Which pair of statements correctly identifies the origins of two alkaloid classes?

• A. Tropane alkaloids from threonine; Indole alkaloids from tryptophan
• B. Isoquinoline alkaloids from tyrosine; Indole alkaloids from tryptophan
• C. Quinoline alkaloids from tyrosine; Tropane alkaloids from threonine
• D. Isoquinoline alkaloids from tyrosine; Tropane alkaloids from threonine

Answer: (B)

Alkaloids often trace back to a specific amino acid that seeds their ring structure. Isoquinoline alkaloids come from tyrosine, which is converted through a series of steps to form the benzylisoquinoline framework. Indole alkaloids come from tryptophan, providing the indole ring that is central to their core. Tropane alkaloids, on the other hand, are built from ornithine-derived units (putrescine) rather than threonine, so linking them to threonine isn’t correct. Quinoline alkaloids aren’t classically tied to tyrosine in this context either. Therefore, the pairing isoquinoline alkaloids from tyrosine and indole alkaloids from tryptophan reflects established biosynthetic origins.