Amino acids not elsewhere specified — including their esters (limited to a single oxygen-function type) and corresponding salts — serve as critical intermediates in pharmaceutical synthesis, animal-feed supplementation, and specialty food-ingredient manufacturing. Classification under this residual heading requires confirming that the compound is not captured by a more specific amino-acid provision, making precise chemical characterization essential before entry. Importers should be aware that certain amino acids used in dietary supplements or pharmaceutical preparations may trigger FDA review at the port of entry.

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