Compounds of formula (I): wherein X is N, CH, CCF3, or C(C1-12 aliphatic); R4 is sulfonic acid, C1-12 aliphatic-sulfonyl, sulfonyl-C1-12 aliphatic, C1-12 aliphatic-sulfonyl-C1-6 aliphatic, C1-6 aliphatic-amino, R7-sulfonyl, R7 sulfonyl-C1-12 aliphatic, R7-aminosulfonyl, R7aminosulfonyl-C1-12 aliphatic, R7-sulfonylamino, R7-sulfonylamino-C1-12 aliphatic, aminosulfonylamino, di-C1-12 aliphatic amino, di-C1-12 aliphatic aminocarbonyl, di-C1-12 aliphatic aminosulfonyl, di-C1-12 aliphatic amino, di-C1-12 aliphatic aminocarbonyl, di-C1-12 aliphatic aminosulfonyl-C1-12 aliphatic, (R8)1-3-Arylamino, (R8)1-3-Arylsulfonyl, (R8)1-3-Aryl-aminosulfonyl, (R8)1-3-Aryl-sulfonylamino, Het-amino, Het-sulfonyl, Het-aminosulfonyl, aminoiminoamino, or aminoiminoaminosulfonyl, R5 is hydrogen; and further wherein R4 and R5 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.