Enantiomers of fused heterocycles selected and uses thereof

pharmaceutical compositions containing them and uses for cancer prophylaxis. Claim 1: An enantiomer characterized in that responds to a compound of formula (1), including a pharmaceutically acceptable salt or hydrolyzable ester thereof in vivo, wherein: X is selected from -C (CH3) - or -S - with the proviso that when X is -S- then Y is -C (CH3) -; Y is selected from -C (CH3) - or -O- or -S- with the proviso that when Y is -C (CH3) - then X is not - C (CH3) -; m is 0 or 1; R1 is F when m is 1; R2 and R3 are independently selected from H or C1-3 alkyl; wherein if both R2 and R3 are selected from C1-3alkyl they are identical; n is 2 or 3; R4 and R5 are independently selected from H or C1-3 alkyl; Z is optionally substituted phenyl, or optionally substituted benzothiophene wherein the amount of optional substituted is 1 or 2 and each is independently selected from F, Cl, Br, CH3 or CH2CH3; and * O represents a chiral center; wherein said enantiomer is substantially free of the other enantiomer; and wherein the optical rotation of the enantiomer, when said enantiomer is dissolved at a concentration of 1 mg / ml in methanol at 589 nM measured 20.0sC is (+).