Provided are a novel neterocvclic compound and salt thereoi applicable in the selective inhibmon o f the degradation of p27 kip1 . The compound and the salt thereof are represented in formula (1). [In the formula: A represents an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group, and group A can have a substituent group ring B represents a 5 - t o 8 - membered monocyclic heterocyclic ring or a condensed ring containing this monocyclic heterocyclic ring, and ring B can have a substituent group ring C represents an aromatic ring, and ring C can have a substituent group L represents a linker having 3-5 atoms in the main chain selected :from carbon atoms, nitrogen atoms, oxygen atoms, and sulfur atoms, ana having at least one heteroatom selected :from nitrogen atoms, oxygen atom, and linker L may have a substituent group and n represents 0 or1]
