Review Question - QID 109197

A 10-year-old boy presents to the pediatrician with a three day history of sore throat and fever of 101°F (38.3°C). On physical exam, his oral mucosa is shown in Figure A. He also has tender anterior cervical lymph nodes. A rapid strep test returns negative. Three weeks later, the boy presents with painful joints and nodular swelling on his skin. Erythrocyte sedimentation rate (ESR) is obtained and found to be 76 mm/hr. A reaction to which of the following compounds is most likely responsible for the patient’s return presentation?