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
Which vitamin can be synthesized from tryptophan: 
Select and explain. 
A. Niacin, B. Riboflavin, C. Cobalamin, D. Folic acid
A: Niacin
Answer: A: Niacin 
Explanation: 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.