Catalyzes the conversion of chorismate to isochorismate. chorismate = isochorismate Quinol/quinone metabolism; 1,4-dihydroxy-2-naphthoate biosynthesis; 1,4-dihydroxy-2-naphthoate from chorismate: step 1/7. Quinol/quinone metabolism; menaquinone biosynthesis. Belongs to the isochorismate synthase family.