Compound of formula I where X=O or .dbd.N--OH group, R represents a group chosen from A=hydrogen or together with B a carbon-carbon bond, B=hydrogen, hydroxy or together with A a carbon-carbon bond, C, D, E, F=hydrogen or together with D a carbon-carbon bond, or the one of its addition salts with pharmaceutically acceptable acids, with the exception of a few compounds, as a medicament, use in particular as neuroprotectors, novel compounds of formula I and pharmaceutical compositions.