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Enantiomerically pure diphenic ester 3 was obtained by a-and p-anomers (7 (4:l). The natural product praecoxin B esterification of acyl chloride 2 with the glucose derivative 1 (8) was obtained by hydrogenative debenzylation. A second by kinetic resolution. Hydrolysis of the ester 3, acylation of member of the ellagitannin group pterocarinin C (11) was the free OH groups at C-4 and C-6 of the diol4 with acid 5 obtained from the common intermediate 7 by acylation in the followed by irradiation led to the anomerically deprotected anomeric position to 10 followed by debenzylation.Praecoxin B and pterocarinin C (11) [4,5] are members of the large class of glycosidic natural products from vegetable extracts known as ellagitannin~[~.~j. At present, over 500 structurally characterized ellagitannins are identified[*]. These plant polyphenols are commercially used in the leather and wine industryL6] as well as in the traditional herbal Therefore much attention was focused on the development of general approaches to the compounds of this c l a~s [~-'~] in the past years (for a reviewwe reported about the synthesis of the ellagitannin ~trictinin['~~'~] using a stereoselective esterification reaction. The successful kinetic resolution (see below) of racemic biaryls prompted us to investigate the synthesis of the natural products praecoxin B and pterocarinin C (11) [4,5] in enantiomerically pure form employing a similar strategy. Now we report about the total synthesis of 8 and 11 starting from racemic diphenic acid chloride 2[17] and the glucoside derivative (l)[1s319]. We used a modified method of Steglich for esterification reactions[l61 to produce diester 3 in a diastereoselective manner. The use of an excess of 4-(dimethy1amino)pyridine (DMAP) (three equivalents) accelerated the esterification to give diester 3 in 38% yield with respect to the sugar component 1 corresponding to a 76% theoretical yield. 'H and I3C NMR-data of diester 3 unambiguously show the purity of this diastereomer (de > 97%), followed by the absence of the corresponding isomer. To determine the absolute configuration of this stereoisomer, the diester 3 was subjected to hydrolysis using anhydrous potassium hydroxide prepared from potassium tert-butoxide and a trace of water in THF as proposed by Gassman ["]. An optically pure (5')-hexabenzyloxydiphenic acid was obtained from this reaction as shown by comparison of its specific rotation with that reported for (S)-atropi~omer['~l. Thus, the absolute configuration of the observed stereoisomeq' 3 was unam- In a preceedingI biguously determined to be (S). We also obtained a polar fraction which has not yet been fully characterized, but it is assumed to be most probably disacharide of (R)-diphenic acid [21]. Treatment of diester 3 with 2 N HCI in THF then gave the diol4 in 91% yield as a yellow crystalline material. The diol 4 was acylated with acid 5[223231 in the presence of 1,3-dicyclohexylcarbodiimide (DCC) and DMAP to afford the digalloylated compound 6 in 78% yield with respect to the diol compone...

The total syntheses of the enantiomerically pure unusual ellagitannins 1,4,6-tri-O-galloyl-2,3-(R)-hexahydroxydiphenoyl-β-d-glucopyranoside (1) and 4,6-di-O-galloyl-2,3-(R)-hexahydroxydiphenoyl-d-glucoside (2) are reported. The NMR data of the synthetic ellagitannins 1 and 2 are not identical with those reported for cercidinin A and B. Thus, the proposed structures for cercidinin A and B must be revised.

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