Provided herein are peptoids capable of inhibiting or reversing amyloid β (Aβ) fibril or plaque production. The peptoids form a helical structure with three monomers per helical turn and have at least two monomers with a side-chain having an arylalkyl group having the same chirality positioned such that the side-chains are on the same side of the peptoid. Also provided are methods of using the peptoids to inhibit or reverse aggregation of Aβ and methods of treating subjects with Alzheimer's disease (AD) or slowing the progression of AD.