'Not further fused' means the quinoline or isoquinoline bicyclic system is not joined to any additional ring. Compounds where a third ring is fused onto the quinoline core — such as acridine (three fused rings) — are excluded and must be classified under a different heading. The structural formula should be reviewed to confirm ring count before classification.

Pharmaceutical synthesis is the dominant demand driver, with quinoline derivatives serving as APIs or intermediates for antimalarials, antibacterials, and kinase-inhibitor oncology drugs. Demand can be sensitive to public health events — antimalarial compound procurement, for example, has historically spiked during malaria outbreak responses.