 
This compound can be obtained by cultivating a microorganism belonging to 
actinomycetes.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described below in greater detail. 
Physicochemical Properties of UCE6: 
(1) Molecular weight: 436. 
(2) Molecular formula: C.sub.24 H.sub.20 O.sub.8. 
(3) Mass spectrometry: secondary ion mass spectrum (matrix: m-nitrobenzyl 
alcohol): m/z; 437 (M+H).sup.+, 375, 350, 329, 280, 278, 238, 222, 207. 
High-resolution fast atom bombardment (FAB) mass spectrum (matrix: 
m-nitrobenzyl alcohol): m/z found: 437.1242 (M+H).sup.+ calculated: 
437.1236 (for C.sub.24 H.sub.21 O.sub.8). 
(4) Specific rotation: [.alpha.].sub.D.sup.22 =+350.degree. (c=0.0021, 
methanol). 
(5) Ultraviolet absorption spectrum: (measured in methanol) 
.lambda..sub.max nm (.epsilon.); 477 (15,000), 334 (14,800), 307 (27,600), 
294 (25,300), 283 (26,100), 240 (25,300), 217 (23,500). 
(6) Infrared absorption spectrum (KBr method): .upsilon..sub.max cm.sup.-1 
; 361, 1695, 1655, 1603, 1441, 1377, 1323, 1277, 1217. 
(7) .sup.13 C-NMR spectrum (100 MHz, DMSO-d.sub.6 solution): .delta. ppm; 
184.5, 182.6, 167.0, 162.2, 158.7, 139.0, 137.7, 132.3, 129.5, 128.9, 
128.2, 123.7, 121.3, 118.9, 116.9, 111.8, 108.9, 107.7, 62.7, 51.4, 50.0, 
23.8, 8.3 (having an unobserved signal). 
(8) .sup.1 H-NMR spectrum (500 MHz, DMSO-d.sub.6 solution): .delta. ppm; 
ca. 13.5 (1H, br. s), 7.75 (1H, m), 7.14 (1H, m), 7.00 (1H, m), 6.82 (1H, 
m), 4.22 (2H, m), 4.17 (1H, m), 2.68 (1H, dd, J=15.7, 7.3 Hz), 2.57 (1H, 
dd, J=15.7, 5.0 Hz), 1.99 (3H, d, J=1.8 Hz), 1.13 (3H, d, J=6.2 Hz). 
(9) Solubility: soluble in dimethylsulfoxide (DMSO), N,N-dimethylformamide 
and pyridine and hardly soluble in water, ethanol, methanol, ethyl acetate 
and chloroform. 
(10) Color reaction: positive in anisaldehyde and iodine. 
(11) Appearance: a red powder. 
(12) Thin layer chromatography: Rf 0.61 [developed with n-hexane: ethyl 
acetate: methanol (5:5:1, v/v) on a silica gel thin layer (HPTLC plate 
Art. 5715, mfd. by Merck). Rf 0.49 [developed with 
chloroform:methanol=10:1]. After the completion of the development, a spot 
of UCE6 can be detected by UV absorption. 
The pharmaceutically acceptable salts of UCE6 include pharmaceutically 
acceptable metal salts. As the metal salt, there are alkali metal salts 
such as sodium salt and potassium sats, alkaline earth metal salts such as 
magnesium salt and calcium salt. 
Biological activities of UCE6 is described below. 
(A) Inhibition on the Growth of HeLaS3 Cells 
0.1 ml portions of a 3.times.10.sup.4 cell/ml suspension of HeLaS3 cells 
[American Type Culture Collection (ATCC) CCL2.2]. in Minimum Essential 
Medium (MEM) medium (mfd. by Nissui Seiyaku) containing 10% of calf fetal 
serum and 2 mM of glutamine (hereinafter referred to as the medium A) were 
pipetted into a 96-well microtiter plate. 0.05 ml of the test compound 
optionally diluted with the medium A is added to each well, followed by 
incubating in a carbon dioxide gas incubator at 37.degree. C. for 72 
hours. After removing supernatant the culture 0.1 ml of the medium A 
containing 0.02% of Neutral Red is added to the residue. The cells are 
cultivated in the carbon dioxide gas incubator at 37.degree. C. for 
additional one hour to thereby stain the cells. After removing the 
supernatant of culture, the residue was washed with saline once. The 
pigment is extracted with 0.001 N hydrochloric acid/30% ethanol and the 
absorbance at 550 nm is measured with a microplate reader. Then IC.sub.50 
(the concentration of the test compound capable of inhibiting the growth 
of the cells at a ratio of 50%) is calculated on the basis of the 
comparison between the absorbance of untreated cells and that of the test 
compound-treated cells (at various concentration of the test compound). 
Results are shown in Table 1. 
TABLE 1 
______________________________________ 
Compound IC.sub.50 (.mu.M) 
______________________________________ 
UCE6 0.018 
______________________________________ 
A method for producing UCE6 is described below. 
UCE6 can be obtained by cultivating a microorganism (belonging to 
actinomycetes and being capable of producing UCE6) in medium, accumulating 
UCE6 in a culture and recovering UCE6 from the culture. 
As a UCE6-producing microorganism, any strain may be used so long as it 
belongs to actinomycetes and capable of producing UCE6. Furthermore, 
mutants of such a strain obtained by artificial mutation techniques (for 
example, UV irradiation, X-ray irradiation, treatment with mutagenic 
agent) or spontaneous mutation are also usable in the present invention. 
As a typical example of the strain, strain UOE6 may be cited. 
The mycological characteristics of the actinomycetes strain UOE6 are as 
follows. 
1. Morphology 
In a usual agar medium, the strain UOE6 forms branched substrate hyphae 
having septal walls. Neither the formation of aerial hyphae nor 
characteristic segmentation in the substrate hyphae is observed. Neither 
any spore, sporangium nor sclerotium is formed. 
2. Growth in Various Media 
The strain UOE6 moderately or vigorously grows in synthetic and natural 
media which are commonly employed and shows orange or brown substrate 
hyphae. In some media, it produces a brown soluble pigment. 
The characteristics of the growth and the color observed when the strain 
UOE6 is cultivated in various media at 28.degree. C. for 20 days are given 
hereinbelow. Colors are expressed in accordance with the classification 
described in Color Harmony Manual [Container Corporation of America]. 
1. Glucose/aspargine Agar Medium 
Growth and color of substrate hyphae: somewhat good, light tan (3 gc). 
Soluble pigment: formed, pale brown. 
2. Glycerol/aspargine Agar Medium 
Growth and color of substrate hyphae: somewhat poor, light apricot (4 ea). 
Soluble pigment: none. 
3. Sucrose/nitrate Agar Medium 
Growth and color of substrate hyphae: moderate, light apricot (4 ea). 
Soluble pigment: slightly formed, pale brown. 
4. Starch/inorganic Salt Agar Medium 
Growth and color of substrate hyphae: moderate, pastel orange (4 ic). 
Soluble pigment: formed, pale brown. 
5. Tyrosine Agar Medium 
Growth and color of substrate hyphae: moderate, dusty orange (4 lc). 
Soluble pigment: none. 
6. Enriched Agar Medium 
Growth and color of substrate hyphae: poor, light tan (3 gc). 
Soluble pigment: slightly formed, pale brown. 
7. Malt Extract/yeast Extract Agar Medium 
Growth and color of substrate hyphae: good, pastel orange (4 ic). 
Soluble pigment: slightly formed, pale brown. 
8. Oatmeal Agar Medium 
Growth and color of backside: somewhat good, light orange (4 ia). 
Soluble pigment: slightly formed, pale brown. 
3. Physiological Properties 
Physiological properties of the strain UOE6 are described below. The growth 
temperature range is determined after incubating the strain for 7 days, 
while other data are obtained after incubating it for 1 to 3 weeks. 
(1) Utilization of carbon source: on agar medium, L-arabinose, D-xylose, 
D-glucose, D-fructose, sucrose, L-rhamnose, raffinose and D-mannitol are 
utilized for the UOE6. But inosital is not utilized for the UOE6. 
(2) Action on milk: it causes neither coagulation nor liquefaction. 
(3) Hydrolysis of starch: yes. 
(4) Growth temperature range: 15 to 35.degree. C. 
(5) Production of melanoid pigment: not observed on definite media 
(tyrosine agar medium, peptone/yeast/iron agar medium). 
(6) Liquefaction of gelatin: not grown on a definite medium 
(glucose/peptone gelatin medium). 
4. Formation of Cell Wall 
Amino acids including alanine, glutamic acid, 3-hydroxy-diaminopimelic acid 
and glycine and saccharides including xylose and arabinose are detected 
from the cell wall of the strain UOE6 prepared by the method of Kawamoto 
et al. [J. Bacteriol., 146, 57-534 (1981)] (cell wall type II, saccharide 
pattern D). 
Based on these characteristics of the UOE6, the strain UOE6 is classified 
into actinomycetes. Since no spore is adhered to UOE6 it is difficult to 
determine the genus of the strain. 
Under the Budapest treaty, this strain has been deposited with Fermentation 
Research Institute of the Agency of Industrial Science and Technology of 
1-3, Higashi 1-chome, Tsukuba-shi, Ibaraki 305 Japan as the accession 
number FERM BP-3877 since May 28, 1992. 
A method for incubating the UCE6-producing strain is described below. 
In order to cultivate the UCE6-producing strain in the present invention, a 
usual cultivation method of actinomycetes can be used. As a medium of 
cultivation, either a synthetic medium or a natural medium may be used so 
long as it contains an utilizable carbon source, a nitrogen source, 
inorganic matters and required promoting substances of the growth of the 
strain and/or of the production of UCE6. 
As the carbon source, for example, glucose, starch, dextrin, mannose, 
fructose, sucrose, lactose, xylose, arabinose, mannitol and molasses may 
be used either singly or combinedly. Furthermore, hydrocarbons, alcohols 
and organic acids are also usable, so long as it is utilized for the 
strain. 
As the nitrogen source, for example, ammonium chloride, ammonium nitrate, 
ammonium sulfate, sodium nitrate, urea, peptone, meat extract, yeast 
extract, dry yeast, corn steep liquor, soybean flour and casamino acids 
may be used either singly or combinedly. In addition, the medium may 
contain inorganic salt(s) such as sodium chloride, potassium chloride, 
magnesium sulfate, calcium carbonate, potassium dihydrogen phosphate, 
ferrous sulfate, calcium chloride, manganese sulfate, zinc sulfate or 
copper sulfate, if required. Furthermore, it may contain appropriate trace 
component(s) capable of promoting the growth of the strain and/or the 
production of UCE6. 
As the cultivation method, liquid culture or submerged agitation culture 
may be suitably selected. The incubation is carried out at a temperature 
of 16.degree. to 37.degree. C., preferably 25.degree. to 32.degree. C., 
and at a pH 4 to 10, preferably 6 to 8. Usually, the cultivation is 
completed within 1 to 7 days and thus the target product UCE6 is formed 
and accumulated in the culture broth and cells. The pH value of the 
culture medium is controlled with the use of aqueous ammonia or an 
ammonium carbonate solution. When the content of the product in the 
culture medium reaches the maximum level, the incubation is ceased. 
The product UCE 6 is isolated and purified from the culture by a method 
commonly used for isolating and purifying a microbial metabolite from its 
culture. For example, the culture is divided into the culture supernatant 
and cells by filtering and the cells are extracted with, for example, 
chloroform or acetone. Then the extract is combined with the culture 
supernatant and passed through a column packed with a polystyrene 
adsorbent such as Diaion HP20 (mfd. by Mitsubishi Kasei Corporation) for 
adsorption of the active component. The active component is eluted with, 
for example, ethyl acetate or acetone. The eluate is concentrated and UCE6 
is obtained therefrom by, for example, silica gel column chromatography or 
high performance liquid chromatography. During the incubation and 
purification procedures, the behaviors of UCE6 can be monitored by using 
the UV absorption of UCE6 as an indicator. 
The UCE6 can be prepared by basically the known synthetic method as 
described in Cameron, D. W. et al, Tetrahedron Letters, 3, 5593-5596 
(1992). 
In case that salts of UCE6 are desired to be obtained, when the crude UCE6 
is obtained in the form of a salt, UCE6 may be purified as it is. Further 
in case that UCE6 is obtained in a free form, salts may be formed in a 
conventional manner. 
The UCE6 is useful as an anti-tumor agent, which can be used directly as 
such, or in various dosage forms. For example, where UCE6 is used in the 
form of an injeciton, it may be dissolved in a diluent conventinally used 
in the art, such as a physiological saline, or glucose, lactose or 
mannitol solution for injection. Alternatively, UCE6 may be freeze-dried 
according to a conventional manner to give a product for injection or may 
be prepared into injectable powder by adding sodium chloride thereto. In 
addition, the injection may also contain an auxiliary agent such as 
polyethylene glycol, HCO-60 (surfactant manufactured by Nikko Chemical 
Co., Ltd.), as well as a carrier such as ethanol and/or liposome or 
cyclodextrin. These injection are generally used for intraveous 
administration but may also be used for intra-arterial, intra-peritoneal 
or intra-thoracial administration. 
UCE6 may also be administered orally by mixing with an appropriate 
excipient, a disintegrator, a binder, a lubricant, etc. in a conventional 
manner to prepare a tablet, a granule, a powder or a syrup. Furthermore, 
UCE6 may be mixed with a conventionally used carrier and formed into a 
suppository for rectum administration. 
Dosage may appropriately vary depending upon the administration route, the 
age of a patient and the condition of a patient. The administration route, 
may also be varied according to the condition of a patient and the dosage. 
For example, UCE6 can be intermittently administered in a dose of 10 to 60 
mg/kg once a day. 
The following Example is provided to further illustrate the present 
invention, but it is not to be construed to limit the scope of the present 
invention. 
EXAMPLE 1 
Actinomycetes strain UOE6 (FERM BP-3877) was used as a seed strain. This 
strain was inoculated into 300 ml of a seed medium (pH 7.2 before 
sterilization) comprising 5 g/l of Bacto Trypton (mfd. by Difco), 5 g/l of 
yeast extract, 3 g/l of meat extract, 10 g/l of soluble starch, 10 g/l of 
glucose and 5 g/l of calcium carbonate contained in a 2 l Erlenmeyer flask 
and then incubated at 28.degree. C. for 120 hours under shaking at 200 
rpm. 
The seed culture medium thus obtained was transferred at a ratio of 5% by 
volume into 18 l of a fermentation medium of the following composition 
contained in a 30 l jar fermentor. The seed culture was cultivated therein 
at 28.degree. C. under aerating at a rate of 18 l/min and agitating at 200 
rpm. 
Composition of fermentation medium: 50 g/l of soluble starch, 15 g/l of 
soybean flour, 0.5 g/l of KH.sub.2 PO.sub.4, 0.5 g/l of 
MgSO.sub.4.7H.sub.2 O, 0.5 g/l of Mg.sub.3 (PO.sub.4).sub.2.8H.sub.2 O (pH 
7.0 before sterilization, adjusted with NaOH). 
The cultivation was continued for 144 hours without controlling the pH of 
the medium. 
36 l of methanol was added to the culture to thereby extract UCE6. To the 
methanol extract was added 18 l of water and the mixture was passed 
through a column packed with a nonionic porous resin Diaion HP20 (mfd. by 
Mitsubishi Kasei Corporation). Then, active substance (including UCE6) was 
adsorbed with the resin. After eluting the impurities with a mixture of 
methanol and water (85:15, v/v), the active substance was eluted with 
methanol. The methanol fraction was concentrated and poured onto a silica 
gel column (Lichroprep-Si60, Art 9390, mfd. by Merck), followed by 
developing with hexane/ethyl acetate/methanol (8:5:1, v/v). The active 
fraction thus eluted was concentrated and poured onto a Sephadex LH20 
column (mfd. by Pharmacia), followed by eluting with methanol. The active 
fraction thus eluted was concentrated and dried. Thus 38 mg of UCE6 was 
obtained as a red purple powder. 
According to the present invention, a novel fermentation product UCE6 
having an antitumor activity is provided. 
While the invention has been described in detail and with reference to 
specific examples thereof, it will be apparent to one skilled in the art 
that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.