| abstract |
A cyclic hexapeptide represented by the formula: n n n n cyclo[A-Asp(R¹)-Y-NH-CHR²-CO-C-D-Trp(N in -R³)-] (I) n n n nwherein A is a D-acidic-α-amino acid residue; Y is an acidic-α-amino acid residue; C is an L-α-amino acid residue; R¹ is a group represented by the formula:n n wherein X¹ and X² are independently H, C₁₋₆ alkyl, C₁₋₆ alkoxy, halogen or nitro, and may bind together to form a ring in cooperation with the adjacent carbon atom; R² is C₁₋₆ alkyl, C₃₋₇ cycloalkyl, C₃₋₇ cycloalkyl-C₁₋₃ alkyl, C₁₋₆ alkylthio-C₁₋₃ alkyl, C₃₋₇ cycloalkylthio-C₁₋₃ alkyl, C₁₋₅ alkoxy-C₁₋₃ alkyl, C₃₋₇ cycloalkoxy-C₁₋₃ alkyl, C₁₋₆ alkylthio, C₃₋₇ cycloalkylthio, C₁₋₅ alkoxy or C₃₋₇ cycloalkoxy; R³ is H, C₁₋₆ alkyl, C₃₋₇ cycloalkyl, -COR⁴, - COOR⁵ or -CONHR⁶; when X¹, X² and R³ are all hydrogen atoms, R² is not an isobutyl group, or a saalt thereof, which exhibits excellent antagonistic action against endothelin receptors, particularly endothelin B receptors. |