. "r hand, when Y is a sulfur atom, (9) In the specification of Japanese Patent Kokoku No. 55-42076, the compounds described by the general formula: ##STR12## (wherein Rn represents a hydrogen atom or an ethoxycarbonyl group and symbol m' represents an integer of four to six) have been disclosed, (10) in the specification of Japanese Patent Kokoku No. 56-3345, the compounds described by the general f" . . .