A method of treatment with compounds having the formula

wherein
R¹ is hydrogen, C₁₋₆-alkyl which may be branched, C₃₋₇-cycloalkyl, benzyl, phenyl which may be substituted, acyl, hydroxy, C₁₋₆-alkoxy, CH₂CO₂R' wherein R' is hydrogen or C₁₋₆-alkyl which may be branched, CH₂CN, CH₂CONR IV R V wherein R IV and R V independently are hydrogen or C₁₋₆-alkyl, or CH₂C(=NOH)NH₂;
R² is hydrogen, benzyl, C₁₋₆-alkyl which may be branched, or C₃₋₇-cycloalkyl;
R⁴, R⁵, R⁶, R⁷ independently are hydrogen, C₁₋₆-alkyl which may be branched, phenyl, halogen, C₁₋₆-alkoxy, NO₂, CN, SO₂NR''R''' wherein R'' and R''' independently are hydrogen or C₁₋₆-alkyl, or CF₃; or R⁶ and R⁷ together form an additional 4 to 7 membered ring which may be aromatic or partial saturated and which may be substituted with halogen, NO₂, CF₃, CN, SO₂NR''R''' wherein R'' and R''' independently are hydrogen or C₁₋₆-alkyl, and R⁴ and R⁵ have the meanings set forth above, are disclosed, as well as pharmaceutical compositions thereof. Certain of the compounds are novel. The compounds and pharmaceutical compositions containing the compounds are useful in the treatment of central nervous system disorders and especially conditions sensitive to excitatory amino acids.