Mild hydroxypropylation of polyflavonoids obtained under pilot-plant scale

GARCÍA, D.; FUENTEALBA, C.; SALAZAR, J.P.; PÉREZ, M.A.; ESCOBAR, D.; PIZZI, A.:
Industrial Crops and Products, 87, 350-362 (2016).

DOI: 10.1016/j.indcrop.2016.04.034

Abstract

Condensed tannins from pine (Pinus radiata), mimosa (Acacia mearnsii), and quebracho (Schinopsis lorenzii) were modified with propylene oxide (PO) via a mild derivatization (20 °C, 24 h). The hydroxypropylation to three PO/C₁₅ ratio (1, 2, 3) produced polyphenolic derivatives in reasonable yields (60–90%). Evidense of modification was described by functional group analysis, and tannin biological properties (binding-, and antioxidant-capacity). Isolated products were characterized by physicochemical methods (solubility test, molecular weight distribution, and thermal analysis). 

¹H NMR provided evidence of strong structure-properties relationship in function of the A-ring type, and C→C linkage features. Pine tannin fractions exhibited the best PO-uptake. Acetoxy signal intensity of acetylated derivatives revealed that mimosa and quebracho tannins are less reactive polyflavonoids toward hydroxypropylation at room temperature. Thermal behavior, solubility, and antioxidant-, and binding-capacity were affected by the modification. However, pine tannins behavior differ from those highly purified polyflavonoids.