X is CH₂, N—R⁷, S or O;

R⁷ is selected from the group of hydrogen, alkyl, Ar, Ar-alkyl, alkylcarbonyl, alkyloxycarbonyl and mono- and di(alkyl)aminocarbonyl;

R¹ and R² are each selected from the group of hydrogen, halo, hydroxy, —OSO₂H, —OSO₂CH₃, alkyloxy, alkyloxyalkyloxy, alkyloxyalkyloxyalkyloxy, tetrahydrofuranyloxy, alkylcarbonyloxy, alkyloxyalkylcarbonyloxy, pyridinylcarbonyloxy, alkylcarbonyloxyalkyloxy, alkyloxycarbonyloxy, alkenyloxy, alkenyl-carbonyloxy, mono- or di(alkyl)aminoalkyloxy, —N—R¹⁰R¹¹, alkylthio, Alk and Het,

with the proviso that at least one of R¹ and R² selected from the group consisting of

Alk and Het, wherein

Alk is cyano, CN—OH, CN-oxyalkyl, alkyl, alkyloxyalkyl, alkyloxyalkyloxyalkyl, alkyloxyalkyloxyalkyloxyalkyl, alkylcarbonylalkyl, alkylcarbonyloxyalkyl, alkyloxycarbonylalkyl, Ar-alkyl, Ar-carbonylalkyl, Ar-oxyalkyl, mono- or di(alkyl)aminoalkyl, mono- or di(alkylcarbonyl)aminoalkyl, mono- or di(alkyl)aminocarbonylalkyl, Het-alkyl, formyl, alkylcarbonyl, alkyloxycarbonyl, alkyloxyalkylcarbonyl, mono- or di(alkyl)aminocarbonyl, Ar-carbonyl and Ar-oxycarbonyl;

Ar is phenyl or naphthyl, optionally substituted with one or more halo, cyano, oxo, hydroxy, alkyl, formyl, alkyloxy or amino radicals;

Het is a heterocyclic radical selected from the group consisting of Het¹, Het² and Het³;

Het¹ is an aliphatic monocyclic heterocyclic radical selected from the group consisting of pyrrolidinyl, dioxolyl, imidazolidinyl, pyrrazolidinyl, piperidinyl, dioxyl, morpholinyl, dithianyl, thiomorpholinyl, piperazinyl and tetrahydrofuryl;

Het² is a semi-aromatic monocyclic heterocyclic radical selected from the group consisting of 2H-pyrrolyl, pyrrolinyl, imidazolinyl and pyrrazolinyl;

Het³ is an aromatic monocyclic heterocyclic radical selected from the group consisting of pyrrolyl, pyrazolyl, imidazolyl, furyl, thienyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl and triazinyl; or an aromatic bicyclic heterocyclic radical selected from the group consisting of quinolinyl, quinoxalinyl, indolyl, benzimidazolyl, benzoxazolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl, benzofuranyl and benzothienyl;

wherein each Het¹, Het² and Het³-radical may optionally be substituted on either a carbon or heteroatom with halo, hydroxy, alkyloxy, alkyl, Ar, Ar-alkyl, formyl, alkylcarbonyl or pyridinyl;

R¹⁰ and R¹¹ are each, independently from each other, selected from the group consisting of hydrogen, alkyl, Ar, Ar-alkyl, pyrrolidinylalkyl, piperidinylalkyl, homopiperidinylalkyl, piperazinylalkyl, morpholinylalkyl, mono- or di(alkyl)aminoalkyl, alkylcarbonyl, alkenylcarbonyl, Ar-carbonyl, pyridinylcarbonyl, alkyloxycarbonyl, mono- or di(alkyl)aminocarbonyl, mono- or di(Ar)aminocarbonyl, mono- or di(alkyloxycarbonylalkyl)aminocarbonyl, pyrrolidinylcarbonyl, aminoiminomethyl, alkylaminoiminomethyl, N-benzylpiperazinyliminomethyl, alkylsulphonyl and Ar-sulphonyl ; or

R¹⁰ R¹¹ may be taken together and with the N may form a monovalent radical selected from the group of

wherein:

R¹² is selected from the group consisting of hydrogen, alkyl, Ar, Ar-alkyl, Ar-alkenyl, alkylcarbonyl, alkyloxycarbonyl, alkyloxyalkylcarbonyl and mono-or di(alkyl)aminocarbonyl;

each ring being optionally substituted with q radicals R¹³, each radical independently from each other selected from the group of alkyl, oxo, Ar, Ar-alkyl, Ar-alkenyl and alkyloxycarbonyl and q being an integer ranging from 0 to 6 ;or

R¹ and R² may be taken together to form a bivalent radical —R¹-R² —selected from the group consisting of —CH₂—CH₂—CH₂—CH₂—, —CH═CH—CH₂—CH₂—, —CH₂—CH₂—CH═CH—, —CH₂—CH═CH—CH₂—and —CH═CH—CH═CH;

a and b area symmetric centers;

(CH₂)m is a straight hydrocarbon chain of m carbon atoms, m being an integer ranging from 1 to 4;

Pir is a radical according to any one of Formula (IIa), (IIb) or (IIc)

optionally substituted with n radicals R⁸, wherein:

each R⁸ is independently from each other, selected from the group of hydroxy, amino, nitro, cyano, halo and alkyl;

n is an integer ranging from 0 to 5;

R⁹ is selected from the group consisting of hydrogen, alkyl and formyl;

R³ represents an optionally substituted aromatic homocyclic or heterocyclic ring system together with an optionally substituted and partially or completely hydrogenated hydrocarbon chain of 1 to 6 atoms long with which said ring system is attached to the Pir radical and of which may contain one or more heteroatoms selected from the group of O , N and S;

alkyl represents a straight or branched saturated hydrocarbon radical having from 1 to 6 carbon atoms or a cyclic saturated hydrocarbon radical having from 3 to 6 carbon atoms, optionally substituted with one or more halo, cyano, oxo, hydroxy, formyl or amino radicals;

alkenyl represents a straight or branched unsatured hydrocarbon radical having one or more double bonds, optionally substituted with one or more halo, cyano, oxo, hydroxy, formyl or amino radicals ; and

halo is fluoro, chloro, bromo and iodo.