Rhizoxin derivatives and their use as anti-tumor agents

A compound of the formula (I):

• ##STR13## in which:
• n represents an integer of from 1 to 25,
• A represents an oxygen atom,
• X represents a sulfur atom or NR and
• when X represents a sulfur atom,
• R represents a hydrogen atom;
• an aliphatic carboxylic acyl group having from 1 to 25 carbon atoms, which group is unsubstituted or has at least one substituent selected from the group consisting of substituents (a), defined below;
• an alkoxycarbonyl group in which the alkoxy part has from 1 to 25 carbon atoms and is unsubstituted or has at least one substituent selected from the group consisting of substituents (a), defined below;
• an alkylthio group in which the alkyl part has from 1 to 25 carbon atoms and is unsubstituted or has at least one substituent selected from the group consisting of substituents (a), defined below;
• or a benzylthio group;
• when X represents NR,
• R is independently selected from the group consisting of R.sup.1 and R.sup.2, where R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen atoms, alkyl groups, aliphatic carboxylic acyl groups, alkoxycarbonyl groups, in which said acyl and alkyl groups and the alkyl part of said alkoxycarbonyl has from 1 to 25 carbon atoms and is unsubstituted or has at least one substituent (a) selected from the group consisting of
• a halogen atom, a carboxy group, a hydroxy group, a group of the formula --COO--Rhz, where Rhz is as defined below, a 2,4-dicyclohexylallophanyl group, a phenyl group, a nitrophenyl group, and a cyanophenyl group;
• RhZ represents a group of the formula (II):
• ##STR14## and a ring-opened acid corresponding to said compound of formula (I) and salts and esters of said acid.