Letermovir is the first representative of the nonnucleoside 3,4 dihydro-quinazoline class of human cytomegalovirus (HCMV) viral terminase complex inhibitors (Verghese and Schleiss, 2013). Originally developed by Bayer AG (Wuppertal, Germany), with further preclinical and clinical development through phase II by AiCuris GmbH & Co. KG (Wuppertal, Germany), letermovir is now under development by Merck & Co. (Kenilworth, NJ, USA). Letermovir is now in phase III development for the prevention of HCMV infection in allogeneic hematopoietic cell transplant (HCT) recipients (clinical trials NCT02137772). Owing to its development history, letermovir is variously known as BAY 73-6327, AIC246, and MK-8228. The chemical name of letermovir is 2-((4S)-8-fluoro-2-(4-(3-methoxyphenyl)piperazin-1-yl)-3-(2-methoxy-5)-trifluoromethyl)phenyl)-4H-quinazolin-4-yl)acetic acid (PubChem Open Chemistry Database, 2016), the molecular formula is C₂₉H₂₈F₄N₄O₄, and its molecular weight is 572.55 g/mol. The chemical structure is shown in Figure 220.1. Figure 220.1 Chemical structure of letermovir. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315152110/ab8dce28-617a-47c6-8bc5-aa360149bab9/content/fig220_1.tif"/>