This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
[{'content': 'Which vitamin can be synthesized from tryptophan: \nSelect and explain. \nA. Niacin, B. Riboflavin, C. Cobalamin, D. Folic acid', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) NiacinRef: Harpers Biochemistry, 30th ed. pg. 557* Niacin is synthesized from tryptophan via kynurenine and quinolinic acids as key biosynthetic intermediates.* Refer to above explanation for more details.', 'role': 'assistant'}]