Flavylium chlorides prepn. by reducing flavones - with magnesium and sulphuric acid, and adsorbing the flavylium chloride on a resin

摘要

Prepn. of flavylium chlorides (I) from the corresp. flavone (II) (opt. substd. with OH or glycoside gps.) comprises (i) reducing (II) with a mixt. of Mg and H2SO4 in a solvent (pref. a mixt. of DMF and MeOH); (ii) neutralising the excess H2SO4 pref. with aq. ammonia to pH 4-4.5, extracting the impurities with ethyl acetate and adsorbing the residue on a resin and removing the mineral salts by washing with water; and (iii) eluting (I) from the resin with HCl/MeOH. (I) have vitamin P activity. Rhamnoglucosyl-3-cyanidine is partic. effective against night blindness. The process makes possible the direct reduction of hydroxyflavones. (I) is obtd. in good yield. The resin is pref. a polystyrene of Type XAD2 (Amberlite RTM). In an example, 5 g. rutine gave 4.1 g. (82% yield) rhamnoglucosyl-3-cyanidine.