Catalyzes the dehydration of chorismate into 3-[(1-carboxyvinyl)oxy]benzoate, a step in the biosynthesis of menaquinone (MK, vitamin K2). chorismate = 3-[(1-carboxyvinyl)-oxy]benzoate + H2O kcat is 1.27 sec(-1). Quinol/quinone metabolism; menaquinone biosynthesis. Belongs to the MqnA/MqnD family. MqnA subfamily.