Pyrroloquinoline Quinone Disodium Salt (PQQ)

Pyrroloquinoline quinone is a tricyclic ortho-quinone, IUPAC name 4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid, formula C14H6N2O8, molar mass 330.21, CAS 72909-34-3. It is the redox cofactor of the bacterial quinoproteins, where it sits in a distinctive six-bladed beta-barrel enzyme fold. The article of commerce is not the free acid but the disodium salt, CAS 122628-50-6, formula C14H4N2Na2O8, molecular weight 374.17, because deprotonating two of the three carboxylic acids gives the water solubility a supplement or beverage formulator actually needs. Supplied material is a yellow to reddish-brown crystalline powder assaying not less than 99.0% on the dry basis, which is the figure the EU novel food specification also sets. Commercial PQQ is made by bacterial fermentation on a methanol substrate, typically with Hyphomicrobium denitrificans, followed by recovery and crystallisation; the EU Union list entry describes the authorised novel food specifically as the disodium salt produced by the non-genetically-modified bacterium Hyphomicrobium denitrificans strain CK-275, so EU-bound material should be matched against that published specification, source organism included, before shipment is committed. Two practical points follow from the chemistry. Use levels are very small - the EU cap is 20 mg per day - so content uniformity, not bulk density, is the formulation problem, and 1% or 5% triturations on microcrystalline cellulose are usually the sensible way to hit a 10 or 20 mg capsule or tablet reliably. And the material is intensely coloured, so it will tint a white powder blend, a chewable or an uncoated tablet; plan the finished-product colour around it rather than being surprised at first pilot batch. PQQ is not an officially recognised vitamin. A 2003 report proposed it as a new B vitamin, that proposal was challenged in 2005, and it has never been adopted as an essential vitamin - a point that matters for tariff classification as well as for label copy. It does occur naturally in food, reported at 7-34 micrograms per kilogram in fruits and vegetables, 18.24 micrograms per kilogram in legume seeds, and 60-800 micrograms per kilogram in fermented products, though the ingredient supplied here is fermentation-derived and purified rather than food-extracted. On regulatory status: the disodium salt is an authorised EU novel food under Commission Implementing Regulation (EU) 2018/1122, restricted to food supplements for adults excluding pregnant and lactating women at a maximum of 20 mg per day, with the mandatory on-pack statement that the supplement is for adults only excluding pregnant and lactating women; the original applicant's five-year data protection expired on 2 September 2023, so conforming generic material may now be placed on the EU market. In the United States the ingredient is covered by a dietary ingredient notification filed in 2007 and by several GRAS notices on FDA's inventory, including GRN 625, GRN 641, GRN 701 and GRN 709. Composition and established cofactor chemistry only are described here; no health or disease claim is made or supported.