Antitumoral compounds

A compound of formula I, or a pharmaceutically acceptable salt thereof:

• wherein:
• X is —NH— or —O—;
• R1 is —OH or —CN;
• R2 is a —C(═O)Ra group;
• R3 is hydrogen or a —ORb group;
• R4 is selected from hydrogen, —CH2OH, —CH2O—(C═O)Rc, —CH2NH2 and —CH2NHProtNH;
• Ra is selected from hydrogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, and substituted or unsubstituted C2-C12 alkynyl;
• Rb is selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl and substituted or unsubstituted C2-C12 alkynyl;
• Rc is selected from substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, and substituted or unsubstituted C2-C12 alkynyl;
• and
• ProtNH is a protecting group for amino;
• with the proviso that when R4 is hydrogen then X is —O—;
• where substituted groups are substituted at one or more available positions by one or more substituents selected from OR′, ═O, SR′, SOR′, SO2R′, NO2, NHR′, NR′R′, ═N—R′, NHCOR′, N(COR′)2, NHSO2R′, NR′C(═NR′)NR′R′, CN, halogen, COR′, COOR′, OCOR′, OCONHR′, OCONR′R′, CONHR′, CONR′R′, protected OH, protected amino, protected SH, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, aryl, and heterocyclic group;
• where each of the R′ groups is independently selected from the group consisting of hydrogen, OH, NO2, NH2, SH, CN, halogen, COH, COalkyl, CO2H, C1-C12 alkyl, C2-C12 alkenyl, C2-C12 alkynyl, aryl, and heterocyclic group.