P2X3 receptor antagonists for treatment of pain

A compound of structural formula III and VII:

• or pharmaceutically acceptable salts and individual enantiomers and diastereomers thereof wherein:
• R2 represents H, C1-6 alkyl, CF3, OH;
• R3 is selected from the group consisting of (CHRY)npyridyl, (CHRY)noxidopyridyl, (CHRY)npyrimidinyl, (CHRY)ntriazolyl, (CHRY)nphenyl, (CHRY)npyrazinyl, (CHRY)npyrazolyl, (CHRY)noxadiazolyl, (CHRY)nthiazolyl, (CHRY)nthiadiazolyl, (CHRY)nindazopyridyl, C1-6 alkyl, and (CHRY)nC3-6 cycloalkyl, wherein RY represents H, C1-6 alkyl optionally substituted with Ra, CF3, or OH
• or R2 and R3 can be combined with the nitrogen to which they are attached to form a C5-10 heterocyclyl optionally substituted with 1 to 3 groups of Ra;
• R6 represents hydrogen, OR2, (CH2)nCF3, halogen, C(R2)2OR2, C2-6 alkenyl, C2-6 alkynyl, (CH2)nC6-10 aryl, (CH2)nC5-10 heterocyclyl, said alkyl, cycloalkyl, aryl and heterocyclyl optionally substituted with 1 to 3 groups of Ra;
• R6a is R6;
• Ra represents C1-6 alkyl, halogen, hydroxyl, OR2 (CH2)nCF3, —O—, C3-6 cycloalkyl, NR2C(O)R2, C(O)N(R2)2, C(R2)2OR2, C(O)R2, O(CH2)nC(O)N(R2)2, O(CH2)nC(O)OR2, C(O)C5-10heterocyclyl, NO2, CN, N(R2)2, C(O)OR2, SO2R2, OR2, (CH2)nC5-10 heterocyclyl, or (CH2)nC6-10 aryl, said alkyl, heterocyclyl and aryl optionally substituted with 1 to 3 groups of C1-6 alkyl, halogen, hydroxyl, (CH2)nCF3, or CN;
• and
• n represents 0 to 4.