A compound of formula, or a pharmaceutically-acceptable salt, or pro-drug thereof, wherein Ring A is 2,6-pyrazindiyl optionally substituted on an available carbon atom by one or two substituents independently selected from linear alkyl, alkenyl, alkynyl, alkoxy, methoxymethyl, amino and cyano; X is =O or =S; Ring B is 1,4-phenylene optionally substituted on an available carbon atom by one or two substituents independently selected from halo, amino, cyano, alkyl, alkenyl, alkynyl, alkoxy and alkoxy- alkyl; Y 1 is a direct bond between Ring B and Ring C or Y 1 is -O-, -S- or -NRa- wherein Ra is hydrogen or alkyl; Y 2 is -(CH 2) r - wherein r is 2 or 3, and Y 2 is linked at the same carbon atom as Y 1 in Ring C and Y 2 is linked at an adjacent carbon atom to Y 1 in Ring B; n is 0 or n is 1 when Y 1 is a direct bond between Ring B and Ring C and when Ring B is 1,4-phenylene and Ring C is cycloalkane, so that a 5- or 6-membered spiro-ring system is formed and Ring C is tri-linked; Ring C is a di-linked (excluding links via the same or adjacent atoms) ring or ring system chosen from cycloalkane, bicycloalkane and tricycloalkane each optionally substituted on an available carbon atom, including the ring carbon atom bearing the Z-containing group, by one substituent selected from hydroxy, alkyl, alkoxy and alkoxy alkyl; or Ring C is a di-linked (excluding links via the same or adjacent atoms) ring selected from phenylene, pryidindiyl, piperidinediyl N-linked to Y 1, piperazinediyl, furandiyl, thiophendiyl, pyrroldiyl, oxazoldiyl, thiazoldiyl, imidazoldiyl, isoxazoldiyl, isothiazoldiyl, pyrazoldiyl and azabicyclo[3.1.0]hexanediyl; each optionally substituted on an available carbon atom by up to four substituents independently selected from fluoro, chloro, bromo, cyano, alkyl, alkoxy and alkoxy alkyl; L is a direct bond to Ring C, -O-, -S- or -NH-; p is 0 (when L is a direct bond), 1 or 2 and when p is 1 or 2 R A1 and R A2 are each independently hydrogen or alkyl or R A1 and R A2 are linked together to form a spiroalkyl ring; Z is carboxy or a mimic or bioisostere thereof, hydroxy or -CONRbRc wherein Rb and Rc are independently selected from hydrogen and alkyl, which alkyl group may be optionally substituted by carboxy or a mimic or bioisostere thereof; and wherein any carbon atom in a linear alkyl, alkoxy, alkyl or alkoxy containing group defined above may be optionally substituted by up to 3 fluoro atoms; wherein a mimic or bioisostere of a carboxy group is selected from -SO 3 H, -S 2 NHR 13, S 2 NHC R 13, -CH 2 S 2 R 13, -C NHS 2 R 13, -C NHOH, -C NHCN, -CH(CF 3)OH, C(CF 3) 2 OH, -P 2 and groups of sub-formula (a)-(i') below wherein where p in sub-formula (k) is 1 or 2, R 27 and R 28 are independently selected from hydrogen, hydroxy, alkoxy, thiol, alkylthio, -C R 29, -S R 30, -SO 2 R 31, -NR 32 R 33, -NHCN, halogen and trihalomethyl, where R 29, R 30 and R 31 are -OR 34, alkyl, -NR 32 R 33 or trihalomethyl, R 32 and R 33 are independently selected from hydrogen, alkyl, -SO 2 R 34 and - COR 35, where R 35 is alkyl or trihalomethyl, and R 34 is hydrogen, alkyl or trihalomethyl and R 13 is selected from hydrogen, alkyl, hydroxy, halo, amino, cyano, ( alkyl)CONH-, carboxy, alkoxy, alkoxycarbonyl, carbamoyl, N-( alkyl)carbamoyl, halo( alkyl) (such as trifluoromethyl), alkylsulphonyl or alkylsulphinyl; and wherein a pro-drug thereof is an ester of a carboxy group selected from a alkyl ester, a alkoxymethyl ester, a alkanoyloxymethyl ester, a phthalidyl ester, a cycloalkoxycarbonyloxy alkyl ester, a 1,3-dioxolan-2-ylmethyl ester, a alkoxycarbonyloxyethyl ester, an aminocarbonylmethyl ester and a mono- or di- N-( alkyl) version of an aminocarbonylmethyl ester.