The invention relates provides a novel crystal structure of the fibrillogenic part of amyloid β-peptide (Aβ). More specifically the crystal structure is Aβ-IgNAR and, accordingly the present invention also relates to selecting and/or designing compounds that modulate amyloid β-peptide (Aβ) activity using techniques such as in silico screening and crystal soaking experiments. The invention further relates to compounds and methods for inhibiting interaction between amyloid β-peptide (Aβ) monomers, more particularly, inhibiting or disrupting amyloid β-peptide (Aβ) oligomer formation and toxic activity.