Piperazine derivatives as 5-HT1B antagonists

A compound of formula (I) or a pharmaceutically acceptable salt thereof:

• 6
• in which Ra is a group of formula (i)
• 7
• wherein P1 is phenyl, naphthyl or heteroaryl;
• R1 is halogen, C1-6alkyl, C3-6cycloalkyl, COC1-6alkyl, C1-6alkoxy, hydroxy, hydroxyC1-6alkyl, nitro, CF3, cyano, SR6, SOR6, SO2R6, SO2NR6R7, CO2R6, CONR6R7, OCONR6R7, NR6R7, NR6CO2R7, NR6CONR7R8, CR6═NOR7 where R6, R7 and R8 are independently hydrogen or C1-6alkyl;
• a is 0, 1, 2 or 3;
• or Ra is a group of formula (ii)
• 8
• wherein
• P2 is phenyl, naphthyl, heteroaryl or a 5 to 7 membered heterocyclic ring;
• P3 is phenyl, naphthyl or heteroaryl;
• A is a bond or oxygen, carbonyl, CH2 or NR4 where R4 is hydrogen or C1-6alkyl;
• R2 is as defined above for R1 in formula (i) or R2 is heteroaryl optionally substituted by C1-6alkyl, halogen or COC1-6alkyl or is a 5-7 membered heterocyclic ring optionally substituted by oxo;
• R3 is halogen, C1-6alkyl, C3-6cycloalkyl, C1-6alkoxy, COC1-6alkyl, hydroxy, nitro, CF3, cyano, CO2R6, CONR6R7, NR6R7 where R6 and R7 are as defined above;
• b and c are independently 0, 1, 2 or 3;
• Y is a single bond, CH2, O or NR5 where R5 is hydrogen or C1-6alkyl;
• W is —(CR9R10)t— where t is 2, 3 or 4 and R9 and R10 are independently hydrogen or C1-6alkyl or W is a group —CH═CH—;
• Rb is hydrogen, halogen, hydroxy, C1-6alkyl, CF3 , COC1-6alkyl, cyano or C1-6alkoxy;
• Rc is hydrogen or C1-6alkyl;
• Rd and Re are independently C1-4alkyl.