compounds of formula : wherein x is n , ch , ccf 3 , or c ; r 4 is sulfonic acid , c 1 - 12 aliphatic - sulfonyl , sulfonyl - c 1 - 12 aliphatic , c 1 - 12 aliphatic - sulfonyl - c 1 - 6 aliphatic , c 1 - 6 aliphatic - amino , r 7 - sulfonyl , r 7 sulfonyl - c 1 - 12 aliphatic , r 7 - aminosulfonyl , r 7 - aminosulfonyl - c 1 - 12 aliphatic , r 7 - sulfonylamino , r 7 - sulfonylamino - c 1 - 12 aliphatic , aminosulfonylamino , di - c 1 - 12 aliphatic amino , di - c 1 - 12 aliphatic aminocarbonyl , di - c 1 - 12 aliphatic aminosulfonyl , di - c 1 - 12 aliphatic amino , di - c 1 - 12 aliphatic aminocarbonyl , di - c 1 - 12 aliphatic aminosulfonyl - c 1 - 12 aliphatic , 1 - 3 - arylamino , 1 - 3 - arylsulfonyl , 1 - 3 - aryl - aminosulfonyl , 1 - 3 - aryl - sulfonylamino , het - amino , het - sulfonyl , het - aminosulfonyl , aminoiminoamino , or aminoiminoaminosulfonyl , r 5 is hydrogen ; and further wherein r 4 and r 5 are optionally joined to form a fused ring , pharmaceutical formulations comprising them and their use in therapy , especially in the treatment of diseases mediated by cdk2 activity , such as alopecia induced by cancer chemotherapy or radiotherapy .