Compounds of formula (I) as defined herein: inhibit the formation of the β-amyloid peptide (β-A4) and are, therefore, useful in the treatment of pathologies in which a β-amyloid peptide (β-A4) formation inhibitor provides a therapeutic benefit. Particular such pathologies are senile dementia, Alzheimer's disease, Down's syndrome, Parkinson's disease, amyloid angiopathy, cerebrovascular disorders, frontotemporal dementias and Pick's disease, post-traumatic dementias, pathologies linked to neuroinflammatory processes, Huntington's disease and Korsakov's syndrome.