GATE 2024 BT Q.45: solution and answer

Official answer: A, C, DSource: Official answer key, GATE 2024 BT (IISc Bengaluru)

1. Alkaloids are nitrogen-containing secondary metabolites, usually basic, made from amino acids. A quick first screen is the molecular formula: a compound with no nitrogen cannot be an alkaloid.

2. (A) Ajmalicine, ${\text{C}}_{21}{\text{H}}_{24}{\text{N}}_2{\text{O}}_3$, is a monoterpenoid indole alkaloid from Catharanthus roseus and Rauvolfia. It is built from tryptamine and secologanin, and it is used as an antihypertensive. It contains nitrogen and is an alkaloid, so (A) is correct.

3. (B) Azadirachtin, ${\text{C}}_{35}{\text{H}}_{44}{\text{O}}_{16}$, contains no nitrogen. It is a limonoid, a highly oxidised triterpenoid from neem (Azadirachta indica), and it acts as an insect antifeedant. It is a terpenoid, not an alkaloid, so (B) is wrong.

4. (C) Camptothecin, ${\text{C}}_{20}{\text{H}}_{16}{\text{N}}_2{\text{O}}_4$, is a quinoline alkaloid from Camptotheca acuminata. It inhibits topoisomerase I, and topotecan and irinotecan are derived from it. It is an alkaloid, so (C) is correct.

5. (D) Vinblastine, ${\text{C}}_{46}{\text{H}}_{58}{\text{N}}_4{\text{O}}_9$, is a dimeric terpenoid indole (vinca) alkaloid from Catharanthus roseus. It binds tubulin and is used as an anticancer drug. It is an alkaloid, so (D) is correct.

6. Only azadirachtin is non-nitrogenous and terpenoid, so the correct options are A, C and D.