32. Which one of the following compound is NOT a part of alkaloid class of secondary metabolites?
(1) Lignin
(2) lndole
(3)Tropane
(4) Pyrroidine
Correct answer: (1) Lignin
Lignin is a complex phenolic polymer providing structural support in plant cell walls, not an alkaloid (nitrogen-containing heterocyclic compounds). Indole, tropane, and pyrrolidine are recognized alkaloid structural classes.
Option Analysis
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(1) Lignin — NOT an alkaloid. Complex polyphenolic polymer from phenylpropanoid pathway, lacks nitrogen heterocyclic structure defining alkaloids.
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(2) Indole — Alkaloid class (e.g., indole alkaloids like vinblastine, reserpine from tryptophan).
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(3) Tropane — Alkaloid class (e.g., atropine, cocaine from ornithine).
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(4) Pyrrolidine — Alkaloid class (pyrrolidine alkaloids like hygrine; pyrrolizidine alkaloids contain fused pyrrolidine rings).
Lignin, unlike indole, tropane, and pyrrolidine alkaloids, belongs to phenolic polymers formed via phenylpropanoid biosynthesis for plant structural integrity rather than nitrogenous alkaloid defense chemistry.
