FIELD: medicine, pharmaceutics.SUBSTANCE: invention refers to to new compounds of formula (1) or their pharmaceutically acceptable salts, optionally in the form of (1S)-isomers showing the properties of polo-like kinase (serine-threonine kinase) PLK1 inhibitor. In the compounds of formula (1) , R1 represents a halogen atom； a lower alkyl group having 1-2 carbon atoms, which can be substituted by 3 fluorine atoms； or a cyclopropyl group； R2 represents a hydrogen atom； one of R3 and R4 represents a hydrogen atom while the other one of R3 and R4 represents: a) a lower alkyl group substituted by NRaRb wherein each Ra and Rb, which can be identical or different, represent a lower alkyl group, or each Ra and Rb, which can be different, represent a hydrogen atom, a lower alkyl group or a cycloalkyl group having 3-6 carbon atoms wherein a cycloalkyl group can be substituted by one ore more substitutes which can be identical or different and specified in a group 1): a lower alkyl； b) a 4-6-member aliphatic heterocyclic group specified in an azetidinyl group, a pyrrolidinyl group and a piperidinyl group； c) a lower alkyl group substituted by a 4-6-member aliphatic heterocyclic group specified in an azetidinyl group, a pyrrolidinyl group and a piperidinyl group； d) a 6-member aromatic heterocyclic group specified in a pyridyl group wherein each of an aliphatic heterocyclic group and an aromatic heterocyclic group can be substituted by substitutes specified in a group 1) described above； R5 represents a hydrogen atom, a cyano group, a halogen atom or a lower alkyl group.EFFECT: compounds can find application in treating oncological diseases.10 cl, 4 dwg, 8 tbl, 42 exИзобретение относится к новым соединениям формулы (I) или их фармацевтически приемлемым солям, возможно в виде (1S)-изомеров, обладающих свойствами ингибитора семейства поло-подобных киназ(серино-треониновых киназ) PLK1. Соединения могут найти применение при лечении опухолевых заболеваний. В соединениях формулы (I
