Pyrido[2,3-d]pyrimidine derivatives (I) are new. Pyrido[2,3-d]pyrimidine derivatives of formula (I) are new. R 1 = 1-6C alkyl, 1-6C alkyl-3-7C cycloalkyl, CH 2C(O)R 3 or phenyl (optionally substituted by OH, halo or 1-6C alkyl)； R 3 = OH, 1-4C alkoxy, amino, 1-4C alkylamino or di(1-4C alkyl)amino； Ar 1 = fused heterocyclic moieties of formulae (a)-(f)； X = O or S； R 2 = H, 1-6C alkyl or (CH 2) nNR 4R 5； R 4 = H, 1-4C alkyl, 1-6C alkyl-3-7C cycloalkyl, C(=NH)NH 2 or 1-6C alkylsulfonyl； and R 5 = as R 4 plus 1-4C alkylcarbonyl, 3-7C cycloalkylcarbonyl, aroyl, arylsulfonyl, tert-butoxycarbonyl or benzyloxycarbonyl； or NR 4R 5 = azetidino, pyrrolidino, piperidino, piperazino or morpholino (all optionally substituted by 1-6C alkyl, 1-4C alkyl-OH or 1-6C alkoxycarbonyl)； Ar 2 = phenyl (optionally substituted by 1-5 halo, 1-4C alkyl, CF 3 or 1-4C alkoxy)； and n = 1-3. An independent claim is included for a composition (A) comprising (I) and an excipient. [Image] [Image] ACTIVITY : Cytostatic； Dermatological； Vasotropic； Anti-HIV； Antilipemic； Antirhemuatic； Antiarthritic； MECHANISM OF ACTION : Tumor cell proliferation inhibitor. The ability of (I) to inhibit tumor cell proliferation was tested using biological assays and (I) exhibited IC 50 values of 1 nM-10 mu M.
