[Problem] To provide a novel compound that is useful as an agent for preventing/treating cancer. [Solution] One aspect of the present invention provides a compound expressed by the chemical formula (1) or a pharmaceutically permissible salt thereof; the A in the chemical formula (1) is as defined in the specification. Furthermore, another aspect of the present invention pertains to a medicine containing the aforementioned compound or pharmaceutically permissible salt thereof as an active ingredient, as a use for the aforementioned compound. Yet another aspect of the present invention provides an agent for preventing and/or treating cancer, comprising the medicine.