A proposed crystal structure of lifitegrast sesquihydrate Form A, (C ₂₉ H ₂₄ Cl ₂ N ₂ O ₇ S) ₂ (H ₂ O) ₃

A proposed crystal structure of lifitegrast Form A has been derived using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Lifitegrast sesquihydrate Form A crystallizes in space group P2 1 (#4) with a = 18.2526(4), b = 5.15219(6), c = 30.1962(6) Å, β = 90.8670(19), V = 2839.35(7) Å 3 , and Z = 4 at 295 K. The crystal structure consists of discrete lifitegrast molecules linked by hydrogen bonds among carboxylic acid groups, carbonyl groups, and water molecules into a three-dimensional framework. The water molecules occur in clusters. Each water molecule acts as a donor in two O–H⋯O hydrogen bonds, and as an acceptor. One water molecule acts as an acceptor in a water–water O–H⋯O hydrogen bond, and all three water molecules are acceptors in C–H⋯O hydrogen bonds. Each carboxylic acid group acts as a donor in a strong discrete O–H⋯O hydrogen bond; one to a water molecule and the other to a carbonyl group. The amino groups both form N–H⋯O hydrogen bonds to carbonyl groups. The powder pattern has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).