2-Butyl-3-((2'-(2-trityl-2H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl)methyl)-1,3-diazaspiro[4.4]non-1-en-4-one-D4 is an intermediate used in the synthesis of Irbesartan-d4 (I751004), which is the labeled analogue of Irbesartan (I751000), an angiotensin II type 1 (AII1)-receptor antagonist.