X is CH₂, N—R⁷, S or O;

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

R¹, R², R¹⁴ R¹⁵ are each, independently from each other, selected from the group consisting of

hydrogen;

halo;

a radical selected from the group consisting of hydroxy, —OSO₂H, —OSO₂CH₃, alkyloxy, alkyloxyalkyloxy, alkyloxyalkyloxyalkyloxy, tetrahydrofuranyloxy, alkylcarbonyloxy, alkyloxyalkylcarbonyloxy, pyridinylcarbonyloxy, alkylcarbonyloxyalkyloxy, alkyloxyalkylcarbonyloxyalkyloxy, alkyloxycarbonyloxy, alkenyloxy, alkenylcarbonyloxy, mono- or di(alkyl)aminoalkyloxy, mono- or di(alkyl)aminocarbonyloxyalkyloxy;

a radical selected from the group consisting of cyano, CN—OH, CN-oxyalkyl, alkyl, alkyloxyalkyl, alkyloxyalkyloxyalkyl, alkyloxyalkyloxyalkyloxyalkyl, alkylcarbonylalkyl, alkylcarbonyloxyalkyl, alkyloxycarbonylalkyl, Ar-alkyl, Arcarbonylalkyl, 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;

—N—R¹⁰R¹¹ wherein R¹⁰ and R¹¹ each, independently from each other, are selected from the group consisting of hydrogen, alkyl, Ar, pyridinyl, 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 and R¹¹ may be taken together and with the N may form a monovalent radical selected from the group consisting 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 R¹³ is, independently from each other, selected from the group consisting of alkyl, oxo, Ar, Ar-alkyl, Ar-alkenyl and alkyloxycarbonyl;

q is an integer ranging from 0 to 6;

alkylthio;

Ar and Het;

with the provisio that at least one of R¹⁴ and R¹⁵ is not hydrogen;

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 of quinolinyl, quinoxalinyl, indolyl, benzimidazolyl, benzoxazolyl, benzisoxazolyl, benzothiazolyl, benzisothiazolyl, benzofuranyl and benzothienyl; wherein each Het-radical may optionally be substituted on either a carbon or heteroatom with halo, hydroxy, alkyloxy, alkyl, Ar, Ar-alkyl, formyl, alkylcarbonyl or pyridinyl;

a and b are asymmetric 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 R is independently from each other, selected from the group consisting 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 and

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