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All equilibrium and rate constants of heavenly blue anthocyanin (HBA 1) as well as the derivatives with two (HBA 2) or none (HBA 3) acylated units were determined. The three acylated units of the sugar in position 3 of the peonidin chromophore of HBA 1 are essential to confer the peculiar stability of its purple and blue colors. The sugars generate an efficient protective environment around position 2 (and 4) of the flavylium cation, through an intramolecular sandwich-type stacking that retards 35-fold the hydration reaction (kh) and increases 8.8-fold the dehydration reaction (k–h), when compared with the peonidin chromophore HBA 3. The conjugation of these two rates lowers 308-fold the hydration equilibrium constant (Kh), corresponding to a raise of the energy level of the hemiketal by 14.2 kJ mol–1. Conversely, the pKa of the quinoidal base in HBA 1 is only slightly stabilized in comparison with that of HBA 2 and HBA 3. The energy level of hemiketal increases with the number of acylated units, but the ...

[reaction: see text] A novel and efficient synthesis of cyanidin 3-O-beta-D-glucoside (1) was accomplished the first time by a biomimetic oxidation route. From (+)-catechin, 3-OH was glucosylated, and the 4-position of the nucleus was then oxidized and dehydrated to give the 5,7,3',4'-tetra-O-(tert-butyldimethylsilyl)flav-3-en-3-ol 3-O-glucoside (8) as a key intermediate. 8 was deprotected and oxidized under air in hydrogen chloride-MeOH to give 1.

Reduction of the periodate oxidation products of zooxanthelletoxin-A with NeBH 4 gave the fragment 2 (C 47 H 76 O 14 ) and its elongeted fragment 1 (C 56 H 91 O 22 SNa) to which the polyhydroxylated polyene structure (1), which possesses a 1,3-diepoxide and a sulfte ester functionality, was assigned on the basis of spectral data