This invention relates to the compounds of the formula [I] and salts thereof, which are useful for treatment of liver disorders, ##STR1## wherein X is oxygen or sulfur; PA0 R.sup.1 is lower alkyl which can be substituted by hydroxy, carboxy or lower alkoxycarbonyl; PA0 R.sup.2 is hydrogen, lower alkanoyl, phenyl lower alkanoyl or phenyl lower alkyl, and said phenyl ring of phenyl lower alkanoyl or phenyl lower alkyl can be substituted by lower alkyl or lower alkoxy; and PA0 A is straight or branched C.sub.1 -C.sub.6 alkylene.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to the compounds of the formula [I] and salts 
thereof (hereinafter referred to as the "Compound"), which are useful for 
treatment of liver disorders, 
##STR2## 
wherein X is oxygen or sulfur; 
R.sup.1 is lower alkyl which can be substituted by hydroxy, carboxy or 
lower alkoxycarbonyl; 
R.sup.2 is hydrogen, lower alkanoyl, phenyl lower alkanoyl or phenyl lower 
alkyl, and said phenyl ring of phenyl lower alkanoyl or phenyl lower alkyl 
can be substituted by lower alkyl or lower alkoxy; and 
A is straight or branched C.sub.1 -C.sub.6 alkylene. 
The same shall be applied hereinafter. 
The terms defined above are explained as follows in more detail. The term 
"lower alkyl" intends to designates straight or branched C.sub.1 -C.sub.6 
alkyl exemplified by methyl, ethyl, propyl, isopropyl and hexyl, "lower 
alkoxy" intends to designates straight or branched C.sub.1 -C.sub.6 alkoxy 
exemplified by methoxy, ethoxy, propoxy, isopropoxy or hexyloxy, and 
"lower alkanoyl" intends to designates straight or branched C.sub.2 
-C.sub.6 alkanoyl exemplified by acetyl, propionyl, hexanoyl, isopropionyl 
and pivaloyl. 
The Compound can be converted into pharmaceutically acceptable salts. 
Examples of the salts are sodium salt, potassium salt, magnesium salt and 
calcium salt. 
There are few studies on N-alkyl-thiazolidine-2-thione derivatives. Only 
Nagao et al. reported such N-alkyl-thiazolidine derivatives (Chem. Pharm. 
Bull., 36(2), 495 (1988)). They studied the rearrangement reaction from 
2-alkylthiothiazolidine derivatives, which was synthesized by the reaction 
of thiazolidine-2-thione derivatives with alkyl halide, to 
N-alkyl-thiazolidine-2-thione. 
There are also few studies on N-alkyl-thiazolidine-2-one derivatives. Only 
N-p-methoxybenzyl derivative was known as a synthetic intermediate of 
(+)-latrunclin B which is a natural toxin (J. Am. Chem. Soc., 108, 2451 
(1986)). 
As mentioned above, there are few studies on N-alkyl derivatives of 
thiazolidine 2-thione (or 2-one), especially compounds having N-alkyl 
group substituted by a sulfur atom have not been known. 
Thereupon, we studied synthetic methods of N-alkyl-thiazolidine-2-thione 
(or 2-one) derivatives wherein N-alkyl group contains a sulfur atom and 
have succeeded in obtaining various novel compounds. Furthermore, we 
studied applications of the Compound to drugs and found that the Compound 
would be useful for treatment of liver disorders. 
The Compound can be prepared by such methods as the follows. 
##STR3## 
In the formula, R.sup.3 is hydrogen or lower alkyl. 
The Compound can be prepared by a reaction of the compound of the formula 
[II] with the compound of the formula [III]. 
When R.sup.1 is carboxy or lower alkoxycarbonyl in the formula [I], if 
necessary, the compound can be reduced and convert into the compound of 
the formula [V], which is included in this invention, with reducing 
reagent such as lithium aluminium hydride. 
When R.sup.2 in the formula [I] or [V] is lower alkanoyl, phenyl lower 
alkanoyl or phenyl lower alkyl and intended to use as a protective group, 
the protective group can be removed by a known method to give thiol 
compound. 
The Compound has stereoisomers because of the existence of one or more 
asymmetric carbon atom, and these isomers are included in this invention. 
The Compound is useful as a medical substance, especially for treatment of 
liver disorders such as acute hepatic failure, acute hepatitis, chronic 
hepatitis and liver cirrhosis. 
The acute hepatic failure model reported by Feruluga J. et al., (Agent and 
Actions, 9, 566 (1979)) is known as an animal model to examine effects of 
a drug on liver disorders. We examined effects of the Compound on liver 
disorders using this model. As the result of our experiment, we found that 
the mortality of the animal group treated with the Compound was lower than 
that of the control group. The result proves that the Compound is useful 
for treatment of liver disorders. 
The Compound can be administered either orally or parenterally. Examples of 
dosage forms are tablet, capsule, powders, granules, injection and the 
percutaneous. The dosage is adjusted depending on symptom, dosage form, 
etc., but usual daily dosage is 1 to 5000 mg in one or a few divided 
doses. 
Examples of formulations are shown below. 
1) Tablet 
The following tablet can be prepared by a usual method. 
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Compound 100 mg 
crystalline cellulose 20 mg 
lactose 40 mg 
hydroxypropylcellulose 5 mg 
magnesium stearate 5 mg 
total 170 mg 
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2) Capsule 
The following capsule can be prepared by a usual method. 
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Compound 5 mg 
lactose 142 mg 
magnesium stearate 3 mg 
total 150 mg 
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By changing the ratio of the Compound and lactose, capsules which contains 
10 mg, 30 mg, 50 mg or 100 mg of the Compound, can be prepared. 
3) Granules 
The following granules can be prepared by a usual method. 
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Compound 50 mg 
lactose 55 mg 
starch 20 mg 
hydroxypropylcellulose 4 mg 
talc 1 mg 
total 130 mg 
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