Absolute configuration of arylglycerol-beta-aryl ethers obtained by asymmetric reduction of the corresponding alpha-ketonic compound with intact Fusarium solani cells

When (+/-)-alpha -oxo-guaiacylglycerol-beta-(vanillic acid) ether (1) is de graded by Fusarium solani M-13-1, the a-ketone is initially reduced to give erythro and three guaiacylglycerol-beta- (vanillic acid) ethers (2), arylg lycerol-beta -aryl ethers, both of which are enantiomerically pure. The abs olute configuration in each 2 was determined by Mosher's method; the produc ts were converted to alpha,gamma -di-(R)-alpha -methoxy-alpha -trifluoromet hylphenylacetates (MTPA esters) (3') of erythro (-)- and three (+)-veratryl glycerol-beta-(methyl vanillate) ethers (3), whose H-1 nuclear magnetic res onance (NMR) spectra were examined and compared with those of four di-(R)-M TPA ester (3') diastereomers from chemically synthesized erythro (+/-)-3 an d three (+/-)-3. To assign the alpha- and gamma -MTPA-OCH3 peaks, the H-1 N MR scans of several compounds that have substructures of 3' and their 3,4,5 -trimethoxyphenyl analogues were examined. When a racemic alcohol reacts wi th (R)-MTPA to give a pair of (R)-MTPA ester diastereomers, the Delta delta value was defined as the absolute value of the difference in the H-1 chemi cal shifts of the peak between the diastereomers. It was found that the Del ta delta values of alpha -MTPA-OCH3 were larger than those of gamma -MTPA-O CH3 owing to a shielding effect of the veratryl ring located on the alpha - MTPA-OCH3, and that the alpha -MTPA-OCH3 peaks in the 3,4,5-trimethoxypheny l compounds shifted downfield relative to those in the veratryl compounds. On the basis of the H-1 NMR data of (R)-MTPA esters, the absolute configura tion of the four chemically prepared diastereomers (3') were determined. Th e catabolic erythro 3' [from erythro (-)-3] and three 3' [from three (+)-3] were identical to (R, alphaS, betaR)-eryrhro 3' and (R, alphaS, betaS)-thr eo 3', respectively. An hydrogen species in the fungal reduction would atta ck the a-ketone from re-face of both (betaR)-1 and (betaS)-1, giving erythr o (alphaS, betaR)-2 and three (alphaS, betaS)-2, respectively.