O-methyltransferase that mediates the formation of 3-methoxy-5-methyl-1-naphthoate from 3-hydroxy-5-methyl-1-naphthoate in the biosynthesis of the antitumor antibiotic azinomycin B. 3-hydroxy-5-methyl-1-naphthoate + S-adenosyl-L-methionine = 3-methoxy-5-methyl-1-naphthoate + H(+) + S-adenosyl-L-homocysteine Inhibited by different divalent cations, such as Mg(2+), Mn(2+), Fe(2+), Cu(2+) and Zn(2+). kcat is 0.44 min(-1). Antibiotic biosynthesis. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family.