Triaromatic vitamin D analogues

A triaromatic vitamin D analogue having the structural formula (I) below:

• 3
• in which:
• —X—Y represents the following structural bonds:
• —CH2—CH2——CH2—O——O—CH2——CH2—N(R4)—
• R4 having the meanings given below,
• R1 represents a methyl radical or an ethyl radical,
• R2 represents an ethyl radical, a propyl radical or an isopropyl radical,
• R3 represents an ethyl radical or a trifluoromethyl radical,
• R4 represents a hydrogen atom, a methyl radical, an ethyl radical or a propyl radical, and the optical and geometrical isomers of the said compounds of formula (I), and also the salts thereof.