Quercetin (Sophora japonica)

Quercetin is the flavonol aglycone 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one, CAS 117-39-5, EINECS 204-187-1, C15H10O7, molecular weight 302.24. Thovek supplies it from the dried unopened flower buds of Styphnolobium japonicum (L.) Schott (Fabaceae) — the accepted botanical name for the tree still traded as Sophora japonica L. and known in the Chinese materia medica as huai mi. The buds are one of the richest natural sources of rutin, quercetin-3-O-rutinoside (CAS 153-18-4, C27H30O16, MW 610.52); the USP monograph for Japanese Sophora Flower Bud Powder sets rutin at not less than 13% and not more than 25%, and published drying studies on the buds report 18.9% to 30.5%. Rutin is recovered by alkali extraction and acid precipitation, then acid-hydrolysed to quercetin plus the disaccharide rutinose and recrystallised. Because the rutinose is cleaved away, the theoretical mass yield of quercetin from rutin is only about 49.5%, which is the main cost driver behind this material. One commercial point matters more than any marketing line, because it is where quercetin contracts most often go wrong. Quercetin crystallises as a dihydrate — quercetin dihydrate, CAS 6151-25-3, C15H10O7·2H2O, MW 338.27, carrying 10.7% water of crystallisation — and almost all bulk trade material is the dihydrate. A quotation of "quercetin 95%" against the dihydrate therefore corresponds to roughly 85% anhydrous quercetin, while the USP limit of not less than 98.0% and not more than 102.0% is expressly calculated on the anhydrous basis. Two suppliers quoting "95%" can be selling materially different goods. Thovek states the basis on the specification sheet and on every certificate of analysis, and will run the assay on whichever basis the buyer's own release specification uses. The second technical constraint to design around is solubility: quercetin is practically insoluble in water and only sparingly soluble in ethanol (about 2 mg/mL), freely soluble in DMSO (about 30 mg/mL) and soluble in aqueous alkali, melting at 314-317 °C with decomposition. Brands formulating for aqueous systems normally move to phytosome, solid-dispersion or micronised routes, and micronised and granular grades are available for that reason. Every lot ships with a full certificate of analysis: HPLC assay and identity, Karl Fischer water, sulphated ash, heavy metals by ICP-MS, residual solvents against ICH Q3C, pesticide screening and microbiology. The material is plant-derived and vegan, with no bovine, porcine, marine, dairy, egg, fish, crustacean, nut, sesame or gluten input; the source tree is a legume (Fabaceae) but is not soy, peanut or lupin and is not a declarable legume allergen. Bud origin is declared on each lot. On tariff treatment, purified quercetin is a separate chemically defined organic compound and belongs in Chapter 29, not in the plant-extract heading 1302 that appears on many Indian export sheets — see the classification note. Bud-origin Sophora japonica extracts at lower quercetin strengths, and rutin itself, are quoted as separate products with their own classifications.