FUSED TRICYCLIC COMPOUND AND MEDICINAL USE THEREOF

The present invention provides a compound which has a PDHK inhibitory activity and is useful for treating or preventing diabetes (type 1 diabetes, type 2 diabetes, etc.), insulin resistance syndrome, metabolic syndrome, hyperglycemia, hyperlactatemia, diabetes complications (diabetic neuropathy, diabetic retinopathy, diabetic nephropathy, cataract, etc.), heart failure (acute heart failure, chronic heart failure), cardiomyopathy, myocardial ischemia, myocardial infarction, angina pectoris, dyslipidemia, atherosclerosis, peripheral arterial disease, intermittent claudication, chronic obstructive pulmonary disease, brain ischemia, stroke, mitochondrial disease, mitochondrial encephalomyopathy, cancer, pulmonary hypertension, Alzheimer's disease, vascular dementia, glaucoma, retinopathy of diabetes, retinopathy of prematurity, retinal vein occlusion, ischemic optic neuropathy or chronic kidney disease. The present invention pertains to a compound represented by formula [I-a] or a pharmaceutically acceptable salt thereof. [In the formula, each symbol is as defined in the description.]