Biguanide derivatives and their rearrangement products for use in the treatment of cancer

A compound of formula (II) or (III)

• wherein
• Y′ is —SR4 or —OR5,
• R4 is selected from C1-C6 alkyl and protecting groups selected from any group linked by a disulfide function, thioesters, alkyl, alkenyl and alkynyl thioethers, benzyl thioethers, alkylarylmethyl thioethers, and triarylmethylthioethers;
• R5 is selected from protecting groups selected from esters, silylated ethers, alkoxymethyl ethers, benzyl ethers tetrahydropyranyl ethers, pentoses, and hexoses;
• each R′ is independently selected from halogen, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 haloalkyl, —OH, —NR″R′″, —NO2, —CN and —(CO)—R;
• n is 0 to 4;
• R3 is selected from C1-C6 alkyl, C3-C6 cycloalkyl, C1-C6 haloalkyl, C2-C6 alkenyl, C2-C6 alkynyl, heterocyclyl having 5 to 10 ring atoms, aryl having 6 to 10 ring atoms, heteroaryl having 5 to 10 ring atoms and C7-C16 aralkyl, said alkyl, cycloalkyl, haloalkyl, alkenyl, alkynyl, heterocyclyl, aryl, heteroaryl and aralkyl being optionally substituted with one or more substituents independently selected from halogen, C1-C6 alkyl, C1-C6 alkoxy, C1-C6haloalkyl, —OH, —NR″R″, —NO2, —CN and —(CO)—R;
• each R is independently selected from H, C1-C6 alkyl, C1-C6 alkoxy and —NR″R″ ‘;
• each R″ and R’ is independently selected from H and C1-C6 alkyl.