PURPOSE: To provide a new compd. as an intermediate for the synthesis of 2-substd.-3-hydroxy-1,4-naphthoquinone which is useful for prevention and treatment for infections by protozoan.

CONSTITUTION: This invention provides a compd. expressed by formula I (R is 1 to 10C alkyl) or its salts. The compd. is, for example, 2-(4'-t- butylcyclohexyl)-3-hydroxy-1,4-naphthoquinone. The compd. of formula I is obtd. by alkali hydrolysis of a compd. expressed by formula II (X is halogen) in a solvent such as aqueous methanol by using an alkali metal hydroxide (e.g. potassium hydroxide). The obtd. compd. shows activity against protozoan, especially against Plasmodium falciparum which causes human malaria, and against Eimeria acervulina which causes coccidiosis of birds. The compd. is also useful as an intermediate of an antiphlogistic.