This protocol will enroll and randomize 12 subjects with moderate to severe active CD (CD Activity Index [CDAI] 220 to 450, inclusive) for 4 weeks of daily study drug treatment (9 subjects will receive 100 mg STA-5326 mesylate and 3 will receive placebo). Subjects will be evaluated for safety that will include monitoring of adverse events and concomitant medications, clinical laboratory testing, electrocardiogram (ECG) tracings, and physical examinations including vital signs. Efficacy assessments will include the CDAI, the Simple Endoscopic Score for CD (SES-CD), results from the Inflammatory Bowel Disease Questionnaire (IBDQ), and changes from Baseline for plasma C reactive protein (CRP) (measured by high sensitivity assay). In addition, immunologic effects (lymphocyte phenotyping cytokine secretion from peripheral blood and lamina propria mononuclear cells [LPMCs]) will be assessed. Descriptive statistics (n, mean, median, standard deviation, minimum and maximum range) will be used to summarize data for each treatment group.