The present invention provides a compound selected from the group including: 1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-4-phenyl-phthalazine; 4-(3,5-dichloro-pyridin-4-ylmethyl)-7-methoxy-1H-phthalazin-2-carboxylic acid methyl ester; benzyl-{3-{1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-phthalazin-5-yl}-prop-2-ynyl}-methyl-amine; 1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-5-(5-morpholin-4-yl-pent-1-ynyl)-phthalazine dihydrochloride; 3-{1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-phthalazin-5-yl}-prop-2-yn-1-ol; 1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-4-morpholin-4-yl-phthalazine; 1-(3,5-dichloro-pyridin-4-ylmethyl)-6-methoxy-4-(1,2,4)triazol-1-yl-phthalazine; N→O derivatives thereof; and pharmaceutically acceptable salts thereof. The invention also provides a pharmaceutical composition which includes a therapeutically effective amount of the above compound in admixture with a suitable carrier.