Tetrahydropyran derivative

A tetrahydropyran derivative represented by the following general formula (I) or a salt thereof

• (symbols in the formula mean as follows;
• R1 and R3:
• the same or different and each represents H or lower alkyl,
• R2:
• H, halogen, Ra-lower alkyl-, or R20O—CO—,
• Ra:
• H, R21O—CO—, R22R23N—, R24R2N—CO—, R26O—, cyano, or optionally-substituted hetero ring-,
• R4, R5, R6 and R7:
• the same or different and each represents H, halogen, haloalkyl, cyano, lower alkyl, lower alkyl-O—, R21O—CO-lower alkyl-, R27—CO—, or R2R29N—S(O)2
• R8 and R9:
• the same or different and each represents H, lower alkyl, R30-lower alkyl-, R31R32N—, optionally-substituted hetero ring-, or R33R34R35C—, with the proviso that R8 and R9 may together form a optionally-substituted hetero ring
• X:
• N, or CR36,
• R20, R22 to R26, R28, R29, R32, R35 and R36:
• the same or different and each represents H, or lower alkyl,
• R21:
• H, lower alkyl, or aryl-lower alkyl-,
• R27:
• HO—, lower alkyl-O—, or optionally-substituted hetero ring-,
• R30:
• optionally-substituted aryl, optionally-substituted hetero ring-, or lower alkyl-O—,
• R31:
• optionally-substituted aryl, or optionally-substituted hetero ring-,
• R33:
• HO-lower alkyl-, or optionally-substituted hetero ring-lower alkyl-, and
• R34:
• optionally-substituted aryl).