Patent ID: 6869971

Claim:
A compound represented by formula (I): wherein R 1 represents hydrogen, or lower alkyl, NR 9 R 10 , SR 12 or OR 13 ; R 2 is hydrogen or is combined with R 3 to represent a bond; R 3 represents hydrogen, OR 15 or halogen, or is combined with R 2 to represent a bond; R 4 represents hydrogen, CO 2 R 16 or CONR 17 R 18 ; R 5 represents hydrogen or is combined with R 6 to represent a bond; R 6 represents hydrogen or OR 19 , or is combined with R 5 to represent a bond; R 7 represents hydrogen or is combined with R 8 to represent ═O; R 8 represents hydroxy or is combined with R 7 to represent ═O; R 9 and R 10 independently represent hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl or OR 11 , or R 9 and R 10 are combined together with the adjacent N to form a substituted or unsubstituted heterocyclic ring; R 11 represents hydrogen or lower alkyl; R 12 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl; R 13 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, or substituted or unsubstituted lower alkynyl; R 15 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aralkyl, or substituted or unsubstituted lower alkanoyl; R 16 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl; R 17 and R 18 independently represent hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl, or R 17 and R 18 are combined together with the adjacent N to form a substituted or unsubstituted heterocyclic ring; R 19 represents hydrogen, substituted or unsubstituted lower alkyl, substituted or unsubstituted lower alkenyl, substituted or unsubstituted lower alkynyl, substituted or unsubstituted aralkyl, or substituted or unsubstituted lower alkanoyl; ---- represents a single bond or a double bond; and a represents an oxygen atom or both carbon atoms to which a is bound are joined by a double bond, or a pharmaceutically acceptable salt thereof with the proviso that R 1 does not represent hydrogen when R 2 and R 3 are combined to represent a bond, R 4 represents carboxy, R 5 represents hydrogen, R 6 represents hydroxy, R 7 and R 8 are combined to represent ═O, and ---- and a both represent a single bond.