Novel aldol addition reactions of dihydroxyacetone (DHA) and hydroxyacetone (HA) to a variety of aldehydes catalyzed by D-fructose-6-phosphate aldolase (FSA) are presented. In a chemical-enzymatic cascade reaction approach, 1-deoxynojirimycin and 1-deoxymannojirimycin were synthesized starting from (R)- and (S)-3-(N-Cbz-amino)-2-hydroxypropanal, respectively. Furthermore, 1,4-dideoxy-1,4-imino-D-arabinitol and 1,4,5-trideoxy-1,4-imino-D-arabinitol were prepared from N-Cbz-glycinal. 1-Deoxy-D-xylulose was also synthesized by using HA as the donor and either 2-benzyloxyethanal or 2-hydroxyethanal as acceptors. In both cases the enzymatic aldol addition reaction was fully stereoselective, but with 2-hydroxyethanal 17 % of the epimeric product at C2, 1-deoxy-D-erythro-2-pentulose, was observed due to enolization/epimerization during the isolation steps. It was also observed that D-(-)-threose is a good acceptor substrate for FSA, opening new synthetic possibilities for the preparation of important novel complex carbohydrate-related compounds from aldoses. To illustrate this, 1-deoxy-D-ido-hept-2-ulose was obtained stereoselectively by the addition of HA to D-(-)-threose, catalyzed by FSA. It was found that the reaction performance depended strongly on the donor substrate, HA being the one that gave the best conversions to the aldol adduct. The examples presented in this work show the valuable synthetic potential of FSA for the construction of chiral complex polyhydroxylated sugar-type structures.

Pine (Pinus pinaster) bark is a rich source of procyanidin oligomers. From a total polyphenolic extract, we have generated fractions of different procyanidin composition. The mixtures, devoid of gallate esters, were active as free radical scavengers against ABTS(*+), DPPH, and HNTTM. Pine bark fractions were tested for antioxidant activity in solution (hydrogen donation and electron transfer) and emulsion (inhibition of lipid peroxidation) and compared with their galloylated counterparts from grape origin. While galloylation clearly influenced the free radical scavenging efficiency in solution, it did not seem to play a determinant role in protection against lipid peroxidation in emulsion. The fractions were very mild inhibitors of cell proliferation. Because gallate esters appear to interfere with crucial cell functions, gallate free pine procyanidins may be the innocuous chemopreventative agents of choice for many applications in food and skin protection.

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