Five New Tamarixetin Glycosides from Griseb. Including Some Substituted with the Rare 3-Hydroxy-3-methylglutaric Acid and Their Collagenase Inhibitory Effects In Vitro.

Along with the known kaempferol-3--α-l-rhamnopyranosyl-(1 → 2)-[6--(3-hydroxy-3-methylglutaryl)]-β-d-galactopyranoside (), five new flavonoids, containing the rarely isolated aglycon tamarixetin, were isolated from a methanolic extract of the endemic Balkan species Griseb. Three of the new compounds are substituted with 3-hydroxy-3-methylglutaryl residue (HMG), untypical for the genus . The compounds were identified as tamarixetin-3--α-l-rhamnopyranosyl-(1 → 2)-[6--(3-hydroxy-3-methylglutaryl)]-β-d-galactopyranoside (), tamarixetin-3--(2,6-di--α-l-rhamnopyranosyl)-β-d-galactopyranoside (), tamarixetin 3--β-d-apiofuranosyl-(1 → 2)-β-d-galactopyranoside (), tamarixetin-3--β-d-apiofuranosyl-(1 → 2)-[6--(3-hydroxy-3-methylglutaryl)]-β-d-galactopyranoside (), and tamarixetin-3--β-d-apiofuranosyl-(1 → 2)-[α-l-rhamnopyranosyl-(1 → 6)]-β-d-galactopyranoside ().