<p>ALZ-801 (valiltramiprosate) is an orally bioavailable, small-molecule inhibitor of β-amyloid (Aβ) oligomer formation in late-stage clinical development as a potential disease-modifying treatment for Alzheimer’s disease (AD). ALZ-801, (S)-3-(2-amino-3-methylbutanamido) propane-1-sulfonic acid, is a valine-conjugated prodrug of tramiprosate. Structural, polymorphic analysis of the active pharmaceutical ingredient (API) of ALZ-801 showed extra peaks when high throughput transmission mode XRPD analysis was utilized. After extensive investigation, the extra peaks were determined to be an artifact of transmission mode XRPD, which was not observed in either reflectance or capillary mode XRPD analyses. Reflectance mode XRPD was demonstrated as the most appropriate methodology to monitor the crystal form of ALZ-801 API. In conclusion, ALZ-801 API is a single, pure polymorph form.</p> Graphical Abstract <p>A single crystalline form of ALZ-801 is observed in a range of crystal morphologies, the risk of a change in solid form affecting the delivery of this potential new disease modifying therapy for Alzheimer’s disease is negligible</p> <p>Phase light microscopy image of ALZ-801 crystal pattern 1 (single polymorph). ALZ-801 crystals occur in diverse ranges of morphologies, i.e., tetrahedron (a), bladed, needles, dodecahedron, slices(b), prismatic (c) and tabular (d) forms</p>