The present invention relates to a compound of the general formula (I) wherein Het is an optionally substituted 4-, 5-, 6- or 7-membered heterocyclic ring having at least one nitrogen atom; R1 is hydrogen, hydroxy, C.sub.1-C.sub.4 alkyl, C.sub.3-C.sub.4 cycloalkyl, C.sub.2-C.sub.4 alkenyl or C.sub.2-C.sub.4 alkynyl; R2 and R3 is each and independently selected from hydrogen, C.sub.1-C.sub.4 alkyl, C.sub.3-C.sub.4 cycloalkyl, C.sub.2-C.sub.4 alkenyl, C.sub.2-C.sub.4 alkynyl, C.sub.1-C.sub.4 alkoxy, halogen and cyano, provided that R2 and R3 may not both be hydrogen; R4 is C.sub.1-C.sub.4 alkyl, C.sub.3-C.sub.4 cycloalkyl, C.sub.2-C.sub.4 alkenyl or C.sub.2-C.sub.4 alkynyl; Ar is an optionally substituted aromatic ring system selected from pyridinyl; 1-naphthyl; 5,6,7,8-tetrahydro-1-naphthyl; quinolinyl; 2,3-dihydro-1,4-benzodioxinyl; 1,3-benzodioxolyl; 5,6,7,8-tetrahydroquinolinyl; 5,6,7,8-tetrahydroisoquinolinyl; 5,6,7,8-tetrahydroquinazolin-4-yl; 1-benzo[b]thiophen-7-yl; 1-benzo[b]thiophen-4-yl; 1-benzo[b]thiophen-3-yl; isoquinolinyl; quinazolinyl; and indan-4-yl; or Ar is substituted phenyl; or an enantiomer thereof or any salt thereof; to a pharmaceutical composition containing said compounds and to the use of said compounds in therapy. The present invention further relates to processes for the preparation of compounds of formula I and to new intermediates used in the preparation thereof. ##STR00001##